synthesis of piroxicam- related heterocyclic molecules and

Synthesis of Piroxicam-related

Heterocyclic Molecules and Evaluation of Their Biological Activities

WASEEQ AHMAD SIDDIQUI

SESSION (2003-2007)

03-Ph.D-GCU-Chem-03

DEPARTMENT OF CHEMISTRY

GOVERNMENT COLLEGE UNIVERSITY LAHORE

Synthesis of Piroxicam-related

Heterocyclic Molecules and Evaluation of Their Biological Activities

Submitted to GC University, Lahore

in partial fulfillment of the requirements for the award of degree of

DOCTOR OF PHILOSOPHY IN

CHEMISTRY

By

Waseeq Ahmad Siddiqui Session (2003-2007)

03-Ph.D-GCU-Chem-03 Department of Chemistry

GOVERNMENT COLLEGE UNIVERSITY LAHORE

DECLARATION

I, Waseeq Ahmad Siddiqui Roll No. 03-Ph.D-GCU-Chem-03 student of Ph.D

in the subject of Chemistry, Session 2003-2007, hereby declare that the matter

printed in the thesis titled Synthesis of Piroxicam-related Heterocyclic

Molecules and Evaluation of Their Biological Activities is my own research

work and has not been printed, published and submitted as research work, thesis,

publication or in any form in any University, Research Institution etc. in Pakistan

or abroad.

Waseeq Ahmad Siddiqui Dated:

RESEARCH COMPLETION CERTIFICATE

Certified that the research work contained in this thesis titled: Synthesis of

Piroxicam-related Heterocyclic Molecules and Evaluation of Their Biological

Activities has been carried out and completed by Mr. Waseeq Ahmad Siddiqui

Roll No. 03-Ph.D-GCU-Chem-03 under my supervision during his Ph.D

(Chemistry) studies in the laboratories of the Department of Chemistry.

_ ___

Co-supervisor Supervisor

Dr. Saeed Ahmad Dr. Islam Ullah Khan Chairman, Department of Chemistry, University of Science & Technology, Bannu, N.W.F.P Dated:

Submitted Through

Prof. Dr. M. Akram Kashmiri

Chairperson, Department of Chemistry, Government College University, Lahore.

Controller of examination, Government College University,

Lahore.

CERTIFICATE OF EXAMINERS

Certified that the quantum and quality of the research work contained in

this thesis titled: Synthesis of Piroxicam-related Heterocyclic Molecules and

Evaluation of Their Biological Activities is adequate for the award of the degree

of Doctor of Philosophy.

Dr. Saeed Ahmad Dr. Islam Ullah Khan External Examiner

___ Prof. Dr. M. Akram Kashmiri Chairperson, Department of Chemistry, Government College University, Lahore.

DEDICATION

Dedicated To All Those

Who

Follow

the Right Path

ACKNOWLEDGEMENTS

All praises to almighty Allah, Who induced the man with intelligence, knowledge,

sight to observe and mind to think. Peace and blessings of Allah almighty be upon

the Holy Prophet, Hazrat Muhammad (Salal La Ho Alaihey Wassalam) who

exhorted his followers to seek for knowledge from cradle to grave.

My joy knows no bound to express my cordial gratitude to my learned

research mentor Dr. Islam Ullah Khan, Professor, Department of Chemistry,

Government College University, Lahore. His keen interest, scholarly guidance and

encouragement were a great help throughout the course of this research work.

I feel great pleasure in expressing my sincere gratitude and profoundest

thanks to the most respected, honorable, Prof. Dr. Muhammad Akram

Kashmiri, Chairperson, Department of Chemistry, Government College

University Lahore, for providing all facilities to undertake this research work.

I am much obliged to Professor Dr. Saeed Ahmad, Chairman, Department

of Chemistry, University of Science & Technology, Bannu, N.W.F.P who co-

supervised the entire research work. Thanks are due to Dr. Hamid Latif Siddiqui,

Institute of Chemsitry, University of the Punjab, Dr. Abdul Malik, H.E.J. Research

Institite of Chemistry, University of Karachi, Dr. Masood Pervez, Department of

Chemsitry, University of Calgary, Alberta, Canada, Dr. George W. Weaver,

Department of Chemistry, Loughborough University, UK, Dr. Richard C. D.

Brown, School of Chemistry, University of Southampton, UK and Dr. Beining

Chen, Sheffield University, UK for their assistance in spectral analyses of my

research samples, X-ray crystallographic facility and determination of biological

activities during the course of this research work.

My cordial prays are for my beloved Father and Mother who departed me

near completion of this research work. May Allah Subhanahu Taala fill their

graves with His “NOOR”, shower His blessings, forgive their sins, replace them

with virtues and enter them in Paradise without any questioning or calculations.

Their everlasting love, guidance and encouraging passion will remain with me

Insha Allah till my last breath. All my family members, wife and siblings are

always a source of inspiration to me. I am thankful to them for their full support,

encouragement and sincere prayers for my success.

My heart-felt thanks are due to all my teachers, friends and those who

contributed in this research work in any way, especially Brother Nadeem Arshad

Qadri, Hafiz Muhammad Shafiq, Brother Nadeem Sadiq Sheikh and the group-

mates of Dr. Richard Brown (at Southampton, UK) and Miss Saima Sherif, a Ph.D

scholar at University of Education, Lahore.

And finally but in no way least thanks are due to Mr. Naeem Ahmad

Baloch, S.O and respected Islam Sb., Senior Technician, ACRC, PCSIR, for

extending their co-operation during my visits to PCSIR, Lahore, Pakistan.

I express my feelings of gratitude to all the members of non-teaching staff

of the Department especially Mr. Hanif, Mr. Rahmat, Mr. Mohayy-ud-din, Mr.

Arif, Mr. Zulfiqar, Hafiz Ehsan, Hafiz Athar, Mr. Imran Hafeez and Mr. Abdul

Ghafoor for their constant help. Thanks and gratitude are due to Mr. Abdul

Waheed (Chief librarian), Mr. Qaiser, Miss Samreen and Mr. Ghulam Murtaza

among the main library staff. My worthy thanks are due to Mr. Shafiq Mughal

(Treasurer), Mr. Waseem Shahzad (Deputy treasurer) and Mr. Misbah-ul-Ain.

Throughout the course of my Ph.D I have had help from numerous people. I

have tried to thank everybody but if I’ve missed someone I’m sorry and it’s just

down to my forgetfulness.

(Waseeq Ahmad Siddiqui)

Contents

iii

Contents

Abstract i

List of Publications viii

List of Tables ix

List of Figures x

CHAPTER-1 INTRODUCTION

1.1 The Non-steroidal anti-inflammatory drugs (NSAIDs) 01

1.1.1 Properties of NSAIDs

1.1.2 Classification of NSAIDs

1.2 The Oxicams 04

1.3 Benzothiazinone dioxides 05

1.3.1 Nomenclature

1.3.2 Piroxicam ( 1,2-benzothiazine………. ) 06

1.3.3 Chemistry of Piroxicam 07

1.3.4 Mode of Action 08

1.3.5Structure-Activity Relationships 09

1.3.6 Piroxicam Metabolism 11

1.4 Applications of Benzothiazine derivatives 12

1.4.1 Fungicide 13

1.4.2 Herbicide 14

1.4.3 Agrochemicals 15

1.4.4 Metal Analysis

1.4.5 Use in Polymers and Plastics 16

1.4.6 Dyes and Pigments

1.4.7 Photography and Photochromism 17

1.4.8 Fodder Additives and Preservatives 18

1.5 Biological Activities of Benzothiazine derivatives

1.5.1 Anti-inflammatory

1.5.2 Analgesic and Antipyretic 20

Contents

iv

1.5.3 Antimicrobial and Antiviral 21

1.5.4 Antibacterial Activity

1.5.5 Antitumor and Anticancer Activities 22

1.5.6 Antidiabetic and Antihypertensive 23

1.5.7 Ca2+ -Antagonists 23

1.5.8 Alzheimer’s and Parkinson’s disease treatment 24

1.5.9 Multiple Pharmacology 27

1.5.9.1 Writhing Syndrome Antagonism

1.5.9.2 Migraine treatment

1.5.9.3 Osteo-arthritic Activity

1.5.10 Prostaglandin (PGEs) Synthetase Inhibitors 28

1.5.11 Antioxidant Action 29

1.5.12 CNS Stimulating Activity 31

1.6 Plan of Work 32

Schemes 1-6 33-37

CHAPTER-2 LITERATURE SURVEY 38-74

CHAPTER-3 EXPERIMENTAL

3.1 SYNTHESIS OF PIROXICAM 76

3.1.1 Synthesis of Methyl 1,2-benzothiazoline-3-(2H)-one-2-acetate

1,1-dioxide (2)

3.1.2 Synthesis of 4-Hydroxy-3-carbomethoxy-2H-1,2-benzothiazine 78

1,1-dioxide (3)

3.1.3 Synthesis of 4-Hydroxy-3-carbomethoxy-2-methyl-2H-

1,2-benzothiazine 1,1-dioxide (4) 80

3.1.4 Synthesis of Methyl 2-[N-(methoxycarbonyl)sulfamoyl]benzoate (5) 81

3.1.5 Synthesis of Methyl 2-[N-(methyl)-N-(methoxycarbonyl)

sulfamoyl] benzoate (6) 82


1,2-benzothiazine 1,1-dioxide (4) from (6) 83

Contents

v


1,2-benzothiazine 1,1-dioxide (4) from (2) 83

3.1.8 Synthesis of 4-hydroxy-2-methyl-N-(2-pyridinyl)-2H-

1,2-benzothiazine-3-carboxamide 1,1-dioxide (Piroxicam) (7) 84

Scheme-1 86

3.2 Synthesis of 4-Hydroxy-2-Methyl-(2H)-1,2-Benzothiazine

3-Sulfonic Acid 1,1-Dioxide (13a) 87

3.2.1 Synthesis of N-hydroxymethyl saccharin (9)

3.2.2 Synthesis of N-chloromethyl saccharin (10) 88

3.2.3 One-step Synthesis of N-chloromethyl saccharin (10) 89

3.2.4 Synthesis of saccharin- N-methane sulfonic acid (11)

3.2.5 One-pot synthesis of saccharin-N-methane sulfonic acid (11) 90

3.2.6 Synthesis of Methyl [2-(methoxycarbonyl)phenylsulfonamido]-

methylsulfonate (12)

3.2.7 Synthesis of Methyl 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-

3-sulfonate 1,1-dioxide (13) 91

3.2.8 Synthesis of 3-bromo-3,4-dihydro-2-methyl-4-oxo-2H-


3.2.9 Synthesis of 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-

3-sulfonic acid 1,1-dioxide (13a) from (15) 93

3.2.10 One-pot synthesis of 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-

3-sulfonic acid 1,1-dioxide (13a) 94

Scheme-2 95

3.3 Synthesis of 4-(alkoxycarbonylmethylene)-3,4-dihydro-2H-1,2-

benzothiazine 1,1-dioxide (23a-b) 96

3.3.1 Synthesis of [2-(phenylsulfonamido)]acetic acid methyl ester (18)

3.3.2 Synthesis of 2-(phenylsulfonamido)acetic acid (19) 97

3.3.3 Synthesis of 4-oxo-2H-1,2-benzothiazine 1,1-dioxide (20)

3.3.4 General Procedure for the Preparation of Salts of Wittig Reagent 98

Contents

vi

3.3.5 Synthesis of 4-(Alkoxycarbonylmethylene)-3,4-dihydro-2H-

1,2-benzothiazine 1,1-dioxide (23a-b) 98

3.3.6 Synthesis of Alkyl 3-oxo-4-(phenylsulfonamido)butanoate (24a-b) 101

3.3.7 Synthesis of 4-(Alkoxycarbonylmethylene)-3,4-dihydro-2H-

1,2-benzothiazine 1,1-dioxide (23a-b) 102

Scheme-3 103

3.4 Synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine

1,1-dioxide (27) 104

3.4.1 Synthesis of N-chloromethyl saccharin (10)

3.4.2 Synthesis of nitromethylsaccharin (25)

3.4.3 One-pot synthesis of nitromethylsaccharin (25) 105

3.4.4 Synthesis of Methyl [2-(nitromethyl)sulfamoyl]benzoate (26)

3.4.5 Synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine

1,1-dioxide(27) 106

3.4.6 Synthesis of 3-bromo-3,4-dihydro-2-methyl-4-oxo-2H-


3.4.7 Synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine

1,1-dioxide (27) from (15)

3.4.8 One-pot synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-


Scheme-4 109

3.5 Derivatization

3.5.1 Synthesis of Sulfonamide Derivatives of saccharin- N-methane

sulfonic acid (11) 110

3.5.2 Synthesis of Sulfonamide Derivatives of Methyl 4-hydroxy-2-

methyl-(2H)-1,2-benzothiazine-3-sulfonate 1,1-dioxide (13) 119

3.5.3 Synthesis of Derivatives of 4-(methoxycarbonylmethylene)-3,4-

dihydro-2H-1,2-benzothiazine 1,1-dioxide (23a) 126

3.5.4 Synthesis of Open-ring derivatives of Saccharin 130

3.5.5 Synthesis of 3-Carboxamide Derivatives of 4-Hydroxy-

Contents

vii

3-carbomethoxy-2H- 1,2-benzothiazine 1,1-dioxide (265-266) 140

3.6 Biological Activities Determination 142

3.6.1 Antimicrobial Testing:

Tables VI-X 144-48

CHAPTER-4 RESULTS AND DISCUSSION 149-55

REFERENCES 156-78

PUBLICATIONS

1. Siddique, W.A.; Ahmad, S.; Ullah, I.; Malik, A. Jour. Chem., Soc.

Pak., 2006, 28(6), 583-89 179-85

2. Siddiqui, W.A.; Ahmad, S.; Khan, I.U.; Siddiqui, H.L.; Weaver,

G.W. Synth. Commun., 2007, 37, 767-73 186-92

3. Waseeq A. Siddiqui, Saeed Ahmad, I. U. Khan, Hamid L. Siddiqui,

Viqar ud Din Ahmad, J. Chem. Soc. Pak. 2007, 29 (1), 44-47 193-96

4. Waseeq A. Siddiqui, Saeed Ahmad, I. U. Khan, Hamid L. Siddiqui

and Masood Pervez, Acta Cryst. 2007, E63, o4116 197

Chapter: 1 INTRODUCTION

INTRODUCTION

1.1 The Non-steroidal Anti-inflammatory Drugs (NSAIDs)

These are non-narcotic drugs1 that produce relief of pain and lower elevated body

temperature. As these drugs also produce anti-inflammatory effect, so they are known as

non-steroidal anti-inflammatory drugs (NSAIDs). As a group, NSAIDs tend to cause less

gastric irritation and the dosing schedule of some is simpler. Because of the importance

of gastric ulceration in patients taking anti-inflammatory doses of the NSAIDs,

considerable effort has gone into preventing this complication or reducing its severity.2

Inflammation is the reaction of living tissues to all forms of injury. It is associated with

many diseases like rheumatism, hepatitis, trauma injury, tuberculosis, cancer3 etc. Mainly

there are two classes of drugs prescribed for rheumatism and inflammation, steroidal and

non-steroidal. Non-steroidal anti-inflammatory drugs (NSAIDs) are better in use than

steroidal drugs due to following properties:

1.1.1 Properties of NSAIDs

• mildly analgesic

• antipyretic

• anti-inflammatory

• act on sub-cortical sites such as thalamus and hypothalamus

• no affinity for morphine receptors2

• in addition, tolerance and drug dependence do not develop to these drugs

in patients.

1.1.2 Classification of NSAIDs The NSAIDs are composed of the following major classes:

1


• Salicylic acid derivatives:

COOHOCOCH3

e.g., Acetylsalicylic acid (aspirin), sodium salicylate and methyl salicylate.

Aspirin

• Para-aminophenols:

NHCOCH3

OH

e.g., Paracetamol.

Paracetamol • Pyrazolone derivatives:

e.g., Phenylbutazone,oxyphenbutazone.

N N

O O

Phenylbutazone • Indole derivatives:

e.g., Indomethacin, sulindac.

N

O

OH

O

O

Cl

Indomethacin • Propionic acid derivatives:

2


e.g., Ibuprofen, fenoprofen, ketoprofen, naproxen.

H3C COOH

CH3

CH3Ibuprofen

• Fenamates (anthranilic acid derivatives):

COOHHN

CH3H3Ce.g., Mefanamic acid.

Mefanamic acid • Arylacetic acid derivatives:

e.g., Diclofenac sodium, fenclofenac. H

N

COONaCl

Cl

Diclofenac sodium • Oxicams:

SN

OH

O OCH3

NH

O

N

e.g., Piroxicam, Meloxicam.

Piroxicam

We wish to synthesize the heterocyclic molecules belonging to the oxicam class of

NSAIDs.

3

Chapter: 1 INTRODUCTION 1.2 The Oxicams The term ‘oxicams’ has been adopted by the USAN Council to describe the

relatively new enolic acid class of 4-hydroxy-1,2-benzothiazine carboxamides with anti-

inflammatory and analgesic properties.4 Structures of some famous oxicam drug

molecules are shown below:

SN

O OCH3

NH

O

N

OH3C

O

CH3O

Ampiroxicam

SN

O OCH3

NH

OOH

NO

CH3

Isoxicam

SN

O OCH3

O N

O

N

O

Droxicam

SN

O OCH3

NH

OOH N

S CH3

Meloxicam

SN

O OCH3

NH

O

N

OH

Piroxicam

SNH

O O

NH

OOH

N N

O

O

Cinnoxicam

H

Figure 1.1 Structural Formulas of Some Oxicams (1,2-Benzothiazine derivatives)

These structurally distinct agents resulted from extensive studies by the Pfizer group in

an effort to produce non-carboxylic acid, potent, and well-tolerated anti-inflammatory

agents. As part of this study, several series were prepared and evaluated including 2-aryl-

1,3-indanediones, 2-arylbenzothiophen-3-(2H)-one 1,1-dioxides, dioxoquinoline-4-

carboxamies, and 3-oxa-2H-1,2-benzothiazine-4-carboxamide 1,1-dioxide. These results,

combined with the previously known activity of 1,3-dicarbonyl derivatives such as

4

Chapter: 1 INTRODUCTION phenylbutazone, led to the development of the oxicams. The first member of this class,

piroxicam,5 was introduced in the United States in 1982 as Feldene (Pfizer) and gained

immediate acceptance in the United States where it was among the top 50 prescription

drugs for several years. Thus the oxicams represent a potentially growing class of non-

steroidal anti-inflammatory agents (NSAIAs) belonging to the benzothiazinone dioxide

series of heterocyclic molecules.

1.3 Benzothiazinone dioxides

The thiazinone dioxide nucleus is a six membered ring which has two heteroatoms, a

nitrogen atom and a sulfur atom. Several structural isomers are possible for the

benzothiazinone dioxide ring system. The structures and nomenclature of the isomeric

benzothizazinone dioxides6 are shown below:

1.3.1 Nomenclature

SNH

O O

O

2H-1,2-Benzothiazin-3(4H)one 1,1-dioxide

I

S

NH

O O

O


II

NH

SO

O

O


III

NH

S

O

O

O 1H-2,1-Benzothiazin-4(3H)one 2,2-dioxide

IV

5


S

HN


V

O

O O

SNH

O O


VI

O

NH

S


VII

OO

O

NH

S


VIII

OO

O

NH

S 1H-2,1-Benzothiazin-3(4H)one 2,2-dioxide

IX

O

O

O

NH

S


X

O

O O

Figure 1.2 Structural Formulas of Isomeric Benzothiazines

Of the above ten possible isomers, the first six (1-VI) have been synthesized7-47 and their

properties,48-50 pharmacology51-76 and some derivatization77-93 have been reported till

date.

1.3.2 Piroxicam (1,2-benzothiazine………. )

Piroxicam94-113 & Meloxicam114-122 are currently the most widely used NSAIDs for the

treatment of inflammatory conditions in patients suffering from rheumatism. These

6

Chapter: 1 INTRODUCTION oxicam drugs123-39 contain 1,2-benzothiazine nucleus substituted mainly with

carboxamide function at 3-position. The importance of 1,2-benzothiazines stems from the

fact that since the time of its first synthesis by Braun45 in 1923, thousands of its

derivatives have been synthesized and found biologically active as analgesic,140-42

antipyretic,143 hypoglycaemic,144 anti-hypertensive,145 anti-inflammatory146 etc.

Derivatives such as thienothiazines147-158 and pyridothiazines159-162 have also been

reported to exhibit analgesic, herbicidal, fungicidal activities besides better anti-

inflammatory and less ulcerogenic behaviour. Some are shown to be useful in the

treatment of diseases related to prostaglandins and leukotrienes, and also in the treatment

of complications of diabetes mellitus.

1.3.3 Chemistry of Piroxicam

Piroxicam is a 1,2-benzothiazine 1,1-dioxide derivative. Benzothiazine163 is the

heterocyclic compound which has bicyclic ring system, consisting of benzene and a

thiazine ring. In benzothiazine ‘benzo’ represents benzene and ‘thiazine’ symbolizes for

the six-membered unsaturated heterocycle having sulfur and nitrogen as hetero atoms.

The nomenclature and numbering system in piroxicam is shown below (Figure1.3)

SN

O O

OH

NH

O

CH3

N

1 23

45

6

7

8

Benzenering

Thiazinenucleus

Thia-function Aza-function

Carbonyl group

2-amino-pyridylgroup

N-2-pyridyl carboxamide

Figure1.3 Piroxicam [4-Hydroxy-2-methyl-N-(2-pyridyl)-1,2-benzothiazine-3-

carboxamide 1,1-dioxide]

7

Chapter: 1 INTRODUCTION 1.3.4 Mode of Action

The way that the benzothiazine derivatives (NSAIDs) work to decrease inflammation is

still being studied by scientists. The best mechanism for inflammation and then its

inhibition by a benzothiazine derivative has been proposed by Katzung2 and is not very

complicated.

It is well known that cell membrane contains phospholipids. Any stimuli (injury,

microorganisms or allergens) stimulate the enzyme system that starts the cascade actions

resulting in the formation of prostaglandins from phospholipids. Prostaglandin is the

cause of inflammation. Arachidonic acid which is produced with the help of

phospholipase from phospholipids becomes the reason of prostaglandins production. The

generation of prostaglandins (PGs) from arachidonic acid is mediated by

cyclooxygenase.164 Cyclooxygenase is the key enzyme165 in the biosynthesis of

Prostanoids, biologically active substances involved in several physiological processes

and also in pathological conditions such as inflammation. Cyclooxygenase (also known

as Prostaglandin synthase) is present around the joints and mostly on the inner membrane

of endoplasmic reticulum. It has been well known over the last ten years that this

enzyme exists under two forms: a constitutive (COX-1) and an inducible form (COX-2).

Both enzymes are sensitive to inhibition by conventional NSAIDs. Observations were

made that COX-1 was mainly involved in homeostatic processes and some protective

properties like protection against formation of stomach ulcers, while the COX-2

expression was associated with pathological conditions leading to the development of

COX-2 selective inhibitors. Thus it is desirable to hamper COX-2 activity without

disturbing COX-1 functions. Several methods have been reported166-79 for the evaluation

of the COX-1 and COX-2 inhibitory potency and selectivity of conventional or COX-2

selective NSAIDs. Here job of meloxicam (a benzothiazine derivative) starts because it is

among COX-2 selective NSAIDs and possesses the ability to inhibit prostaglandin

biosynthesis via COX-2 only.

A schematic layout of the mechanism of inflammation and drug action is shown below

(Figure 1.4):

8


Inflammatory stimuli Disturbance of cell membrane

Phospholipids

Arachidonic acid

Benzothiazine derivative

Meloxicam

COX-2 COX-1

Meloxicam binds COX-2 and supresses the formation of Prostaglandins

Endoperoxide Endoperoxide

ProstaglandinSynthase

ProstaglandinSynthase

Prostaglandins Prostaglandins

InflammationPain, Fever

Gastrointestinal &Stomach Ulcer Protection

Figure 1.4 Schematic Representation of Mechanism of Inflammation & Drug Action

1.3.5 Structure-Activity Relationships (SAR)

Within the series of 4-hydroxy-1,2-benzothiazine carboxamides represented by

the following structure (Figure 1.5), optimum activity was observed when R1 was a

methyl substituent. The carboxamide substituent R, is generally an aryl or heteroaryl

9

Chapter: 1 INTRODUCTION substituent because alkyl substituents are less active. Oxicams are acidic compounds4

with pKas that range between 4 and 6.

S

N

O O

OH

NH

O

R

12

345

6

7

8R1

Figure 1.5 General Structural Formula of 1,2-benzothiazine carboxamides

The N-heterocyclic carboxamides are generally more acidic than the corresponding N-

aryl carboxamides and this enhanced acidity was attributed to stabilization of the enolate

anion by the pyridine nitrogen atom as illustrated in tautomer A and additional

stabilization by tautomer B (Figure 1.6).

This explains the observation that primary carboxamides are more potent than the

corresponding secondary derivatives because no H-H bond would be available to enhance

SN

O O

OH

NH

O

CH3

N

SN

O O

NH

O

CH3

N

H+

OO

SN

O O

NH

O

CH3

N

OO

SN

O O

N

O

CH3

N

OO

H

AB

+

Piroxicam

(i)

(ii)

Figure 1.6 (i) Acidic Character of Piroxicam (ii) Stabilized tautomers A & B

the stabilization of the enolate anion. When the aryl group is o-substituted variable results

were obtained, whereas m-substituted derivatives are generally more potent than the

corresponding p-isomers. In the aryl series, maximum activity is observed with a

10

Chapter: 1 INTRODUCTION m-chloro substituent. No direct correlations were observed between acidity and activity,

nor with partition coefficient, electronic or spatial properties in this series. Two major

differences, however, are observed when R = heteroaryl rather than aryl: pKas are

generally between 2 and 4 units lower and anti-inflammatory activity increases as much

as seven-fold. The greatest activity is associated with the 2-pyridyl (as in piroxicam), 2-

thiazolyl, or 3-(5-methyl) isoxazolyl ring systems, the latter derivative (isoxicam) having

been withdrawn from the European market in 1985 following several reports of severe

skin reactions. In addition to possessing activity equal to or greater than indomethacin in

the carrageenan rat paw edema assay, the heteroaryl carboxamides also possess longer

plasma half-lives providing an improvement in dosing scheduling regimens.

1.3.6 Piroxicam Metabolism

Although the metabolism of piroxicam varies quantitatively from species to species,

qualitative similarities are found in the metabolic pathways found in humans, rats, dogs,

and rhesus monkeys. It is extensively metabolized in humans with less than 5% of an

administered dose being excreted unchanged. The major metabolites in humans result

from hydroxylation of the pyridine ring and subsequent glucuronidation, other

metabolites being of lesser importance. Aromatic hydroxylation at several positions of

the aromatic benzothiazine ring also occurs; two hydroxylated metabolites have been

extracted from rat urine. On the basis of NMR deuterium-exchange studies,

hydroxylation at the 8-position was ruled out indicating that hydroxylation occurs at two

of the remaining positions. Other novel metabolic reactions occur. Cyclodehydration

gave a tetracyclic metabolite (the major metabolite in dogs), whereas ring contraction

following amide hydrolysis and decarboxylation eventually yields saccharin. All known

metabolites of piroxicam lack anti-inflammatory activity. For example, sudoxicam (the

N-2-thiazolyl analogue) undergoes primarily hydroxylation of the thiazole ring followed

by ring-opening, whereas isoxicam undergoes primarily cleavage reactions of the

benzothiazine ring. The metabolism of piroxicam is illustrated in figure 1.7 below:

11


SN

O O

OH

NH

O

CH3

N

SN

O O

OH

NH

O

CH3

NHO

SN

O O

OH

NH

O

CH3

N

OH

SN

O OCH3

N N

O

SN

O O

OH

OH

O

CH3 SN

O O

O

CH3 SNH

O O

O

Piroxicam major human metabolite

minormajor metabolite in dogs

Figure 1.7 Metabolism of Piroxicam

1.4 Applications of Benzothiazine derivatives

Benzothiazine derivatives possess versatile type of applications and biological

activities.180-81 Beginning with the electrochemical adsorption studies182 on alloys for

corrosion inhibition, involvement as electrophilic asymmetric fluorination183 agents,

stabilizers184 in rubber vulcanization, fading prevention agents185 to improve colour

image stability and light-fastness, these derivatives cover divergent biomedical186 aspects,

including treatment of immunodeficiency conditions187-190 like asthmatic therapy,191

hyaluronidase inhibition,192-93 anthelmintic activity,194 propanolol comparable β–

sympatholitic activity195 and serving as cytostatic agents.196-97

Benzothiazine derivatives serve as raw material for the syntheses of a wide variety of

molecules of high molecular mass like substituted benzothiazepines,198 play role during

organ operations199-200 and transplantation, reduce gastrointestinal toxicity,201-3 activate

metabolism,204 improve hearing205 in various formulations, antithrombotic, 206-7

hypothermic208 and antihypoxic activities,209 act as histamine receptor antagonist210 and

have been synthesized as potassium channel openers (KCOs) exhibiting the high

vasorelaxant potency211 that is considerably higher than that of the reference

levcromakalim (LCRK). They find their use as matrix metalloprotease inhibitors and

prodrugs for the treatment of joint disease, cancer metastasis, inflammation and

12

Chapter: 1 INTRODUCTION periodontitis.212 The COX-2 pathways have been observed to be involved in bradykinin

B1 receptor-sensitized responses213 that are associated with human umbilical vein. The

1,4-disubstituted benzo-fused urea derivatives act as cytokine inhibitors.214

In short a large number of applications and biological activities have been shown by

the benzothiazine derivatives. A brief description of which is given below:

1.4.1 Fungicide

Fungicides are biological or chemical agents215 that are effective against the fungal

pathogens which can have severe adverse effects on crop yields and quality without

harming the crop. It has been noted that certain fungicides are used to mitigate or prevent

pathogen attack by activating certain defensive responses of plants. Fungicides are

applied in the form of sprays to protect crops against leaf, stem or fruit diseases. They are

safe and effective products to protect crops against fungal diseases or to stop initial

infestation.

During recent years, among new active ingredients, an innovative generation of

fungicides (benzothiazine derivatives) has been developed and introduced216-19 in order to

improve the control in key plant and animal diseases like downy mildew, powdery

mildew, late blight, rynchosporium net blotch and eyespot in plants and infections in

animals. The azole derivatives of benzothiazine were synthesized and evaluated for the

in- vitro and in-vivo activity against Candida albicans. Some of these derivatives showed

very good efficacy against systemic candidiasis in a murine experimental model.220 The

antifungal activities are correlated with well-defined chemical characteristics of the

molecules including the presence of ether function at the side chain. In fact, ether

derivatives are the most active compounds in vivo, although they have little anti-Candida

effect in vitro.221 This discrepancy could be attributed to the fact that benzothiazines are

metabolized to active antifungal compounds and may have in-vivo activity through

improvement of protective immune response and direct antifungal effects. These

derivatives also show immunomodulating activity so that the direct antifungal activity, in

combination with the capability to stimulate the immune response, could result in a

significant increase in in-vivo efficacy.

Agricultural fungicides containing benzothiazine derivatives as active ingredients are

useful to control rice diseases and vegetable phytophythore rot diseases. For example,

13

Chapter: 1 INTRODUCTION application of 3-methylbenzo 1,3-thiazine-2-thione-4-one at 1000 ppm to rice plants with

pyricularia oryzae spores were 100% effective in curing rice blast diseases. In the same

way 3-phenyl-N-(2,2-dimethoxyethyl)-3,4-dihydro-2H-1,4-benzothiazine showed 16-fold

greater anti-fungal activity222 compared to miconazole (reference fungicide) against

Aspergillus niger. In animals opportunistic fungal infections represent a significant cause

of morbidity and mortality223 in immunocompromised patients, including those with

AIDs, cancer and organ transplants. Despite the increase in fungal infections, therapeutic

options are very limited and are often unsatisfactory because of elevated toxicity and an

inability to eradicate infections. The most widely used drug for treatment of Candidiasis

is fluconazole (FCZ). Recently, a new derivative216 of 1,4-benzothiiazine compound FS5,

has been developed. FS5 has an appreciable protective effect against murine Candidiasis.

The results show that intraperitoneal injection of FS5 in mice significantly prolongs the

survival and decreases the kidney fungal burden. This new antifungal agent appears to

work in vivo as a toxic agent against C. Albicans and is a promoter of antifungal

mechanism in natural immune cells.

1.4.2 Herbicide

The undesired vegetation (weeds) in the heart of fields eventually culminates in poor

yield and quality of the crop of particular interest. The most sensitive of these are wheat,

rice, sugar-cane, corn etc.. Benzothiazine derivatives224-25 have also proven their ability to

kill these herbs or at least control their growth, without affecting the main crop

significantly. For instance, these are useful for complete control against Poa annua,226

Speedwell227 and the common weed Echinochloa.228 A diluted emulsion of a herbicide

containing 7-Fluoro-6-(4,5,6,7-tetrahydrophthalimido)2H-1,4-benzothiazine-3(4H)-one

derivatives completely controlled Echinochloa crus-galli, Abutilon theophrasti and

Ipomoca purpurea229 seeded in plowed field soil by pre-emergence soil surface treatment.

Likewise, were controlled Panicum crus-galli, Cyperus difformis, C. serotinus and

Scirpus hotarui, without damage to rice230 in pots experiments.

There are examples of synergistic herbicides containing benzothiazinone oxide

derivatives231 and dichlorothiocarbamoylbenzene, for turf. In such cases, a wettable

powder containing 20% of the benzothiazinone oxide derivative and 30% of the

substituted carbamoylbenzene compound is formulated using white carbon, kaolin clay,

14

Chapter: 1 INTRODUCTION Sorpol 5039 and Sorpol 5050. This type of formulation at a dosage of 1.5 g/m2 of the

field area, completely controlled Cyperus brevifolius and C. rotundus without any

detrimental effect on Z. matrella, by both soil and postemergent treatment. Another

formulation containing a benzothiazine derivative, diatomaceous earth, Na dinaphthyl

methanesulfonate and Na ligninsulfonate232 in 50, 45, 2 and 3% respectively, showed

100% prophylactic effect against Piricularia oryzae in vivo.

1.4.3 Agrochemicals

Chemicals, synthetic or natural which are useful for the betterment of land or crop, one

way or the other, fall in the category of agrochemicals. Some benzothiazine derivatives,

particularly fluoro substituted233 and acrylanilide234 in origin, serve as agrochemicals235

or agrochemical intermediates236 possessing pesticidal and antimicrobial type of

activities.

1.4.4 Metal Analysis

Benzothiazine derivatives form metal complexes with many transition metals in which

mostly they act as bidentate or multidentate ligand237 to donate lone electron pairs into

the partial or completely empty orbitals of metals to form coordinate complexes.

Piroxicam ternary complexes of Fe(II), Fe(III), Co(II), Ni(II), Cu(II) and Zn(II) with

glycine and DL-phenylalanine and platinum(II)-piroxicam complexes238-39 are the well

known examples. A series of copper (II) complexes240 with esters and amides of 3-

carboxylic acids, 1,1-dioxide, 4-hydroxy-2-alkyl-2H-1,2-benzothiazine have been

synthesized and their magnetic measurements made. This complex forming activity of the

benzothiazine derivatives has been utilized as a tool for metal content determinations in

various formulations.

An excellent example is of Piroxicam (a 1,2-benzothiazine 1,1-dioxide derivative) that

has been employed for the spectrophotometric determination of iron (III) in ore,

pharmaceutical formulations, plant material and foodstuff.241 The method is based on the

formation of a chloroform soluble red-color complex (1:1) by the reaction of Fe(III) with

piroxicam in Walpole buffer. Beer’s law is valid over the concentration range of 0.4-6.4

ppm. The coloured complex exhibits an absorption maximum at 510 nm with molar

absorptivity of 1.82 X 104 l.mol-1. cm-1. and Sandell’s sensitivity of 17.32 ng.cm-2. The

absorbances increase linearly with increase in concentration of iron, which are

15

Chapter: 1 INTRODUCTION corroborated by the calculated correlation coefficient value (0.9992). Statistical

comparison of the results with those of direct atomic absorption spectrometry (AAS)

method shows geed agreement and indicates no significant difference in precision.

1.4.5 Use in Polymers and Plastics

Dihydrobenzothiazine derivatives have been reported242 to be useful as stabilizers for

polymers. These stabilizers do not discolourise the polymers or interfere with their cross-

linking pattern. The ‘tensile-strength’ and ‘break-elongation’ parameters of such

polymers have been studied and found good in agreement with the working standards.

Tetrahydro-hydroxy-pyrazino-82 and thio- derivatives86 of 1,2-benzothiazine 1,1-dioxide

have also been synthesized. They absorb UV light above 300 nm. (є = 10800 at λ = 350

nm.), and are useful as U.V. screening material. Because of their general solubility in

organic materials, they may be used as U.V. absorbers in plastics and resins, such as, for

example, polystyrene, polyethylene, polypropylene, polyacrylics (e.g., methacrylate

resins, polyacrylamides, polyacrylonitrile fibers, etc.), polyamide (e.g., nylon) fibers and

polyester fibers. The inclusion of about 0.01-5.0 percent of the absorber, based on the

polymer weight, is usually sufficient to render protection against U.V. light, such as in

plastic films, filters, etc. The absorber may be incorporated into the mixture of monomers

before polymerization to form the polymer, or it may be incorporated into the polymer at

other stages during its handling, as by milling into the polymer together with other

compounding ingredients, or during the spinning of the polymers into fibers, etc.

1,4-benzothiazine readily undergoes aldolization to give mainly two pairs of

diastereoisomeric trimers and tetramers.243 In strongly acidic media, the oligomers are

depolymerized to give 2H-1,4-benzothiazine which, at slightly acidic or neutral pH, is

converted to a mixture of the same trimers and tetramers. These results provide an

improved background to look into the biosynthesis of pheomelanins which are known to

originate by polymerization of 1,4-benzothiaazine intermediates.

1.4.6 Dyes and Pigments

Benzothiazino-anthraquinone, naphthoquinone, anthraquinone and 1,4-benzothiazine

derivatives are used as colorants244 for near-infrared liters, dyes and intermediates245 and

for colouring organic polymers.246 The colour and functionality of thiazine pigments are

due to their so-called supramolecular conjugation247 rather than to their inherent

16

Chapter: 1 INTRODUCTION intramolecular indigo H-chormophore. Of particular importance is their very high opacity

coupled with highly chromatic colours.

Benzothiazine arylidene dyes248 have been found to undergo thermal bleaching in gel

coatings in the presence of base precursors. A photothermographic element is composed

of a support, at least one aqueous coatable photothermopraphic layer, and at least one

aqueous coatable filter dye, wherein the filter dye layer comprises a heat-bleachable

composition consisting of at least one light-absorbing filter dye that is a benzothiazine

arylidene dye, in association with a base precursor. The structure of a yellow-orange

pigment extracted by dilute alkali from the feathers of the new Hampshire strain

chicken249 has also been determined. Certain branched benzoxazinophenothiazine ring

systems are intensely coloured, high-melting solids suitable for application as

pigments.250 Their ease of reduction with sodium dithionide and the ready oxidation of

the reduced compounds to the quinoid forms by atmospheric oxygen suggest their

applicability also as vat dyes.

1.4.7 Photography and Photochromism

Benzothiazine derivatives such as 2,2′-Bi-(2H-1,4-benzothiazines) show

photochromism251 and thermochromism. The colour change is thermally and

photochemically reversible. The photochromism was ascribed to the cis-trans

isomerization about the central double bond, the yellow trans isomer being more stable.

The quantum yield of formation of the cis-benzothiazine revealed that the excited singlet

state of π, π* character is the originating state for the photochromism since there is no

experimental evidence of a triplet intermediate. Durable electrophotographic

photoreceptor suited for use in copiers and printers has also been claimed, which

comprises a substrate, an interlayer, and a photosensitive layer.252 The interlayer consists

of an alcohol soluble resin composition containing a benzothiazine derivative, and the

latent image-forming exposure step employs a light source providing a mid-wavelength >

700 nm. The interlayer reduces the loss of contrast with use and the blemishes caused by

redisual images and substrate surface defects.

PHB (photochemical-hole-burning) recording material containing benzothiazine

derivatives carry out recording253 in the wavelength region of a semiconductor laser. A

toner obtained from butyl methacrylate-styrene copolymer 100, phthalocyanine type blue

17

Chapter: 1 INTRODUCTION dye 10, and 3-benzoyl-2-(2-piperidinoethyl)-3,4-dihydro-2H-1,2-benzothiazine-4-one

1,1-dioxide 5 parts on mixing with iron powder carrier254 produced a developer which

gave high quality blue copy images and showed good durability. The effects of various

factors on the electro-photographic developing properties255-57 of benzothiazine

derivatives have also been studied extensively.

1.4.8 Fodder Additives and Preservatives

Substituted alkyl, aryl, heteroaryl, cyano, nitro etc. 1,4-benzothiazine derivatives have

shown usefulness as animal growth substances258 and improve animal feed utilization .

These have been anti-infective agents to serve as preservatives and given complete

inhibition of Streptococcus and Klebsiella species in agar.

1.5 Biological Activities of Benzothiazine derivatives Benzothiazine derivatives are mainly applied as NSAIDs. Various formulations, separate

or in combinations with other incipients such as β-cyclodextrin,259-61 azithromycin,262

cefixime,263 melatonin,264 maltodextrin,265 amtolmetin guacyl (AMG)266 and

phospholipids267-8 have been prepared either as tablets,269 aerosols270-1 or in the form of

aqueous formulations.272 The drug administration by topical application,273 transdermal

delivery system,274-81 and the bioavailability in blood plasma282 after gastro-intestinal

permeability283 has been extensively studied. Iontophoretic284-6 skin pre-treatments, drug-

polymer interactions287 and additive-influence288-89 on to the drug binding affinity290 has

also been reported. Structural elucidation291-4 of benzothiazine derivatives, crystals,295

complexes and salts296 is continued.

Biological activities of benzothiazine derivatives may be summarized as follows:

1.5.1 Anti-inflammatory

In the past, various attempts have been made to obtain new and better anti-inflammatory

agents.297-309 For the most part, these efforts have involved the synthesis and testing of

various steroidal compounds such as the corticosteroids or non-steroidal substances of an

acidic nature such as phenylbuazone, indomethacin and the like, including the new agent

known as piroxicam. It is specifically an N-(2-pyridyl)-2-methyl-4-hydroxy-2H-1,2-

benzothiazine-3-carboxamide 1,1-dioxide derivative of 1,2-benzothiazine. Its

18

Chapter: 1 INTRODUCTION monoethanolamine salt called ‘Piroxicam Olamine’ is particularly valuable310 in

pharmaceutical dosage forms as a non-steroidal therapeutic agent for the treatment of

painful inflammatory conditions, such as those caused by rheumatoid arthritis, since it is

a crystalline, non-hygroscopic, rapidly-dissolving solid with high water solubility.

Benzothiazine derivatives are major drugs against inflammation and pain. They are well

known inhibitors of cyclooxygenases (COXs). However, many studies indicate that they

may also act on other targets. Acidosis is observed in inflammatory conditions311 such as

chronic joint inflammation, in tumors and after ischemia, and greatly contributes to pain

and hyperalgesia. Administration of these NSAIDs reduces low pH-induced pain. The

acid sensitivity of nociceptors is associated with activation of H+-gated ion channels.

Several of these, cloned recently, correspond to the acid-sensing ion channels (ASICs)

and others to the vanilloid receptor family. Studies have shown:

• that AASIC mRNAs are present in many small sensory neurons along with

substance P and isolectin B4 and that, in case of inflammation, ASIC1a

appears in some larger Aβ fibers.

• that NSAIDs prevent the large increase of ASIC expression in sensory

neurons induced by inflammation, and

• that NSAIDs such as aspirin, diclofenac, and flurbiprofen directly inhibit

ASIC currents on sensory neurons and when cloned ASICs are heterologously

expressed.

These results suggest that the combined capacity to block COXs and inhibit both

inflammation-induced expression and activity of ASICs present in nociceptors is an

important factor in the action of benzothiazine derivatives (NSAIDs) against pain.

In order to determine the minimal inhibitory concentrations (MICs) the benzothiazine

derivatives are applied as their quaternary ammonium salts,312 complexes with

metals313 such as copper (II) or in combinations with β-cyclodextrins314-5, as ointment

bases or gels.316 Mostly the carrageenan induced rat paw edema method is applied to

check the anti-inflammatory activity. Compositions comprising benzothiazine

derivative and magnesium stearate and microcrystalline cellulose or lactose and

starch or aerosil, or magnesium or calcium stearate, or polyethylene glycol 4000

(PEG 4000) as additional accessory substances have been formulated to enhance the

19


anti-inflammatory functions and decrease the ulcerogenic effects.317-8 Indices to

predict topical efficiency of a series of nonsteroidal anti-inflammatory drugs have

been determined experimentally319 by in-vitro studies.

The in-vitro interaction and synergistic activity of the combination of fluconazole

with some nonsteroidal anti-inflammatory drugs has been investigated in Candida

albicans strains (n = 7) by the microdilution checkerboard assay.320 The results were

evaluated visually and by a spectrophotometric microplate reader at 492 nm

wavelength. Fractional inhibitory index was calculated for every strain and

combination according to the minimal inhibitory concentration (MIC). The data

suggested that combination of fluconazole with sodium salicylate, tenoxicam (a

benzothiazine analogue) and diclofenac sodium may prove to be useful as

chemotherapeutic agents for the treatment of C. albicans infections caused by

especially fluconazole-resistant strains.

Using the isolated perfused bovine udder321 as an in-vitro model of skin inflammation,

the effects of topically administered arachidonic acid on prostaglandin and leukotriene

synthesis have also been shown previously. The effect of meloxicam has been found

significant on the inhibition of prostaglandin E2 synthesis, thus reducing the

inflammation. In another experiment eighteen 1-3 month old veal calves322 were induced

with local lung-inflammation and the effect of flumetasone and meloxicam on the

selected hematological and mineral variables was examined. The assayed parameters

were packed red cell volume (PCV), Hb concentration, the number of platelets, red blood

cells, total and differentiated number of white blood cells (WBC) in whole blood of the

calves and Fe, Zn, Cu concentrations in their blood serum by the atomic absorption

spcetrophotometry.

1.5.2 Analgesic and Antipyretic

The analgesic activity of the newly synthesized benzothiazine derivatives is investigated

by acetic acid-induced Writhing Syndrome.323 Most of the derivatives have shown

antipyretic and higher analgesic activities324-34 than acetylsalicylic acid (i.e., aspirin).

Piroxicam-β-cyclodextrin (PBC) is the 1st nonsteroidal anti-inflammatory drug in which

the active substance is complexed with the cyclic oligosaccharide cyclodextrin, which

acts as an artificial receptor. This complex allows single molecules of the NSAID to be

20

Chapter: 1 INTRODUCTION released adjacent to the gastrointestinal mucosa, instead of crystals. Since the piroxicam

is immediately bioavailable in this formulation, the onset of action is similar to that of a

parenteral drug. 335 Since the time of contact with gastric mucosa is reduced, the risk of

direct-contact gastric irritation is also reduced. There is good evidence that PBC is

beneficial in managing acute nonspecific back-pain (BP) but sufficient evidence on

chronic BP is lacking. Thirty one eligible patients, resistant to previous therapy with

different NSAIDs, were treated with PBC. Global assessment of efficacy and tolerability

by physician and patients was performed at the last visit. The results suggested that the

newly developed dosage form of piroxicam is effective and well tolerated in the

treatment of patients with chronic BP. PBC may be an important new treatment option in

this condition.

1.5.3 Antimicrobial and Antiviral

Microbicides which have low toxicity and are useful for controlling slimes, sludges,

bacteria, fungi, and algae in aqueous systems, such as in paper manufacturing, contain the

1,4-benzothiazine and benzoxazine derivatives.336-9 The formulations comprise of

wettable powder, which at 0.63 ppm have shown complete control over Chlorella

vulgaris and Pharmidium foveolarum.

A series of sulfoxides and sulfones were prepared by oxidation of 3,4-dihydro-2H-1,4-

benzothiazines. The antiviral activity340 was evaluated against two RNA viruses

(polio-virus and vesicular stomatitis virus) and one DNA virus (herpes simplex virus

type 1). Polio-virus was susceptible to most of the compounds but neither sulfoxide nor

sulfone derivatives improved activities of the corresponding 3,4-dihydro-2H-1,4-

benzothiazines.

1.5.4 Antibacterial Activity

Benzothiazine derivatives have been synthesized and tested for their activity as

bactericide.341-4 Certain derivatives have shown marginal345-6 antibacterial activities only.

However, compounds such as pyridobenzothiazines,347 have shown minimal inhibitory

concentrations (MICs) in the range of 0.5-2 µg/ml against Escherichia coli. The

benzothiazines produced by reactions of oximes348 with thiourea were screened for

antimicrobial activities and were found to possess antibacterial activity against

Staphylococcus albus, S. aureus and E. coli.

21

Chapter: 1 INTRODUCTION The 1,2-benzothiazine derivatives obtained by reaction of 6-aminopenicillanic acid with

the p-nitrophenyl esters of 4-hyderxy-2-methyl-2H-1,2-benzothiazine-3-carboxylic acid

1,1-dioxide, inhibited Neisseria gonorrhoeae besides S. aureus at concentrations of 31-

500 and 67-500 µg/ml in the form of their potassium salts. The hydroxymethyl-

aminobenzothiazino-rifamycins349 have shown MICs of 0.02-2.5 µM against

Micrococcus luteus and five other bacteria whereas, those of 1,4-benzothiazin-

ethylpiperidine carboxylic acid and oxalate derivatives350 have shown MICs of ≤ 4 µg/ml

against S. aureus Oxford, S. aureus WCUH29, S. pneumoniae 1629, S. pneumoniae

N1387, S. pneumoniae ERY 2, Enterococcus faecalis I, E. faecalis 7, Haemophilus

influenzae Q1, H. influenzae NEMC1, Moraxella catarrhalis 1502, and E. coli 7623.The

substituted piperidinyl-naphthyridinyl ethanol amine derivatives of 3-oxo-3,4-dihydro-

2H-1,4-benzothiazine-6-carboxaldehyde351-2 have MICs ≤ 2 µg/ml against S. epidermidis

CL7, S. aureus WCUH29 and inhibition of DNA gyrase.

1.5.5 Anti-tumor and Anticancer Activities

The mechanisms by which cyclooxygenase inhibitors exert antitumor effects are not

completely defined353 but are postulated to involve antiangiogenic effects and induction

of apoptosis.354 Methods have been disclosed for inhibiting mammalian topoisomerase II

and inhibiting the growth and inducing the regression of malignant cells in mammals355

by the action of substituted pyridobenzothiazine carboxylic acids. Evaluation studies of

treatment with doxorubicin and piroxicam for multicentric lymphoma in dogs,356 under

nonrandomized clinical trials have shown an increase in antitumor activities by 5% only.

The ability of potential chemopreventive agents to prevent vinyl carbamate-induced lung

tumors357-8 was determined in two different experiments. Dexamethasone and piroxicam,

provided in the diet were found to significantly inhibit lung tumors induced by 60 mg/kg

vinyl carbamate at twenty four weeks. Standard non-steroidal anti-inflammatory drugs

(NSAIDs) reduce the risk of colorectal cancer359 by 40-60% and inhibit the telomerase

activity,360-1 but the mechanism by which this occurs is uncertain. Benzothiazines and

their analogues as agents for improving the effect of anticancer drugs, their preparation

and formulations containing them, have also been reported,362-6 particularly interesting

22

Chapter: 1 INTRODUCTION are nitrosourea derivatives of 6-bromo- and 6-chloro-2,3-dihydro-1,4-benzothiazines

synthesized367-8 by isocyanation and successive nitrosation.

The reverse transcriptase-polymerase chain reaction369 and Western blot analysis showed

that cyclooxygenase-2 (COX-2) but not COX-1 was expressed in human non-small-cell

lung cancer (NSCLC) cell lines (A549 and PC14). In a human small-cell lung cancer cell

line (H841), neither COX-1 nor COX-2 was detected. Meloxicam inhibited the growth of

and PGE2 production by both A549 and PC14, but not H841 cells. These findings suggest

that COX-2 may play an important role in pathogenesis and progression of NSCLC, and

that meloxicam may be a useful therapeutic agent in the treatment of NSCLC.

1.5.6 Anti-diabetic and Antihypertensive

Aldose reductase inhibitors370-1 are useful for the treatment of complications associated

with diabetes. In general, among benzothiazine derivatives 3-thioxo compounds were

found more potent inhibitors372 of aldose reductase from human placenta in vitro than the

corresponding 3-oxo derivatives. While many were not very effective in inhibiting

sorbitol accumulation in the rat sciatic nerve in vivo. The 3-thioxo compounds bearing an

isopropyl group at 2-position showed highly potent activity in the in-vivo assay.

1,4-benzothiazin-3-one derivatives373 were found to induce decreased hypertension in

rats. In-vitro inhibitory activity of angiotensin-converting enzyme (ACE) was examined

using 1,4-benzothiazin-3-ones and were found to possess poor ACE inhibitory activity.

However, the 2-ethyl-2H-2,3-dihydro-3-oxo-4H-1,4-benzothiazine-4-acetic acid374 is the

most effective.

1.5.7 Ca2+ -Antagonists

Aminoalkyl-methoxyphenyl substituted benzothiazines were synthesized and their Ca2+

antagonistic activity was measured375 with isolated depolarized guinea pig taenia cecum.

On the basis of their potent Ca2+ antagonistic activity, six benzothiazines were selected

and further evaluated for their vasocardioselectivity. The results suggest that certain

stereospecific isomers would exhibit less adverse effects due to cardiac inhibition than

the reference diltiazem and verapamil in therapeutic use. The substituted benzothiazines

were also found effective as vasodilators376 and cellular Ca2+ antagonists in rabbit’s

aortas at 10-5 M concentrations.

23

Chapter: 1 INTRODUCTION The novel enantiomerically pure benzothiazinone derivatives (HOE 166),377 as their

dihydrochlorides were studied in different experimental animals. It was observed that

their stereoselectivity inhibited KCl, but not noradrenaline-induced contractions of guinea

pig pulmonary arteries, rabbit aorta, rat mesenteric artery preparations, and k-strophantin-

induced enhancement of guinea pig papillary muscle contraction in a dose-dependent

manner. KCl-induced smooth muscle contraction was inhibited by HOE 166 with 50%

inhibitory concentration (IC50) values of ~70 nM (5-11 times less potent than nifedipine,

2-16 times more potent than verapamil), the respective S-(-) enantiomer being ~ 10-fold

less potent. HOE 166 decreased the upstroke velocity of the slow action potential in

partially depolarized guinea pig papillary muscle at similar concentrations as nifedipine.

In heart, brain, and skeletal muscle transverse-tubule membranes, HOE 166 was a 4-15

times more potent inhibitor of reversible (+)-[3H]PN200-110, (-)-[3H]desmethoxy-

verapamil and d-cis-[3H]diltiazem binding compared to its pharmacologically less active

(S)-(-)-enantiomer, with IC50 values in the low nanomolar range. HOE 166 may exert its

Ca2+-antagonistic effect by binding to a Ca2+–channel- associated drug receptor which is

distinct from the 1,4-dihydropyridine, phenylalkylamine, or benzothiazepine-selective

domain. The HOE 166 selective site is, however, allosterically linked to the other sites of

the Ca2+–antagonist receptor complex. Thus HOE 166 is a novel calcium antagonist.

In general, benzothiazine derivatives are potent calcium antagonists378-84 with lesser side

effects than the known reference compounds like diltiazem and verapamil.

1.5.8 Alzheimer’s and Parkinson’s disease treatment

Inventions have been made to provide a drug combination385 comprising of an HMG-

CoA reductase inhibitor and a selective COX-2 inhibitor, which is useful for treating,

preventing and delaying the onset of and/or reducing the risk of developing Alzheimer’s

disease. One object of the invention is to administer the above described combination

therapy to people who do not yet show clinical signs of Alzheimer’s disease, but who are

at risk of developing it. These individuals may already show signs of mild cognitive

impairment. Towards this end, the invention provides methods for preventing or reducing

the risk of developing Alzheimer’s by administering the above-described combination

therapy to the at-risk persons. Such treatment may halt or reduce the rate of further

24

Chapter: 1 INTRODUCTION cognitive decline or, in fact, reverse cognitive impairment or reducing cognitive decline

or impairment resulting from stroke, cerebral ischemia or demyelinating disorders.

Another method is provided utilizing benzothiazine derivatives for preventing, delaying

or reversing the progression of Alzheimer’s disease386 by administering an Aβ42-lowering

agent to a mammal under conditions in which levels of Aβ42 are selectively reduced,

levels of Aβ38 are increased, and levels of Aβ40 are unchanged. The invention provides

methods and materials for developing and identifying Aβ42 -lowering agents. In addition,

the invention provides methods for identifying agents that increase the risk of developing,

or hasten progression of Alzheimer’s disease. The invention also provides compositions

of Aβ42–lowering agents and antioxidants, Aβ42 lowering agents and non-selective

secretase inhibitors, and Aβ42 lowering agents and acetylcholinesterase inhibitors. The

invention further provides kits containing Aβ42–lowering agents, antioxidants, non-

selective secretase inhibitors and/or acetylcholinesterase inhibitors.

The 2-phenyl-3-oxo-2H-1,4-benzothiazine derivatives have been found effective387 in

treatment of brain infarction, cerebral ischemia, brain edema, brain hemorrhage, brain

disorders from injuries, dementia, psychosis, neuropathy, Alzheimer’s disease, etc..

In recent reports, 388-9 it has been hypothesized that a key step underlying the

degeneration of pigmented dopaminergic neurons in the substantia nigra pars compacta

(SNc) in Parkinson’s disease, is an accelerated rate of oxidation of intraneuronal

dopamine in the presence of L-cysteine (CySH) to form initially 5-S-cysteinyldopamine

(5-S-CyS-DA). 5-S-CyS-DA, however, is more easily oxidized than dopamine in a

reaction which leads to the dihydrobenzothiazine (DHBT) 7-(2-aminoethyl)-3,4-dihydro-

5-hydroxy-2H-1,4-benzothiazine-3-carboxylic acid (DHBT-1), a putative endogenously-

formed metabolite that may be responsible for inhibition of mitochondrial complex I and

α-ketoglutarate dehydrogenase, characteristic defects in the Parkisnonian SNc. In this

investigation it is demonstrated that glutathione (GSH) dramatically attenuates the

oxidative transformation of 5-S-CyS-DA into DHBT-1 by two major pathways. In one

pathway, GSH displaces the cysteinyl residue from the o-quinone proximate oxidation

product of 5-S-CyS-DA forming the corresponding glutathionyl conjugate that is attacked

by GSH, to form 2,5-di-S-glutathioneyldopamine, or by released CySH to give 2-S-

cysteinyl-5-S-glutathionyldopamine. The former is the precursor of 2,5,6-tris-S-

25

Chapter: 1 INTRODUCTION glutathionylyldopamine, a major reaction product. However, intramolecular cyclization

of the o-quinone proximate product of 2-S-cysteinyl-5-S-glutathionyldopamine is the first

step in a pathway leading to glutathionyl conjugates of 8-(2-aminoethyl)-3,4-dihydro-5-

hydroxy-2H-1,4-benzothiazine-3-carboxylic acid (DHBT-5). The second pathway

involves nucleophilic addition of GSH to the o-quinone proximate oxidation product of

5-S-CyS-DA forming 2-S-cysteinyl-5-S-glutathionyldopamine the precursor of a number

of glutathionyl conjugates of DHBT-1. These results raise the possibility that strategies

which elevate intraneuronal levels of GSH in dopaminergic SNc cells in Parkinson’s

disease patients may block formation of the putative mitochondrial toxin DHBT-1 and

hence be neuroprotective.

Acetylsalicylic acid, a COX-1/COX-2 inhibitor was used in comparison with meloxicam,

a preferential COX-2 inhibitor to study the possible role of the isoenzymes of cyclo-

oxygenase COX-1 and COX-2 in the MPTP (1-methyl-4-phenyl-1,2,3,6-

tetrahydropyridine) mouse model of Parkinson’s disease.390 As markers of protection the

effects on MPTP-induced striatal dopamine depletion, locomotor activity, cell loss, and

tyrosine hydroxylase immunoreactivity (TH-IR) in the sunbstantia nigra pars compacta

was determined. Male C57BL/6 mice (n = 82) were treated with a single dose of

acetylsalicylic acid (10, 50, 100 mg/kg i.p.) or meloxicam (2, 7.5, 50 mg/kg i.p.)

immediately prior to administration of MPTP (30 mg/kg s.c.) or saline. After 7 days the

mice were sacrificed to analyze striatal dopamine and metabolite levels. Nigral sections

were processed for Nissl-staining and TH-IR. In the saline-treated MPTP control group

striatal dopamine levels were reduced to 15.9% of control values. Dopamine depletion

was significantly attenuated to values of 37.1 and 38.6% of saline control values by

acetylsalicylic acid (50 and 100 mg/kg) and to values of 36 and 40% by meloxicam (7.5

and 50 mg/kg) respectively. MPTP-induced decrease of locomotor activity was

significantly attenuated by acetylsalicylic acid and meloxicam. Remarkably, the MPTP-

induced decrease of TH-IR as well as the loss of nigral neurons was nearly completely

prevented by acetylsalicylic acid (100 mg/kg) and meloxicam (7.5 and 50 mg/kg). In

conclusion, the inhibition of either COX-1/COX-2 by acetylsalicylic acid or

preferentially COX-2 by meloxicam provided a clear neuroprotection against MPTP-

toxicity on the striatal and nigral levels.

26


1.5.9 Multiple Pharmacology

1.5.9.1 Writhing Syndrome Antagonism: Ring expansion products of

2H-1,4-benzothiazin-3-(4H)-ones with trimethylhalosilane, hydrogen peroxide and water

were tested for biological activities. The derivatives391 at 60 mg/kg i.p. in mice gave

100% antagonism of the Writhing Syndrome induced by i.p. injection of 10 ml/kg 0.7%

HOAc-saline solution and, at 60 mg/kg i.p. decreased rectal temperature 1.1º in rats with

yeast-induced pyresis.

Hydroxy and acyloxy derivatives of benzothiazine and benzothiadiazine used as AMPA

receptor modulators392-3 showed activity greater than similar prior art compounds. These

can be used for treatment or prevention of age-related mnemo-cognitive disorders,

anxious or depressive syndromes, progressive neurodegenerative disorders, Azheimer’s

disease, Pick’s disease, Huntington’s chorea, schizophrenia and the sequela of acute

neurodegenerative disorders, ischemia, and epilepsy. Nine specific examples were

prepared. For instance, 6-methoxy-1,1-dioxo-1,2-dihydrobenzo[d]benzoisothiazole-3-one

was converted to invention compound in 7 steps. The intermediate underwent a sequence

of: (1) N-alkylation by chloroacetone, (2) base-catalyzed rearrangement to give an acetyl-

substituted benzothiazinol, (3) acid-catalyzed deacetylation in ethylene glycol with

concomitant ketalization, (4) methanolysis of the ketal, (5) hydrogenolysis of the formed

ketone, (6) demethylation of the methoxy group and (7) benzoylation of the resultant

hydroxyl group. In a test of AMPA-induced excitatory currents in Xenopus oocytes,

strongly potentiated the effects of AMPA. In particular, some derivatives gave a 2-fold

increase in current at 11.9 µM and a 5-fold increase at 49.2 µM.

1.5.9.2 Migraine treatment: Pharmaceutical compositions useful in the

treatment of migraine contain metoclopramide394 and one or more NSAIDs (e.g.

naproxen) in unit dosage form. By selecting NSAIDs that are non-acidic or segregating

the metoclopramide and NSAID, the storage life of the compositions has been increased.

Also disclosed are coordinated dosage forms for the sequential release of drugs. The

invention encompasses methods of treating migraine using any of these dosage forms.

27


1.5.9.3 Osteo-arthritic Activity: Since non-steroidal anti-inflammatory

drugs (NSAIDs) may impair the ability of the chondrocyte to repair its damaged

extracellular matrix, exploration of changes in the metabolism of newly synthesized

proteoglycan and hyaluronan (HA) molecules produced by aceclofenac, diclofenac and

meloxicam395 in human osteoarthritic (OA) cartilage, has been made. Explants were

sampled from the medial femoral condyle and were classified by use of the Mankin’s

histological- histochemical grading system. In contrast, and in a dose-dependent manner,

aceclofenac and meloxicam both increased the synthesis of proteoglycans and HA in

explants with MOA and SOA. These two NSAIDs also reduced significantly the net loss

of [-3H]-proteoglycans and [-3H]-HA molecules from cartilage explants. The data

obtained in short-term in-vitro cultures indicated that, at the concentrations found in

synovial fluid, aceclofenac and meloxicam may exert a favourable effect on the overall

metabolism of proteoglycans and HA in cartilage with MOA and symptomatic

osteoarthritis (SOA).

Efficacy and safety of an NSAID (piroxicam) gel396 in the treatment of osteoarthritis of

the knee has been evaluated in comparison with a homeopathic gel. Radiographically

confirmed 184 patients with symptomatic osteoarthritis of the knee were entered into a

pragmatic randomized, double-blind controlled trial and treated with 1 g of gel three

times daily for four weeks. The two types of gels were found equally effective. Further, it

was observed that the homeopathic gel supplemented by simple analgesics may provide a

useful treatment option for patients with osteoarthritis.

1.5.10 Prostaglandin (PGEs) Synthetase Inhibitors

In rats, administration of ketoprofen, flurbiprofen, sudoxicam, naproxen, fenoprofen or

indomethacin (30 mg/kg, orally), inhibited the prostaglandin synthetase activity.397-8

Injection of bacterial lipopolysaccharide (LPS) into male rats activates genes that in turn

induce many enzymes that participate in the animals response to LPS. There is induction

of inducible NO synthase (iNOS) and cyclo-oxygenase-2 (COX-2) in many tissues. This

induction could result from combination with cell-surface LPS receptors that directly

induce both genes, or the NO released as a result of iNOS induction could induce COX-2.

To distinguish between these two possibilities, specific inhibitors of iNOS and COX-2

activity, aminoguanidine (AG) and meloxicam (MLX), respectively were injected either

28

Chapter: 1 INTRODUCTION peripherally or intracerebroventricularly into rats, and their effect on the NO and PGE

production induced by LPS in the medial basal hypothalamus (MBH) and anterior

pituitary gland (AP) were determined. Peripheral injection of AG blocked iNOS-derived

NO production in the AP but not in the MBH. When AG was injected, iNOS-derived NO

production in the MBH was blocked. MLX injected peripherally blocked COX-2-derived

PGE2 production in the MBH and AP, whereas AG injected peripherally or i.c.v. was

ineffective.

Term and preterm labor are associated with increased fetal hypothalamic-pituitary-

adrenal (HPA) activation399 and synthesis of prostaglandins (PGs) generated through the

increased expression of prostaglandin H synthase-II (PGHS-II) in the placenta. During

meloxicam infusion there were significant decreased in-fetal plasma PGE2, ACTH, and

cortisol concentrations, and PGFM concentrations in maternal plasma. In control animals,

frequency of uterine contractions, maternal plasma PGFM, fetal plasma PGE2, ACTH,

and cortisol concentrations increased after RU486 administration, and continued to rise

during saline infusion until delivery occurred.

1.5.11 Anti-oxidant Action

Piroxicam was used in healthy chickens kept under controlled conditions to prevent

and/or reverse Ascites Syndrome (AS) in broilers,400 and thus reduced mortality.

Piroxicam at 0.40 mg/kg, lowered the thiobarbituric acid reactive substances (TBARS)

pool for 2-3 weeks in the lung, liver and heart, thus decreasing the oxidative status in

these tissues. These doses of daily administered piroxicam were well tolerated. Among

these three tissues, the lung had a higher TBARS pool. Piroxicam treatment did not

modify feed consumption nor feed conversion of broilers. Treatment with non-steroidal

anti-inflammatory drugs caused a slight mortality increase without a statistical

significance. Thus, piroxicam treatment decreased TBARS but did not reduce mortality

caused by AS.

In-vitro effects of widely used non-steroidal anti-inflammatory drugs (NSAIDs) and

paracetamol were studied on oxidative stress-related parameters of human red blood cells

(RBC). Membrane lipid integrity, activity of erythrocyte antioxidant enzymes; i.e.,

glutathione S-transferase (GST),401 selenium-dependent glutathione peroxidase (Se-GPx),

29

Chapter: 1 INTRODUCTION and catalase (CAT), and hemolytic/stabilizing action of the drugs on erythrocyte

membrane were assessed. Diclofenac, indomethacin and paracetamol at the therapeutic

and higher concentrations, and dipyrone at the high concentration exerted a statistically

significant inhibition on hydrogen peroxide forced erythrocytic membrane lipid

peroxidation (EMLP). Increased hemolysis was observed by Na-salicylate, naproxen and

ketorolac at therapeutic and higher concentrations, and by diclofenac and tiaprofenic acid

at high concentrations, while the others seemed to stabilize the membrane at the same

conditions. Na-salicylate inhibited GST activity at the therapeutic dose, however

activated the same enzyme at high concentrations. Naproxen, tiaprofenic acid and

piroxicam caused a decrease in GST activity at therapeutic doses. Paracetamol caused

activation at a high dose. Tiaprofenic acid, ketorolac, naproxen and piroxicam caused a

significant Se-GPx inhibition. Erythrocyte CAT activity was increased by Na-salicylate,

acemetacin, and tenoxicam at the therapeutic, and by dipyrone at the high concentration.

The results suggest that NSAIDs and paracetamol may be involved in oxidative/anti-

oxidative processes of human erythrocytes. Also, the in-vitro EMLP method can be

considered as a simple test for evaluating possible antioxidant potency of chemicals.

In another study the aim was to compare the effects of two NSAIDs, members of the

same family with a different cyclooxygenase (COX) inhibition selectivity, meloxicam,

preferent COX-2 inhibitor, and piroxicam, preferent COX-1 inhibitor, on oxygen radical

generation in rat gastric mucosa.402 Therefore, the activity of oxidative stress-related

enzymes such as xanthine oxidase (XO), superoxide dismutase (SOD) and glutathione

(GSH) homeostasis were studied in rats. Gastric prostaglandins (GPs) were also assessed

as a measure of COX-1 inhibition. Both oxicams produced a similar extent of the gastric

mucosal damage and a significant decrease in PGE2 synthesis, however only piroxicam

induced an increase of both myeloperoxidase (MPO) activity and tumor necrosis factor

(TNF)-α content in the gastric mucosa, indicating that neutrophil-derived free radicals

were involved in gastric injury. Furthermore, both compounds reduced SOD activity and

increased XO activity in gastric mucosa. The results also revealed modifications in GSH

metabolism: although glutathione peroxidase (GSH-px) activity was unaffected by

meloxicam or piroxicam administration, both glutathione reductase (GSSG-rd) activity

and total GSH content were significantly decreased after dosing. These results suggest

30

Chapter: 1 INTRODUCTION that under the experimental conditions, meloxicam, preferential COX-2 inhibitor causes

gastric lesion in rats comparable to those seen with the traditional NSAID piroxicam,

preferential COX-1 inhibitor. In addition to suppression of systemic COX activity,

oxygen radicals probably derived via the XO, and neutrophils play an important role in

the production of damage induced by both oxicams. Moreover, the decrease in SOD

activity and changes in glutathione homeostasis and gastric mucosa may also contribute

to pathogenesis of meloxicam- or piroxicam-induced gastropathy.

1.5.12 Central Nervous System (CNS) Stimulating Activity

Benzothiazine derivatives have shown activities both as central nervous system (CNS)

depressants403 and anti-depressants.404

An experimental study was made to check whether NS-398, a selective cyclo-oxygenase-

2 (COX-2) enzyme inhibitor, and piroxicam,405 an inhibitor of COX-2 and the

constitutively expressed COX-1, protect neurons against hypoxia/re-oxygenation injury.

Rat spinal cord cultures were expressed to hypoxia for 20 hours followed by re-

oxygenation. Hypoxia/re-oxygenation increased lactate dehydrogenase (LDH) release,

which was inhibited by piroxicam (180-270 µM) and NS-398 (30 µM). Cell counts

confirmed the neuro-protection. Western blotting revealed no COX-1 or COX-2 proteins

even after hypoxia/reoxygenation. Production of prostaglandin E2 (PGE2), a marker of

COX activity, was barely measurable and piroxicam and NS-398 had no effect on the

negligible PGE2 production. Hypoxia/reoxygenation increased nuclear factor-kappa

B(NF-kB) binding activity, which was inhibited by piroxicam but not by NS-398. AP-1

binding activity after hypoxia/reoxygenation was inhibited by piroxicam but strongly

enhanced by NS-398. However, both COX inhibitors induced activation of extracellular

signal-regulated kinase (ERK) in neurons and phosphorylation of heavy molecular weight

neurofilaments, cytoskeletal substrates of ERK. It is concluded that piroxicam and NS-

398 protect neurons against hypoxia/reperfusion. The protection is independent of COX

activity and not solely explained by modulation of NF-kB and AP-1 binding activity.

Instead, piroxicam and NS-398-induced phosphorylation through ERK pathway may

contribute to the increased neuronal survival.

31


1.6 Plan of Work

In-depth review of literature has shown clearly that an attempt has always been made,

particularly at positions 2-, 3- and 4- of the 1,2-benzothiazine 1,1-dioxide nucleus, to

attach some substituted carbonyl and carboxamide derivatives in order to enhance its

biological activity. Sulfonamide derivatives have never been tried. Further, reactions of

Wittig reagent at any of these positions have also not been explored. Therefore, we

devised following schemes to perform experimental research work:

(P.T.O)

32


S

O

O O

SN

O

O O

O

O

CH3

(1)

(2)

SNH

O O

OH

O

O

CH3

(3)

(4)(6)

NaOMe

DMF

MeIDMF

1. NaOMe/ DMF2. MeI or DMS

3. HCl

1. MeI/DMF/ NaOH2. HCl

1. NaH/DMF2. HCl

Path c

Path b

NaOMeMeOH

Path a

DMF

NNa

O

O

CH3Cl

S NHO O

O

OCH3

O

O

CH3

(5)

SN

O O

OH

O

O

CH3

CH3S N

O O

O

OCH3

O

O

CH3

CH3

NH2N

xylenereflux

7

SN

O O

OH O

CH3

NNH

(Piroxicam)

Scheme-1: Lay-out for the synthesis of 4-hydroxy-N-(2-pyridyl)-2-

methyl-2H- 1,2-benzothiazine 1,1-dioxide (Piroxicam)

33


SNH

O

O OS

N

O

O O

OH

SN

O

O O

Cl

SN

O

O O

SO3H

SN

O OCH3

O

SN

O OCH3

O

Br

SN

O OCH3

OHSO3R

SNH

O

O O

OCH3

SO3CH3

13 R = CH313a R = H

14 15

8 9

1011

12

1. NaH, DMF

2. MeI3. HCl

reflux, 5 min.

SOCl2reflux10 min.

Formaldehyde-sodium bisulfite adduct

SOCl2

1. Formaldehyde- sodium bisulfite adduct / SOCl22. NaI, Acetone3. Na2SO34. HCl

1. NaI, Acetone

2. Na2SO33. HCl

1.MeONa, MeOH2. HCl

NBS, AIBN

CCl4

1. NaI, Acetone2. Na2SO33. HCl1. N

BS, AIBN / CCl 4

2. NaI, A

cetone

3. Na2S

O3

One-pot

CH2O

Scheme-2: Lay-out for the synthesis of 3-sulfonic acid 1,2-

benzothiazine 1,1-dioxide

34


ClO O

O

OR'

SNH

O O

SO2R

H2NOCH3

O

SNH

O O

O

O

Cl

O

SNH

OO

O

HOH3C

OH-

PPA

16 18

20

23(a-b)

24(a-b)

R = 16 = OH 16a = NH2

1. Zn Benzene2. H+, rt

Na/R'OH

19

xylene

SNH

O O

O

SNH

O O

O

OR'Ph3P

OR'

OR'

O PPh3

SNH

O

OR'

O OS

NH

O O

O

OR'

H

O

O

R'O

23 R'

a = CH3 b = C2H5

17

21

22

Scheme-3: Lay-out for the synthesis of 4-(alkoxycarbonylmethylene)-

3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (23a-b)

35


SNH

O

O OS

N

O

O O

Cl

SN

O

O O

NO2

SN

O OCH3

O

SN

O OCH3

O

Br

SN

O OCH3

OHNO2

SNH

O

O O

OCH3

NO2

14

15

8

9

10

2526

1. MeON a (1 equiv.) MeOH

2. HCl

NBS, AIBN CCl4

1. NBS, AIBN / CCl42. NaNO2 / DMSO3. HCl

27

One-pot

1. NaNO2, DMF

2. HCl

NaNO2 DMF rt

1. CH2O-NaHSO

3Aadduct / SOCl2One-pot

1. NaH, DMF2. MeI 3. HCl

1. MeONa (3 equiv.) MeOH2. MeI3. HCl

2. NaNO2, DMF

Scheme-4: Lay-out for the synthesis of 3-nitro-1,2-

benzothiazine 1,1-dioxide

36


O

OR

SNH

O O23

SNH

O

O O

SN

O

O O

SO3H

SN

O OCH3

OHSO3R

13

SN

O OCH3

OHNO2

27

11

H2N R"Corresponding derivatives.

where: R"= aliphatic, aromatic, alicyclic, heteroaromatic etc. groups.

1

SN

O O

OH

O

O

H

3

CH3

SN

O O

OH

O

O

CH34

CH3

Scheme-5: Derivatization

37

Chapter: 2 LITERATURE SURVEY

LITERATURE SURVEY

Since the time Braun et al., synthesized the first benzothiazine45 in 1923, a new

class of heterocyclic compounds began to flourish to produce thousands of lead

compounds for the treatment of various diseases. The anti-inflammatory and analgesic

action of these drugs came into evidence first by Abe406 and co-workers in 1957. This

was the beginning of thousands of benzothiazine derivatives with potent biomedical,407

agrochemical and microbicidal activities.408 In recent years, therefore, interest has been

cultivated to synthesize these new heterocyclic molecules. A brief history of already

known 1,2-benzothiazine 1,1-dioxide derivatives is presented as follows:

Abe and co-workers17 were the first to apply the principle of Gabriel-Colman

rearrangement of phthalimides to the rearrangement of N-phenacylsaccharin which gave

3-benzoyl-2H-1,2-benzothiazin-4-(3H)-one 1,1-dioxide (3a) as shown in Scheme-6.

SN

O O

R

O

EtOH

2 NaOEt SNH

R

OO

O O

(HOCH2)2

SNH

O O2 3 28

O O

CH3I

SN

O

O OCH3

14

NaH

R'NCOSN

NH

OOH

O O

R'

CH3

29

H+

H+

Scheme-6

3a = R = C6H53b = R = CH33c = R = OCH3

O

2a = R = C6H52b = R = CH32c = R = OCH3

38


Zinnes et al., applied these conditions46 to N-acetonylsaccharin (2b) to obtain

(3b). Ketalization of (3b) also resulted in deacetylation to yield (28). After N-methylation

and hydrolysis of the ketal (28), the 1,2-benzothiazine (14) was obtained. They reported a

failure to condense (14) with esters such as EtOAc or dimethyl oxalate in presence of

base. This result was attributed to the rapid self-condensation of (14). Subsequently, o-

acetylation of (14) was observed with acetyl chloride.

However, condensation of (14) with aryl and alkyl isocyanates using NaH as base

was achieved by Lombardino and co-workers.409 Because of the rapid self-condensation

of (14) the simultaneous addition of a combination of (14) and isocyanate to the hydride

was found to be a practical technique. By this procedure a number of previously

unknown 3-carboxamides of 2-methyl-4-hydroxy-2H-1,2-benzohiazine 1,1-dioxide (29)

were made and their anti-inflammatory activity determined.

To avoid the preparation of various isocyanates, (3c) was proposed to give the

same examples of carboxamide (29) after reaction with suitable amines. In analogy with

the work of Abe on N-phenylacylsaccharin, rearrangement in basic media of 3-oxo-1,2-

benzoisothiazoline-2-acetic acid methyl ester (2c) was expected to produce (3c).

SN

O O

O

O SNH

OO

O O2c 3c

SN

NH

OOH

O O

R'

CH3

29Scheme-7

OCH3 CH3

Sodium methoxide (NaOMe) was used in a variety of solvents in an effort to maximize

yields of this rearrangement and it was eventually found that the best results were

obtained in dimethylsulfoxide (DMSO). N-alkylation of (3c) followed by reaction with

amines under forcing conditions then provided the desired structural variants of (29). No

39

Chapter: 2 LITERATURE SURVEY useful yields of products could be realized by reaction of (3c) itself with amines in a

variety of solvents, even at temperatures above 150°. Even after N-alkylation of (3c),

heating of the resulting ester with an amine to 130° for 18 hr in dimethyl formamide

(DMF) or xylene was required to produce optimum yields of amides of type (29).

The compounds of the type (29) appeared to be of particular interest, since a

paper describing their metabolism was published56 by Lombardino et al., in 1971. Zinnes

and co-workers found this type of compounds to be potent anti-inflammatory agents410

and prepared a variety of derivatives in an effort to find more active compounds and

define structure-activity relationships. Lombardino et al., synthesized compound (31) and

its derivatives (3c, 31a-b), by the base-catalyzed reaction of ketones (14, 30a-b) with a

variety of isocyanates (See Table I-III, page 66-70, compounds 32-73). Difficulties

arising from base-catalyzed self-condensation of (30) were over-come by the slow

addition of a mixture of (30) and the isocyanate to a suspension of sodium hydride in

DMF.

SN

NH

OOH

O O29

SN

O

OOH

O O31

Scheme-8

SN

O

O O30

R1

14, 30a, R1= CH2CO2CH3 b, R1= CH2CN

1.NaH in THF2. R2NCO3. H3O

+

R2

R1

29a, R1 =H, R2 = aryl, heterocycle, b, R1 =CH3, R2 = aryl, heterocycle,

R4

R1

Method A

Method BR2NH2 in xylene

3c, 31a, R1= H; R4=C2H5 b, R1= CH3;R4=C2H5 c, R1= R4=CH3

40


Zinnes and co-workers prepared compounds (33-35), (45-50) and (52) by the

same reaction but employed a different experimental technique. They adopted a

convenient method for the preparation of the pre-formed anion (30) with a minimum of

self-condensation. The procedure (designated method A) was also utilized with ethyl

isothiocyanate and phenyl isothiocyanate to prepare the thioamides (65) and (66)

respectively, but the same conditions employed with ethyl isocyanate, failed to give more

than trace amounts of (64). The latter was ultimately obtained in 78% yield by the use of

method C as shown in table I and II (page 66-69). Compound (64) was also obtained in

11% yield by the reaction of ethyl isocyanate with the bromo-magnesium derivative,

generated by treatment of (14) with isopropyl magnesium bromide (Scheme-8).

Compounds (51) and (54-58) were prepared by reacting ester (31b) with an

appropriate amine in refluxing xylene (method B). This is essentially the method

described by Lombardino et al., except that Zinnes et al., have employed 4A molecular

sieves rather than a tedious intermittent distillation for removal of the alcohol formed.

Scheme-9

SN

O O74

CH3

COCl2, Et3N

in benzene

Method C

N

SN

O O75

CH3

N

R2R3NH, Et3N

SN

O O76

CH3

N CONR2R3

R2= alkyl, aryl R3= H, alkyl, aryl

SN

O O29b

CH3

OHCONR2R3

H3O+

Cl

O

41

Chapter: 2 LITERATURE SURVEY The aforementioned authors reported their in-ability to carry out aminolysis reactions

with the 2-unsubstituted ester (3c), though they did obtain the desired product, (32), by

catalytic debenzylation of the corresponding 2-benzyl derivative. Zinnes et al., have

successfully employed method B for the direct conversion of (31a) to (29b) (Scheme-9).

The N-methyl derivative (40) was obtained by alkylation of (33) using sodium

hydride and diethyl sulfate tetrahydrofuran as well as by method C. In this completely

new method the enamine (74) derived from ketone (30) was reacted with phosgene to

give the acid chloride (75). The latter reacts with an amine to give enamine-amide (76)

which can be hydrolyzed to (29b). The prototype (29b) has the same order of activity as

phenylbutazone when evaluated against adjuvant-induced polyarthritis as well as

carrageenin-induced edema. Its acute toxicity is less than that of phenylbutazone. The

structural modifications described herein all resulted in decreased or complete loss of

activity in the carrageenin test.

Six new chiral heterocyclic systems (77-82) were prepared411 by Todd et al., in

which the sulfur, nitrogen and carbon of the sulfoximide function were part of the ring

system. Two general strategies for synthesis are envisioned, the first of which involves

reactions of a sulfoximide already present in the ring. All three protons of A are slightly

acidic, and by proton abstraction with base might be turned into nucleophilic reaction

sites. In addition to the two potential nucleophilic sites of B, substituent ‘a’

HC S

NH

O

HC

A

S

N

O

C

a

*S

O

C

a

C D

H

H H

S

N

O

C

H

BFigure 2.1 General structures for abstraction of protons by Todd’s methods

42

Chapter: 2 LITERATURE SURVEY of the aromatic ring might be manipulated for synthetic purposes. In the second approach,

the sulfoximide unit might be generated from a sulfoxide in a ring-closing nitrenation

reaction (C → D). The synthesis of these six type of systems makes use of one or the

other of these two strategies.

1-phenyl-3-oxo-1,2-thiazet-1-ine oxide (77) was obtained from S-methyl-S-

phenylsulfoximide, butyllithium and carbon dioxide and 1-p-tolyl-4-oxo-2,5-

dihydroisothiazole oxide (78b) was formed from S-methyl-S-p-tolylsulfoximide.

S

NH

O

CH3C6H5 S

N

O

C6H5

O

1. 2 BuLi2. CO2 3. H3O+

90a 77

Scheme-10

The similarly prepared phenyl analogue (78a) with diazomethane gave 1-phenyl-4-oxo-

2,5-dihydroisothiazole oxide methyl ether (83). Treatment of S,S-dimethylsulfoximide

S

NH

O

CH3

90a, R= H b, R = CH3

p-RC6H41. NaH2. BrCH2CO2R' S

N

O

CH3p-RC6H4

CH2CO2R'

91a, R= H; R' = C4H9 b, R = CH3; R' = C2H5

NaH,

S

N

OHO

p-RC6H4

78a, R= H b, R = CH3

S

N

O

CH3p-RC6H4

CH2CO2H

H2O

H+ or OH-

H2O, OH-

83, R = CH3Scheme-11

90 91

7883

43

Chapter: 2 LITERATURE SURVEY with 1,3-diphenylpropynone and sodium hydride gave 1-methyl-3,5-diphenyl-1,2-

thiazene oxide (84). Similarly optically active (-)-(R)-1-p-tolyl-3,5-diphenyl-1,2-thiazene

H3C

SH

Op-CH3C6H4

NH(-)-(R)

+ C CC

O

C6H5C6H5NaH

(CH3)2SON

HS

O

C6H5 C6H5(-)-(R)

Scheme-12

90b 79, 84

R

79, R = p-CH3C6H4

84, R =CH3

oxide [(- (R)-3] was prepared from (-)-(R)-S-methyl-S-p-tolylsulfoximide [(- )-(R)].

Methyl 2-methylthio-5-methylphenyl ketone (85) was used to synthesize 4H-1,6-

dimethyl-3-oxo-1,2-thiazanaphthalene oxide (80) and 1,5-dimethyl-3-oxobenzo[d]-1,2-

isothiazole oxide (86).

H3C

S CH3

C

O

CH3 H3C

S CH3

CH2

1. Willgerodt

2. H3O+

CO2H

NaIO4

H3C

S CH3

CH2

CO2H

O

85 93 94

NaN3, H2SO4

NS

CH3O

H3C O80

1. Br2, KOH2. H3O+

H3C

S CH3

CO2H

O

92H3C

S

C

86

O CH3

N

O

Scheme-13

NaN3, H2SO4

Methyl 2-methylsulfinyl-5-methylphenyl ketone (95) was used to obtain 1,3,6-

trimethylbenzo[e]-1,2,4-thiadiazene oxide (81), 1,6-dimethyl-3-oxobenzo[e]-4H-1,2,4-

44


H3C

S CH3

C

O

CH3

NaN3, H2SO4

95

N

NS

CH3O

H3C

81

Scheme-14

O

CH3

NH2

NHS

CH3O

H3C96

10% NaOH,HCl, AcOH

N

NS

CH3O

H3C 89N

NS

CH3O

H3C87

CO2CH3

HCO2H

NH

NS

CH3O

H3C

82

O

N H3O+ Cl-

N

NS

CH3O

H3C

88

CO2-

H

+

N)2CO

thiadiazine oxide (82), 1,6-dimethyl-3-carbomethoxybenzo[e]-1,2,4-thiadiazene oxide

(87), 1,6-dimethyl-3-carboxylbenzo[e]-1,2,4-thiadiazene oxide (88), and 1,6-

dimethylbenzo[e]-1,2,4-thiadiazene oxide (89).

Next advancement came in synthesis of benzothiazine class of compounds when

Lombardino synthesized412 for the first time, the metabolites of piroxicam, the then

known anti-inflammatory drug belonging to the 1,2-benzothiazine 1,1-dioxide class of

compounds. He synthesized four possible pyridine monohydroxylated metabolites of the

anti-inflammatory agent piroxicam for comparison with a natural pyridine-hydroxylated

metabolite of this compound. In addition, another metabolite of piroxicam, derived from

dehydration of the parent drug, was made and characterized.

45

Chapter: 2 LITERATURE SURVEY Ferrari et al., synthesized413 a new benzothiazine derivative, after Lombardino, in

1982. It was N-(2-pyridyl)-2-methyl-4-cinnamoyloxy-2H-1,2-benzothiazine-3-

carboxamido-1,1-dioxide obtained by the reaction of piroxicam with cinnamic acid or

cinnamoyl chloride. Owing to its peculiar ester structure, the new product was endowed

with outstanding pharmacological and toxicological activities, particularly with reference

to its tolerableness, to make it a therapeutically valuable anti-inflammatory drug.

SN

O O

OH

NH

ON

CH3

CHCl

O+ N

or Et3N

SN

O O

O

NH

ON

CH3

HC

O

7 98 99

Scheme-15

rt, 2h

Jagadish and co-workers414 synthesized 4-Hydroxy-N-[5-(hydroxymethyl)-3-

isoxazolyl]-2-methyl-2H-1,2-benzothiazine-3-carboxamde 1,1-dioxide (101), the major

oxidative human metabolite of isoxicam (100), and [(5-methyl-3-

isoxazolyl)amino]oxoacetic acid (102), the major rat metabolite of isoxicam (100), in

1985. The metabolite (101) was synthesized by condensation of the known benzothiazine

ester (104) with the isoxazolamine (105b) that was synthesized in a nine-step sequence

starting with 5-methyl-3-isoxazolecarboxylic acid (106). Bromination of (106) by N-

bromosuccinimide (NBS) gave 5-(bromomethyl)-3-isoxazolecarboxylic acid, which was

converted to the carbamate ester via a Curtius rearrangement of the acid azide.

Displacement of bromine with silver acetate gave the acetoxy compound that on

hydrolysis produced the unstable 3-isoxazolamine derivative (105a), which was

converted to the OSiMe, derivative (105b). The compound (102) was synthesized by

46

Chapter: 2 LITERATURE SURVEY reaction of ethyl oxalyl chloride with 5-methyl-3-isoxazolamine followed by base

hydrolysis.

SN

O O

OH

NH

O

CH3

100

NO CH3

NO CH3

HOOCOCHN

102

SN

O O

OH

NH

O

CH3

103

NO CH3

OH

Figure 2.2 Isoxicam (100) and its human metabolites

NO CH3

HOOC

NO

H2NOR

SN

O O

OH

CH3

104

COOCH3

105

106

9 steps

+S

N

O O

OH O

CH3

101

NO

NH OH

105 a, R = H b, R = SiMe3Scheme-16

A series of novel oxyethyl derivatives of certain selected enolic oxicam

compounds was disclosed by Charles415 in 1988, including certain novel oxyethyl

derivatives of 4-hydroxy-2-methyl-N-(2-pyridinyl)-1,2-benzothiazine-3-carboxamide

1,1-dioxide (piroxicam). These particular compounds are useful in therapy as prodrug

forms of the known anti-inflammatory and analgesic oxicams. Typical and preferred

member compounds include 4-(2-hydroxyethyloxy)-2-methyl-N-(2-pyridinyl)-2H-1,2-

benzothiazine-3-carboxamide 1,1-dioxide, 4-(2-hydroxyethyloxy)-2-methyl-N-(6-methyl-

2-pyridinyl)-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide and N-[1-(2-hydroxy-

ethyl)-2-pyridinium]-2-methyl-2H-1,2-benzothiazine-3-carboxamide 1,1-dioxide 4-

enolate. The synthesized new derivatives are of the following general formula:

47


SN

O O

OH

NH

ON

CH3

107 108 109

R1

SN

O O

NH

ON

CH3

R1

SN

O O

O

NH

ON

CH3

R1

CH2CH2OR2 CH2CH2OR2-O

e.g., R = H=7 (piroxicam)

Figure 2.3 Oxyethyl derivatives of 1,2-benzothiazine 1,1-dioxide

Ikeda et al., reported416 the synthesis of tranilast, pioxicam and the anthranilic

acid bearing 1,2-benzothiazine 1,1-dioxide derivatives (110-112). 2´-(tetrazole-5-yl)-4-

hydroxy-2-methyl-2H-1,2-benzothiazine-3-carboxanilide, 1,1-dioxide which was

designed by the structural hybridization of tranilast and piroxicam, markedly exhibited

the inhibitory effects on the antigen-induced histamine release from rat FIX, 48 h

homologous passive cutaneous anaphylaxis (PCA) in rats and the carrageenin-induced

paw edema in mice. 3-carboxamides of 4-hydroxy-2-methyl-2H-1,2-benzothiazine 1,1-

dioxide have been reported to possess excellent anti-inflammatory activities, and N-(2-

pyridinyl-4-hydroxy-2-methyl-2H-1,2-benzothiazine 1,1-dioxtde (piroxicam) is currently

applied for the clinical treatment of various inflammatory diseases as a non-steroidal

acidic anti-inflammatory drug. On the other hand, N-3´,4´-dimethoxycinnamoyl)

anthranilic acid (tranilast) has been clinically used as an orally applicable anti-allergic

drug which specifically inhibits the IgE-mediated reaction. In the experimental models,

tranilast has been shown to inhibit the release of chemical mediators induced by antigen-

antibody reactions and the homologous PCA as its characteristic pharmacological

actions. In the present study, they investigated the anti-allergic and anti-inflammatory

properties of 2´-carboxyl-4-hydroxy-2-methyl-2H-1,2-benzothiazine-3-carboxanilide 1,1-

dioxide (111) bearing anthranilic moiety like the structure of tranilast.

48


SN

O O

OH

CH3

7

NH

O

N

SN

O O

OH

CH3

111

NH

O

COOHS

N

O O

OH

CH3

112

NH

O

COOH

OH3C

OH3C

Piroxicam Tranilast

Figure 2.4 Anthranilic acid bearing 1,2-benzothiazine derivatives and piroxicam

The Endothelin antagonists were prepared by Berryman et al.,417 via the

intermediacy of a 4-trifluoromethanesulphonyloxy-benzothiazine dioxide derivative

which underwent: (i) displacement with a suitably substituted sodium thiophenoxide,

followed by hydrolysis, to afford the compounds of general formula (113) (See Table

SN

O O

S

113

COOH

R1

R3

R2

SN

O O

114

COOH

R1

R3

R2

Figure 2.5 General formula for Berryman’s 1,2-benzothiazine derivatives

IV, page 71-72, compounds 115-140) or alternatively, (ii) a palladium mediated aryl

cross-coupling reaction, followed by hydrolysis, to afford the compounds of general

formula (114) (See Table V, page 73-74, compounds 141-162).

Both procedures proved to be particularly general and were tolerant of a number

of thiophenols and boronic acids. The requisite thiophenols were readily prepared by

treatment of aryl lithiums with elemental sulphur or from the reaction of the

49

Chapter: 2 LITERATURE SURVEY corresponding aryl iodides with thiourea and a nickel catalyst. The boronic acid

derivatives were generated by trapping the aryl lithium, or Grignard, with

trimethylborate.

Novel methods for the facile construction of 3,3-disubstituted and 3,3-spiro

2H,4H-benzo[e][1,2]-thiazine-1,1-diones (165a-h) were described by Liu and co-

workers418 in 2001 while working in the Toyama Medical and Pharmaceutical University,

Japan. o-Methyl lithiation of N-Boc-o-toluenesulfonamide (163), followed by reaction

with a variety of ketones gave the corresponding carbinol sulfonamides (164a-g), which

underwent cyclization under acidic (methanesulfonic acid) or neutral

(NaI/TMSCl/MeCN) conditions to afford the sultams (165a-h) in high yields. The chiral

spiro sultams (165g-h) were subjected to FClO3 fluorination to give the N-fluorosultams,

which were tested for electrophilic asymmetric fluorination of aryl ketone enolates. As a

result, the N-fluorosultam from (165g) exhibited modest asymmetric inducing abilities

SO2NHBoc

CH3

1) BuLi, THF, -78°C

2) R1COR2

163

SO2NHBoc

OH

R1R2

165R1

R2

NHS

OO

164

Scheme-17

with the highest enantiomeric excess (ee), reaching 70% for enantioselective fluorination

of the lithium enolate of 2-methyl-1-tetralone.

Ahn et al., have frequently used 1,2-Benzisothiazoline-3-one 1,1-dioxide (168),

known as saccharin,419 as a key component of biologically active compounds. Also, it is a

cheap and versatile starting material for the synthesis of related heterocyclic derivatives.

Among those derivatives, 3-substituted-ones are readily accessible through direct

50

Chapter: 2 LITERATURE SURVEY nucleophilic additions to the carbonyl carbon using strong nucleophiles such as alkyl- and

aryllithium reagents or corresponding Grignard reagents. The substitution reactions

proceed at mono- or di-addition stage depending on the reagents and reaction

SO2NHBoc

CH3

But

164

164bH+

-H3O+H+

-Boc

CH3

But

167

SO2NH2

H+ CH3

But

SO2NH2

H+165

Scheme-18

conditions. The monoaddition reactions lead to 3-substituted saccharins (169), while the

diadditions provide benzosultam analogues (170). Ahn and co-workers have devised an

efficient and practical synthetic route to various enantiomeric 3-substituted benzosultams

such as (171) starting from saccharin via the nucleophilic addition and subsequent

catalytic reduction steps.

SNH

O O168

O

SN

O O169

R

SNH

O O170

R R'

SNH

O O171

R

R = Me, t-Bu

SNH

O O172: R = H173: R = CH2Ph

R COOH

Figure 2.6 Saccharin and other benzo-sultams

As a continuing study on the synthesis and application of chiral benzosultam

derivatives, they have been interested in chiral 3-carboxy-substituted benzo-sultams.

Although the direct nucleophilic addition approaches are useful for the synthesis of 3-

alkyl- or 3-arylsubstituted derivatives, they were unsuccessful in introducing directly a

51

Chapter: 2 LITERATURE SURVEY functional moiety such as cyano group. To synthesize 3-functionalized saccharin

derivatives, particularly 3-carboxy analogues (172) and (173), they studied two indirect

approaches, an asymmetric approach and a racemic synthesis followed by chemical

resolution approach. They reported the synthetic results which provide some useful

chemistry on the C-3 functionalization of saccharin and 3-carboxybenzosultams.

Winkle and co-workers investigated420 Suzuki cross-coupling reaction, to form

the methyl ester (175), after briefly exploring Negishi-type cross-coupling strategies

SN

O O

COOH

F3C

SN

O O

CO2CH3

F3C174 175

Figure 2.7 Endothelin A antagonist and its methyl ester

utilizing an arylzincate. A potent endothelin A antagonist (174) was considered for the

treatment of pulmonary hypertension. 3,5-dimethylphenylmagnesium bromide was

reacted with triisopropyl borate to give 3,5-dimethylphenylboronic acid and bis(3,5-

dimethylphenyl)borinic acid. Conditions were found which allowed the clean preparation

of bis(3,5-dimethylphenyl)borinic acid, which was coupled with a vinyl triflate using

Suzuki cross-coupling conditions. Both aryl groups were efficiently transferred from

boron in the Suzuki step.

52

Chapter: 2 LITERATURE SURVEY Clerici et al., presented421 the reaction of NaN3 with 5-substituted 3-diethylamino-

4-(4-methoxyphenyl)-isothiazole 1,1-dioxides affording [2-cyano-l-diethylamino-2-(4-

methoxyphenyl)-ethylidene]-sulfamic acid derivatives, 3-diethylamino-1,1-dioxo-4-(4-

methoxyphenyl)-1,2-dihydro-[1,2]thiazete-4-carbonitrile, 3-diethylamino-7-methoxy-1,1-

dioxo-1,4-dihydrobenzo[e][1,2]thiazine-4-carbonitrile or triazole derivatives. The

outcome of the reaction strongly depends on the C-5 substituent and the correct choice of

the reaction conditions allows direction of the reaction towards the formation of the

sulfamic esters or the [1,2]thiazete carbonitrile or the triazoles in satisfactory yield. 5-

Bromo-3-diethylamino-4-(4-methoxyphenyl)isothiazole 1,1-dioxide (176) was allowed to

react with an equi-molecular amount of NaN3 (180) in refluxing methanol affording

(181a) in satisfactory yield (77%). The same reaction performed in ethanol, 1-propanol or

2-propanol afforded (181b-d), demonstrating the participation of the nucleophilic solvent

in the reaction (Scheme 19).

H3C

176 180

182

N

S

Ar O

O

CN

Et2N183

SN

O O

184

CN

O

NEt2

Scheme-19

181a = R = CH3b = R = C2H5c = R = n-Prd = R = i-Pr

53

Chapter: 2 LITERATURE SURVEY Compounds (181a-d) are very stable under prolonged heating or basic treatment

(ROH/RO-; ROH/NaN3; CH3CN/TEA). Compound (176) was allowed to react with (180)

in several non-nucleophilic solvents (TBF, dioxane, ethyl acetate, acetonitrile) and the

NS

OOMeSO2

Ar NEt2

NaN3CH3CN

N

S

Ar O

O

CN

Et2N

177 180 183Ar = 4-MeOC6H4

Scheme-20

+

best results were obtained in acetonitrile both at reflux or at room temperature. When

performing the reaction in solvent at reflux, compounds (182-184) were obtained. The

easy transformation of (182) into (183) was confirmed independently, by stirring pure

NS

OO

R

Ar NEt2

NaN3CH3CN

178, 179 180 185

Scheme-21

+ N

N NH

R

Ar

178, 185a R = MeS, Ar = 4-MeOC6H4179, 185b R = Ph, Ar -MeC6H4

(182) in acetonitrile (CH3CN) at room temperature (several days), or in presence of a

catalytic amount of triethylamine (TEA). To evaluate the real importance of the

substituent on C-5 for the course of the reaction, reaction was performed on (177-179) in

acetonitrile as the solvent.

54


Scheme-22

N

N

N

Ar

X

N

-SO2

NEt2

-N2 , -MeSO2-

X = MeSO2

183-N CN

Et

Et

-SO2

X = Ph, MeS-F

N

N

Ar

N

O2S

NEt2

-NX

N

N

Ar

N

O2S

NEt2

N-X-

Nu

B C

Nu=ROH-N2

CN

Ar N

O2S

NEt2186

H

OR

C

Ar N

O2S

NEt2187

N

H

N3

N

SO2Ar

CN

Et2N

183

ROH

CN

Ar N

O2S

NEt2D

N3

-

Nu=N3-

path a

185a,b

Ar

N

O2S

NEt2

X

N3

-

A

Ar

N

O2S

NEt2

X

N3-

O2S

N

NC NEt2

MeO E

path b

188

SO2

NH

CN

NEt2

MeO

55


Defazio and Cini reported422 in 2003, the synthesis, X-ray structural

characterization and solution studies of metal complexes containing the anti-

inflammatory drugs, meloxicam and tenoxicam. The reaction of tenoxicam (H2ten, 4-

hydroxy-2-methyl-N-2-pyridyl-2H-thieno[2,3-e]-1,2-thiazine-3-carboxamide-1,1

dioxide), with M(CH3COO)2 (M = Cd, Co, Zn; 2:1 molar ratio) in hot methanol produced

the microcrystalline compounds: CdII(Hten)2 .2CH3OH (189), CoII(Hten)2·CH3OH·3H2O

(190), ZnII(Hten)2·2CH3OH (191). Single crystals of trans,trans-[CoII(Hten)2(dmso)2]

(192) were obtained on cooling hot dmso solutions of (189). trans-[PtCl2 (η2-

C2H4)H2ten)], (193) and trans-[PtCl2 (η2-C2H4) H2mel)] ·0.5C6H6 (194) ·0.5C6H6 were

obtained from the reaction of the Zeise's salt (K[PtCI3 (η2-C2H4)] ·H2O) with tenoxicam

and meloxicam (4-hydroxy-2-methyl-N- (5-methyl-2-thiazolyl)-2H- 1,2-benzothiazine-3-

carboxammide- 1, 1 -dioxide), respectively (1:1 molar ratio) in ethanol solution and

subsequent recrystallization from benzene. Microcrystalline FeII(Hmel)2·4H2O·2CH3OH

(195), was prepared by reacting Fe(CH3COO)2 with H2mel in refluxing methanol at a 1:2

molar ratio, under an atmosphere of ultrapure nitrogen. The X-ray diffraction structure of

(S) consists of pseudo-octahedral complex molecules in which the two chelating Hten-

anions (trans to each other) occupy the equatorial positions.

Figure 2.8 Sequence of numbering in tenoxicam, meloxicam and piroxicam

56


Fig.2.9 ORTIP drawing of the complex molecule for trans, trans -[CdII(dmso)2

(Hten)2 ], 192, with labeling of the atoms

Fig. 2.10 ORTIP drawing of the complex molecule for trans-[PtCl2 (h2-C2 H4 ) (H2 ten)], 193, with labeling of the atoms

57


Wells et al., prepared423 a series of peptide mimetic aldehyde inhibitors of Calpain

I in which the P2 and P3 amino acids were replaced by substituted 3,4-dihydro-1,2-

benzothiazine-3-carboxylate 1,1 - dioxides. The effect of 2, 6, and 7-benzothiazine

substituents and the P1 amino acid was examined. Potency of these inhibitors, against

human recombinant Calpain I is particularly dependent upon the 2-substituent, with

methyl and ethyl generally more potent than hydrogen, isopropyl, isobutyl, or benzyl.

The more potent diastereomer of (196) possesses the (S) absolute configuration at the 3-

position of the 3,4-dihydro-1,2-benzothiazine. Potency of the best inhibitors in this series

(IC50) 5-7 nM) compares favourably with that of conventional N-benzyloxycarbonyl

dipeptide aldehyde inhibitors bearing L-Leu or L-Val residues at P2.

C

SN

O O

196

O

O

Et

O

NH C

O

HC

SN

O O

197

O

O

O

NH C

O

H

R4

R3

R2

R1

197 a R1 = CH3, R2 = H; R3 = R4 = Cl b R1 = CH3, R2 = H; R3 = R4 = OCH2CH2O c R1 = CH2CH3, R2 = H; R3 = R4 = CH2CH2O d R1 = CH3, R2 = OCH3; R3 = R4 = H

Figure 2.11 Two potent Calpain I inhibitors, 196 and 197

The achiral unsaturated 1,2-benzothiazine analogues (197a-d) are also potent Calpain I

inhibitors, while 3 ,4-dihydro-2,1–benzoxathiin, 1,2,4- benzothiadiazine, and tetrahydro-

isoquinolinone analogues are less potent.

58


In continuation to their work on synthesis of Calpain inhibitors, Bihovsky et al.,

reported another series of potent 1,2-benzotiazine 1,1-dioxide α-ketoamides424 in 2004,

while working in the Department of Medicinal Chemistry, Cephalon, Westchester, USA.

Previously, they reported the discovery and synthesis of a series of 3,4-dihydro- 1 ,2-

benzothiazine-3-carboxylate 1,1-dioxide aldehydes as potent reversible Calpain I

inhibitors. This novel class of peptide mimetics displayed comparable potency to

previously reported di-and tripeptide aldehydes (e.g., Z-Val-Phe-H, IC50 = 11 nM), and

compared favourably as well to another novel class of peptide mimetics discovered in

this laboratory, N-alkanesulfonyl dipeptide aldehydes and α-ketoamides possessing d-

amino acid residues in the P2 region, from which they were designed.

SNH

O

NH

H

O

O OS

NH

O

NH

H

O

O O

Superimpose P2-P3

phenyl groups

(IC50 = 20 nM) (IC50 = 7 nM)

198 199

Scheme-23

In an effort to improve the inherent liabilities generally observed with aldehydes

(e.g., rapid metabolism, lack of selectivity, potential toxicity), they embarked on a

program to replace this functionality with one intrinsically more stable and amenable to

drug development. Since the experience with several previously reported classes of

irreversible inhibitors (e.g., halomethyl-, acyloxymethyl-, and benzotriazolyloxymethyl

59

Chapter: 2 LITERATURE SURVEY ketones; phosphorous-based oxymethyl ketones) was generally unfavourable, α-

ketoamide group was chosen to be incorporated as one, more likely to impart desirable

physico-chemical and biological properties. This and related α-dicarbonyl derivatives

have previously been shown to inhibit cysteine and serine proteinases reversibly with

good potency and selectivity.

Kharisov et al., synthesized new β-aminovinylketones425 with heterocyclic 1,2-

benzothiazine-1,1-dioxide and antipyrine moieties (LH) and their 3d-metal (CoII, NiII,

CuII, ZnII) chelates. Two types of chelates can be obtained based on the coordination of

the ligand (LH), depending when an available carbonyl (C=O) group of the antipyrine

fragment is coordinated (M = Co, Ni) or not (M = Cu) to the metal center. The molecular

structure of compound (201b) was obtained by X-ray diffraction, indicating that the

ligand (200b) forces the complex to adopt a highly distorted tetracoordinate square-

planar structure. Detail on the syntheses and characterization of these complexes has also

been discussed.

C

SN

O O

200

NH

O

N

N

C6H5

C6H5

CH3

O

CH3

200a R = H b R = CH3 c R = CH2CH3

R

C

SN

O O

201

N2

O

N

N

C6H5

C6H5

CH3

O

CH3

201a R = H b R = CH3 c R = CH2CH3

R

M/

Figure 2.12 Molecular structures of compounds 200 and 201, representing their character as ligands

Layman and co-workers developed426 new 1,2-benzothiazine derivatives by

reaction of alkyl enolates with iodo-containing compounds. 2-iodobenzenesulfonamide

60

Chapter: 2 LITERATURE SURVEY (202a) underwent photo-stimulated SRN1 reactions in liquid NH3 with the potassium

enolates derived from acetone, pinacolone, butanone, and 3-methyl-2-butanone to give

fair to good yields of 2H-1,2-benzothiazine 1,1-dioxides (203). Reductive dehalogenation

SNH2

I

O OS

NH

O O

RO-

R'R

Scheme-24

NH3 , hv

R'

202a 203

of (202a) was found to predominate in photoinduced reactions of (202a) with 3-

pentanone, 2-methyl-3-pentanone, and 2,4-dimethyl-3-pentanone, the extent of reduction

being proportional to the number of β-hydrogen atoms present in the ketone enolate.

SNH

O O

R

R'

SNH2

X

O OS

NH

O O

RO-

R'R

O-

ROR-

O

Scheme-25

203 208202202 a = I b = H

OD3C CD3

DD

CD3 CD3

NH3

OD3C CD3

HH

CD3 CD3

D3C CD3H

CD3 CD3

KNH2O-K+

(1)

(2) H+210b202b

Scheme-26

204

61

Chapter: 2 LITERATURE SURVEY Isotopic labeling studies with 2,4-dimethyl-3-pentanone-d14 (204) confirmed the major

role of the β-hydrogens in the reduction process. Reactions of (202a) with

cyclopentanone, cyclohexanone, and cyclooctanone enolates afforded new tricyclic

benzothiazine derivatives (205-207).

202a

O-K+

(CH2)n

hv

liq NH3 SNH

O O

(CH2) n

205, n = 1206, n = 2207, n = 3

+

Scheme-27

Attempts to extend the hetero-annulation reaction to the preparation of 2H-1,2-

benzothiazin-3(4H)-one 1,1-dioxides (208) (R = H, Ph) through reactions of (202a) with

tert-butyl acetate and ethyl phenylacetate enolates resulted only in hydrodehalogenation

of (202a). However, oxazoline anion (209), a synthetic equivalent of ethyl phenylacetate,

was successfully employed in an alternative SRN1-based synthesis of benzothiazine (208)

(R = Ph).

Zia-ur-Rehman et al., working during the year 2005 in Applied Chemistry

Research Centre of the PCSIR Laboratories Lahore, Pakistan have efficiently made use

of ionic liquids for preparing 1,2-benzothiazine 1,1-dioxide derivatives.427 An

SO O211

SN

O O

O

O

[buPy ]BF4+ OCl

O R

R

O

212 213

R, a = CH3 = 2c, b= C2H5, c = CH(CH3)2

Scheme-28

NNa

62

Chapter: 2 LITERATURE SURVEY environment friendly method has been described for the synthesis of various 2-alkyl-4-

hydroxy-2H- 1,2-benzothiazine-3-carboxamide- 1, 1 -dioxides starting from N-alkylation

of sodium o-benzosulfimide in an ionic liquid for the first time.

Ring cleavage and ring closure of the resulting product was achieved in a single

step in a cost-effective solvent (methanol), followed by N-alkylation of resulting alkyl 4-

hydroxy-2H-1,2-benzothiazine-3-carboxylate in ionic liquid while boron triflouride was

used as a catalyst along with molecular sieves in carboxamide formation step.

SN

O O

O

O

MeOH / NaOMe

SNH

O

OO

O O214 215

SN

O

OOH

O O

R

216

Scheme-29

O

R R

R1I[byPy ]BF4

R1S

NNH

OOH

O O

7, 33, meloxicam,217

R1

R2NH2R2

R, a = CH3 = 2c, b= C2H5, c = CH(CH3)2

R, a = CH3 = 3c, b= C2H5, c = CH(CH3)2

R1, a = CH3 b = C2H5,

217R1 = C2H5

R2, a = Ph b = 2-Py c = 5-Me-2-thiazolyl

Recently, Harmata and co-workers428 have reported palladium catalyzed synthesis

of 1,2-benzothiazine 1,1-dioxides using alkynes. The reaction of S-2-bromophenyl-S-

methylsulfoximine with terminal alkynes in the presence of a palladium catalyst resulted

in the formation of both 1,2-benzothiazines and 1,2-benzoisothiazoles. A preference for

63

Chapter: 2 LITERATURE SURVEY the former was seen with alkylalkynes, while the latter were preferentially formed with

alkynylarenes.

SNH2

O O SN

R

O

218 219Br

PdCl2(PPh3)2

HCCR, DMF

CH3

SN

O

R

CH3

+

220

Scheme-30

Last year Tatiana et al., synthesized piroxicam benzoate429 according to a

modified procedure and have studied the crystalline structure. Single crystals of (221),

grown from ethyl acetate, are monoclinic, with one molecule in the asymmetric unit. The

geometric parameters of the piroxicam group in (221) are similar to those in β-piroxicam.

SN

O

O

O

NNH

O

O221

Fig. 2.13 Molecular structure of piroxicam benzoate

In continuation of their work, Zia-ur-Rehman and co-workers have recently

reported430 the crystal structure of anthranilamide derivative of 1,2-benzothiazine 1,1-

dioxide in the year 2007.

SN

O

NH

O

O222

OH

NH2O

Fig. 2.14 Anthranilamide derivative of piroxicam

64

Chapter: 2 LITERATURE SURVEY In the compound, N-[2-(Aminocarbonyl)phenyl]-4-hydroxy-2-methyl-2H-1,2-

benzothiazine-3-carboxamide 1,1-dioxide dimethyl sulfoxide solvate, the thiazine ring

adopts a distorted half-chair conformation. The enolic H atom is involved in both

intramolecular and intermolecular O—H·····O hydrogen bonds, the latter linking the

Fig. 2.15 The molecular structure of (222), showing displacement ellipsoids at the 50% probability level for non-H atoms. Dashed lines denote hydrogen bonds

molecules into centrosymmetric pairs. Both anthranilamide ‘H’ atoms are involved in

hydrogen bonding to ‘O’ atoms of dimethyl sulfoxide molecules, linking the pairs of

molecules into chains.

After going through in-depth review of all the literature, a part of which has been

mentioned above, we observed that positions 2-, 3- and 4- have always been exploited for

the synthesis of new, more potent and biologically active 1,2-benzothiazine 1,1-dioxide

compounds. Hence we decided to embark on a program to replace functionalities at these

positions with ones more stable and amenable ones to drug development in search of

divergent new oxicams containing 1,2-benzothiazine 1,1-dioxide heterocyclic ring

system.

65

Chapter: 2 LITERATURE SURVEY Table-1 3-Carboxamide derivatives of 1,2-benzothiazine 1,1-dioxide _____________________________________________________________________________________

S

N

O O

O

R1

CO

N

R3R4

R2

Compd. No. R1 R2 R3 R4 m.p.°C

_____________________________________________________________________________________

032 H H H H 261-268 (dec.)

033 CH3 H H H 217-218.5

034 CH2CO2CH3 H H H 238-239.5

035 CH2CN H H H 240-241

036 CH3 CH2CH2CH3 H H 151-153

037 CH3 CH(CH3) 2 H H 199-200

038 CH3 CH3CO H H 195-197 039 CH3 H OH H 162-164 040 CH3 H CH3 H 175-178 041 CH3 H C2H5 H 150-152 042 CH3 H C6H5 H 186-189

043 CH3 CH3CO CH3CO H 206-210 044 CH3 C=O CH3CO H 262-263.5 045 CH3 H H O-NO2 336.5-337.5 046 CH3 H H O- CO2CH3 221-222.5 047 CH3 H H O- C6H5 164-165 048 CH3 H H p- C6H5 262-262.5

(Continued…)

66

Chapter: 2 LITERATURE SURVEY (Continued…….) Table-1 3-Carboxamide derivatives of 1,2-benzothiazine 1,1-dioxide _____________________________________________________________________________________

Compd. No. R1 R2 R3 R4 m.p.°C

_____________________________________________________________________________________

049 CH3 H H O

H2CO

3,4- 266-266.5

050 CH3 H H O

H2CO

2,3- 243-245

051 CH3 H H S

N

CH3

p-

295-296 (dec.)

67

Chapter: 2 LITERATURE SURVEY Table-II 4-Hydroxy-_and 4-mercapto- derivatives of 1,2-benzothiazine 1,1-dioxide ______________________________________________________________________________________

S

N

O O

OH

CH3

R

X

Compd. No. X R m.p.°C

_____________________________________________________________________________________

052 O ON

H 208-209

053 O SN

H 250-252

054 O NH

NHN

277-278 (dec.)

055 O NH

N

HN

266-267 (dec.)

056 O N

OHN

Ph 225-227 (dec.)

057 O N

OHN CH3

CH3 249-250 (dec.)

058 O NH

HN CH3

CH3 260-263 (dec.)

059 O N

200-202

060 O N

173-174

061 O

HN

251-253 (Continued…)

68

Chapter: 2 LITERATURE SURVEY (Continued…) Table-II 4-Hydroxy-_and 4-mercapto- derivatives of 1,2-benzothiazine 1,1-dioxide

______________________________________________________________________________________

Compd. No. X R m.p.°C

_____________________________________________________________________________________

062 O N

220-222

063 O NH2 244-248 (dec.)

064 O NHC2H5 194-196

065 S NHC2H5 221-222

066 S NHPh 235-237.5 _____________________________________________________________________________________

69

Chapter: 2 LITERATURE SURVEY Table-III 4-Pyrolidinone derivatives of 1,2-benzothiazine 1,1-dioxide _____________________________________________________________________________________

S

N

O OCH3

R

ON

Compd. No. R m.p.°C

_____________________________________________________________________________________

067 NHPh 207-209

068 142-144 -N(C2H5)C6H5

069 N

177-179 (dec.)

070 N

182-185 (dec.)

071 N

224-226 (dec.)

072 -NH (1-adamantyl) 160-162 (dec.)

073 NHC2H5 185-187

70

Chapter: 2 LITERATURE SURVEY Table-IV The Endothelin antagonists prepared by Berryman. (4-mercapto….) ______________________________________________________________________________________

SN

O O

S

113

COOH

R1

R3

R2

______________________________________________________________________________________ Compd. No. R1 R2 R3 ET*

A IC50 (nM) ETA IC50 (nM) ______________________________________________________________________________________ 115 3,4-OCH2O- 3,4-OCH2O- H 210 6100

116 3,4-OCH2O- 3,4-dimethoxy H 230 8200

117 3,4-OCH2O- 3,4,5-trimethoxy H 230 22000

118 3,4-OCH2O- 3,4-OCH2 CH2O- H 420 5600

119 3,4-OCH2O- 4-OMe H 440 21000

120 3,4-OCH2O- 4-Me H 450 20000

121 3,4-OCH2O- 3-OMe H 460 11000

122 3,4-OCH2O- H H 540 22000

123 3,4-OCH2O- 4-Cl H 790 20000

124 3,4-OCH2O- 3,4-dichloro H 800 20000

125 3,4-OCH2O- 3,4-OCH2O- H 580 3900

5-OMe

126 H 3,4-OCH2O- H 230 16000

127 4-Me 3,4-OCH2O- H 370 5300

128 3,4,5-trimethoxy 3,4-OCH2O- H 460 19000

(Continued…)

71

Chapter: 2 LITERATURE SURVEY (Continued…)

Table-IV The Endothelin antagonists prepared by Berryman. (4-mercapto….) ______________________________________________________________________________________

SN

O O

S

113

COOH

R1

R3

R2

______________________________________________________________________________________ Compd. No. R1 R2 R3 ET*

A IC50 (nM) ETA IC50 (nM) ______________________________________________________________________________________ 129 4-Cl 3,4-OCH2O- H 530 14000

130 3,4-OCH2O-6-Cl 3,4-OCH2O- H 590 13000

131 3,4-dichloro 3,4-OCH2O- H 520 19000

132 4-methoxy 3,4-OCH2O- H 800 3900

133 3,4-OCH2O- 3,4-OCH2O- 8-OMe 280 11000

134 3,4-OCH2O- 3,4-OCH2O- 7,8-dimethoxy 100 4000

135 3,4-OCH2O- 3,4-OCH2O- 7-methoxy 240 5300

136 3,4-OCH2O- 3,4-OCH2O- 6,7-OCH2O- 290 2100

137 3,4-OCH2O- 3,4-OCH2O- 7-Cl 530 4500

138 3,4-OCH2O- 3,4-OCH2O- 6-Cl 670 17000

139 3,4-OCH2O- 3,4-OCH2O- 6,7-dimethoxy 800 5200

140 3,4-OCH2O- 3,4-OCH2O- 6-OMe 2700 20000

______________________________________________________________________________________ * Endothelin receptor A with 50% inhibitory concentration of the drug derivative.

72

Chapter: 2 LITERATURE SURVEY Table-V The Endothelin antagonists prepared by Berryman. (4-aryl….) _____________________________________________________________________________________

SN

O O

114

COOH

R1

R3

R2

______________________________________________________________________________________ Compd. No. R1 R2 R3 ET*

A IC50 (nM) ETA IC50 (nM) ______________________________________________________________________________________ 141 3,4-OCH2O- 3,4-OCH2O- H 380 2500

142 3,4-OCH2O- 3,4-dimethoxy H 2000 4400

143 3,4-OCH2O- 3,4,5-trimethoxy H 15000 25000

144 3,4-OCH2O- 3,4-OCH2 CH2O- H 630 6500

145 3,4-OCH2O- 4-OMe H 5700 21000

146 3,4-OCH2O- 3-OMe H 1400 13000

147 3,4-OCH2O- 4-Cl H 11000 33000

148 3,4-OCH2O- 3,4-OCH2O- H 540 2900

5-OMe

149 H 3,4-OCH2O- H 410 9300

150 4-Me 3,4-OCH2O- H 900 32000

151 3,4,5-trimethoxy 3,4-OCH2O- H 530 18000

152 4-Cl 3,4-OCH2O- H 700 13000

153 3,4-OCH2O-6-Cl 3,4-OCH2O- H 980 2700

154 3,4-dichloro 3,4-OCH2O- H 2300 15000

(Continued…)

73

Chapter: 2 LITERATURE SURVEY (Continued…)

Table-V The Endothelin antagonists prepared by Berryman. (4-aryl….) Compd. No. R1 R2 R3 ET*A IC50 (nM) ETA IC50 (nM) ______________________________________________________________________________________ 155 4-OMe 3,4-OCH2O- H 450 5100

156 3,4-OCH2O- 3,4-dimethoxy 8-OMe 1400 7400

157 3,4-OCH2O- 3,4,5-trimethoxy 7-OMe 12000 8300

158 3,4-OCH2O- 3,4-OCH2 CH2O- 6,7-OCH2O- 2800 1300

159 3,4-OCH2O- 4-OMe 7-Cl 3900 8900

160 3,4-OCH2O- 3-OMe 6-Cl 390 3800

161 3,4-OCH2O- 4-Cl 6,7-dimethoxy 830 1700

162 3,4-OCH2O- 3,4-OCH2O- 6-methoxy 1800 1700

______________________________________________________________________________________

* Endothelin receptor A with 50% inhibitory concentration of the drug derivative.

74

Chapter: 3 EXPERIMENTAL

75

EXPERIMENTAL

During this research work all air and/or moisture sensitive reactions were carried

out under inert atmosphere, in oven-dried glassware. “Brine” refers to a saturated

aqueous solution of sodium chloride. Dichloromethane and dichloroethane were dried by

distillation from CaH2 and THF was distilled from Na/ benzophenone prior to use. Where

appropriate, all other solvents and reagents were purified according to standard

methods.435 Reactions were monitored by TLC using aluminium backed plates coated

with silica gel 60 or alumina (0.2 mm) containing a fluorescent indicator active at 254

nm. The chromatograms were visualized under UV light (254 nm) and by staining with,

most commonly, cerium sulphate/ ammonium molybdate in 2M aq. H2SO4 or 10% aq.

KMnO4.

Melting points were determined in open capillary tubes on Gallenkamp melting

point apparatus and are uncorrected. 1H-NMR and 13C-NMR spectra were recorded on

Bruker AC300, Bruker AM300 or Bruker DPX-400 spectrometers in deuterated

chloroform (calibrated to δ 7.26 ppm 1H, 77.36 ppm 13C) as standard with various other

deuterated solvents calibrated as per Gottlieb’s paper.436 IR spectra are reported in

wavenumbers (cm-1) and were collected on Perkin Elmer 1600FT spectrometer and on a

Matterson Satellite spectrometer fitted with a Specarch Golden Gate ATR sampling

platform. The samples were applied as solids, neat liquids or as KBr discs for IR analysis.

Low-resolution mass spectra (LRMS) were obtained on a Fisons VG platform single

quadrapole mass spectrometer in either chemical ionization or electron impact ionization

mode or recorded on a Jeol SX-102 instrument.


76

A part of this research work has been performed at School of Chemistry,

University of Southampton, UK during a six-month visit on a scholarship from Higher

Education Commission (HEC), Islamabad, Pakistan under its International Research

Support Initiative Programme (IRSIP). High-resolution mass spectra (HRMS), CHN and

X-ray analyses were performed there at University of Southampton and in collaboration

with Department of Chemistry, University of Calgary, Canada.

Beginning with the synthesis of Piroxicam, new methodologies were developed to

better synthesize, first this drug molecule. Cost effective, cheaper and indigenously

feasible, easy to handle synthetic route has been devised437 with best yields and purity.

Subsequently, piroxicam-related new heterocyclic molecules were synthesized and

characterized by the above mentioned techniques.

EXPERIMENTAL PROCEDURES

3.1 SYNTHESIS OF PIROXICAM

Following three different pathways, the precursor 4-hydroxy-3-carbomethoxy-2-methyl-

2H-1,2-benzothiazine 1,1-dioxide, (4) was first synthesized. Reaction of (4) with 2-

aminopyridine in xylene produced Piroxicam (7) (Scheme-1, page 86).

3.1.1 Synthesis of Methyl 1,2-benzothiazoline-3-(2H)-one-2-acetate 1,1-dioxide (2)

S

O

O O

(1)

NNa

DMF

(2) C10H9NO5SMol. Wt.: 255.25

OCH3

O

ClOCH3

O

S

O

O O

N


77

Methyl chloroacetate (11.9 g, 109.6 mmol.) was added to a solution of sodium saccharin

(15.0 g, 73.1 mmol.) in dimethylformamide (30 ml). The mixture was heated at 100°C for

3 hours. The reaction mixture was cooled to room temperature and poured into cold water

(60 ml), resulting in an immediate formation of white solid, which was filtered and

washed with water. The solid was dried (70°C, overnight) to produce (2) (17.3 g, 67.8

mmol., 93%) as white crystalline solid.

m.p 115-116°C

FT-IR (KBr) nmax 2980, 1750, 1730, 1320, 1180 cm-1

1H-NMR (400 MHz) (CDCl3) d: 8.38-7.90 (4H, m, aromatic), 4.60 (2H, s, CH2),

3.85 (3H, s, CH3)

LRMS (EI) m/z: 255 [M+], 224 [M+ - OCH3]

HRMS (EI) Calcd. 255.0201, Found 255.0205

X-ray Structure:


78

3.1.2 Synthesis of 4-Hydroxy-3-carbomethoxy-2H-1,2-benzothiazine 1,1-dioxide (3)

(2)

OCH3

OS

O

O O

N

SNH

O O

OH

O

O

CH3

(3)

NaOMe

DMF C10H9NO5SMol. Wt.: 255.25

Method A

Ester (2) (10.0 g, 39.0 mmol.) was added to a suspension of sodium methoxide (4.2 g,

78.0 mmol.) in dry dimethylsulfoxide (40 ml) in 1 portion with rapid stirring. Colour

changes yellow-orange-red were observed as the temperature was maintained near 30°C

by periodic immersions in an ice-bath. After 4 minutes the deep red solution was poured

into hydrochloric acid (3N, 100 ml) and extracted 3 times with chloroform. After drying

(CaSO4) and evaporation, the residue was recrystallised from absolute ethanol to give the

desired ester (3) (5.1 g, 20.0 mmol., 52%).

Method B

Sodium metal (5.4 g, 230 mmol.) was added to dry methanol (100 ml) in small portions.

Once all the sodium had dissolved the solution was concentrated in vacuum and the final

traces of methanol were removed under high vacuum. Sodium methoxide was suspended

in dry DMF (65 ml). Dissolved ester (2) (20.0 g, 78.4 mmol.) in DMF (30 ml), cooled to

0°C, and freshly prepared sodium methoxide suspension was added into it over 7 minutes.

Stirred this solution (at 0°C) for 30 minutes. Added hydrochloric acid (1N, 430 ml) to the

reaction mixture, filtered and washed precipitates with water. Dried precipitate at 52°C

under vacuum, overnight to give ester (3) (12.6 g, 49.4 mmol., 63%).


79

Method C

A solution of sodium methoxide was prepared from sodium (0.92 g, 40.0 mmol.) in

methanol (15 ml). The solution was refluxed and ester (2) (2.60 g, 10.2 mmol.) was

added all at once as powder in the hot solution. After a few minutes orange slurry was

poured into concentrated HCl (15 ml). The solid formed was filtered off, washed with

water and recrystallised from methanol to get ester (3) (1.27 g, 4.9 mmol., 49%).

Method D

A solution of sodium methoxide was prepared from sodium (24.5 g, 1.065 mol.) in

absolute methanol (40 ml). To the cooled solution in an ice-bath ester (2) (38.3 g, 0.150

mol.) was added immediately and the colour changes from yellow to orange were noted.

After 5 minutes, the mixture was refluxed for 1 hour and the orange slurry was poured

into ice-cold concentrated hydrochloric acid (100 ml). The mixture was cooled in an ice-

bath and precipitate filtered off, washed with water and recrystallised from diluted

methanol to get ester (3) (23.7 g, 0.093 mol., 62%).

m.p 168-171°C (lit.168-169°C)409

FT-IR (KBr) nmax 3240, 1660, 1350, 1150 cm-1

1H-NMR (400 MHz) (CDCl3) d: 11.5 (1H, s, OH), 8.3-7.1 (4H, m, aromatic),

6.5 (1H, s, NH), 4.1 (3H, s, CH3)

LRMS (EI) m/z: 255 [M+], 254 [M+ - H], 224 [M+ - OCH3]



80

X-ray Structure:

3.1.3 Synthesis of 4-Hydroxy-3-carbomethoxy-2-methyl-2H-1,2-benzothiazine 1,1-

dioxide (4)

SNH

O O

OH

O

O

CH3

(3) (4)

SN

O O

OH

O

O

CH3

CH3

MeI

DMF

C11H11NO5SMol. Wt.: 269.27

Method A

Methyl iodide (5.5 g, 38.5 mmol.) was added to a well-stirred solution of (3) (2.95 g, 11.6

mmol.) in ethanol (40 ml), water (11 ml) and sodium hydroxide (1N, 12 ml). A yellow

solution was formed immediately. After standing at room temperature for 18 hours, the

resulting heavy yellow precipitate was filtered, washed with water and dried to afford (4)

(2.4 g, 9.0 mmol., 78%).

Method B

Ester (3) (3.2 g, 12.5 mmol.) was added in ethanol (160 ml) and cooled to 5°C. Sodium

hydroxide (1N, 20 ml) was added dropwise keeping temperature below 10°C, which is


81

followed by the addition of dimethyl sulfate (1.8 g, 15.0 mmol.) and the reaction mixture

was stirred for 3 hours at 25°C. Acidification with hydrochloric acid (6N) afforded

product (4) (2.8 g, 10.6 mmol., 85%).

m.p 162-165°C (Lit. 162-163°C)431

FT-IR (KBr) nmax 3437, 2920, 1667, 1360, 1190 cm-1

1H-NMR (400 MHz) (CDCl3) d: 12.04 (1H, s, OH), 8.20-7.61 (4H, m, aromatic),

3.95 (3H, s, CH3), 2.94 (3H, s, CH3)

13C-NMR (100 MHz) d: 169.78, 158.78, 135.58, 132.84, 132.18, 127.81, 126.52,

123.77, 109.95, 52.81, 38.50

LRMS (EI) m/z: 269 [M+], 254 [M+ - CH3], 238 [M+ - OCH3]


3.1.4 Synthesis of Methyl 2-[N-(methoxycarbonyl)sulfamoyl]benzoate (5)

(2)

OCH3

OS

O

O O

NNaOMe

MeOH S NHO O

O

OCH3

O

O

CH3

(5) C12H15NO5SMol. Wt.: 285.32

Ester (2) (3.0 g, 11.8 mmol.) was added to a solution of sodium methoxide (0.79 g, 14.2

mmol.) in methanol (9 ml). The reaction mixture was stirred for 5 minutes and poured

into ice-water (20 ml). It was acidified to pH = 3 with hydrochloric acid (15%) and

resulted solid was filtered, washed with cold water and dried (70°C, overnight) to

produce (5) (3.1 g, 10.8 mmol., 92%).

m.p 94-95°C


82

FT-IR (KBr) nmax 3345, 1765, 1735, 1360, 1180 cm-1

1H-NMR (400 MHz) (CDCl3) d: 8.45-7.82 (4H, m, aromatic), 6.95 (1H, t, NH),

4.26 (3H, s, CH3), 4.13 (2H, d, CH2), 3.82 (3H, s, CH3)

LRMS(EI) m/z: 287[M+], 256 [M+ – OCH3]

HRMS(EI) Calcd. 287.2934, Found 287.2933

3.1.5 Synthesis of Methyl 2-[N-(methyl)-N-(methoxycarbonyl) sulfamoyl]benzoate (6)

S NHO O

O

OCH3

OCH3

O

(5) (6)

S NO O

O

OCH3

OCH3

O

CH3

1. MeI / DMF NaOH

2. HCl

C12H15NO6SMol. Wt.: 301.32

Methyl iodide (0.6 g, 4.2 mmol.) was added dropwise to a solution of (5) (0.5 g, 1.8

mmol.) in dimethylformamide (8 ml) keeping the temperature between 0-5°C. The ice-

bath was removed and solution stirred at room temperature for 30 minutes and poured

into ice-water (20 ml). The mixture was then acidified to pH = 3 with hydrochloric acid

(15%). The solid obtained was filtered, washed with water and dried to afford (6) (0.46 g,

1.53 mmol., 85%).

m.p 98-99°C

FT-IR (KBr) nmax 1760, 1730, 1350, 1170 cm-1

1H-NMR (400 MHz) (CDCl3) d: 8.20-7.75 (4H, m, aromatic), 4.52 (3H, s, CH3),

4.21 (2H, s, CH2), 3.81 (3H, s, CH3), 3.50 (3H, s, CH3)

HRMS (EI) m/z: 301[M+], 286 [M+ – CH3], 270 [M+ – OCH3]



83


dioxide (4) from (6)

(6)

S NO O

O

OCH3

OCH3

O

CH3(4)

SN

O O

OH

OCH3

O

CH3

1. NaH / DMF

2. HCl

C11H11NO5SMol. Wt.: 269.27

Sodium hydride (50% dispersion in oil; 0.25 g, 5.2 mmol.) was suspended in

dimethylformamide (3 ml) under nitrogen. The suspension was cooled to 0-5 °C and a

solution of (6) (0.54 g, 1.8 mmol.) in dimethylformamide (3 ml) was added dropwise,

keeping the temperature under 5°C. The reaction mixture was then stirred at room

temperature for 10 minutes. (note: the reaction mixture turned green) and poured into ice-

water (20 ml). It was then acidified to pH = 3 with hydrochloric acid (15%). The solid so

produced was then filtered and dried to obtain (4) (0.28 g, 1.0 mmol., 60%).

m.p 162-164°C

Rf value, IR and 1H-NMR spectral data is in good agreement with already synthesized (4)


dioxide (4) from (2)

(4)

SN

O O

OH

OCH3

O

CH3

1. NaOMe / DMF

2. MeI or DMS3. HCl

C11H11NO5SMol. Wt.: 269.27

(2)

OCH3

OS

O

O O

N


84

Dry ester (2) (1.2 g, 4.7 mmol.) was dissolved in dimethylformamide (3 ml) in a three-

neck round-bottom flask under nitrogen. Added sodium methoxide (0.3 g, 5.4 mmol.),

dimethylformamide (3 ml), and methanol (0.3 ml) keeping the temperature between 17-

22°C and stirred for 10 minutes. Then all volatile compounds were removed under

vacuum during 5 minutes and set the temperature to 0°C, followed by the addition of

sodium hydride (0.47 g, 9.8 mmol.). The cooling-bath was removed and the reaction

mixture stirred for 15 minutes at room temperature, followed by dropwise addition of

methyl iodide (1.2 g, 8.4 mmol.), during another 15 minutes. The temperature reached to

33°C and the stirring was continued for additional 30 minutes at room temperature. The

reaction mixture was poured over ice-water (20 ml) and acidified to pH = 3 with

hydrochloric acid (15%). The precipitates were filtered and dried (70°C, overnight)

giving (4) (0.58 g, 2.2 mmol., 46.8%).

m.p 159-161°C. Recrystallization from ethanol (96%) gave pure

(4) mp 163-165°C.

3.1.8 Synthesis of 4-hydroxy-2-methyl-N-(2-pyridinyl)-2H-1,2-benzothiazine-3-

carboxamide-1,1-dioxide (Piroxicam) (7)

NH2N

xylene, reflux

(7)

SN

O O

OH O

CH3

NNH

(Piroxicam)(4)

SN

O O

OH

OCH3

O

CH3 C15H13N3O4SMol. Wt.: 331.35

A mixture of Methyl 4-hydroxy-2-methyl-2H-1,2-benzothiazine-3-carboxylate-1,1-

dioxide (4) (67.3 g, 250 mmol.) and 2-aminopyridine (28.3 g, 300 mmol.) in 250 ml of

xylene was refluxed for a period of 12 hours in a Soxhlet apparatus having Linde type A4


85

molecular sieves. Half of the xylene was then distilled off and the remaining contents

were allowed to stand overnight at room temperature. Crystals were filtered and

recrystallized from dioxane to get white crystalline solid (50.5 g, 152.5 mmol., 61%).

m.p 198-200°C

FT-IR (KBr) nmax 3412, 1648, 1365 and 1181 cm-1

1H-NMR (400 MHz) (CDCl3 ) d: 2.94 (3H, s, CH3), 6.95-7.28 (2H, d, Py), 7.60-

8.40 (6H, m, C6H4 and 2H of Py), 8.85 (1H, b, NH)

LRMS (EI) m/z 331 [M+], 316 [M+ - CH3 ], 238 [M+ - C5H5NNH]

HRMS (EI) Calcd. 331.0627; Found 331.0624


86

S

O

O O

SN

O

O O

OCH3

O

(1)

(2)

SNH

O O

OH

OCH3

O

(3)

(4)(6)

NaOMe

DMF

MeIDMF

1. NaOMe/ DMF2. MeI or DMS

3. HCl

1. MeI/DMF/ NaOH2. HCl

1. NaH/DMF2. HCl

Scheme-1: Overall Layout of different pathways for the synthesis of Piroxicam

Path c

Path b

NaOMeMeOH

Path a

DMF

NNa

OCH3

O

Cl

S NHO O

O

OCH3

OCH3

O

(5)

SN

O O

OH

OCH3

O

CH3S N

O O

O

OCH3

OCH3

O

CH3

NH2N

xylenereflux

7

SN

O O

OH O

CH3

NNH

(Piroxicam)


87

3.2 Synthesis of 4-Hydroxy-2-Methyl-(2H)-1,2-Benzothiazine-3-Sulfonic Acid

1,1-Dioxide (13a)

A convenient synthesis of 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-3-sulfonic acid

1,1-dioxide (13a), in a novel one-pot procedure has been achieved.438 The synthesis

involves two transformations starting from 2-methyl-2H-1,2-benzothiazin-4-(3H)-one

1,1-dioxide (14) with an overall yield better than that from the stepwise process, as well

as the alternate procedure starting from saccharin (8). One-pot synthesis of an important

intermediate, saccharin-N-methane sulfonic acid (11) is also described.

3.2.1 Synthesis of N-hydroxymethyl saccharin (9)

SNH

O

O OS

N

O

O O

OH

(8) (9)

reflux, 5 min.

CH2O

C8H7NO4SMol. Wt.: 213.21

A mixture of (8) (5 g, 27 mmol.) and formaline (5 ml, 67 mmol.) in water (15 ml) was

heated under reflux for 5 minutes,432-33 cooled to room temperature and filtered. The solid

was washed with cold water and dried to produce (9) (5.4 g, 24.8 mmol., 92%).

m.p 136-137 °C

FT-IR (KBr) nmax 3280, 1745, 1175, 1055 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 2.05 (1H, s, OH), 5.19 (2H, s, CH2), 7.92-

8.26 (4H, m, C6H4)

LRMS (EI) m/z 213 (M+), 197, 183, 132, 120, 104, 75

CHN Anal. Calcd. for C8H7NO4S: C, 45.07; H, 3.31; N, 6.57

Found: C, 45.05; H, 3.30; N, 6.59


88


SN

O

O O

OH

(9)

SN

O

O O

Cl

C8H6ClNO3SMol. Wt.: 231.66

SOCl2

reflux, 10 min.

(10)

A mixture of thionyl chloride (10 ml) and (9) (5 g, 23 mmol.) was heated under reflux for

10 minutes under anhydrous conditions and concentrated under vacuum. The residue was

dried overnight to obtain (10) (4.8 g, 20.5 mmol., 89%).

m.p 137-138 °C

FT-IR (KBr) nmax 1755, 1180, 1052 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 5.25 (2H, s, CH2), 7.84-8.10 (4H, m, C6H4)

LRMS (EI) m/z 233.4 (M+), 231.5 (M+), 196, 182, 118, 76

CHN Anal. Calcd. for C8H6ClNO3S: C, 41.48; H, 2.61; N, 6.05

Found: C, 41.42; H, 2.58; N, 6.09

X-ray Structure:


89

3.2.3 One-step Synthesis of N-chloromethyl saccharin (10)

SNH

O

O O(8)


SOCl2 SN

O

O O

Cl

(10) C8H6ClNO3SMol. Wt.: 231.66

A mixture of (8) (1.72 g, 9.41 mmol.), formaldehyde-sodium bisulfite adduct (6.31 g,

47.05 mmol.) and thionyl chloride (15 ml) was refluxed gently overnight. Excess of

thionyl chloride was removed under vacuum and the residue in methylene chloride (80

ml) was washed with brine (30 ml), water (30 ml) and dried over anhydrous sodium

sulfate. Removal of the solvent yielded (10) (2.2 g, 8.6 mmol., 91%)

mp 137-138 °C. Other spectroscopic results are the same as quoted above.

3.2.4 Synthesis of saccharin- N-methane sulfonic acid (11)

SN

O

O O

Cl

(10)

SN

O

O O

SO3H

(11) C8H7NO6S2Mol. Wt.: 277.27

1. NaI, Acetone

2. Na2SO33. HCl

N-chloromethyl saccharin (10) (0.25 g, 1.0 mmol.) and sodium iodide (0.18 g, 1.2 mmol.)

in acetone (25 ml) were stirred at room temperature for 15 minutes and filtered. A

solution of sodium sulfite (0.15 g, 1.2 mmol.) in water (25 ml) was added to the filtrate

and heated under reflux for 15 minutes. The reaction mixture was cooled to 5 °C,

acidified to pH = 4 with 2N-HCl and concentrated under vacuum. The resulting

precipitates were filtered, washed with cold water and dried to give (11) (0.16 g, 0.45

mmol., 45%).

m.p 186-187 °C


90

FT-IR (KBr) nmax 3260, 1735, 1180, 1057 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 2.01 (1H, s, OH), 5.25 (2H, s, CH2), 7.26-

8.23 (4H, m, C6H4)

13C-NMR (100 MHz) δ 62.8, 128.1, 128.2, 128.9, 133.1, 133.9, 141.7, 169.1

LRMS (EI) m/z 277 (M+), 182, 139, 103, 75

CHN Anal. Calcd. for C8H7NO6S2: C, 34.65; H, 2.54; N, 5.05; S,

23.13. Found: C, 34.69; H, 2.55; N, 5.02; S, 23.11

3.2.5 One-pot synthesis of saccharin-N-methane sulfonic acid (11)

A mixture of (8) (1.72 g, 9.4 mmol.), formaldehyde-sodium bisulfite adduct (6.31 g, 47.0

mmol.) and thionyl chloride (15 ml) was refluxed gently overnight. Excess thionyl

chloride was removed under vacuum and the residue neutralized with ammonium

hydroxide. Sodium iodide (1.55 g, 10.4 mmol.) in acetone (40 ml) was added and stirred

at room temperature for 20 minutes along with subsequent addition of sodium sulfite (1.3

g, 10.4 mmol.) in water (25 ml) and a reflux of 25 minutes. The reaction mixture was

cooled to 5 °C, acidified to pH = 4 and concentrated to half volume. The resulting

precipitates were filtered, washed with water and dried to give product (1.28 g, 4.6

mmol., 49%) mp 186-188 °C. IR, NMR etc. results are the same as quoted above.

3.2.6 Synthesis of Methyl [2-(methoxycarbonyl)phenylsulfonamido] methylsulfonate

(12)

SN

O

O O

SO3H

(11)

SNH

O

O O

OCH3

SO3CH3

(12) C10H13NO7S2Mol. Wt.: 323.34

1. MeONa, MeOH

2. HCl


91

Sulfonic acid (11) (1.0 g, 3.6 mmol.) was added to a solution of sodium methoxide (0.40

g, 7.5 mmol.) in dry methanol (25 ml). The reaction mixture was heated under reflux for

15 minutes, cooled to room temperature and acidified to pH = 3 with 15% HCl. The solid

was filtered, washed with cold water and dried (40 °C) to produce (12) (0.97 g, 2.9

mmol., 83%).

m.p 92-93 °C

FT-IR (KBr) nmax 3450, 3295, 1680, 1175, 1050 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 2.01 (1H, s, NH), 3.35 (3H, s, SO3CH3), 3.45

(3H, s, OCH3), 5.19 (2H, s, CH2), 7.39-8.26 (4H, m, C6H4)

13C-NMR (100 MHz) δ 50.2, 52.1, 62.1, 128.3, 131.3, 132.0, 132.3, 134.9, 141.3,

168.1

LRMS (EI) m/z 323 (M+), 228, 215, 135, 75

CHN Anal. Calcd. for C9H11NO7S2: C, 34.95; H, 3.58; N, 4.53;

Found: C, 34.88; H, 3.53; N, 4.49

3.2.7 Synthesis of Methyl 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-3-sulfonate

1,1-dioxide (13)

SN

O OCH3

OHSO3CH3

SNH

O

O O

OCH3

SO3CH3(13)(12)

1. NaH, DMF

2. MeI3. HCl C10H11NO6S2

Mol. Wt.: 305.33

In a flame dried three-neck round-bottom flask, under N2 atmosphere was placed sodium

hydride (1.2 g, 24 mmol., 50% dispersion in mineral oil). The mineral oil was removed

by n-hexane washing, followed by addition of (12) (1.85 g, 6.0 mmol.) in DMF (20 ml).


92

The mixture was heated to 40 °C for 30 minutes and brought to room temperature.

Methyl iodide (0.4 ml, 6.4 mmol.) in DMF (10 ml) was added to the reaction mixture and

stirred for additional 30 minutes. The precipitates after acidification (pH = 3) were

washed and dried to get (13) (0.23 g, 1.4 mmol., 23%).

m.p 219-220 °C

FT-IR (KBr) nmax 3320, 3290, 1175, 1050 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 3.25 (3H, s, NCH3, 3.75 (3H, s, SO3CH3),

7.21-8.10 (4H, m, C6H4), 11.05 (1H, s, OH)

13C-NMR (100 MHz) δ 34.5, 52.7, 95.3, 127.7, 128.1, 129.3, 129.9, 132.2, 138.6,

162.1

LRMS (EI) m/z 305 (M+), 210, 178 107, 75

CHN Anal. Calcd. for C9H9NO6S2: C, 37.11; H, 3.11; N, 4.81; S,

22.02. Found: C, 37.09; H, 3.10; N, 4.82; S, 22.03

3.2.8 Synthesis of 3-bromo-3,4-dihydro-2-methyl-4-oxo-2H-1,2-benzothiazine 1,1-

dioxide (15)

SN

O OCH3

O

SN

O OCH3

O

Br

(14) (15)

NBS, AIBN

CCl4

C9H8BrNO3SMol. Wt.: 290.13

A mixture of (14) (2.1 g, 9.9 mmol.), N-bromosuccinimide (1.9 g, 11.0 mmol.) and

azoisobutyronitrile (0.01 g) in carbon tetrachloride (25 ml) was heated under reflux for 1

hour, cooled to room temperature and filtered. Evaporation of solvent under reduced


93

pressure afforded a solid which was recrystallized from ethanol-diethyl ether (50:50) to

get (15) (2.2 g, 7.4 mmol., 75%).

m.p 72-73 °C

FT-IR (KBr) nmax 1680, 1180, 1055 cm-1

1H-NMR (400 MHz) (CDCl3): δ 3.11 (3H, s, CH3), 7.22-8.10 (4H, m, C6H4)

13C-NMR (100 MHz) δ 32.4, 79.9, 128.2, 130.7, 130.8, 132.7, 134.4, 140.1, 194.5

LRMS (EI) m/z 290 (M+), 210, 165, 101, 75

CHN Anal. Calcd. for C9H8BrNO3S: C, 37.26; H, 2.78; N, 4.83

Found: C, 37.22; H, 2.71; N, 4.82

3.2.9 Synthesis of 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-3-sulfonic acid 1,1-

dioxide (13a) from (15)

SN

O OCH3

OHSO3H

(13a)

SN

O OCH3

O

Br

(15)

C9H9NO6S2Mol. Wt.: 291.3

1. NaI, Acetone

2. Na2SO3 3. HCl

A mixture of (15) (2.5 g, 8.6 mmol.) and sodium iodide (1.4 g, 9.5 mmol.) in acetone (50

ml) was stirred at room temperature for 30 minutes and filtered. Sodium sulfite (1.2 g, 9.5

mmol.) in water (50 ml) was added to the filtrate and stirred at 40 °C for 4 hours. The

reaction mixture was cooled to 5 °C, acidified to pH = 4 and concentrated under vacuum.

The precipitates so obtained were filtered, washed with cold water and dried to get (13a)

(1.3 g, 4.6 mmol., 53%).

m.p 228-229 °C

FT-IR (KBr) nmax 3320, 3275, 1180, 1057 cm-1


94

1H-NMR (400 MHz) (DMSO-d6) δ 2.01 (1H, s, SO3H), 3.25 (3H, s, CH3), 7.20-

8.15 (4H, m, C6H4), 11.03 (1H, s, OH)

LRMS (EI) m/z 291 (M+), 210, 178, 75

3.2.10 One-pot synthesis of 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-3-sulfonic

acid 1,1-dioxide (13a)

SN

O OCH3

O

(14)

1. NBS, AIBN / CCl4 2. NaI, Acetone

3. Na2SO3 One-potS

N

O OCH3

OHSO3H

(13a) C9H9NO6S2Mol. Wt.: 291.3



hour and cooled to room temperature. Sodium iodide (1.64 g, 10.9 mmol.) in acetone (25

ml) was added and stirred for 15 minutes, followed by addition of sodium sulfite (1.38 g,

10.9 mmol.) in water (45 ml). The reaction mixture was heated under reflux for 30

minutes, cooled, filtered and the filtrate acidified to pH = 4 with 2N-HCl. The solution

was concentrated and precipitates filtered, washed with cold water and dried to give

product (2.9 g, 4.0 mmol., 41%) mp 228-230 °C.


95

SNH

O

O OS

N

O

O O

OH

SN

O

O O

Cl

SN

O

O O

SO3H

SN

O OCH3

O

SN

O OCH3

O

Br

SN

O OCH3

OHSO3R

SNH

O

O O

OCH3

SO3CH3

13 R = CH313a R = H

14 15

8 9

1011

12

1. NaH, DMF

2. MeI3. HCl

Scheme-2 Synthesis of 4-Hydroxy-2-Methyl-(2H)-1,2-Benzothiazine-3-Sulfonic Acid 1,1-Dioxide (13a)

reflux, 5 min.

SOCl2reflux10 min.


SOCl2

1. Formaldehyde- sodium bisulfite adduct / SOCl22. NaI, Acetone3. Na2SO34. HCl

1. NaI, Acetone

2. Na2SO33. HCl

1. MeONa, MeOH2. HCl

NBS, AIBN

CCl4

1. NaI, Acetone2. Na2SO33. HCl

1. NBS, A

IBN / CCl 4

2. NaI,

Acetone

3. Na2

SO3

One-pot

CH2O


96

3.3 Synthesis of 4-(Alkoxycarbonylmethylene)-3,4-Dihydro-2H-1,2-

Benzothiazine 1,1-Dioxide (23a-b)

A convenient methodology has been developed for the synthesis of 4-

(alkoxycarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (23a-b) and is

described below:

3.3.1 Synthesis of N-benzenesulfonyl glycine methyl ester (18)

SO3H

H2NOCH3

O

SNH

O O

O

O

H3C

(16) (18)

DCM

(17)

C9H11NO4SMol. Wt.: 229.25

A mixture of benzene sulfonic acid (16) (0.5 g, 3.16 mmol.), glycine methyl ester

hydrochloride (0.4 g, 3.16 mmol.) and anhydrous sodium carbonate (0.7 g, 1.58 mmol.)

was added to a round-bottom flask in dichloromethane (50 ml). The mixture was heated

under Dean-stark apparatus for 2 hours, cooled to room temperature and washed with

brine (20 ml) followed by washings with water (2 X 20 ml). Finally the solid was

recrystallised from ether and dried to give the ester (18) (0.6 g, 2.9 mmol., 91%).

m.p 60-61ºC

FT-IR (neat) nmax NH 3345, CO 1735, SO2 1360, 1180 cm-1

1H-NMR (300 MHz) (CDCl3): δ 3.64 (3H, s, CH3), 3.70 (2H, s, CH2), 5.13 (1H,

br s, NH), 7.50-7.92 (5H, m, C6H5)

13C-NMR (100 MHz) 44.0, 52.5, 127.1, 129.1, 132.9, 139.2, 169.1

CHN Anal. Calcd. for C9H11NO4S (229.040): C, 47.15; H, 4.84;

N, 6.11 Found: C, 47.10; H, 4.85; N, 6.11


97

3.3.2 Synthesis of 2-(phenylsulfonamido)acetic acid (19)

SNH

O O

O

O

SNH

OO

O

HOH3C

OH-

(18) (19) C8H9NO4SMol. Wt.: 215.23

Ester (18) (5.0 g, 21.8 mmol.) was heated under reflux in a solution of sodium hydroxide

(10%, 15.5 ml) for 4 hours. The reaction mixture was cooled and acidified with dilute

hydrochloric acid to pH = 4. Extraction of reaction mixture with ethyl acetate (4 X 25 ml)

produced on drying the acid (19) (4.4 g, 20.5 mmol., 94%).

m.p 164-165º C

FT-IR (neat) nmax NH 3312, OH 3271, CO 1729, SO2 1348, 1157 cm-1

1H-NMR (300 MHz) (MeOD): δ 3.60 (2H, s, CH2), 4.79 (1H, s, NH), 7.61-

7.82 (5H, m, Ph)

13C-NMR (100 MHz) 44.8, 128.0, 129.8, 130.1, 133.7, 141.7, 172.1

CHN Anal. Calcd. for C8H9NO4S (215.023): C, 44.64; H, 4.21; N,

6.51 Found: C, 44.63; H, 4.18; N, 6.50

3.3.3 Synthesis of 4-oxo-2H-1,2-benzothiazine 1,1-dioxide (20)

SNH

OO

O

HO

PPA

(19) (20)

O

SNH

O O C8H7NO3SMol. Wt.: 197.21

A mixture of acid (19) (3.4 g, 16 mmol.) and polyphosphoric acid (20 g) was heated to

125ºC and maintained at this temperature for 5 minutes with constant stirring. The


98

resulting mixture was cooled and poured over ice-water (100 ml). The precipitated ketone

(20) was filtered, washed with cold water and dried (2.6 g, 13.3 mmol., 83%), mp 156-

158 ºC (lit.434 157-158 ºC).

3.3.4 General Procedure for the Preparation of Salts of Wittig Reagent

Alkyl haloacetate (10 mmol.) was added to a dilute solution of triphenylphosphine (10

mmol.) in benzene and heated under reflux. The pace of reaction was monitored by TLC

analysis. On completion of reaction, the reaction mixture was cooled to room temperature

and filtered. The precipitates formed were washed with n-hexane and dried in vacuum

desiccator till constant melting point.

3.3.5 Synthesis of 4-(Alkoxycarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine

1,1-dioxide (23a-b)

General Procedure

Method A. From Wittig reagent:

Na/R'OH

O

OR'Ph3P

(21)

(20)

O

SNH

O O

O

OR'

SNH

O O(23)

23 R' a = CH3 b = C2H5

A solution of the salt of Wittig reagent (10 mmol.) in dry alcohol was added cautiously to

a stirred solution of sodium alkoxide (12 mmol.) in alcohol in an atmosphere of nitrogen.

The solution of ketone (20) prepared in the corresponding alcohol was added into it. The


99

reaction mixture was stirred at room temperature for 1 hour and worked up in

conventional way to get the alkoxycarbonylmethylene product (23a-b) (68-89%).

Method B. From alkyl chloroacetate:

Cl

O

1. Zn, Benzene2. H+, rt

OR'

(22)

(20)

O

SNH

O O

O

OR'

SNH

O O(23)

23 R' a = CH3 b = C2H5

Ketone (20) (10 mmol.) and alkyl chloroacetate (12 mmol.) were added stepwise to zinc

dust (77 mmol., previously washed with dilute hydrochloric acid, water, acetone and

dried) and a few crystals of iodine, in dry benzene (40 ml) and dry ether (40 ml). The

reaction mixture was heated under reflux for 30-60 minutes, cooled and made

homogeneous by adding glacial acetic acid. Then it was decanted from zinc into water,

acidified to pH = 1 and stirred at room temperature for additional 45 minutes.

Subsequently, it was extracted with diethylether (4 X 50 ml). The combined extracts were

dried and evaporated under reduced pressure to give ester (23a-b) (53-81%).

The physical and spectroscopic data of the synthesized compounds (23a-b) is as follows:

(a) 4-(methoxycarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide

(23a)

m.p 201-202ºC


1H-NMR (300 MHz) (DMSO-d6): δ 1.91 (1H, br s, NH), 3.75 (3H, s, CH3), 3.81


100

(2H, s, CH2), 6.21 (1H, s, C=CH), 7.21-7.82 (4H, m, Ph)

13C-NMR (100 MHz) δ 46.1, 52.5, 118.5, 126.3, 126.7, 127.9, 130.5, 131.1, 136.7,

152.6, 166.1

LRMS (EI) m/z 253 (M+), 238 (M+- CH3), 193 (M+- HCO2CH3), 152

(C6H50SO2+), 140, 77, 76


N, 5.53; S, 12.66 Found: C, 52.15; H, 4.37; N, 5.53; S,

12.63

(b) 4-(ethoxycarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide

(23b)

m.p 215-217ºC (EtOH)


1H-NMR (300 MHz) (DMSO-d6): δ 1.25 (3H, t, J 7.0 CH3), 1.82 (1H, br s, NH),

3.75 (2H, s, NH-CH2), 4.11 (2H, q, J 7.0 CO2CH2), 6.20

(1H, s, C=CH), 7.24-7.82 (4H, m, Ph)

13C-NMR (100 MHz) δ 14.3, 46.1, 62.5, 116.2, 126.3, 126.9, 127.8, 131.2, 131.7,

137.5, 152.8, 166.3

LRMS (EI) m/z 267 (M+), 238 (M+- C2H5), 193 (M+- HCO2C2H5), 152

(C6H50SO2+), 140, 77


N, 5.24 Found: C, 53.90; H, 4.87; N, 5.25; S, 12.01. S,

12.00


101

3.3.6 Synthesis of Alkyl 3-oxo-4-(phenylsulfonamido)butanoate (24a-b)

24 R' a = CH3 b = C2H5

ClO O

S

16a 24(a-b)

SNH

O O

OR' O

O

R'O

OO

NH2

A mixture of sulfonamide (16a) (1.4 g, 9.0 mmol.) and alkyl 4-chloroacetoacetate (18.0

mmol.) in chloroform (25 ml) was heated under reflux for 6-10 hours. The reaction

mixture was cooled, filtered and washed first with brine (25 ml) and then with water (2 X

25 ml) to give desired ester (24a-b) (91-95%). The physical and spectroscopic data of

these compounds is given as follows:

(a) Methyl 3-oxo-4-(phenylsulfonamido)butanoate (24a)

m.p 70-71ºC (Et2O)

FT-IR (neat) nmax NH 3350, CO2R′ 1740, CO 1615, SO2 1380, 1175 cm-1

1H-NMR (300 MHz) (CDCl3): δ 3.45 (2H, s, COCH2CO), 3.70 (3H, s, CH3),

4.35 (2H, s, NHCH2CO), 8.32 (1H, br s, NH), 7.44-7.83

(5H, m, Ph)

13C-NMR (100 MHz) δ 45.5, 50.3, 51.2, 126.9, 127.1, 128.7, 129.1, 131.6, 139.2,

167.5, 205.1

LRMS (EI) m/z 271 (M+), 212 (M+- CO2CH3) 152, 140, 77



102

N, 5.16; S, 11.82 Found: C, 48.71; H, 4.85; N, 5.15; S,

11.80

(b) Ethyl 3-oxo-4-(phenylsulfonamido)butanoate (24b)

m.p 75-76ºC (Et2O)

FT-IR (neat) nmax NH 3370, CO2R′ 1735, CO 1610, SO2 1340, 1175 cm-1

1H-NMR (300 MHz) (CDCl3): δ 1.25 (3H, t, J 7.2 CH2CH3), 3.37 (2H, s,

COCH2CO), 4.10 (2H, q, J 7.2 CH2CH3), 4.25 (2H, s,

NHCH2CO), 7.41-7.84 (5H, m, Ph), 8.13 (1H, br s, NH)

13C-NMR (100 MHz) δ 14.2, 45.0, 50.5, 60.8, 126.7, 127.3, 128.9, 129.3, 131.5,

139.2, 167.7, 205.3

LRMS (EI) m/z 285 (M+), 212 (M+- CO2 C2H5) 152, 140, 77


N, 4.91; S, 11.24 Found: C, 50.49; H, 5.27; N, 4.92; S,

11.23

3.3.7 Synthesis of 4-(Alkoxycarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine

1,1-dioxide (23a-b)

General Procedure:

A mixture of ester (24a-b) (10 mmol.) and polyphosphoric acid (20 g) was heated to

125ºC and maintained at this temperature for 30-120 minutes with stirring. The resulting

mixture was cooled and purified by column chromatography on silica using a mixture of

chloroform and diethyl ether as eluent to give the alkoxycarbonylmethylene (23a-b) (25-

39%).


103

ClO O

O

OR'

SNH

O O

SO2R

H2NOCH3

O

SNH

O O

O

O

Cl

O

SNH

OO

O

HOH3C

OH-

PPA

16 18

20

23(a-b)

24(a-b)

R = 16 = OH 16a = NH2

1. Zn Benzene2. H+, rt

Na/R'OH

19

xylene

SNH

O O

Scheme-3 Schematic image for the synthesis of 4-(Alkoxycarbonylmethylene)-3,4-dihydro- 2H-1,2-benzothiazine 1,1-dioxide (23a-b)

O

SNH

O O

O

OR'Ph3P

OR'

OR'

O PPh3

SNH

O

OR'

O OS

NH

O O

OOR'

H

O

O

R'O

23 R'

a = CH3 b = C2H5

17

21

22


104

3.4 Synthesis of 4-Hydroxy-3-Nitro-2-Methyl-(2H)-1,2-Benzothiazine 1,1-

Dioxide (27)

The synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (27) is

described in a novel one-pot reaction. It involves five steps starting from saccharin (8)

and only two transformations starting from 2-methyl-2H-1,2-benzothiazin-4-(3H)-one

1,1-dioxide (14) with an overall yield better than that from the stepwise process. One-pot

synthesis of both (27) and an important intermediate, nitromethylsaccharin (25) is also

described starting from (14) and (8) respectively.


It has been reported earlier in scheme-2 above (See articles 3.2.1 & 3.2.2, page 87-88).

3.4.2 Synthesis of nitromethylsaccharin (25)

SN

O

O O

Cl

SN

O

O O

NO2

(10) (25)

NaNO2 / DMF, rt

C8H6N2O5SMol. Wt.: 242.21

N-chloromethyl saccharin (10) (0.25 g, 1.0 mmol.) and sodium nitrite (0.30 g, 4.0 mmol.)

in DMF (25 ml) were stirred at room temperature for 12 hours, diluted with cold water

(25 ml) and filtered. The residue was extracted with ethyl acetate and the extract

evaporated to give (25) (0.05 g, 0.21 mmol., 21%).

m.p 164-165°C

FT-IR (neat) nmax 3260, 1735, 1550, 1360 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ 6.20 (2H, s, CH2), 7.26-8.23 (4H, m, Ph)


105

13C-NMR (100 MHz) δ 80.7, 126.3, 128.2, 128.9, 133.1, 133.9, 141.7, 169.1

LRMS (EI) m/z M+= 242.2

CHN Anal. Calcd. for C8H9N2O5S: C, 39.67; H, 2.50; N, 11.57; S,

13.24 Found: C, 39.66; H, 2.51; N, 11.57; S, 13.20

3.4.3 One-pot synthesis of nitromethylsaccharin (25)

1. CH2O-NaHSO3 adduct SOCl2

2. NaNO2 / DMFS

N

O

O O

NO2

(25) C8H6N2O5SMol. Wt.: 242.21

SNH

O

O O(8)

A mixture of (8) (1.72 g, 9.4 mmol.), formaldehyde-sodium bisulfite adduct (6.31 g, 47.0

mmol.) and thionyl chloride (15 ml) was refluxed gently overnight. Excess thionyl

chloride was removed in vacuum. Sodium nitrite (2.28 g, 33.1 mmol.) in DMF (40 ml)

was added and stirred at 60 °C for 4 hours, diluted with cold water (200 ml) and filtered.

The residue was extracted with ethyl acetate and dried to give product (0.71 g, 2.9 mmol.,

31%) mp 164-166°C.

3.4.4 Synthesis of Methyl [2-(nitromethyl)sulfamoyl]benzoate (26)


2. HClSN

O

O O

NO2

(25)

SNH

O

O O

OCH3

NO2

(26) C9H10N2O6SMol. Wt.: 274.25

Nitromethylsaccharin (25) (1.0 g, 4.1 mmol.) was added to a solution of sodium

methoxide (0.25 g, 4.5 mmol.) in dry methanol (15 ml). The reaction mixture was heated

under reflux for 30 minutes, cooled to room temperature and acidified to pH = 3. The


106

solid was filtered, washed with cold water and dried to produce (26) (1.06 g, 3.9 mmol.,

94%).

m.p 97-98°C

FT-IR (neat) nmax 3450, 3295, 1680,1560, 1375 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ 2.01 (1H, s, NH), 3.35 (3H, s, CH3), 6.25

(2H, s, CH2), 7.39-8.26 (4H, m, Ph)

13C-NMR (100 MHz) δ 52.1, 82.3, 128.3, 131.3, 132.0, 132.3, 134.9, 141.3, 168.1

LRMS (EI) m/z M+ = 274.25

CHN Anal. Calcd. for C9H10N2O6S: C, 39.42; H, 3.68; N, 10.21;

S,11.69 Found: C, 39.43; H, 3.66; N, 10.22; S, 11.68

3.4.5 Synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide

(27)

1. NaH / DMF

2. MeI 3. HClSNH

O

O O

OCH3

NO2

(26)

SN

O OCH3

OHNO2

(27) C9H8N2O5SMol. Wt.: 256.24

In a flame dried three-neck round-bottom flask, under N2 atmosphere was placed sodium

hydride (1.2 g, 24 mmol., 50% dispersion in mineral oil). The mineral oil was removed

by n-hexane washing, followed by addition of (26) (1.65 g, 6.0 mmol.) in DMF (20 ml) at

0°C. The mixture was stirred at 0-30 °C for 30 minutes. Methyl iodide (0.4 ml, 6.4

mmol.) was added to the reaction mixture, stirred for 30 minutes at room temperature and

acidified to pH = 3. The precipitates were washed and dried to get (27) (1.31 g, 5.2

mmol., 86%).


107

m.p 168-169°C

FT-IR (neat) nmax 3320, 3290, 1575, 1350 cm-1

1H-NMR (400 MHz) 3.75 (3H, s), 7.21-8.10 (4H, m), 11.05 (1H, s)

13C-NMR (100 MHz) δ 34.5, 118.3, 127.7, 128.1, 129.3, 129.9, 132.2, 138.6,

162.1

LRMS (EI) m/z M+ = 256.42


S, 12.51. Found: C, 42.20; H, 3.14; N, 10.92; S, 12.54

3.4.6 Synthesis of 3-bromo-3,4-dihydro-2-methyl-4-oxo-2H-1,2-benzothiazine 1,1-

dioxide (15)

This synthesis has already been mentioned in Scheme-2 above (See article 3.2.8, page

92).

3.4.7 Synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide

(27) from (15)

1. NaNO2 / DMF

2. HCl SN

O OCH3

OHNO2

(27) C9H8N2O5SMol. Wt.: 256.24

SN

O OCH3

O

Br

(15)

A mixture of (15) (2.5 g, 8.6 mmol.) and sodium nitrite (1.2 g, 17.2 mmol.) in DMF (50

ml) was stirred at room temperature for 5 hours, diluted with cold water (250 ml) and

filtered. The precipitates were washed and dried to get (27) (1.0 g, 3.9 mmol., 45%) mp

167-168°C.


108

3.4.8 One-pot synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine 1,1-

dioxide (27)

SN

O OCH3

O

(14)

1. NBS, AIBN / CCl42. NaNO2 / DMSO3. HCl One-pot S

N

O OCH3

OHNO2

(27) C9H8N2O5SMol. Wt.: 256.24



hour. Carbon tetrachloride was distilled out under vacuum. Sodium nitrite (1.31 g, 19.0

mmol.) in DMSO (25 ml) was then added and stirred at 50°C for 2 hours. The reaction

mixture was cooled, diluted with cold water (200 ml) and filtered to give product (1.4 g,

5.3 mmol., 53%) mp 166-168°C.


109

SNH

O

O OS

N

O

O O

Cl

SN

O

O O

NO2

SN

O OCH3

O

SN

O OCH3

O

Br

SN

O OCH3

OHNO2

SNH

O

O O

OCH3

NO2

14

15

8

9

10

2526

Scheme-4 Synthesis of 4-hydroxy-3-nitro-2-methyl-(2H)-1,2-benzothiazine 1,1- dioxide (27)


2. HCl

1. NBS, AIBN / CCl42. NaNO2 / DMSO3. HCl

27

One-pot

1. NaN

O2 / D

MF

2. HCl

NaNO2 DMF rt

1. CH2O-NaHSO

3 Aadduct / SOCl2One-pot

1. NaH / DMF2. MeI 3. HCl

1. MeONa (3 equiv.) MeOH2. MeI3. HCl

2. NaNO2 / DMF

NBS / AIBNCCl4


110

3.5 DERIVATIZATION

3.5.1 Synthesis of Sulfonamide Derivatives of saccharin- N-methane sulfonic acid

(11)

S

N

O

O O

SO3H+

(11)

S

N

O

O O

SO

O

HN R

Scheme-31

H2N REt3N / xylene

(223-237)

General Procedure:

To a round-bottom flask (25 ml) fitted with Dean-stark apparatus was added the

sulfonic acid (11) (1.0 g, 3.6 mmol.), amino-group containing reagent (3.9 mmol.) and 15

ml of xylene. In cases where the amino-group containing reagents were found in liquid

states, the reactions were carried out neat (without xylene) using amino-reagent in excess

(5-10 ml). The reaction mixture was subjected to reflux and the pace of reaction

monitored by TLC. After completion, the reaction mixture was allowed to stand till room

temperature and the solid derivative obtained was filtered and washed with distilled

water. In case of neat reaction the work-up was done with saturated ammonium chloride(

20 ml), followed by the treatment with dilute HCl to pH = 6.5, and finally with brine (20

ml). The dried product was recrystallised in a suitable organic solvent. (For physical data


111

see table VI, page 143). The spectroscopic data of the synthesized derivatives (223-237)

is as follows:

S

N

O

O O

SO

O

HN

(a) N-(phenylaminosulfonylmethyl)-saccharin (223)

(223)

FT-IR (neat) nmax 3400, 1625, 1350, 1057 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 2.50 (1H, s, NH), 5.25 (2H, s, CH2), 7.12-

7.37 (4H, m, Ph), 7.70-7.99 (5H, m, Ph)

13C-NMR (100 MHz) δ 62.5, 116.6, 116.7, 119.3, 127.7, 127.9, 128.1, 129.7,

129.9, 132.5, 132.8, 138.3, 140.7, 167.5

LRMS (EI) m/z M+ = 252.39

CHN Anal. Calcd. for C14H12N2O5S2: C, 47.72; H, 3.43; N, 7.95;

S, 18.20 Found: C, 47.70; H, 3.41; N, 7.96; S, 18.19

(b) N-[(p-methoxyphenyl)aminosulfonylmethyl]-saccharin (224)

S

N

O

O O

SO

O

HN

(224)

OCH3

FT-IR (neat) nmax 3390, 1630, 1375, 1050 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 2.20 (1H, s, NH), 3.75 (3H, s, CH3), 5.19 (2H,

s, CH2), 6.79-7.01 (4H, m, Ph), 7.73-7.98 (4H, s, Ph)

13C-NMR (100 MHz) δ 53.7, 62.5, 114.3, 114.7, 117.1, 117.5, 127.3, 127.6, 127.8,


112

130.2, 132.3, 132.7, 140.5, 150.9, 167.7

LRMS (EI) m/z M+ = 382.41


S, 16.77 Found: C, 47.10; H, 3.67; N, 7.30; S, 16.76

(c) N-[(o-methoxyphenyl)aminosulfonylmethyl]-saccharin (225)

(225)S

N

O

O O

SO

O

HN

H3CO

FT-IR (neat) nmax 3380, 1650, 1375, 1055 cm-1


s, CH2), 6.63-6.91 (4H, m, Ph), 7.71-7.99 (4H, s, Ph)

13C-NMR (100 MHz) δ 55.5, 62.9, 115.4, 118.1, 120.1, 122.3, 127.5, 127.7, 127.9,

129.0, 132.3, 132.8, 140.6, 148.0, 167.7

LRMS (EI) m/z M+ = 382.41


S, 16.77 Found: C, 47.12; H, 3.68; N, 7.32; S, 16.77

(d) N-[(p-methylphenyl)aminosulfonylmethyl]-saccharin (226)

S

N

O

O O

SO

O

HN

(226

CH3

FT-IR (neat) nmax 3420, 1630, 1375, 1057 cm-1


113


s, CH2), 6.53-6.81 (4H, m, Ph), 7.75-8.10 (4H, s, Ph)

13C-NMR (100 MHz) δ 25.3, 62.4, 116.2, 116.4, 127.2, 127.4, 127.7, 128.6, 129.3,

129.4, 132.2, 132.5, 134.5, 140.3, 168.3

LRMS (EI) m/z M+ = 366.41


S, 17.50 Found: C, 49.16; H, 3.84; N, 7.63; S, 17.47

O

OHHNS

O

OO

NS

OO

(e) p-[(saccharin-N-methyl)sulfonylamino]benzoic acid (227)

(227)

FT-IR (neat) nmax 3425, 1650, 1630, 1380, 1050 cm-1


dd, J = 8.7, Ph), 7.31-7.72 (4H, m, Ph), 7.78 (2H, dd, J =

8.7, Ph), 11.5 (1H, s, CO2H)

13C-NMR (100 MHz) δ 63.0, 116.3, 116.5, 127.3, 127.4, 127.7, 132.3, 132.5,

132.5, 132.6, 140.2, 142.6, 167.5, 168.3

LRMS (EI) m/z M+ = 396.39


S, 16.18 Found: C, 45.44; H, 3.06; N, 7.05; S, 16.15

O

OH

HNS

O

OO

NS

OO

(f) m-[(saccharin-N-methyl)sulfonylamino]benzoic acid (228)

(228)

FT-IR (neat) nmax 3415, 1645, 1615, 1375, 1055 cm-1


114


6.71 (3H, m, J = 8.6, Ph), 7.32 (1H, s, Ph), 7.72-8.01 (4H,

m, Ph), 11.2 (1H, s, CO2H)

13C-NMR (100 MHz) δ 62.5, 114.3, 122.5, 127.4, 127.5, 127.7, 132.3, 132.6,

132.6, 132.8, 140.1, 142.5, 167.7, 168.4

LRMS (EI) m/z M+ = 396.39


S, 16.18 Found: C, 45.43; H, 3.05; N, 7.03; S, 16.17

(g) N-(benzylaminosulfonylmethyl)-saccharin (229)

S

N

O

O O

SO

O

HN

(229)

FT-IR (neat) nmax 3400, 1650, 1380, 1057 cm-1

1H-NMR (400 MHz) (DMSO-d6) δ 2.20 (1H, t, NH), 3.78 (2H, d, CH2), 5.26 (2H,

s, NCH2SO2), 7.01-7.30 (5H, m, Ph), 7.71-8.11 (4H, m, Ph)

13C-NMR (100 MHz) δ 45.3, 63.0, 126.5, 127.1, 127.2, 127.4, 127.6, 127.8, 128.4,

128.5, 132.0, 132.1, 140.3, 141.5, 167.7

LRMS (EI) m/z M+ = 366.41


S, 17.50 Found: C, 49.16; H, 3.83; N, 7.62; S, 17.49

(h) N-[(2-chloro-4-methylphenyl)aminosulfonylmethyl]-saccharin (230)

S

N

O

O O

SO

O

HN

(230)

Cl

CH3


115

FT-IR (neat) nmax 3410, 1675, 1380, 1057 cm-1


s, CH2), 6.35-6.75 (3H, m, Ph), 7.72-8.11 (4H, m, Ph)

13C-NMR (100 MHz) δ 24.5, 62.7, 117.6, 120.4, 122.5, 127.2, 127.3, 127.5, 127.7,

129.5, 131.9, 132.3, 137.5, 140.2, 168.5

LRMS (EI) m/z M+ = 400.86

CHN Anal. Calcd. for C15H13ClN2O5S2: C, 44.94; H, 3.27; N,

6.99; S, 16.00 Found: C, 44.93; H, 3.25; N, 6.98; S, 16.01

S

N

O

O O

SO

O

NH

N

(231)

(i) N-(2-pyridylaminosulfonylmethyl)-saccharin (231)

FT-IR (neat) nmax 3400, 1650, 1380, 1057 cm-1


7.35 (4H, m, Py), 7.75-8.24 (4H, m, Ph)

13C-NMR (100 MHz) δ 62.7, 110.3, 115.1, 127.3, 127.6, 127.8, 132.2, 132.6,

138.7, 140.5, 148.1, 155.2, 167.7

LRMS (EI) m/z M+ = 353.37

CHN Anal. Calcd. for C13H11N3O5S2: C, 44.19; H, 3.14; N,

11.89; S, 18.15 Found: C, 44.17; H, 3.11; N, 11.85; S,

18.14


116

(j) N-[(2-chlorophenyl)aminosulfonylmethyl]-saccharin (232)

S

N

O

O O

SO

O

NH

(232)

Cl

FT-IR (neat) nmax 3410, 1675, 1380, 1057 cm-1


6.75 (4H, m, Ph), 7.71-8.01 (4H, m, Ph)

13C-NMR (100 MHz) δ 62.5, 117.3, 120.2, 122.6, 127.1, 127.3, 127.5, 127.7,

129.6, 131.7, 132.4, 137.6, 140.3, 168.7

LRMS (EI) m/z M+ = 386.83


7.24; S, 16.58 Found: C, 43.46; H, 2.86; N, 7.23; S, 16.55

(k) N-[(3-chlorophenyl)aminosulfonylmethyl]-saccharin (233)

S

N

O

O O

SO

O

NH

(233)Cl

FT-IR (neat) nmax 3415, 1650, 1380, 1050 cm-1


6.76 (4H, m, Ph), 7.71-8.21 (4H, m, Ph)

13C-NMR (100 MHz) δ 62.5, 114.5, 116.7, 118.5, 127.3, 127.6, 127.8, 131.1,

132.2, 132.6, 135.4, 139.3, 140.2, 167.6

LRMS (EI) m/z M+ = 386.83


7.24; S, 16.58 Found: C, 43.45; H, 2.85; N, 7.24; S, 16.57


117

(l) N-[(4-chlorophenyl)aminosulfonylmethyl]-saccharin (234)

S

N

O

O O

SO

O

NH

(234)

Cl

FT-IR (neat) nmax 3435, 1650, 1375, 1057 cm-1


6.73 (4H, m, Ph), 7.73-8.01 (4H, m, Ph)

13C-NMR (100 MHz) δ 62.1, 117.3, 117.5, 124.2, 127.1, 127.3, 127.5, 129.4,

129.5, 132.3, 132.7, 135.5, 140.3, 168.0

LRMS (EI) m/z M+ = 386.83


7.24; S, 16.58 Found: C, 43.46; H, 2.87; N, 7.23; S, 16.58

(m) N-[(2,3-dimethylphenyl)aminosulfonylmethyl]-saccharin (235)

S

N

O

O O

SO

O

NH

(235)

H3C CH3

FT-IR (neat) nmax 3415, 1625, 1375, 1057 cm-1


s, CH3), 5.28 (2H, s, CH2), 6.30-6.71 (3H, m, Ph), 7.79-

8.10 (4H, m, Ph)

13C-NMR (100 MHz) δ 7.5, 16.6, 63.0, 113.7, 118.5, 122.3, 126.0, 127.2, 127.5,

127.7, 132.3, 132.7, 136.0, 137.3, 140.5, 167.5

LRMS (EI) m/z M+ = 380.44


S, 16.86 Found: C, 50.50; H, 2.23; N, 7.35; S, 16.83


118

(n) N-[(3,4-dimethylphenyl)aminosulfonylmethyl]-saccharin (236)

S

N

O

O O

SO

O

NH

(236)

CH3

CH3

FT-IR (neat) nmax 3445, 1645, 1380, 1050 cm-1


s, CH3), 5.20 (2H, s, CH2), 6.35-6.76 (3H, m, Ph), 7.73-

8.12 (4H, m, Ph)

13C-NMR (100 MHz) δ 17.5, 17.7, 63.2, 113.4, 115.3, 126.5, 127.2, 127.4, 127.5,

129.7, 132.2, 132.5, 134.1, 137.5, 140.3, 167.7

LRMS (EI) m/z M+ = 380.44


S, 16.86 Found: C, 50.49; H, 2.22; N, 7.33; S, 16.85

(o) N-[(2,6-dimethylphenyl)aminosulfonylmethyl]-saccharin (237)

S

N

O

O O

SO

O

NH

(237)

H3C

H3C

FT-IR (neat) nmax 3400, 1625, 1380, 1057 cm-1


s, CH3), 5.19 (2H, s, CH2), 6.31-6.79 (3H, m, Ph), 7.72-

8.10 (4H, m, Ph)

13C-NMR (100 MHz) δ 14.5, 14.9, 62.0, 117.5, 126.3, 126.6, 127.2, 127.4, 127.7,

128.5, 128.7, 131.9, 132.2, 132.5, 140.0, 167.5

LRMS (EI) m/z M+ = 380.44



119

S, 16.86 Found: C, 50.51; H, 2.23; N, 7.35; S, 16.84

3.5.2 Synthesis of Sulfonamide Derivatives of Methyl 4-hydroxy-2-methyl-(2H)-1,2-

benzothiazine-3-sulfonate 1,1-dioxide (13)

SN

O OMe

OH

SO3Me

+

(13)

NH R '

(238-249)

Scheme-32

H2N R 'toluene

refluxS

N

O OMe

OH

S

O

O

General Procedure:

A mixture of the sulfonate ester (13) (1 g, 3.3 mmol.) and the amino group

containing reagent ( 3.6 mmol.) in toluene (25 ml) was subjected to reflux for 4-18 hours,

under Soxhlet containing activated A4 size molecular sieves. On completion, the reaction

mixture was allowed to cool in ice-bath and the separated product filtered, washed with

cold water and recrystallised from a suitable organic solvent. The physical data of the

newly synthesized derivatives (238-249) is given in table-VII (page 144). The

spectroscopic data is given as follows:


120

SN

O OCH3

OHS

HN

O

O

(a) 4-hydroxy-3-(phenylaminosulfonyl)-2-methyl-(2H)-1,2-benzothiazine1,1-dioxide (238)

(238)

FT-IR (neat) nmax 3390, 3320, 3290, 1180, 1050 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.5 (1H, s, NH), 3.25 (3H, s, NCH3), 6.34-6.78

(5H, m, Ph), 7.23-8.11 (4H, m, C6H4), 11.05 (1H, s, OH)

13C-NMR (100 MHz) δ 34.5, 95.3, 115.5, 116.1, 118.0, 126.3, 127.1, 128.0, 128.7,

129.2, 129.6, 131.6, 137.3, 137.5, 162.5

LRMS (EI) m/z M+ = 366.41


S, 17.70 Found: C, 49.15; H, 3.83; N, 7.64; S, 17.69

SN

O OCH3

OH

SHN

O

O

(b) 4-hydroxy-3-[(p-methoxyphenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (239)

(239)

OCH3

FT-IR (neat) nmax 3400, 3325, 3280, 1175, 1052 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.7 (1H, s, NH), 3.25 (3H, s, NCH3), 3.75 (3H, s,

OCH3), 6.21-6.76 (4H, m, Ph), 7.51-7.98 (4H, m, C6H4),

11.10 (1H, s, OH)

13C-NMR (100 MHz) δ 34.7, 54.5, 95.4, 115.3, 116.2, 126.5, 127.2, 128.6, 128.7,

129.3, 129.5, 131.9, 137.3, 137.5, 150.6, 162.5

LRMS (EI) m/z M+ = 396.44


121


S, 16.18 Found: C, 48.43; H, 4.05; N, 7.06; S, 16.17

(c) p-[(4-hydroxy--2-methyl-(2H)-1,2-benzothiazin-3-yl 1,1-dioxide)sulfonylamino]benzoic acid (240)

O

OH

SN

O OCH3

OH

SHN

O

O

(240)

FT-IR (neat) nmax 3425, 3320, 3275, 1180, 1655, 1055 cm-1

1H-NMR (400 MHz) (MeOD)δ 1.9 (1H, s, NH), 3.11 (3H, s, NCH3), 6.37 (2H,

dd, J = 8.7, Ph), 7.51-7.79 (4H, m, C6H4), 7.89 (2H, dd, J =

8.7, Ph), 11.50 (1H, s, CO2H), 12.05 (1H, s, OH)

13C-NMR (100 MHz) δ 34.6, 96.1, 116.5, 116.5, 120.7, 126.3, 127.2, 128.7, 129.3,

131.2, 131.2, 131.7, 137.5, 143.1, 162.3, 169.2

LRMS (EI) m/z M+ = 410.42


S, 15.63 Found: C, 46.80; H, 3.41; N, 6.80; S, 15.62

(d) p-[(4-hydroxy--2-methyl-(2H)-1,2-benzothiazin-3-yl 1,1-dioxide)sulfonylamino]benzoic acid (241)

O

OHS

N

O OCH3

OH

SHN

O

O

(241)

FT-IR (neat) nmax 3400, 3350, 3265, 1180, 1650, 1057 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.9 (1H, s, NH), 3.25 (3H, s, NCH3), 6.45-6.99

(4H, m, Ph), 7.45-7.80 (4H, m, C6H4), 11.35 (1H, s, CO2H),

12.50 (1H, s, OH)

13C-NMR (100 MHz) δ 34.3, 96.2, 116.3, 116.3, 120.5, 126.1, 127.1, 128.3, 129.2,


122

131.5, 131.2, 131.7, 137.3, 143.4, 162.5, 169.1

LRMS (EI) m/z M+ = 410.42


S, 15.63 Found: C, 46.81; H, 3.43; N, 6.82; S, 15.61

SN

O OCH3

OH

SHN

O

O

(e) 4-hydroxy-3-(phenylaminosulfonyl)-2-methyl-(2H)-1,2-benzothiazine1,1-dioxide (242)

(242)

FT-IR (neat) nmax 3385, 3320, 3290, 1185, 1055 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.5 (1H, s, NH), 3.20(3H, s, NCH3), 3.74(2H, s,

CH2), 6.40-6.89 (5H, m, Ph), 7.35-8.01 (4H, m, C6H4),

11.01 (1H, s, OH)

13C-NMR (100 MHz) δ 34.2, 45.2, 95.5, 115.1, 116.3, 118.2, 126.7, 127.1, 128.2,

128.7, 129.1, 129.5, 131.5, 137.3, 137.5, 162.3

LRMS (EI) m/z M+ = 380.44


S, 16.86 Found: C, 50.49; H, 4.21; N, 7.35; S, 16.85

SN

O OCH3

OH

S NHO

O

(243)

Cl

(f) 4-hydroxy-3-[(2-chloro-4-methylphenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (243)

CH3

FT-IR (neat) nmax 3400, 3315, 3285, 1180, 1057 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.6 (1H, s, NH), 2.75 (3H, s, ArCH3), 3.25(3H, s,


123

NCH3), 6.36-6.67 (3H, m, Ph), 7.55-7.99 (4H, m, C6H4),

11.20 (1H, s, OH)

13C-NMR (100 MHz) δ 24.5, 34.2, 95.1, 115.3, 116.5, 118.2, 126.5, 127.3, 128.0,

128.3, 129.3, 129.5, 131.4, 137.3, 137.5, 162.5

LRMS (EI) m/z M+ = 414.88


6.75; S, 15.46 Found: C, 50.47; C, 46.30; H, 3.61; N, 6.74;

S, 15.45

SN

O OCH3

OH

S NHO

O

(244)

Cl

(g) 4-hydroxy-3-[(o-chlorophenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (244)

FT-IR (neat) nmax 3410, 3325, 3250, 1170, 1050 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.6 (1H, s, NH), 3.30 (3H, s, CH3), 6.45-6.77

(4H, m, Ph), 7.54-7.89 (4H, m, C6H4), 11.15 (1H, s, OH)

13C-NMR (100 MHz) δ 34.5, 95.3, 115.5, 116.5, 118.2, 126.5, 127.7, 128.0, 128.3,

129.3, 129.5, 131.5, 137.2, 137.5, 162.0

LRMS (EI) m/z M+ = 400.86


6.99; S, 16.00 Found: C, 44.93; H, 3.26; N, 6.97; S, 16.01

SN

O OCH3

OH

S NHO

O

(245)

(h) 4-hydroxy-3-[(m-chlorophenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (245)

Cl

FT-IR (neat) nmax 3415, 3320, 3255, 1175, 1057 cm-1


124


(4H, m, Ph), 7.54-7.88 (4H, m, C6H4), 11.10 (1H, s, OH)

13C-NMR (100 MHz) δ 34.3, 95.5, 115.3, 116.5, 118.1, 126.5, 127.6, 128.1, 128.2,

129.3, 129.3, 131.5, 137.2, 137.5, 162.2

LRMS (EI) m/z M+ = 400.86


6.99; S, 16.00 Found: C, 44.92; H, 3.25; N, 6.98; S, 16.00

SN

O OCH3

OH

S NHO

O

(246)

(i) 4-hydroxy-3-[(p-chlorophenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (246)

Cl

FT-IR (neat) nmax 3410, 3325, 3252, 1176, 1050 cm-1


(4H, m, Ph), 7.54-7.89 (4H, m, C6H4), 11.15 (1H, s, OH)

13C-NMR (100 MHz) δ 34.4, 95.2, 115.3, 116.2, 118.3, 126.5, 127.6, 128.1,

128.2, 129.3, 129.5, 131.5, 137.2, 137.5, 162.5

LRMS (EI) m/z M+ = 400.86


6.99; S, 16.00 Found: C, 44.93; H, 3.24; N, 6.96; S, 15.99

SN

O OCH3

OH

S NHO

O

(247)

(j) 4-hydroxy-3-[(2,3-dimethylphenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (247) H3C CH3

FT-IR (neat) nmax 3400, 3315, 3285, 1180, 1057 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.6 (1H, s, NH), 2.45 (6H, s, 2 X ArCH3),


125

3.25(3H, s, NCH3), 6.30-6.65 (3H, m, Ph), 7.55-7.99 (4H,

m, C6H4), 11.20 (1H, s, OH)

13C-NMR (100 MHz) δ 8.5, 17.3, 34.2, 95.1, 115.3, 116.5, 118.2, 126.5, 127.3,

127.5, 128.0, 128.3, 129.3, 129.5, 131.4, 137.5, 162.5

LRMS (EI) m/z M+ = 394.47


S, 16.26 Found: C, 51.75; H, 4.59; N, 7.09; S, 16.25

SN

O OCH3

OHS NHO

O

(248)

(k) 4-hydroxy-3-[(3,4-dimethylphenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (248) CH3

CH3

FT-IR (neat) nmax 3410, 3315, 3280, 1180, 1057 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.5 (1H, s, NH), 2.46 (6H, s, 2 X ArCH3), 3.25

(3H, s, NCH3), 6.33-6.67 (3H, m, Ph), 7.54-7.98 (4H, m,

C6H4), 11.15 (1H, s, OH)

13C-NMR (100 MHz) δ 17.1, 17.3, 34.5, 95.3, 115.2, 116.0, 118.3, 126.5, 127.3,

127.5, 128.1, 128.5, 129.4, 129.5, 131.4, 137.5, 162.3

LRMS (EI) m/z M+ = 394.47


S, 16.26 Found: C, 51.73; H, 4.57; N, 7. 07; S, 16.23


126

SN

O OCH3

OH

S NHO

O

(249)

(l) 4-hydroxy-3-[(2,6-dimethylphenyl)aminosulfonyl]-2-methyl-(2H)-1,2-benzothiazine 1,1-dioxide (249) H3C

H3C

FT-IR (neat) nmax 3410, 3320, 3270, 1175, 1050 cm-1

1H-NMR (400 MHz) (MeOD) δ 1.8 (1H, s, NH), 2.47 (6H, s, 2 X ArCH3), 3.20

(3H, s, NCH3), 6.35-6.69 (3H, m, Ph), 7.55-8.01 (4H, m,

C6H4), 11.05 (1H, s, OH)

13C-NMR (100 MHz) δ 15.5, 15.5, 34.5, 95.5, 115.3, 116.0, 118.5, 126.5, 127.3,

127.5, 128.3, 128.5, 129.5, 129.7, 131.2, 137.5, 162.7

LRMS (EI) m/z M+ = 394.47


S, 16.26 Found: C, 51.74; H, 4.59; N, 7. 08; S, 16.25

3.5.3 Synthesis of Derivatives of 4-(methoxycarbonylmethylene)-3,4-dihydro-2H-1,2-

benzothiazine 1,1-dioxide (23a), (250-254)

O

O

SNH

O O

(23a)

+

(250-254)

Scheme-33

H2N R''benzene

reflux

O

SNH

O O

NH

R''CH3

General Procedure:


127

A mixture of the ester (23a) (1 g, 3.9 mmol.) and the amino group containing

reagent (3.9 mmol.) in benzene (25 ml) was subjected to reflux for 8-36 hours, under

Soxhlet containing activated A4 size molecular sieves. On completion, the reaction

mixture was allowed to cool in ice-bath and the separated product filtered, washed with

petroleum ether and recrystallised from a suitable organic solvent. The physical data of

the newly synthesized derivatives (250-254) is given in table-VIII (page 145). The

spectroscopic data is given as follows:

O

SNH

O O

NH

(a) 4-(phenylaminocarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (250)

(250)

FT-IR (neat) nmax NH 3410, 3350, CO 1680, SO2 1350, 1170 cm-1

1H-NMR (300 MHz) (DMSO-d6): δ 2.01 (1H, br s, SO2NH), 3.81 (2H, s, CH2),

6.22 (1H, s, C=CH), 6.50 (1H, s, CONH), 6.85-7.35 (5H, m,

Ph), 7.42-8.02 (4H, m, Ph)

13C-NMR (100 MHz) δ 46.1, 111.5, 121.3, 121.7, 124.5, 126.7, 127.2, 128.5,

129.0, 129.2, 131.5, 131.9, 135.6, 137.2, 152.3, 165.7

LRMS (EI) m/z M+ = 314.36


S, 10.20 Found: C, 61.11; H, 4.47; N, 8.89; S, 10.18


128

O

SNH

O O

NH

(251)

(b) 4-(benzylaminocarbonylmethylene)-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (251)


1H-NMR (300 MHz) (DMSO-d6): δ 1.91 (1H, br s, SO2NH), 3.81 (2H, s,

SO2NHCH2), 3.95 (2H, s, CONHCH2), 6.27 (1H, s, C=CH),

6.59 (1H, s, CONH), 6.75-7.39 (5H, m, Ph), 7.45-8.01 (4H,

m, Ph)

13C-NMR (100 MHz) δ 42.7, 46.5, 111.2, 121.5, 121.7, 124.2, 126.5 127.3, 128.5,

129.1, 129.3, 131.6, 131.7, 135.1, 137.2, 152.3, 165.5

LRMS (EI) m/z M+ = 328.39


S, 9.76 Found: C, 62.17; H, 4.89; N, 8.50; S, 9.73

O

SNH

O O

(252)

(c) 4-[(2-chloro-4-methylphenyl)aminocarbonylmethylene]-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (252)

NH

Cl

CH3



3.85 (2H, s, CH2), 6.32 (1H, s, C=CH), 6.60 (1H, s, CONH),

6.85-7.35 (3H, m, Ph), 7.42-8.02 (4H, m, Ph)

13C-NMR (100 MHz) δ 24.5, 45.8, 111.5, 122.3, 126.1, 126.5, 127.2, 127.5,


129

128.3, 129.6, 131.7, 131.9, 134.5, 136.1, 137.3, 152.5,

166.9

LRMS (EI) m/z M+ = 362.83

CHN Anal. Calcd. for C17H15ClN2O3S: C, 56.27; H, 4.17; N,

7.72; S, 8.84 Found: C, 56.25; H, 4.13; N, 7.71; S, 8.82

O

SNH

O O

(253)

NH

Cl(d) 4-[(o-chlorophenyl)aminocarbonylmethylene]-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (253)

FT-IR (neat) nmax NH 3425, 3320, CO 1675, SO2 1350 , 1160 cm-1


6.35 (1H, s, C=CH), 6.59 (1H, s, CONH), 6.55-7.25 (4H, m,

Ph), 7.37-8.00 (4H, m, Ph)

13C-NMR (100 MHz) δ 45.5, 111.0, 122.1, 126.5, 126.9, 127.2, 127.5, 128.3,

129.0, 131.6, 131.9, 134.5, 136.3, 137.3, 152.5, 166.1

LRMS (EI) m/z M+ = 348.80


8.03; S, 9.19 Found: C, 55.07; H, 3.73; N, 8.01; S, 9.18

O

SNH

O O

NH

(254)

H3C(e) 4-[(2,6-dimethyl)phenylaminocarbonylmethylene]-3,4-dihydro-2H-1,2-benzothiazine 1,1-dioxide (254)

H3C

FT-IR (neat) nmax NH 3410, 3350, CO 1680, SO2 1350 , 1170 cm-1

1H-NMR (300 MHz) (DMSO-d6): δ 2.25 (1H, br s, SO2NH), 2.95 (6H, s, 2 X


130

ArCH3), 3.80 (2H, s, CH2), 6.22 (1H, s, C=CH), 6.50 (1H, s,

CONH), 6.85-7.35 (3H, m, Ph), 7.42-8.02 (4H, m, Ph)

13C-NMR (100 MHz) δ 14.5, 15.5, 46.1, 111.5, 121.3, 121.7, 124.5, 126.7, 127.2,

128.5, 129.0, 129.2, 131.5, 131.9, 135.6, 137.2, 152.3,

165.7

LRMS (EI) m/z M+ = 342.41


S, 9.36 Found: C, 63.13; H, 5.28; N, 8.17; S, 9.35

3.5.4 Synthesis of Open-ring Derivatives of Saccharin (8), (255-264)

SNH

O

O OS NH2

O

O O(8) (255-264)

reflux, 2-9 hours

xylene+ H2N R

Scheme-34

NH

R

A mixture of saccharin (8) (1 g, 5.4 mmol.) and the amino group containing reagent (5.9

mmol.) either neat (when the amino compound was a liquid, it was taken in excess) or in

xylene (25 ml) was subjected to reflux for 2-9 hours, in an inert atmosphere. On

completion, the reaction mixture was allowed to cool in ice-bath and the separated

product filtered, washed with cold water and recrystallised from a suitable organic

solvent. The physical data of the newly synthesized derivatives (255-264) is given in

table-IX (page 146). The spectroscopic data is given as follows:


131

NH

O

S NH2

O O

(a) 2-(N-phenyl)carbamoylbenzenesulfonamide (255)

255

FT-IR (KBr) nmax NH 3304, NH2 3268, 3235, CO 1636, SO2 1339, 1146 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ, 7.12-7.16 (3H, m, J = 6.8, C6H4), 7.70-7.75

(5H, m, C6H5), 7.97-7.99 (1H, m, J = 6.8, C6H4), 10.55 (1H,

s, NH)

13C-NMR (100 MHz) δ 119.7, 120.0, 124.0, 126.8, 127.1, 128.3, 128.6, 129.9,

132.1, 134.7, 138.8, 140.6, 167.0

LRMS (EI) m/z M+ = 276.05

X-ray Structure:


132

NH

O

S NH2

O O

(b) o-[N-(p-methoxy)phenyl]carbamoylbenzenesulfonamide (256)

256

OCH3

FT-IR (KBr) nmax NH2 br 3357, 3274, CO 1632, SO2 1337, 1162 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ, 3.75 (3H, s, CH3), 6.93-6.97 (2H, sex, J =

5.6, C6H4), 7.14(2H, s, NH2), 7.61-7.65(2H, sex, J = 5.6,

C6H4), 7.70-7.99(4H, m, C6H4), 10.55 (1H, s, NH)

13C-NMR (100 MHz) δ 55.1, 113.7, 121.6, 127.1, 128.9, 130.1, 131.8, 132.1,

135.1, 140.7, 155.8, 166.6

LRMS (EI) m/z M+ = 276.05

X-ray Structure:


133

NH

O

S NH2

O O

C

O

OH

(c) p-[(o-sulfamoylphenyl)carbonylamino]benzoic acid (257)

257

FT-IR (KBr) nmax NH2 br 3388, NH 3332, OH 3284, CO1693, 1600, SO2

1336, 1170 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ, 7.15 (2H, s, NH2), 7.73-7.74 (3H, m, C6H4),

7.83-7.85 (2H, m, C6H4), 7.95-7.97(2H, m, C6H4), 8.15 (1H,

m, C6H4), 10.95 (1H, s, COOH)

13C-NMR (100 MHz) δ 121.0, 124.7, 125.7, 127.6, 128.8, 130.4, 131.1, 132.1,

134.7, 139.4, 140.7, 142.8, 161.0, 167.4

LRMS (EI) m/z M+ = 320.05


134

NH

O

S NH2

O O

C O

HO

(d) m-[(o-sulfamoylphenyl)carbonylamino]benzoic acid (258)

258

FT-IR (KBr) nmax NH2 br 3360, 3327, OH 3258, CO1702, 1663, SO2

1330, 1168 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ, 7.16 (2H, s, NH2), 7.22-7.52 (1H, m, C6H4),

7.70-7.74 (4H, m, C6H4), 7.86-7.88(2H, m, C6H4), 8.41-

8.42 (1H, m, C6H4)

13C-NMR (100 MHz) δ 120.7, 124.1, 124.8, 127.2, 128.9, 128.9, 130.3, 131.2,

132.1, 133.8, 134.2, 134.8, 139.0, 140.7, 167.1, 167.1

NH

O

S NH2

O O

(e) 2-(N-cyclohexyl)carbamoylbenzenesulfonamide (259)

259

FT-IR (KBr) nmax NH2 br 3329, CO 1618, SO2 1350, 1155 cm-1

1H-NMR (400 MHz) (DMSO-d6): δ, 1.15-1.98 (11H, m, C6H11), 7.81-8.25 (4H,

m, C6H4), 9.16 (1H, s, NH

13C-NMR (100 MHz) δ 24.5, 24.9, 25.1, 31.5, 31.9, 48.3, 127.7, 129.8, 133.3,

135.1, 140.6, 142.0

LRMS (EI) m/z M+ = 282.1


135

H3C CH3

NH

O

S NH2O O

(f) o-[N-(2,3-dimethyl)phenyl]carbamoylbenzenesulfonamide (260)

260

FT-IR (neat) nmax NH2 3415, 3325, CO 1650, SO2 1343, 1150 cm-1

1H-NMR (300 MHz) (MeOD): δ, 2.30 (3H, s, CH3), 2.35 (3H, s, CH3), 7.12-

7.34 (3H, m, C6H3), 7.63-8.10 (4H, m, C6H4)

13C-NMR (100 MHz) δ 20.8, 21.4, 120.5, 124.2, 129.5, 130.5, 131.7, 132.2, 134.3,

135.4, 137.3, 138.8, 142.2, 169.7

LRMS (EI) m/z M+ = 304.09

X-ray Structure:


136

CH3

NH

O

S NH2O O

(g) o-[N-(3,4-dimethyl)phenyl]carbamoylbenzenesulfonamide (261)

261

CH3

FT-IR (neat) nmax NH2 3425, 3365, CO 1705, SO2 1354, 1167 cm-1


7.32 (2H, m, C6H3), 7.53-7.70 (4H, m, C6H4), 8. 20 (1H, m,

C6H3)

13C-NMR (100 MHz) δ 22.9, 23.5, 122.5, 126.3, 131.6, 132.5, 133.7, 134.2, 136.3,

137.4, 139.2, 140.9, 144.2, 171.8

LRMS (EI) m/z M+ = 304.09

X-ray Structure:


137

NH

O

S NH2

O

O

(h) o-[N-(2,6-dimethyl)phenyl]carbamoylbenzenesulfonamide (262)

262

H3C

H3C

FT-IR (neat) nmax NH2 3423, 3345, CO 1715, SO2 1345 1150 cm-1


7.52 (3H, m, C6H3), 7.68-8.10 (4H, m, C6H4)

13C-NMR (100 MHz) δ 21.1, 22.3, 121.1, 125.3, 130.4, 132.5, 133.7, 134.2, 136.3,

137.4, 139.2, 139.7, 141.2, 168.7

LRMS (EI) m/z M+ = 304.09

X-ray Structure:


138

NH

O

S NH2

O O

(i) 2-[N-(4-chloro)phenyl]carbamoylbenzenesulfonamide (263)

Cl

263

FT-IR (neat) nmax NH 3355, NH2 3265, 3235, CO 1636, SO2 1349, 1157 cm-1

1H-NMR (300 MHz) (DMSO-d6): δ, 6.91-7.10 (4H, m, C6H4), 7.32-7.53

(4H, m, C6H4), 10.55 (1H, s, NH)

13C-NMR (100 MHz) δ 120.3, 121.0, 124.2, 129.0, 128.6, 129.2, 129.9, 129.9,

131.4, 133.8, 138.1, 140.1, 165.7

LRMS (EI) m/z M+ = 310.02

X-ray Structure:


139

NH

O

S NH2

O O

(j) 2-[N-(o-chloro)phenyl]carbamoylbenzenesulfonamide (264)

264

Cl

FT-IR (neat) nmax NH 3405, NH2 3273, 3255, CO 1650, SO2 1337, 1150cm-1

1H-NMR (300 MHz) (DMSO-d6): δ, 6.93-7.11 (4H, m, C6H4), 7.35-7.70

(4H, m, C6H4), 10.45 (1H, s, NH)

13C-NMR (100 MHz) δ 120.2, 121.1, 124.3, 129.1, 128.5, 129.5, 129.8, 129.9,

131.1, 133.5, 138.2, 140.1, 166.9

LRMS (EI) m/z M+ = 310.02

X-ray Structure:


140

3.5.5 Synthesis of 3-Carboxamide Derivatives of 4-Hydroxy-3-carbomethoxy-2H-

1,2-benzothiazine 1,1-dioxide (3) & (4), (265-266)

(3), (4)

SN

O O

OH

O

O

CH3

R xylene, reflux SN

O O

OH

NH

O

RCl

R = H, CH3

265, R = H266, R = CH3

H2N

Cl

Scheme-35

General Procedure:

A mixture of the methyl ester (3) or (4) ( 3.3 mmol.) and o-chloroaniline ( 3.6

mmol.) in xylene (25 ml) was subjected to reflux for 4-6 hours, under Soxhlet containing

activated A4 size molecular sieves. On completion, the reaction mixture was allowed to

cool in ice-bath and the separated product filtered, washed with dilute hydrochloric acid,

then with cold water and recrystallised from a suitable organic solvent. The physical and

spectroscopic data of the newly synthesized derivatives (265-266) is given as follows:

(a) 4-hydroxy-N-(o-chlorophenyl)-2H-1,2-benzothiazine-3-carboxamide-

1,1-dioxide (265)

SN

O O

OH

NH

O

HCl

(265)

m.p 217-218 °C

FT-IR (neat) nmax 3335, 3280, 1345, 1157 cm-1

1H-NMR (300 MHz) (CDCl3) δ 5.07 (1H, s, CONH), 7.12-7.34 (4H, m, C6H4),

7.63-8.10 (4H, m, C6H4), 12.05 (1H, s, OH)

13C-NMR (100 MHz) δ 106.4, 123.5, 125.1, 126.5, 127.3, 127.7, 128,3, 129.0,


141

129.2, 130.5, 131.4, 135.0, 137.7, 155.2, 168.8

LRMS (EI) m/z M+ = 350.01


7.99 Found: C, 51.35; H, 3.16; N, 7.97

(b) 4-hydroxy-2-methyl-N-(o-chlorophenyl)-2H-1,2-benzothiazine-3-carboxamide-

1,1-dioxide (266)

SN

O O

OH

NH

O

CH3

Cl

(266)

m.p 185-186 °C

FT-IR (neat) nmax 3345, 1365, 1150 cm-1

1H-NMR (300 MHz) (CDCl3) δ 2.90 (3H, s, CH3), 5.10 (1H, s, CONH), 7.95-

7.11 (4H, m, C6H4), 7.53-8.11 (4H, m, C6H4), 11.95 (1H, s,

OH)

13C-NMR (100 MHz) δ 37.70, 105.3, 123.2, 125.3, 126.1, 127.2, 127.5, 128,3,

129.0, 129.2, 130.5, 131.4, 135.1, 137.6, 154.2, 168.9

LRMS (EI) m/z M+ = 364.03


7.68 Found: C, 52.65; H, 3.57; N, 7.67

X-ray Structure:


142

3.6 Biological Activity Determination

In a total of four different series of heterocyclic organic compounds synthesized so far,

one series comprising of the two amide functions, one sulfonamide and the other

substituted carboxamide at ortho-position of the benzene ring, have been tested for their

antimicrobial activities as follows:

3.6.1 Antimicrobial Testing: The derivatives (255-264) dissolved in

dimethylformamide were subjected to antimicrobial screening by determining the

minimum inhibitory concentration (MIC) using the agar dilution technique.440 The in-

vitro antimicrobial activity of the prepared derivatives (255-264) against the Gram

positive bacteria (Bacillus cereus and Staphylococcus aureus) and Gram negative bacteria

(Escheichia coli and Legionella monocytogenes) was determined by preparing

suspensions of each microorganism to contain approximately 105-106 CFU (colony

forming units)/well. The test compounds were applied to the wells at concentrations

ranging from 200 to about 3.0 µg ml-1 in dimethylformamide solution, in addition to the 0


143

(control), derivatives (255-264) and the standard Penicillin G. The plates were incubated

for 24 hours at 37 °C and growth assessed by visual inspection. The minimum inhibitory

concentration (MIC) was defined as the lowest concentration of inhibitor at which

microbial growth was not apparent disregarding a single colony or a faint haze caused by

the inoculums. The results obtained are presented in Table X and discussed in the next

chapter.


144

Table-VI Derivatives of Saccharinmethane sulfonic acid (223-237) ________________________________________________________________________

S

N

O

O O

SO

O

HN R

(223-237) Compd. . No. R m.p.°C_____Yield (%) Recry. Solvent. _

223 -Ph 180-181 35% MeOH

224 -Ph-p-OMe 178-179 53% MeOH

225 -Ph-o-OMe 178-180 61% MeOH

226 -Ph-p-Me 132-133 87% (Me)2CO

227 -Ph-p-CO2H 149-150 45% CHCl3

228 -Ph-m-CO2H 154-155 25% CHCl3:AcOEt

229 -CH2-Ph 128-130 97% AcOEt

230 2-Cl-5-Me-Ph 101-103 94% EtOH

231 -2-Py 189-190 78% EtOH

232 -Ph-o-Cl 133-134 82% MeOH

233 -Ph-m-Cl 138-139 87% MeOH

234 -Ph-p-Cl 130-131 95% MeOH

235 -Ph-2,3-di-Me 110-111 88% MeOH

236 -Ph-3,4-di-Me 108-109 91% MeOH

227 -Ph-2,6-di-Me 105-106 97% MeOH ________________________________________________________________________


145

Table-VII Derivatives of 3-sulfonic acid 1,2-benzothiazine 1,1-dioxide (238-249)

NH R'

(238-249)

SN

O O

Me

OH

S

O

O

Compd. No. R' m.p.°C_____Yield (%) Recry. Solvent.

238 -Ph 162-165 48% CHCl3

239 -Ph-p-OMe 138-139 55% MeOH

240 -Ph-p-CO2H 149-150 37% MeOH

241 -Ph-m-CO2H 154-155 61% CHCl3

242 -CH2-Ph 130-132 91% AcOEt

243 2-Cl-5-Me-Ph 104-104 92% MeOH

244 -Ph-o-Cl 133-134 72% CHCl3

245 -Ph-m-Cl 128-129 71% CHCl3

246 -Ph-p-Cl 139-140 82% CHCl3

247 -Ph-2,3-di-Me 115-116 65% MeOH

248 -Ph-3,4-di-Me 106-108 84% MeOH

249 -Ph-2,6-di-Me 110-112 73% MeOH ________________________________________________________________________


146

Table-VIII Derivatives of 4-(alkoxycarbonymethylene)-1,2-benzothiazine 1,1- dioxide (250-254)

________________________________________________________________________

(70-74)

O

SNH

O O

NH

R''

Compd.

No. R'' m.p.°C_____Yield (%) Recry. Solvent.

250 -Ph 172-17 4 15 MeOH:CHCl3 (1:1) 251 -CH2-Ph 193-194 23% AcOEt:CHCl3(1:1) 252 2-Cl-5-Me-Ph 153-154 52% MeOH 253 -Ph-m-Cl 101-102 21% CHCl3 254 -Ph-2,6-di-Me 119-120 47% MeOH

________________________________________________________________________


147

Table-IX Derivatives of 3-Carbamoylbenzene sulfonamide(255-264) ________________________________________________________________________

NH

RO

S NH2

O O 255-264 Compd.

No. R m.p.°C_____Yield (%) Recry. Solvent.

255 Ph 179-180 63 CH2Cl2 256 Ph-4-OCH3 177-178 73 CH2Cl2

257 Ph-4-COOH 203-204 87 AcOEt 258 Ph-3-COOH 207-208 89 AcOEt 259 cyclohexyl 239-240(dec.) 78 Et2O 260 Ph-2,3-di-Me 190-192 66 CH2Cl2

261 Ph-3,4-di-Me 169-170 70 CH2Cl2 262 Ph-2,6-di-Me 222-223 93 CH2Cl2

263 Ph-4-Cl 202-203 45 CH2Cl2

264 Ph-2-Cl 168-169 42 CH2Cl2

________________________________________________________________________


148

Table-X Antibacterial Activity (MIC µg ml-1) of Derivatives of 3-Carbamoylbenzene Sulfonamide (255-264)

________________________________________________________________________

Susceptible microorganisms Compd. Gram positive species Gram negative species No. S. aureus B. cereus L. monocytogenes E. coli ATCC 25923 ATCC 6633 Li6 (isolate) ATCC 1130

255 050 *__ 017 019

256 105 256 012 012

257 003 002 212 216

258 001 007 219 220

259 197 *__ 044 038

260 188 *__ 008 010

261 159 *__ 009 005

262 143 *__ 019 013

263 018 012 255 293

264 015 010 215 111 Penicillin G 0.30 0.35 0.25 0.20

________________________________________________________________________ *__ the derivative is inactive or the MIC exceeds the limit of 200 µg ml-1.

Chapter: 4 RESULTS AND DISCUSSION

149

RESULTS AND DISCUSSION

The pharmacologically important heterocyclic molecules of oxicam class of drugs

emerge from a common precursor 4-hydroxy-3-carbomethoxy-2-methyl-2H-1,2-

benzothiazine 1,1-dioxide (4). In order to find out optimum conditions for maximum

yield of (4), we explored various possibilities as outlined in scheme-1 (page 86).

First path in scheme-1 employs reaction of readily available sodium saccharin

with methyl chloroacetate in DMF to afford (2) in more than 92% yield. The reaction

appeared to be highly solvent dependent because yield dropped to 70% when same

reaction was repeated in aqueous medium.432 It was found in literature323 that treatment of

(2) with 2, 3, 4 and 7 equivalents of sodium methoxide in four separate experimental

conditions409 in DMF, dimethylsulfoxide and methanol with subsequent acidification

resulted in 38%, 68%, 70% and a maximum of 85% yield of (3) respectively.433-34 We

obtained (3) from (2) in 62% yield using sodium methoxide (7 equivalents) in methanol.

It was observed that amount of methanol added to reaction mixture plays very important

role regarding the purity and yield of the product. N-methylation of (3) was achieved in

basic alcoholic medium, utilizing methyl iodide to afford (4) in 75% yield. In another

reaction treatment of (3) with dimethyl sulfate431 afforded (4) in 85% yield utilizing an

expensive solvent (SoLOX). We resolved this problem by achieving the same yield in

ethanol, thus economizing the process.

Pursuing the aim of maximum yield of (4), we investigated stepwise sequence in

path ‘b’ where molar concentration of polar aprotic reagent (i.e., sodium methoxide)


150

decided the fate of conversion of five-member ring into six-member benzothiazine. Use

of 2 equivalents of sodium methoxide in methanol gave (5), the open ring intermediate in

92% yield. N-methylation of (5) was achieved for the first time, in high yield (85%) with

methyl iodide in DMF. Finally (4) was obtained in 60% yield by using 1 equivalent of

metal hydride (NaH) in DMF.

Next we explored the possibility of direct conversion of (2) to (4) in a single step

to reduce number of steps. It involved 1.2 equivalents of sodium methoxide in

dimethylformamide, followed by in-situ N-methylation to give (4) in 47% yield. Same

reaction was repeated in methanol to further economize the conversion. This method has

never been reported previously in literature. In conclusion path c turned out to be the

most successful as it reduced the syntheses of (4) to only two steps with maximum

overall yield of 43%. The white crystalline piroxicam (7) was obtained by refluxing the

2-aminopyridine with (4) in Soxhlet apparatus using A4 type molecular sieves, thus

reducing the time required for this step from 22 hours of reflux to 12 hours only with

better yield (61%).

In connection with our on-going research programme to develop new biologically

active agents, next we synthesized 4-hydroxy-2-methyl-(2H)-1,2-benzothiazine-3-

sulfonic acid 1,1-dioxide (13a). To the best of our knowledge no work has been reported

on such type of compounds and therefore, this research work forms the basic objective of

these studies.

The preparation of saccharin-N-methane sulfonic acid (11) was carried out in a

three-step process (hydroxymethylation, chlorination and sulfonation) where each step

was studied separately with the idea of designing a one-pot procedure (Scheme-2, page


151

95). Reports on N-alkylation of sodium saccharin quoted yields up to 70% in aqueous

phase in literature.435 We synthesized N-hydroxymethyl saccharin (9) upto 92% yield

from insoluble saccharin (8) by reaction with formaline (37%). Chlorination of (9) with

thionyl chloride,436 under anhydrous conditions afforded N-chloromethyl saccharin (10).

Sulfonation of (10) was achieved by treatment with sodium sulfite via an in-situ

iodomethyl derivative437 to yield saccharin-N-methane sulfonic acid (11), in 45% yield.

On the basis of the know-how developed in the step-wise process, possibility of

direct conversion of (8) into (11) in one-pot was explored. It afforded (11) in good yield.

The cleavage of the heterocycle in (11) was achieved by treatment with sodium

methoxide in methanol to get (12) in 83% yield. Cyclization of the later, followed by in-

situ N-methylation accomplished the synthesis of (13) in poor yield (23%).

Further, we devised an excellent route to synthesize (13a) from 2-methyl-2H-1,2-

benzothiazin-4-(3H)-one 1,1-dioxide (14).438 Bromination of (14) by N-

bromosuccinimide (NBS) with azoisobutyronitrile (AIBN)439 in carbon tetrachloride, and

subsequent sulfonation of (15) confirmed the synthesis of (13a). Finally the direct

conversion of (14) to (13a) in one-pot was also successful.

After the synthesis of 3-sulfonic acid derivatives (13, 13a) of 1,2-benothiazine

1,1-dioxide, we intended to synthesize a new 1,2-benzothiazine nucleus by attacking

Wittig reagents at position-4 of 4-oxo-2H-1,2-benzothiazine 1,1-dioxide (20) (Scheme-3,

page 103). Benzene sulfonic acid (16) was reacted readily with glycine methyl ester to

give the N-benzenesulfonyl glycine methyl ester (18) in good yield and purity.

Saponification of methyl ester (18), followed by acidification afforded acid, (19), which

was cyclized in polyphosphoric acid to yield 4-oxo-2H-1,2-benzothiazine 1,1-dioxide


152

(20). This cyclization afforded poor results in polyphosphoric acid in terms of the

formation of some unavaiodable open-ring by-products. This hampered the yield of the

cyclized ketone (20). The issue was resolved by the application of Heck cyclization

reaction using catalytic amounts of a palladium salt. The ketone (20) was reacted with

Wittig reagents to give the 4-alkoxycarbonylmethylene derivatives (23a-e) of 1,2-

benzothiazine 1,1-dioxide. Synthesis of the target molecules (23a-e) was also

accomplished by treating ketone (20) with corresponding alkyl chloroacetates440 in

presence of zinc dust as catalyst .

In order to reduce number of steps in the synthesis of esters (23a-e), benzene

sulfonamide (16a) was treated with alkyl 4-chloroacetoacetate to afford alkyl 3-oxo-4-

(phenylsulfonamido)butanoate intermediates (24a-e). This condensation step is of

particular nature because initially when it was attempted with triethylamine in

dichloromethane, it produced five self-condensation products from alkyl 4-

chloroacetoacetate itself, none of which was among the expected molecules (24a-e).

However, when the same step was tried in chloroform without using any scavenger for

the by-product, it afforded excellent results (up to 95% yield). The intermediates (24a-e)

upon treatment with polyphosphoric acid provided final products (23a-e). This

cyclization step is one of its own types. The electron-withdrawing influence of the

sulfonamide function does not permit the attack of electron density from ortho-position of

the benzene ring on to the electrophilc carbon of carbonyl group to result in a cyclized

product (23a-e). Yet under forcing conditions of high temperature and in presence of

polyphosphoric acid under an inert atmosphere the cyclization was made possible.


153

Isolation of (23a-e) was carried out chromatographically where the unknown fragments

were discarded.

In an analogy to the synthesis of 3-sulfonic acid 1,2-benzothiazine 1,1-dioxide

(13) nucleus (Scheme-2), we carried out the preparation of 3-nitro-1,2-benzothiazine 1,1-

dioxide (27) because a probe into literature revealed this compound to be synthesized for

the first time. The synthesis involved an important intermediate nitromethylsaccharin (25)

that was obtained in a three-step process; hydroxymethylation, chlorination followed by

substitution of chlorine atom by nitro group. The first two steps of hydroxymethylation

and chlorination have already been discussed in detail in scheme-2, where literature

references have been mentioned to highlight the success of high yields as obtained in our

case. Ballini et al., reported439 the substitution of the halogen in alkyl halides with a nitro

group from silver nitrite under very sensitive reaction conditions. We successfully

synthesized nitromethylsaccharin (25) from chloromethylsaccharin (10) by treatment

with commercially available sodium nitrite in DMF at room temperature. This step

afforded poor yield (21%). However, when the same reaction was performed via an in-

situ iodomethylsaccharin intermediate, the yield improved to about double.

After the step-wise process, direct conversion of (8) into (25) in one-pot was

explored. It provided (25) in good yield. The heterocyclic thiazole ring in

nitromethylsaccharin (25) was cleaved by treatment with sodium methoxide (1 equiv.) in

methanol and subsequent quenching with cold dilute hydrochloric acid to get (26) in 94%

yield. Cyclization of the open ring molecule (26), followed by in-situ N-methylation

accomplished the synthesis of (27). Direct conversion of (25) into (27) via Gabriel-

Colman rearrangement was also carried out, using same metal alkoxide (3 equiv.).


154

Further, we devised an excellent route to synthesize (27) from 2-methyl-2H-1,2-

benzothiazin-4-(3H)-one 1,1-dioxide (14) that was obtained by decarboxylation of the

important precursor (4) used for the synthesis of Piroxicam (Scheme-1). Bromination of

(14) by N-bromosuccinimide with catalytic amount of azoisobutyronitrile in carbon

tetrachloride to afford (15), and subsequent substitution of bromo- with nitro- group

confirmed the synthesis of (27). Finally, direct conversion of (14) into (27) in one-pot

was attempted that proved to be unsuccessful in DMF but successful in dimethylsulfoxide

(DMSO).

Derivatization of the nuclei (11), (13), (23) and of course, the starting material (8)

has been carried out and is mentioned in experimental section 3.5.1 onwards.

Biological Activities:

The MICs of the active compounds against susceptible pathogenic organisms are

presented in table-X. It was found that all the newly synthesized compounds (255-264)

have inhibitory activity against S. aureus, a Gram-positive bacterium. Compound (258) is

the most potent derivative with lowest MIC (1.0 µg/ml) against this bacterial specie. The

compounds (255), (259-262) were found to exceed the limit of 200 µg/ml against B.

cereus where (257) caused maximum inhibition (MIC = 2.0 µg/ml), although still many

folds than that of the standard reference (MIC = 0.35 µg/ml).

Among Gram-negative bacteria the derivatives (260) and (261) were found most

active (MICs = 8.0 µg/ml and 5.0 µg/ml) against L. monocytogenes and E. coli,

respectively. In general, the derivatives where the carboxamide function was attached

with an aromatic or alicyclic group further substituted by some alkyl sub-units, the

derivative showed increased inhibitory activity (with lowest MIC). In cases where the


155

carboxamide side-chains were ending in some polar groups (like –Cl, COOH etc.), the

imparted inhibitory responses were poor. From the results obtained, it comes out that

antibacterial activity decreases as the side chain contains more hydrophilic groups. The

increased antibacterial activity is probably due to the lipophilic side-chains that help the

molecule to penetrate through the lipid cell membrane of Gram-negative bacteria.

In conclusion, almost all the derivatives of 3-carbamoyl benzene sulfonamide

series (255-264) have demonstrated potent inhibition against all the strains tested. Further

research in this area is in progress and the compounds are expected to bring fruitful

results. X-ray crystallographic studies have also been attempted and the results are

mentioned in appropriate sub-sections in the experimental chapter.

REFERENCES

156

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