1.1. mannich reaction of coumarins: 3shodhganga.inflibnet.ac.in/bitstream/10603/20757/14/8...mannich...

Chapter I

1

1. INTRODUCTION

Coumarins are a group of naturally occurring lactones with wide ranging

biological activities and benzimidazoles have been recognized as privileged

structures in the field of drug discovery. The work in this chapter involves a

study of Mannich reaction of 2-(4'-coumarinomethyl) benzimidazoles and

hence a brief survey of literature on this reaction which has been reported on

both the ring systems is presented.

1.1. Mannich reaction of Coumarins:

First report on Mannich reaction of coumarins was by Robertson et al [1], who

have found that the reaction of 4-hydroxy coumarin 1 with primary amines and

formaldehyde resulted in the formation of 3-aminomethyl-4-hydroxycoumarins

2 in analytically pure crystalline state. But attempts to prepare the compounds

from paraformaldehyde and amine hydrochlorides did not give Mannich base

2, instead 3,3'-methylenebis-4-hydroxy coumarin 3 was obtained as the

exclusive product.

O

OH

OO

OH

O O

OH

O

CH2

OO

OH

CH2 N

R

R'Paraformaldehyde/

amine hydrochloride

HN

R'

R

HCHO

12 3

Similarly, Mannich reaction of 3-hydroxy coumarin 4 with formaldehyde and

primary or secondary amines resulted in 4-N,N-dialkylaminomethyl-3-hydroxy

coumarins 5 [2].

O O O OHN

R'

R

HCHO

OH OH

NR

R'

4 5

Chapter I

2

Reaction of 7-hydroxy-4-methyl coumarins 6 with aniline/benzyl amine

resulted in the formation of oxazino-4-methyl coumarins 7 or 7-hydroxy-8-

substituted aminomethyl-4-methylcoumarins 8, depending upon whether two

equivalents or one equivalent of formaldehyde was employed [3].

O O O O

CH3

R'

HOO O

CH3

R'

HO O

N

R'

CH3

R'

NH

R''

CH2O+R''-NH2 2CH2O+R''-NH2

6 78

Kontogiorgis and Hadjipavlou-Litina [4] showed that Mannich bases 10, 11 of

7-hydroxy coumarin 9, act as potent anti-inflammatory agents.

O O O OHOO OHO O

N

CH3

N

R'2

CH2O+R1R2-NH 2CH2O+CH3-NH2

R1

R1= H, R2= Aryl, isopropyl, pentyl etcR1&R2 =

N N O N NH

9 1011

Recently it has been observed that Mannich bases 13 derived from 7-hydroxy

coumarins 12 act as good anti-viral agents [5].

O O

R'

HOO O

R'

HO

NR2

R'= H,CH3

NR2= secondary amines

NHR2, HCHO

12 13

Chapter I

3

Garazd et al [6] explored the reactivity of hydroxyl coumarins towards

Mannich reaction, where in 7-hydroxy 14 and 5-hydroxy-4-phenylcoumarins

15 were reacted with number of 1,1-diaminomethanes to give 8-

dialkylaminomethyl-7-hydroxy-4-phenylcoumarins 16 and dialkylaminomethyl

7-hydroxy-4-phenyl coumarins 17.

O OHO O OHO

NR''R'

R

R= H, Cl, Et, Pr

14 16

O O

OH

O O

OH

H3C H3C

N

R''

R'

15 17

Further, Mannich reaction of 7-hydroxy-4-phenyl coumarins 14 with amino

acids and one equivalent of formaldehyde produced 7-hydroxy-8-(N-

aminoacyl)methyl-4-phenyl coumarins 18.

O OHO

O OHO

NH

ROH

O

NH2CHRCOOH

CH2O

14 18

Chapter I

4

Atul Kumar et al [7] developed an efficient non-ionic surfactant catalysed

multi component synthesis of benzylamino coumarins 19 from secondary

amines, aromatic aldehyde and 4-hydroxy coumarin 1 via a Mannich type

reaction in water.

O O

OH

O O

OH

O O

OH

OO

OH

N

O

H

R

H N

R1

R1

R1R1

Organic solvent

Watertrtion x-100

R

R

1 20

19

8-bromo-7-methyl-9H-pyrano[2,3-e]-benzo-1,4-oxazine-2,9-dione 21 was

allowed to undergo Mannich reaction using different secondary amines, namely

diethylamine, piperidine and/or methylpiparazine in the presence of

paraformaldehyde to give the corresponding 8-bromo-7-methyl-3-substituted

9H-pyrano-1,4-oxazinones 22 [8].

OO

NH

O

O

Br

CH3

OO

NH

O

O

Br

CH3

R

R= N(C2H5)2, N N N CH3

HCHO

Sec amine

21 22

Chapter I

5

Ni et al [9] synthesized coumarin-based dyes 24 via the introduction of

functionalised amino methyl group at the 8th

position of ethyl 7-hydroxy-2-oxo-

2H-chromene-3-carboxylate derivatives 23 and studied the relationship

between the structures, the conformations and also measured the quantum

yields of synthesized dyes.

O

X

HO O

O

O

O

X

HO O

O

O

NR2

HCHO, R2NH

CH3CN/H2O,reflux

X= H, F, Cl, Br

R2NH= HN HN N HN N OCH3, ,

23 24

Bolakatti et al [10] synthesized coumarinyl Mannich bases 26 by reacting

3-acetyl coumarin 25 with various substituted secondary amines in presence of

paraformaldehyde. These compounds showed encouraging analgesic and

antipyretic activities.

O O

O

CH3

O O

O

NR1

R2

Paraformaldehyde

NH

R1

R2

R1 & R2 = Diethyl, piperidyl, etc

25 26

1.2. Mannich reaction of Benzimidazoles

Equimolar amounts of benzimidazole 27, formaldehyde, and piperidine

resulted in the formation of of 1-(piperidinomethy1) benzimidazole 28 in 97%

yield [11]. Attempts to use primary amines or higher aldehydes in place of

formaldehyde in the reaction were unsuccessful.

Chapter I

6

NH

N

HNN

N

N

HCHO+ +

27 28

Reaction of 2(3H)-Benzimidazolone/thione 29 with formaldehyde and anilines

resulted in the formation of 1,3-bis(anilinomethyl) benzimidazolones/thiones

30, by a double Mannich reaction at the ring nitrogens [12].

NH

HN

X 2HCHO

NH2

+ + 2

N

NX

NH

NH

X= S,O29 30

Jesudason et al [13] synthesized Mannich bases of benzimidazoles which were

found to possess good anti-inflammatory activity and exhibit high in vitro

bovine corneal permeability as well.

NH

NR1

N

NR1

R2

R2H

HCHO

R1= H, CH3, CH=CH-C6H5

R2= N(CH3)2, N(C2H5)2, N(C6H5)2, N N O

3132

,

Reaction of 2-mercaptobenzimidazole 33 with alkyl/arylalkyl amines and two

equivalents of formaldehyde in presence of ethanol resulted in the formation of

thiadiazinobenzimidazoles 34 [14].

Chapter I

7

N

HN

N

NS

N

R

SH

RNH2/excess CH2O,

EtOH, reflux

R= CH3, CH3CH2, CH(CH3)2, benzyl, C5H4N

33 34

Mannich bases of 2-ethylbenzimidazole 35 were found to exhibit potent

anti -inflammatory and analgesic activities [15].

NH

N CH3

N

N CH3

N

R2

R1

HCl, HCHO,

R1 = R2= Secondary aminesR1 & R2= Primary aromatic amines

NH

R2

R1

35 36

In the light of the interesting chemistry associated with these moieties and the

biological activity of the resulting compounds, it was thought of great interest

to attempt the reaction of aromatic primary amine and formaldehyde on a

molecular system, which contains both coumarin and benzimidazole ring

systems, is described in the next section.

2. PRESENT WORK

Work carried out during the present investigation has been described in

Scheme 1. Reaction of coumarin-4-acetic acids [16] 1 with o-phenylene

diamine 2 using anhydrous phosphoric acid as condensing medium afforded

benzimidazoles 3. (Scheme 1) Anhydrous phosphoric acid was used for

condensation since coumarin-4-acetic acids were insoluble in 4 N HCl and

hence the N-heterocyclisation could not be achieved under the Philip’s aqueous

HCl conditions. Reactants were mixed well and heated in anhydrous

phosphoric acid on an oil bath at 170-180 °C for 4 hours. The contents were

poured into ice cold water and then basified with liquor ammonia. The

resulting solid was filtered and washed with water, dried and recrystallised to

Chapter I

8

obtain the pure product. Further, compounds 3 were refluxed with equimolar

quantities of primary amines and excess of aqueous formalin (37%) in presence

of ethanol for 10 hours, the reaction mixture was concentrated to half and

cooled in ice, solid separated was filtered and washed with cold ethanol with a

view to obtain the Mannich bases 4 expected in this reaction. The actual

products obtained in this reaction corresponded to structure 6, the formation of

which has been explained by a second N-hydroxymethylation on the secondary

amine 4 followed by an intramolecular attack of enolate 5A leading to a C-C

bond formation. This is supported by spectroscopic data for the compounds.

Chapter I

9

O

COOH

O

NH2

NH2O O

N

HN

O O

N

NNH

O O

N

NN

O O

NN

NH

R'

R

R'

R

R'

R

R

R

1 2 3 (a,b)

4

5

6 (a-o)

Anhy.H3PO4

-H2O

HO H

H CH2O/37%

NH2

R'

CH2O/37%

O O

N

NN

R'

R

HO

H

H

5A

(Expected Mannich base)

(Obtained products)

Scheme 1: Synthesis of Tetrahydro Pyrimido Benzimidazolyl Coumarins.

Chapter I

10

3. RESULTS AND DISCUSSION

Formation of benzimidazole coumarin conjugates 3 was well supported by

spectral data. In the IR spectrum, compound 3a ( R= 6-CH3 ) exhibited a sharp

band at 3311 cm-1

due to N-H stretching of benzimidazole and lactone carbonyl

was observed at 1725cm-1

. In 1H-NMR the N-C4-CH2 protons of coumarin

appeared as a singlet at 4.47 ppm and C3-H appeared as a singlet at 6.43 δ ppm

and N-H proton at 12.39 ppm (Spectrum No. 2) which was found to be D2O

exchangeable. The molecular ion peak was observed at m/z 290 (Spectrum No.

1). Further, compounds 3 were refluxed with excess of aqueous formalin (37%)

with a view to obtain secondary amines 4 which are the Mannich bases

expected in this reaction.

Spectral data of the product obtained did not correspond to structure 4. IR

spectrum did not show any peak around 3300 cm-1

and the 1H-NMR did not

indicate any exchangeable NH and the singlet due to N-CH2 protons around

4.50 ppm was also absent. The mass spectrum showed a higher molecular ion

peak exceeding by 12 mass units.

It was apparent that the secondary amine 4 was undergoing a

N-hydroxymethylation leading to tertiary amine 5. In the next step,

deprotonation of the C4-CH2 by the tertiary nitrogen generates an enolate

stabilized carbanion 5A which can attack the N-CH2OH to form a C-C bond

followed by a simultaneous dehydration, leading to compounds 6.

Similar reactions involving second hydroxymethylation is supported by earlier

reports. Formation of oxazino coumarins has been reported (Scheme 2) in the

Mannich reaction of 7-hydroxy-4-methyl coumarins which involved a second

N-hydroxymethylation followed by an intramolecular attack by the C-7

hydroxyl group [3]. Reaction of N-benzyl anilines possessing ortho-hydroxyl

group, with formaldehyde has also resulted in the formation of oxazinones

[17,18]. Formation of C-C and N-C bond in this sequence has been of current

interest. Mannich reaction of iminium salts and ketones has led to the synthesis

Chapter I

11

of piperidones via the intermediacy of β-aminoketones [19]. Present report

illustrates a rare C-C bond forming reaction between the N-hydroxymethylated

product and an enolate stabilized C4-CH2 function attached to the coumarin

ring. Reactivity of the C4- methylene group of coumarin has been demonstrated

by our earlier work related to the reactions of ortho substituted

4-aryloxymethyl coumarins leading to the formation of 4-2' benzo [b] furanyl

coumarins [20], 2,3- dihydrobenzofuranols [21] and the corresponding

arylamines [22,23].

O O O O

CH3

R'

HO O O

CH3

R'

HO O

N

R'

CH3

R"

NH

R''

CH2O+R''-NH2 CH2O

Scheme 2: Second hydroxymethylation in Mannich reaction.

Proposed structure 6 for the products obtained is supported by spectral data. In

the 13

C- NMR, compound 6h exhibited four upfield signals at 21.47, 36.98,

51.05 and 60.72 ppm which agreed with the proposition of a second N-

hydroxymethylation (Spectrum No. 6). In its mass spectrum compound 6h

exhibited molecular ion peak at m/z 407 (Spectrum No. 3). In the 1H- NMR

(Spectrum Nos. 4&5) the prochiral methylene protons flanked between two

nitrogens (-N-CH2-N-) appeared as two doublets in the region of 5.80-6.06

ppm (J = 12.0 Hz). The N-CH2 and coumarin C4-H show AMX pattern of

splitting. The diastereotopic N-CH2 protons appear upfield at 4.41 and 4.05

ppm in the form of four lines for each proton due to geminal (J = 14.0 Hz) and

vicinal coupling (J = 8.8 Hz and 5.6 Hz) with the C-4 proton. The C-4 proton at

4.95 ppm in turn gives two 3JC-H values (5.6 Hz and 8.0 Hz). Further HETCOR

spectrum (Spectrum No. 8) confirmed that the two doublet of doublets at 4.05

and 4.41 ppm each corresponding to one proton correlated to one carbon at

51.05 ppm, and a doublet of doublet at 4.95 corresponding to one proton

correlated to the peak at 36.98 ppm, and two doublets at 5.81 and 6.06

corresponding to one proton each correlated to one carbon at 60.72 ppm.

Chapter I

12

Further 13

C-DEPT (Spectrum no. 7) confirmed that peaks at 51.05 and 60.72

ppm are due to carbons of methylene groups and peak at 36.98 ppm is due to

C-4 carbon. A singlet at 2.41 ppm corresponds to C7-CH3 of coumarin which

correlated with 13

C-signal at 21.47 ppm (Fig. 1). Aromatic protons resonated

between 6.87-7.82 ppm. Similarly all the compounds synthesized have been

confirmed by spectral data.

Fig. 1: 13

C-1H Correlations observed for the -N-CH2-N-CH2-, C4-CH- fragment

(6h).

From the above discussions it is quite clear that the attempted Mannich reaction

on benzimidazole coumarin conjugates 3 has resulted in the formation of 4-(2-

phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-2H-

chromen-2-ones 6.

Mass Spectral Fragmentation for compound 6h

The molecular ion (I) can undergo a 1, 3-(C, N) prototopic shift to (IA) which

can then undergo a retro-Diels alder fragmentation to a high yielding odd-

electron ion (II). Ion (II) still possessing coumarin can expel carbon monoxide

and a H-radical leading to a benzofuran derivative (III) at m/z 273.

Another route for the molecular ion is the probable expulsion of a N-phenyl

aziridine by two 1,3-H shifts leading to a moderately strong odd-electron-ion

(IV) (40%) at m/z 290, which can yield a benzofuran derivative (V) by the

expulsion of carbon monoxide. Expulsion of carbon monoxide is usually

observed in the fragmentation of coumarins (Scheme 3).

O

NN

N

O

H

H H

H

H

60.72

5.81 6.06

4.05

4.4151.05

36.984.98

H3C

Chapter I

13

O O

NN

NH

H3C O O

NN

NH

H3C

H H

Retro Diels Alder

O O

HN

N

H3C

H2C

-CO-H

N

N+

H3C

H2C

O

HH

H

H

O O

HN

N

H3C

H

H

N

+

-CO

HN

N

H3C O

H

H

m/z=407(M+)

(28 %)m/z=302 (72%)

m/z=273( 38%)

m/z=262 (30%)

m/z=290 (40%)

(I)

(IA) (II)

(III)

(V)

Scheme 3: Mass spectral fragmentation of compound 6h.

PHARMACOLOGY

Some of the selected compounds were subjected to pharmacological

evaluation in albino mice. In the in vivo acute toxicity experiments, all the

compounds showed LD50 values around 2000 mg/kg body weight.

The anti-inflammatory activity was evaluated at the dose of 200 mg/kg body

weight by the Carrageenan induced paw edema method. Experimental results

ar presented in Table 1, indicating the changes in paw volumes, percent

inhibition of inflammation monitored over a period of five hours. Relation

between the observed inhibition (%) varying with time is depicted in Fig. 2.

Chapter I

14

Table 1: Paw volume (% inhibition) at different time intervals.

Entry Entry 0 HOUR 1 HOUR 2 HOUR 3 HOUR 4 HOUR 5 HOUR

Control Control 1.042±0.042 1.047±0.042 1.18±0.048 1.21±0.047 1.245±0.091 1.245±0.078

Phenyl

butazone

R R’ Phenyl

butazone

1.043±0.023

(-0.095)

0.95±0.054

(9.26)

0.761±0.078***

(35.59)

0.687±0.062***

(43.22)

0.59±0.068***

(52.61)

0.52±0.035***

(58.23)

6a 6-CH3 H 6a 1.051±0.054

(-0.869)

1.011±0.023

(3.43)

0.91±0.019

(22.88)

0.88±0.094*

(27.27)

0.85±0.058**

(31.72)

0.78±0.074**

(37.34)

6b 6-CH3 4-CH

3 6b 1.017±0.051

(2.39)

1.00±0.043

(4.48)

0.78±0.033**

(33.89)

0.753±0.076**

(37.76)

0.71±0.067**

(42.97)

0.65±0.045**

(47.79)

6c 6-CH3 4-OCH

3 6c 1.024±0.076

(1.72)

1.034±0.062

(1.24)

0.958±0.037

(18.81)

0.93±0.076*

(23.14)

0.91±0.045*

(26.90)

0.85±0.041**

(31.72)

6d 6-CH3 3-CH

3 6d 1.046±0.032

(-0.38)

0.97±0.043

(7.3)

0.763±0.047***

(35.33)

0.75±0.083***

(38.01)

0.69±0.073***

(44.57)

0.63±0.051***

(49.39)

6e 6-CH3 3,4-CH

3 6e 1.072±0.013

(-2.87)

1.034±0..043

(1.21)

0.921±0.054

(21.94)

0.915±0.045**

(24.38)

0.87±0.076**

(30.12)

0.83±0.051**

(33.33)

6f 6-CH3 2,3-CH

3 6f 1.035±0.043

(0.67)

1.023±0.076

(2.29)

0.811±0.052**

(31.27)

0.79±0.046**

(34.71)

0.75±0.042**

(39.75)

0.71±0.054**

(42.97)

6g 6-CH3 4-Cl 6g 1.043±0.032

(0.095)

1.039±0.033

(0.76)

0.946±0.065

(19.83)

0.931±0.061*

(23.05)

0.91±0.031*

(26.90)

0.86±0.024**

(30.92)

6h 7-CH3 H 6h 1.049±0.024

(-0.7)

1.041±0.076

(0.57)

0.914±0.066

(22.59)

0.910±0.036*

(24.79)

0.870±0.024**

(30.12)

0.82±0.027**

(34.13)

6i

7-CH3 4-OCH3 6i

1.035±0.023

(0.67)

1.00±0.045

(4.481)

0.77±0.035**

(34.74)

0.73±0.046***

(39.66)

0.70±0.062***

(43.77)

0.64±0.035***

(48.59)

6j 7-CH3 4-CH3 6j 1.064±0.038

(-2.11)

1.02±0.037

(2.57)

0.77±0.05**

(34.74)

0.69±0.034***

(42.97)

0.61±0.062***

51.00)

0.59±0.053***

(52.61)

RESULTS ARE EXPRESSED IN MEAN± SEM, ANOVA FOLLOWED BY DUNNET T TEST, SIGNIFICANT P<0.05*, P<0.01**, P<0.001***

Chapter I

15

There was gradual increase in edema paw volume in rats in control

(carrageenan treated group) showing its maximum value at 4 h. The result

showed significant anti-inflammatory activity (p< 0.001) by treated

compounds. Maximum percent inhibition of paw edema volume in all

compounds was found at 5 h (Fig. 2). Most of the compounds 6a-6j have

shown considerable inhibition of inflammation (P< 0.01) which is depicted in

Table 1. Amongst tested compound 6j showed maximum inhibition of paw

edema (52.61%) where as phenyl butazone as reference drug showed inhibition

(58.23%) at 5h.

Fig. 2: The graph of % inhibition of paw edema vs. time.

Structure activity relation studies (SAR): have shown that the p-methoxy

group was most effective amongst the four groups in the aryl amino moiety.

Accordingly compound 6b (R= 6-CH3 and R'= 4-CH3), 6d (R= 6-CH3 and

R'= 3-CH3) and 6h (R= 7-CH3 and R'= 4-CH3) showed 47.79, 49.39 and

48.59% inhibition of inflammation at the end of 5 hours. The p-chloro

substitution in the form of compound 6g was found to be the least active

compound in the series with the inhibition of 30.72%. The combination of CH3

and p-OCH3 group was found to be most effective in the case of compound 6j

where in a maximum inhibition of 52.61% was observed; however, its

equivalent 6c was less effective. It is also important to see that there was no

-10

0

10

20

30

40

50

60

0 2 4 6

Phenyl

butazone

6a

6b

6c

6d

6e

% I

nh

ibit

ion

Time in hours

Chapter I

16

quick onset of action because the activity observed at the end of second hour

was only 18%, where as in case of 6j it was 34.74%. Compounds 6a, 6e, 6g

and 6h were also found to be less effective at the end of second hour. The

present studies have shown that the most active compound was 6j.

Table 2: Correlation of anti-inflammatory activity with calculated molecular

parameters.

Compound Log P Polar surface

area (2D)

van der Waal’s

(3D) Surface

area

% inhibition

(at 5th

hour)

6a 5.35 47.36 551.73 37.34

6b 5.86 47.79 584.26 47.79

6c 5.19 56.59 600.45 31.72

6d 5.86 47.36 584.54 49.39

6e 5.86 47.36 584.54 33.33

6f 6.38 47.36 615.99 42.97

6g 5.95 47.36 568.07 30.92

6h 5.35 47.36 551.76 34.13

6i 5.86 47.43 584.19 48.59

6j 5.19 56.59 600.38 52.61

Calculations of molecular and partitioning parameters [24] (Table 2) reveals

that the substituents did not lead to significant variation in the polar surface

area of the compounds. Log P values expectedly are more sensitive to the

substituents. A combination of Log P and higher 3D surface area which can be

found in 6j resulted in the best activity observed during the present work.

Other compounds like 6b, 6d and 6h also exhibit a fair agreement with this

proposition. Less activity observed in the case of 6c emphasizes orientation of

the groups in coumarin and aryl moieties.

Chapter I

17

Sp

ectr

um

No

. 1:

Mas

s S

pec

tru

m o

f C

om

po

un

d 3

a.

Chapter I

18

So

lven

t: D

MS

O-d

6

Sp

ectr

um

No.

2:

1H

NM

R o

f C

om

po

un

d 3

a.

Chapter I

19

Sp

ectr

um

No.

3:

Mas

s S

pec

trum

of

Com

pou

nd

6h

.

Chapter I

20

Solv

ent:

DM

SO

-d6

M+

Sp

ectr

um

No

. 4

: 1H

NM

R o

f C

om

po

und

6h

.

Chapter I

21

Solv

ent:

DM

SO

-d6

Sp

ectr

um

No

. 5

: 1H

NM

R o

f C

om

po

un

d 6

h (

Ex

pan

sion

).

Chapter I

22

So

lven

t: D

MS

O-d

6

Sp

ectr

um

No

. 6

: 1

3C

-NM

R o

f C

om

po

un

d 6

h.

Chapter I

23

Solv

ent:

DM

SO

-d6

Sp

ectr

um

No.

7:

13C

-DE

PT

NM

R o

f C

om

po

un

d 6

h.

Chapter I

24

Spectrum No. 8: 1H-13C HETCOR NMR of Compound 6h.

O

NN

N

O

H

H H

H

H

60.72

5.81 6.06

4.05

4.4151.05

36.984.98

H3C

Chapter I

25

4. EXPERIMENTAL

Melting points were determined in open capillaries and are uncorrected. IR

spectra (KBr disc) were recorded on a Nicolet-5700 FT-IR spectrophotometer.

1H-NMR spectra were recorded on Bruker 300 MHz and 400 MHz

spectrometers using CDCl3 and DMSO-d6 as solvents and TMS as an internal

standard. The chemical shifts are expressed in δ ppm. Mass spectra were

recorded using Shimadzu GCMS-QP2010S. Elemental analyses was carried

out using Hereaus CHN rapid analyzer. Purity of the compounds was checked

by TLC.

Synthesis of coumarin-4-acetic acids 2:

Coumarin-4-acetic acids have been synthesized by literature method [20] by

the cyclization of phenols and citric acid monohydrate using sulfuric acid as the

cyclising agent.

General procedure: Synthesis of 4-((1H-benzo[d]imidazol-2-yl) methyl)-

2H-chromen-2-ones 3:

Substituted coumarin-4-acetic acid (0.01M) and o-phenylene diamine (0.011M)

were mixed with 25 mL of anhydrous phosphoric acid and heated in an oil bath

at 170-180 °C for four hours and cooled, resulting thick syrupy liquid is added

carefully to ice cold water and stirred well. Solid separated was basified

carefully using 25% liquor ammonia till basic. Solid separated was washed

with water and then 5% sodium carbonate solution to remove unreacted

o-phenylene diamine. Then the solid was again washed with water and dried

and recrystallised using ethanol.

Chapter I

26

4-((1H-benzo[d]imidazol-2-yl) methyl)-6-methyl-2H-chromen-2-one 3a:

Off white solid, yield: 65%, mp= 248-50 °C

(ethanol), FT-IR (KBr) cm-1

: 1725 (C=O);

3311 (N-H); 1H-NMR (DMSO, 300 MHz,

TMS) δ ppm: 2.33 (s, 3H, C6- CH3 of

coumarin), 4.46 (s, 2H, C4-CH2), 6.43 (s, 1H,

C3-H coumarin), 7.16 (dd, 2H, J = 3.0, 6.0 Hz,

C5- C6-H benzimidazole), 7.31 (d, 1H, J = 9.0 Hz, C8-H coumarin), 7.43 (d,

1H, J = 9.0 Hz, C7- H coumarin), 7.51 (dd, 2H, J = 3.0, 6.0 Hz C4-, C7-H

benzimidazole), 7.68 (s, 1H, C5-H coumarin), 12.39 (s, 1H, N-H, D2O

exchangeable), 13

C-NMR (DMSO, 75 MHz, TMS) δ ppm: 21.36, 32.21,

116.59, 116.76, 117.29, 119.29, 122.60, 125.84, 125.93, 133.86, 134.56,

151.32, 152.21, 152.24, 160.80; MS (m/z)= (M+) 290 (79%); Anal. Calcd for

C18H14N2O2 (%): C, 74.47; H, 4.86; N, 9.65. Found: C, 74.50; H, 4.83; N, 9.64.

4-((1H-benzo[d]imidazol-2-yl) methyl)-7-methyl-2H-chromen-2-one 3b:


(Ethanol), FT-IR (KBr) cm-1

: 1699 (C=O),

3249 (N-H); 1H-NMR (DMSO 300 MHz,

TMS) δ ppm: 2.38 (s, 3H, C7- CH3 of

coumarin), 4.45 (s, 2H, C4-CH2), 6.42 (s, 1H,

C3-H of coumarin), 7.14 (m, 3H, Ar-H), 7.26

(s, 1H, Ar-H), 7.49 (bs, 2H, Ar-H ), 7.73 (d, 1H, J = 9.0 Hz, Ar-H), 12.37 (s,

1H, N-H, D2O exchangeable), MS (m/z)= (M+) 290 (75%); Anal. Calcd for

C18H14N2O2 (%): C, 74.47; H, 4.86; N, 9.65, Found: C, 74.45;H, 4.84; N, 9.68.

O O

N

HN

H3C

O O

N

HN

H3C

Chapter I

27

General Procedure: 4-(2-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-2H-chromen-2-one 6:

4-((1H-benzo[d]imidazol-2-yl)methyl)-6-methyl-2H-chromen-2-one 3 (0.001

M) was dissolved in 25 mL of absolute alcohol and substituted aromatic amine

(0.001 M) and formalin (0.0025 M) were added and refluxed at 80-90 °C for

10 h and completion of the reaction was monitored by TLC. Then the reaction

mixture was filtered and filtrate was concentrated to three by fourth of its

original volume and cooled and the solid separated was filtered and washed

with cold ethanol. Recrystallisation was done using appropriate solvent.

4-(2-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-

methyl-2H-chromen-2-one 6a:

White solid, yield: 60%, mp= 252-54 °C

(DMF), FT-IR (KBr) cm-1

: 1718 (C=O); 1H-

NMR (DMSO, 300 MHz, TMS) δ ppm: 2.37

(s, 3H, C6-CH3 coumarin), 4.08 (dd, 1H,

3JH-H = 9.0 Hz,

2JH-H= 15.0 Hz, -N-CH2-), 4.41

(dd, 1H, 3JH-H = 6.0 Hz,

2JH-H = 15.0 Hz, -N-

CH2-), 5.00 (t, 1H, C4-H), 5.82, 6.05 (2d, each,

1H, J = 12.0 Hz, -N-CH2-N-), 6.20 (s, 1H, C3-H coumarin), 6.91 (t, 1H, Ar-H),

7.13 (d, 2H, J = 9.0 Hz, Ar-H), 7.23-7.34 (m, 4H, Ar-H), 7.37 (d, 1H, J = 9.0

Hz, Ar-H), 7.50 (d, 1H, J = 9.0 Hz, Ar-H), 7.57 (d, 1H, J = 9.0 Hz, Ar-H), 7.61

(s, 1H, Ar-H), 7.84 (d, 1H, J = 6.0 Hz, Ar-H), MS (m/z)= (M-C6H5NH2)+

314

(6%); Anal. Calcd for C26H21N3O2 (%): C, 76.64; H, 5.19; N, 10.31, Found: C

76.62; H, 5.22; N, 10.34.

O O

NN

NH

H3C

Chapter I

28

4-(2-p-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-

methyl-2H-chromen-2-one 6b:

Pale yellow solid, yield: 50%, mp= 232-34

°C (Ethanol), FT-IR (KBr) cm-1

: 1722

(C=O); 1H-NMR (CDCl3, 300 MHz, TMS),

δ ppm: 2.31 (s, 3H, p-tolyl CH3), 2.41 (s,

3H, C6-CH3 of coumarin), 3.86 (m, 1H, -N-

CH2-), 4.31 (m, 1H, -N-CH2-), 4.89 (m, 1H,

C4-H), 5.62, 5.70 (2d, each, 1H, J = 12.0

Hz, -N-CH2-N-), 6.27 (s, 1H, C3-H coumarin), 6.88 (d, 2H, J = 9.0 Hz, Ar-H),

7.12 (d, 2H, J = 9.0 Hz, Ar-H), 7.30 (s, 2H, Ar-H), 7.39 (m, 3H, Ar-H), 7.51 (d,

1H, J = 9.0 Hz, Ar-H), 7.77 (d, 1H, J = 6.0 Hz, Ar-H), 13

C-NMR (DMSO, 100

MHz, TMS) δ ppm: 20.01, 20.55, 35.87, 51.07, 60.47, 110.28, 115.58, 116.67,

116.77, 117.88, 118.79, 122.08, 124.55, 129.42, 129.68, 129.81, 132.78,

133.02, 133.88, 142.16, 144.50, 149.43, 151.41, 153.83, 159.68; MS (m/z)=

(M+) 421 (65%); Anal. Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N,9.97,

Found; C 76.96; H, 5.46; N, 10.01.

4-(2-(4-methoxyphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]

pyrimidin-4-yl) -6-methyl-2H-chromen-2-one 6c:

Pale yellow solid, yield: 48%, mp= 210-

12 °C (Ethanol), FT-IR (KBr) cm-1

: 1726

(C=O); 1H-NMR (DMSO, 400 MHz,

TMS) δ ppm: 2.48 (s, 3H, C6-CH3

coumarin), 3.66 (s, 3H, O-CH3 p-

anisidine), 3.95 (dd, 1H, 3JH-H = 8.4 Hz,

2JH-H = 13.6 Hz, -N-CH2-), 4.28 (dd, 1H,

3JH-H = 5.6,

2JH-H = 13.6 Hz, -N-CH2-), 4.93 (dd,

1H,

3JH-H = 5.6, 8.0 Hz, C4-H),

5.72, 5.89 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.18 (s, 1H, C3-H

coumarin), 6.83 (d, 2H, J = 9.2 Hz, Ar-H), 7.03 (d, 2H, J = 9.2 Hz, Ar-H), 7.20

O O

NN

NH

H3C

H3C

O O

NN

NH

H3C

H3CO

Chapter I

29

(t, 1H, J = 8.0 Hz, Ar-H), 7.29 (t, 1H, J = 8.0 Hz, Ar-H), 7.35 (d, 1H, J =

8.4Hz, Ar-H), 7.47 (dd, 1H, J = 1.6, 8.4 Hz, Ar-H), 7.56 (d, 2H, J = 8.0 Hz, Ar-

H) 7.79 (d, 1H, J = 8.0 Hz, Ar-H); MS (m/z)= (M+) 437 (6%); Anal. Calcd for

C27H23N3O3 (%): C, 74. 12; H, 5.30; N, 9.60, Found: C 74.15; H, 5.32; N, 9.56.

4-(2-m-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-

methyl-2H-chromen-2-one 6d:

Pale yellow solid, yield: 54%, mp= 215-27 °C


: 1719 (C=O); 1H-

NMR (DMSO 300 MHz, TMS) δ ppm: 2.22

(s, 3H, CH3 m-tolyl), 2.38 (s, 3H, C6- CH3

coumarin), 4.05 (m, 1H, -N-CH2-), 4.38 (m,

1H, -N-CH2-), 5.00 (m, 1H, C4-H), 5.78, 6.03

(2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.19

(s, 1H, C3-H coumarin), 6.70 (d, 1H, J = 7.2 Hz, Ar-H), 6.90 (d, 1H, J = 8.4

Hz, Ar-H), 6.97 (s, 1H, Ar-H), 7.14 (t, 1H, J =7.5 Hz, Ar-H), 7.23-7.39 (m,

3H, Ar-H), 7.51 (d, 1H, J = 8.4 Hz, Ar-H), 7.57 (t, 1H, J = 7.8 Hz, Ar-H), 7.62

(s, 1H, Ar-H), 7.83 (d, 1H, J = 7.5 Hz, Ar-H); MS (m/z)= (M+) 421 (12%);

Anal. Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N, 9.97, Found: C, 76.96;

H, 5.51; N, 10.00.

4-(2-(3,4-dimethylphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6e:

Pale yellow solid, yield: 50%; mp= 234-


: 1727

(C=O); 1H-NMR (CDCl3, 300 MHz, TMS)

δ ppm: 2.19 (s, 6H, 2-CH3 amine), 2.38 (s,

3H, C6-CH3 coumarin), 3.77 (m, 1H, -N-

CH2), 4.28 (m, 1H, -N-CH2-), 4.89 (m, 1H,

O O

NN

NH

H3C

CH3

O O

NN

NH

H3C

CH3

H3C

Chapter I

30

NH), 5.58, 5.67 (2d, each, 1H, J = 11.1 Hz, -N-CH2-N-), 6.26 (s, 1H, C3-H

coumarin), 6.67 (d, 1H, J = 8.1 Hz, Ar-H), 6.78 (s, 1H, Ar-H), 7.02 (d, 1H, J =

8.1 Hz, Ar-H), 7.26-7.37 (m, 5H, Ar-H), 7.48 (d, 1H, J = 6.3 Hz, Ar-H), 7.76

(d, 1H, J = 6.9 Hz, Ar-H), 13

C-NMR (DMSO, 100 MHz, TMS) δ ppm: 18.36,

19.72, 20.56, 35.90, 51.02, 60.44, 110.28, 113.83, 115.55, 116.78, 117.90,

118.00, 118.78, 122.06, 124.48, 128.48, 130.24, 132.82, 133.00, 133.86,

137.13, 142.14, 144.70, 149.43, 151.40, 153.71, 159.66; MS (m/z)= (M+) 435

(12%); Anal. Calcd for C28H25N3O2 (%): C, 77.22; H, 5.79; N, 9.65, Found: C,

77.18; H, 5.75; N, 9.69.

4-(2-(2,3-dimethylyphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6f:

Pale yellow solid, yield: 53%, mp= 254-56 °C


: 1718 (C=O);

1H-NMR (DMSO, 400 MHz, TMS) δ ppm:

2.15, 2.21 (2s, each, 3H, 2-CH3 amine), 2.33

(s, 3H, C6-CH3 coumarin), 3.69 (dd, 1H, 3JH-H

= 6.8 Hz, 2JH-H = 13.0 Hz, -N-CH2-), 3.89 (dd,

1H, 3JH-H = 5.6,

2JH-H = 13.0 Hz, -N-CH2-),

5.03 (t, 1H,

3JH-H = 5.6 Hz, C4-H), 5.37, 5.52 (2d, each, 1H, J = 10.8 Hz, -N-

CH2-N-), 6.14 (s, 1H, C3-H coumarin), 6.94 (d, 1H, J = 8.0 Hz, Ar-H), 6.98 (d,

1H, J = 6.8 Hz , Ar-H), 7.05 (t, 1H, J = 7.6Hz, Ar-H), 7.24 (pd, 2H, J = 1.2, 7.6

Hz, Ar-H), 7.34 (d, 1H, J = 8.4 Hz, Ar-H), 7.46 (dd,1H, J = 1.6, 8.4 Hz, Ar-H),

7.57 (s, 1H, Ar-H), 7.60 (d, 1H, J = 8.4 Hz, Ar-H), 7.69 (d, 1H, J = 8.4 Hz,

Ar-H); MS (m/z)= (M+) 435 (8%); Anal. Calcd for C28H25N3O2 (%): C, 77.22;

H, 5.79; N, 9.65, Found; C, 76.25; H, 5.82; N, 9.68.

O O

NN

NH

H3C

CH3

CH3

Chapter I

31

4-(2-(4-chlorophenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6g:



: 1724

(C=O); 1H-NMR (DMSO, 400 MHz, TMS)

δ ppm: 2.36 (s, 3H, 6-CH3 coumarin), 4.06

(dd, 1H, 3JH-H = 8.4 Hz,

2JH-H = 14.0 Hz,

-CH2-N-), 4.40 (dd, 1H, 3JH-H = 5.2,

2JH-H =

14.0 Hz, -CH2-N-), 5.00 (dd, 1H,

3JH-H = 5.6,

8Hz, C4-H), 5.79, 6.02 (2d, each, J = 10.8 Hz, 1H, -N-CH2-N-), 6.19 (s, 1H,

C3-H coumarin), 7.14 (d, 2H, J = 8.8 Hz, Ar-H), 7.20-7.31 (m, 4H, Ar-H), 7.36

(d, 1H, J = 8.4 Hz, Ar-H), 7.47 (d, 1H, J = 8.4 Hz, Ar-H) 7.55 (d, 1H, J = 8.0

Hz, Ar-H), 7.62 (s, 1H, Ar-H), 7.80 (d, 1H, J = 7.6 Hz, Ar-H); MS (m/z)= (M+)

441 (21%), (M+2)+

443 (7%); Anal. Calcd for C26H20ClN3O2 (%): C, 70.67; H,

4.56; N, 9.51, Found; C, 70.71; H, 4.60; N, 9.48.

4-(2-phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-7-

methyl-2H-chromen-2-one 6h:

White solid, yield: 57%, mp= 156-58 °C


: 1712 (C=O); 1H-

NMR (DMSO 400 MHz, TMS) δ ppm: 2.41

(s, 3H, C7-CH3 coumarin), 4.05 (dd, 1H, 3JH-H

= 8.8 Hz, 2JH-H = 14.0 Hz, -N-CH2- ), 4.41 (dd,

1H, 3JH-H = 5.6,

2JH-H = 14.0 Hz, -N-CH2-),

4.95 (dd, 1H,

3JH-H = 5.6, 8.0 Hz, C4-H), 5.80, 6.06 (2d, each, 1H, J = 12.0 Hz,

-N-CH2-N-), 6.20 (s, 1H, C3-H coumarin), 6.87 (t, 1H, J = 7.2 Hz, Ar-H), 7.11

(d, 2H, J = 8.0 Hz, Ar-H), 7.17 (d, 1H, J = 10.0 Hz, Ar-H), 7.21-7.31 (m, 5H,

Ar-H), 7.53 (d, 1H, J = 8.0 Hz, Ar-H), 7.60 (d, 1H, J = 6.4 Hz, Ar-H), 7.82 (d,

1H, J = 8.0 Hz, Ar-H); 13

C-NMR (DMSO, 100 MHz, TMS) δ ppm: 20.93,

36.46, 50.54, 60.20, 110.30, 114.73, 115.67, 116.40, 116.98,118.77, 120.66,

122.06, 124.79, 125.67, 129.39, 132.76, 142.14, 142.95,146.76, 149.35,

O O

NN

NH

H3C

Cl

O O

NN

NH

H3C

Chapter I

32

153.40, 153.81, 159.70, MS (m/z)= (M+) 407 (27%); Anal. Calcd for

C26H21N3O2 (%): C,76.64; H, 5.19; N, 10. 31, Found: C, 76.61; H, 5.23; N,

10.29.

4-(2-p-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-7-

methyl-2H-chromen-2-one 6i:



: 1731

(C=O); 1H NMR (CDCl3, 300 MHz, TMS),

δ ppm: 2.30 (s, 3H, CH3 p-tolyl), 2.46 (s,

3H, C7- CH3 coumarin), 3.88 (m, 1H, -N-

CH2-), 4.29 (m, 1H, -N-CH2-), 4.85 (m, 1H,

C4-H), 5.69 (m, 2H, -N-CH2-N-), 6.21 (s,

1H, C3-H coumarin), 6.86 (d, 2H, Ar-H), 7.11 (m, 3H, Ar-H), 7.19 (s, 1H, Ar-

H), 7.28-7.37 (m, 3H, Ar-H), 7.51 (d, 1H, Ar-H), 7.77 (d, 1H, Ar-H); 13

C-NMR

(DMSO 100 MHz, TMS) δ ppm: 20.01, 20.95, 36.34, 50.97, 60.46, 110.31,

114.74, 115.69, 116.66, 117.00, 118.76, 122.06, 124.78, 125.69, 129.66,

129.84, 132.77, 142.13, 142.95, 144.42, 149.38, 153.42, 153.84, 159.74, MS

(m/z)= (M+) 421 (60%); Anal Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N,

9.97, Found; C, 76.97; H, 5.48; N, 9.94.

4-(2-(4-methoxyphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-7-methyl-2H-chromen-2-one 6j:



: 1725

(C=O); 1H NMR (DMSO, 400 MHz,

TMS) δ ppm: 2.41 (s, 3H, C7-CH3

coumarin), 3.66 (s, 3H, OCH3 p-

anisidine), 3.95 (dd, 1H, 3JH-H = 8.0 Hz,

2JH-H = 16.0 Hz, -N-CH2-), 4.29 (dd, 1H,

3JH-H = 4.0 Hz,

2JH-H = 14.0 Hz, -N-CH2-), 4.90 (dd,

1H,

3JH-H = 4.0, 8.0 Hz, C4-

O O

NN

NH

H3C

H3C

O O

NN

NH

H3C

H3CO

Chapter I

33

H), 5.72, 5.93 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.21 (s, 1H, C3-H

coumarin), 6.83 (d, 2H, J = 8.0 Hz, Ar-H), 7.03 (d, 2H, J = 8.0 Hz, Ar-H), 7.18

(t, 1H, J = 8.0 Hz, Ar-H), 7.22 (d, 1H, J = 8.0 Hz, Ar-H), 7.29 (t, 2H, J = 8.0

Hz, Ar-H), 7.54 (d, 2H, J = 8.0 Hz, Ar-H), 7.79 (d, 1H, J = 8.4 Hz, Ar-H); MS

(m/z)= (M+) 437 (15%); Anal. Calcd for C27H23N3O3 (%): C, 74.12; H, 5.30; N,

9.60, Found: C, 74.09; H, 5.31; N, 9.63.

4-(2-(3,4-dimethylphenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-7-methyl-2H-chromen-2-one 6k:



: 1727

(C=O); 1H NMR (DMSO 400 MHz, TMS)

δ ppm: 2.08, 2.11 (2s, each, 3H, 2CH3-

amine), 2.41 (s, 3H, C7-CH3 coumarin),

3.98 (dd, 1H, -N-CH2-, 3JH-H = 8.8 Hz,

2JH-H

= 14.0 Hz), 4.33 (dd, 1H, 3JH-H = 5.6,

2JH-H

= 14.0 Hz, -N-CH2-), 4.92 (dd, 1H, 3JH-H = 5.6, 8.8 Hz, C4-H), 5.73, 6.00 (2d,

each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.19 (s, 1H, C3-H coumarin), 6.80 (dd,

1H, J = 2.4, 8.2 Hz, Ar-H), 6.92 (d, 1H, J = 2.4 Hz, Ar-H), 6.97 (d, 1H, J = 8.4

Hz, Ar-H), 7.17 (d,1H, J = 8.4 Hz, Ar-H), 7.22 (d, 1H, J = 8.0 Hz, Ar-H), 7.29

(t, 2H, Ar-H), 7.53 (d, 1H, J = 8.0 Hz, Ar-H), 7.57 (d, 1H, J = 6.0 Hz, Ar-H),

7.81 (d, 1H, J = 8.0 Hz, Ar-H); 13

C-NMR (DMSO, 100 MHz, TMS) δ ppm:

18.36, 19.72, 20.95, 36.21, 50.76, 60.60, 110.55, 113.91, 114.81, 115.66,

117.01, 118.01, 118.39, 122.37, 122.42, 124.73, 125.69, 128.55, 130.27,

132.58, 137.12, 141.15, 143.00, 144.61, 149.36, 153.41, 153.50, 159.69; MS

(m/z)= (M+) 435 (12%); Anal. Calcd for C28H25N3O2 (%): C, 77.22; H, 5.79; N,

9.65, Found: C, 77.25; H, 5.82; N, 9.69.

O O

NN

NH

H3C

CH3

H3C

Chapter I

34

4-(2-m-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-7-

methyl-2H-chromen-2-one 6l:



1723 (C=O);

1H-NMR (DMSO 400 MHz, TMS) 2.21 (s,

3H, -CH3 m-tolyl) 2.42 (s, 3H, C6-CH3

coumarin), 4.04 (dd, 1H, 3JH-H = 8.0,

2JH-H =

14.0 Hz, -N-CH2-), 4.34 (dd, 1H, 3JH-H = 4.0

Hz, 2JH-H = 14.0 Hz, -N-CH2-), 4.95 (dd, 1H,

3JH-H = 4.0 Hz, 8.0 Hz, C4-H), 5.77, 6.03 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-

), 6.19 (s, 1H, C3-H coumarin), 6.69 (d, 1H, J = 8.0 Hz, Ar-H), 6.89 (d, 1H, J =

8.0 Hz, Ar-H), 6.95 (s, 1H, Ar-H), 7.11 (t, 1H, J = 8.0 Hz, Ar-H), 7.20 (t, 1H, J

= 8.0 Hz, Ar-H), 7.21 (t, 1H, J = 8.0 Hz, Ar-H), 7.27-7.31 (m, 2H, Ar-H), 7.54

(d, 1H, J = 8.0 Hz, Ar-H), 7.60 (d, 1H, Ar-H), 7.82 (d, 1H, J = 8.0 Hz, Ar-H);

MS (m/z)= (M+H)+ 422(97%); Anal. C27H23N3O2 (%): C, 76.94; H, 5.50; N,

9.97, Found: C, 76.90; H, 5.46; N, 9.94.

4-(2-(4-chlorophenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-7-methyl-2H-chromen-2-one 6m:



: 1716 (C=O);

1H NMR (DMSO, 400 MHz, TMS) δ ppm:

2.42 (s, 3H, C7-CH3 coumarin), 4.05 (dd, 1H,

3JH-H = 8.0 Hz,

2JH-H = 12.0 Hz, -CH2-N-),

4.40 (dd, 1H, 3JH-H = 4.0 Hz,

2JH-H = 12.0 Hz,

-CH2-N-), 4.96 (dd, 1H,

3JH-H = 4.0, 8.0 Hz,

C4-H), 5.79, 6.07 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.23 (s, 1H, C3-H

coumarin), 7.14-7.19 (m, 3H, Ar-H), 7.22 (d, 1H, J = 8.0 Hz, Ar-H), 7.26-7.31

(m, 4H, Ar-H), 7.53 (d, 1H, J = 8.0 Hz, Ar-H), 7.61 (d, 1H, J = 4.0 Hz, Ar-H),

O O

NN

NH

H3C

CH3

O O

NN

NH

H3C

Cl

Chapter I

35

7.81 (d, 1H, J = 8.0 Hz, Ar-H); 13

C-NMR (DMSO, 100 MHz, TMS) δ ppm:

20.96, 36.39, 50.44, 60.13, 110.35, 114.79, 115.69, 116.98, 118.08, 118.80,

122.11, 124.36, 124.99, 125.69, 129.13, 132.76, 142.15, 142.99, 145.76,

149.35, 153.41, 153.76, 159.72; MS (m/z)= (M+H) +

442 (97%), (M+2+H) +

444 (28%); Anal. Calcd for C26H20ClN3O2 (%): C, 70.67; H, 4.56; N, 9.5,

Found: C, 70.64; H, 4.53; N, 9. 54.

4-(2-(4-bromophenyl)-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-

c]pyrimidin-4-yl)-6-methyl-2H-chromen-2-one 6n:



: 1722 (C=O),

1H- NMR (DMSO, 400 MHz, TMS) δ ppm:

2.37 (s, 3H, C6-CH3 coumarin), 4.07 (dd, 1H

3JH-H = 8.4Hz,

2JH-H = 14.0 Hz, -CH2-N-),

4.40 (dd, 1H, 3JH-H = 5.6,

2JH-H = 14.0 Hz,-

CH2-N-), 5.02 (dd, 1H,

3JH-H = 5.6, 8.4 Hz,

C4-H), 5.81, 6.04 (2d, each, 1H, J = 12.0 Hz, -N-CH2-N-), 6.22 (s, 1H, C3-H

coumarin), 7.11 (d, 2H, J = 9.2 Hz, Ar-H), 7.22 (t, 1H, J = 7.6 Hz, Ar-H), 7.30

(t, 1H, J = 8.0 Hz, Ar-H), 7.36-7.39 (m, 3H, Ar-H), 7.50 (d, 1H, J = 8.4 Hz, Ar-

H), 7.59 (d, 1H, J = 8.4 Hz, Ar-H), 7.65 (s, 1H, Ar-H), 7.82 (d,1H, J = 8.0 Hz,

Ar-H), 13

C-NMR (DMSO, 100 MHz, TMS) δ ppm: 20.52, 35.88, 50.30, 60.01,

110.30, 112.04, 115.60, 116.71, 117.91, 118.40, 118.80, 122.11, 124.79,

131.95, 132.73, 133.04, 133.88, 142.15, 146.21, 149.43, 151.39, 153.81,

159.65, MS (m/z)= (M+H) +

486 (93%), (M+2+H) +

, 488 (90%); Anal. Calcd

for C26H20BrN3O2 (%): C, 64.21; H, 4.14; N, 8.64, Found: C, 64.18; H,4.22; N,

8.65.

O O

NN

NH

Br

H3C

Chapter I

36

4-(2-o-tolyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-6-

methyl-2H-chromen-2-one 6o:

Off white coloured solid, yield: 49%,

mp=241-42 °C (Ethanol), FT-IR (KBr) cm-1

:

1723 (C=O); 1H-NMR (DMSO, 400 MHz,

TMS) δ ppm: 2.25 (s, 3H, CH3 o-toluidine),

2.35 (s, 3H, 6- CH3 coumarin), 3.71 (dd, 1H,

3JH-H = 6.8 Hz,

2JH-H = 13.0 Hz, -N-CH2-), 3.99

(dd, 1H, 3JH-H = 5.2 Hz,

2JH-H = 13.0 Hz, -N-

CH2-), 5.19 (m, 1H, C4-H), 5.56, 5.63 (2d, each, 1H, -N-CH2-N-, J = 11.0 Hz),

6.29 (s, 1H, C3-H coumarin), 7.08-7.25 (m, 4H, Ar-H), 7.36-7.44 (m, 3H, Ar-

H), 7.49 (d, 1H, J = 8.4 Hz, Ar-H), 7.62 (s, 1H, Ar-H), 7.71 (d, 1H, J = 7.6 Hz,

Ar-H), 7.85 (d, 1H, J = 7.2 Hz, Ar-H); MS (m/z)= (M+H)+ 422(87%); Anal.

Calcd for C27H23N3O2 (%): C, 76.94; H, 5.50; N, 9.97, Found: C, 76.97; H,

5.48; N, 9.95.

PHARMACOLOGY

Acute oral toxicity:

Healthy young mice of either sex weighing 22-30 g were used for acute

toxicity study [25] to determine LD50 of test compounds. Each group contained

three animals. The temperature in the experimental room was maintained

around 25 °C. Lighting was natural; sequence being 12 hours dark, 12 hours

light cycle. The conventional laboratory diet was fed with adequate supply of

drinking water. The animals were randomly selected, marked to permit

individual identification and kept in polypropylene cages for one week prior to

dosing, in order for them to acclimatize to laboratory conditions. The test

compounds were prepared as a suspension by triturating with water and 1%

tween 80. The test compounds were administered in a single dose by using a

mice oral feeding needle. Prior to dosing, animals were kept for 12 hours

fasting. The animals were then weighed and test compounds were

O O

NN

NH

H3C

CH3

Chapter I

37

administered. After the administration of dose, food was withheld for a further

3-4 hours. In each step three animals were used in each group. Study began at

50 mg/kg body weight and was continued till 2000 mg/kg body weight.

Observations:

Animals were observed initially after dosing atleast once during the first 30

minutes, periodically during the first 24 hours, with special attention given

during the first 4 hours. In above case, death was observed within first 24

hours. Additional observations like changes in skin, fur, eyes, mucous

membranes, respiratory, circulatory, autonomic, central nervous system,

somatomotor activity and behavior pattern were also noted. Attention was also

given to observation of tremors and convulsions. No tremors and convulsions

were observed upon inspection and a post mortem examination revealed no

hemorrhagic spots.

Evaluation of carrageenan induced inflammation:

Acute inflammation was induced by injecting 0.1 ml of (1%) carrageenan

into plantar surface of rat hind paw [26]. The test samples and

phenylbutazone (100 mg/kg, orally) as reference agent were administered

60 min before carrageenan injection. The paw volumes were measured at 0,

1, 2, 3, 4 and 5 h, using mercury plethysmometer. The mean changes in

injected paw edema, with respect to initial paw volume, were calculated on

respective hours and percentage inhibition of paw edema with respect to

untreated group was calculated using following formula:

i = [1- (∆VTreated/ ∆VControl)] X 100

where, I = % inhibition of paw edema

∆VTreated = Mean change in paw volume of treated rat.

∆VControl = Mean change in paw volume of treated rat.

Chapter I

38

5. CONCLUSIONS

In conclusion, we have observed an unexpected C-C bond formation in the

Mannich reaction of formaldehyde and primary amines of methylene bridged

4-2'-benzimidazolyl coumarins leading to a serendipitous synthesis of 4-(2-

phenyl-1,2,3,4-tetrahydrobenzo[4,5]imidazo[1,2-c]pyrimidin-4-yl)-2H-

chromen-2- ones. The synthesized compounds have been confirmed by spectral

methods. Compounds 6b, 6d, 6h and 6j exhibited good anti-inflammatory

activity, amongst which 6j was found to be most potent.

Chapter I

39

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Chapter I

40

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1.1. mannich reaction of coumarins: 3shodhganga.inflibnet.ac.in/bitstream/10603/20757/14/8...mannich...

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