pharmacognosy i (part 5)

7/23/2019 Pharmacognosy I (Part 5)

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CarbohydratesCarbohydrates



Carbohydrates [CX(H2O)Y] are usually

defined as polyhydroxy aldehydes and

ketones or substances that hydrolyze to yield polyhydroxy aldehydes and ketones.

Simple carbohydrates are no!n as su"ars

or saccharides (#atin saccharum, su"ar) andthe endin" of the names of most su"ars is $

ose. %or e&ample'

. lucose (for the principle su"ar in blood)2. %ructose (for a su"ar in fruits and honey)

*. Sucrose (for ordinary table su"ar)

+. ,altose (for malt su"ar)



Classification of carbohydratesClassification of carbohydrates

MonosaccharideMonosaccharide ((CC66HH1212OO66))

it is a simple carbohydrate- one that one attempted

hydrolysis is not cleaed to smaller carbohydrates.

e.". "lucose

DisaccharideDisaccharide on hydrolysis is cleaed to t!o

monosaccharide- !hich may be the same or

different. e.". sucrose OligosaccharideOligosaccharide (oligos is a ree !ord that

means /fe!0) yields * 1 monosaccharide unit on

hydrolysis. e.". raffinose



PolysaccharidesPolysaccharides are hydrolyed to moreare hydrolyed to more

than 1 monosaccharide units.than 1 monosaccharide units. CelluloseCellulose is ais a

polysaccharide molecule that "iespolysaccharide molecule that "ies

thousands of "lucose molecules !henthousands of "lucose molecules !hen

completely hydrolyed.completely hydrolyed.



MonosaccharidesMonosaccharides

Oer 211 different monosaccharides are no!n.Oer 211 different monosaccharides are no!n. ,onosaccharides are classified accordin" to,onosaccharides are classified accordin

" to''

. 3he number of carbon atoms present in the

molecule.2. 4hether they contain an aldehyde or etone "roup.

5 monosaccharide containin" three carbon atoms

is called a triosetriose6 one containin" four carbon atoms

is called a tetrosetetrose.

5 monosaccharide containin" an aldehyde "roup is

called an aldosealdose6 one containin" a eto "roup is

called a ketoseketose.



(CHOH)n

CH2OH

CH

O

(CHOH)n

CH2OH

C

CH2OH

5n aldose 5 etose

O

CH2OH

5n aldotetrose

C+

CH2OH

C

CH2OH

5 etopentose

O

C7

CHOH

CHOH

CHOH

CHOH

CH

O



D and L Designations ofD and L Designations of

MonosaccharidesMonosaccharides

3he simplest monosaccharide is

"lyceraldehyde- !hich contains a

stereocenter. 3herefore- it e&ist in

t!o enantiomeric forms. 8n 1906- (9):"lyceraldehyde is

desi"nated ;:(9): "lyceraldehyde

and (−): "lyceraldehyde is

desi"nated #:(−): "lyceraldehyde.

3hese t!o compounds sere as

confi"urational standards for all

monosaccharides.

C(R)

CH2OH

COHH

HO

C(S)

CH2OH

CHHO

HO

(9):lyceraldehyde

(:):lyceraldehyde



5 monosaccharide !hose hi"hest numbered

stereocenter (the penultimate carbon) has the

same confi"uration as ;:(9): "lyceraldehyde isdesi"nated as a ; su"ar6 one !hose hi"hest

numbered stereocenter has the same confi"uration

as #:(−): "lyceraldehyde is desi"nated as an #

su"ar.

; and # desi"nations are not related to the optical

rotations of the su"ars to !hich they are applied.

One may encounter other su"ars that are ;:(9): or

;:(−): and ones that are #:(9): or #:(−):.



Structural formulas forStructural formulas for

,onosaccharides,onosaccharides isher !ro"ectionisher !ro"ection

Ha#orth for$%lasHa#orth for$%las

ano$er orano$er orβ

ano$er ano$er

CHO

OHH

HHO

OHH

OHH

CH2OH

H

H OH

HO H

O

H

HOHO

O

H

HO

H

HO

H

OHH

OH

OH

OH

indicates α βor



<ot all carbohydrates e&ist in e=uilibrium

!ith si&:membered hemiacetal rin"s- in

seeral instances the rin" is fi'e

membered.

8f the monosaccharide rin" is si&membered- the compound is called a

pyranose (e.". β:;:"lucopyranose )6 if

the rin" is fie membered- the

compound is desi"nated as a furanose.

(e.". β:;:ribofuranose).

O

O

Pyran

Furan



M%tarotationM%tarotation

3he spontaneous chan"e that taes place in the

optical rotation of α and β anomers of a su"ar !hen

they are dissoled in !ater. 3he optical rotations of

the su"ars chan"e until they reach the same alue. the e&planation for this mutarotation lies in the

e&istence of an e=uilibrium bet!een the open:chain

form of ;:(9):"lucose and the α and β forms of the

cyclic hemiacetals. the concentration of open:chain ;:(9):"lucose inthe concentration of open:chain ;:(9):"lucose in

solution at e=uilibrium is ery small.solution at e=uilibrium is ery small.



> C O>?

OH

>??

HCl(g)

R' OH > C O>?

O>?

>??

Hemiacetal (R'' may be H) An acetal (R'' may be H)

H2O

He$iacetalHe$iacetal' a functional "roup- consistin" of a' a functional "roup- consistin" of a

carbon atom bonded to an alo&y "roup and to acarbon atom bonded to an alo&y "roup and to ahydro&yl "roup. Hemiacetals are synthesied byhydro&yl "roup. Hemiacetals are synthesied by

addin" one molar e=uialent of an alcohol to anaddin" one molar e=uialent of an alcohol to an

aldehyde or a etone.aldehyde or a etone.



(lycoside or$ation(lycoside or$ation

Carbohydrate acetals- "enerally- are called"lycosides- and an acetal of "lucose is called a

"lucoside.

3he methyl ;:"lucosides hae been sho!n to hae

si&:membered rin"- so they are properly named

methyl α :;:"lucopyranoside and β :;:

"lucopyranoside.

lycosides are stable in basic solutions becausethey are acetals.

8n acidic solutions- "lycosides under"o hydrolysis to

produce a su"ar and an alcohol (aglycone).



)%gars that contain nitrogen)%gars that contain nitrogen

1* (lycosyla$ines1* (lycosyla$ines

5 su"ar in !hich an amino

"roup replaces the

anomeric −OH "roup.

5denosine is an e&ample

of a "lycosylamine that isalso called a n%cleoside.

O

H

HO

H

HO

H

H

OHH+H2

OH

-D-Glucoyranosylamineβ



2* ,$ino s%gars2* ,$ino s%gars

5 su"ar in !hich an amino

"roup replaces anonanomeric −OH "roup.

e.". ;:"lucosamine.

;:"lucosamine can be

obtained by hydrolysis of

chitin- a polysaccharide

found in the shells oflobsters and crabs and in

the e&ternal seletons of

insects and spiders.

O

H

HO

H

HO

H

H

+H2

HOH

OH

-D-Glucosamineβ



Other -eactions of MonosaccharidesOther -eactions of Monosaccharides

. @noliation- 3automeriation- and 8someriation. @noliation- 3automeriation- and 8someriation

A ;issolin" monosaccharides in a=ueous base;issolin" monosaccharides in a=ueous base

causes them to under"o enoliations and a seriescauses them to under"o enoliations and a series

of eto:enol tautomeriations that lead toof eto:enol tautomeriations that lead to

isomeriations.isomeriations.



RC

OH

C>2

RC

O

C>2 RC

O

C>2

!nol

!nolate ion

.nols.nols are in e=uilibrium !ith an isomeric aldehyde orare in e=uilibrium !ith an isomeric aldehyde oretone- but are normally much less stable than aldehydesetone- but are normally much less stable than aldehydesand etones.and etones.

.nolate ion.nolate ion is the conBu"ate base of an enol. @nolate ionsis the conBu"ate base of an enol. @nolate ionsare stabilied by electron delocaliation.are stabilied by electron delocaliation.

/a%to$eri$/a%to$eri$ is a process by !hich t!o isomers areis a process by !hich t!o isomers areinterconerted by a moement of an atom or a "roup.interconerted by a moement of an atom or a "roup.@noliation is a form of tautomerism.@noliation is a form of tautomerism.



2. %ormation of @thers2. %ormation of @thers

O

H

HO

H

HO

H

H

OH

OH OCH*

"t#yl glucoside

O

H

HO

H

HO

H

H

OH

O OCH*

O

H

HO

H

HO

H

H

OH

OCH* OCH*

H*C OSO*CH*

OH

3he hydro&yl "roups of monosaccharides are more acidic than those3he hydro&yl "roups of monosaccharides are more acidic than those

of ordinary alcoholsof ordinary alcohols beca%sebeca%se the monosaccharide contains so manythe monosaccharide contains so manyelectrone"atie o&y"en atoms- all of !hich e&ert electron:!ithdra!in"electrone"atie o&y"en atoms- all of !hich e&ert electron:!ithdra!in"

inductie effects on nearby hydro&yl "roups.inductie effects on nearby hydro&yl "roups.

8n a=ueous <aOH- the hydro&yl "roups are conerted to alo&ide ions8n a=ueous <aOH- the hydro&yl "roups are conerted to alo&ide ions

and each of these in turn- reacts !ith dimethyl sulfate to yield a methyland each of these in turn- reacts !ith dimethyl sulfate to yield a methyl

ether.ether.



**..Conersion to @stersConersion to @sters

O

H

H*CCO

H

H*CCO

H

H

OCCH*

OCCH* OCCH*

O

O

O

O

O

O

H

HO

H

HO

H

H

OH

OH OH

(CH$CO)2O

Pyridine%& C

3reatin" a monosaccharide !ith e&cess acetic3reatin" a monosaccharide !ith e&cess aceticanhydride and a !ea base (such as pyridine oranhydride and a !ea base (such as pyridine or

sodium acetate) conerts all of the hydro&yl "roups-sodium acetate) conerts all of the hydro&yl "roups-

includin" the anomeric hydro&yl- to ester "roups.includin" the anomeric hydro&yl- to ester "roups.



+. O&idation >eactions of ,onosaccharides+. O&idation >eactions of ,onosaccharides

,* ehlings sol%tion or enedicts reagent,* ehlings sol%tion or enedicts reagent 5 characteristic property of an aldehyde function is its

sensitiity to o&idation.

Carbohydrates that "ie positie tests !ith %ehlin"Ds or

EenedictDs rea"ents are termed -ed%cing )%gars.

Fetoses are also reducin" su"ars- since under the

conditions of the test- etoses e=uilibrate !ith aldoses by

!ay of enediol intermediates- and the aldoses are o&idied

by the rea"ents.

CH

O

2Cu2' R CO

O

Cu2O $H2O

Alde#yde From coer()

sulate

Hydro*ide

ion

Carbo*ylate

anion

Coer()

o*ide

+ater

> ,HO



* ro$ine 3ater4 the synthesis of aldonic acids* ro$ine 3ater4 the synthesis of aldonic acids

Eromine !ater is a "eneral rea"ent that selectielyEromine !ater is a "eneral rea"ent that selectielyo&idies theo&idies the −−CHO "roup to aCHO "roup to a −−COCO22H "roup.H "roup.

(CHOH)n

CHO

CH2OH

r 2

H2O(CHOH)n

CO2H

CH2OH

Aldose Aldonic acid



C* +itric ,cid O&idation4 ,ldaric ,cidsC* +itric ,cid O&idation4 ,ldaric ,cids

(CHOH)n

CHO

CH2OH

(CHOH)n

CO2H

CO2H

Aldose Aldaric acid

H.O$

;ilute nitric acid $ a stron"er o&idiin" a"ent than;ilute nitric acid $ a stron"er o&idiin" a"ent than

bromine !ater $ o&idies both the $CHO "roup andbromine !ater $ o&idies both the $CHO "roup andthe terminal $CHthe terminal $CH22OH "roup of an aldose to $COOH "roup of an aldose to $CO22HH

"roup. 3hese dicarbo&ylic acids are no!n as"roup. 3hese dicarbo&ylic acids are no!n asaldaric acidsaldaric acids..



D* Periodate o&idations4 o&idati'e clea'age ofD* Periodate o&idations4 o&idati'e clea'age of

!olyhydro&y co$!o%nds!olyhydro&y co$!o%nds

Compounds that hae hydro&yl "roups on adBacentCompounds that hae hydro&yl "roups on adBacent

atoms under"o o&idatie cleaa"e !hen they areatoms under"o o&idatie cleaa"e !hen they are

treated !ith a=ueous periodic acid (H8Otreated !ith a=ueous periodic acid (H8O++).).

8n these periodate o&idations that8n these periodate o&idations that for every C for ever y C − − CCbond broken, a C bond brok en, a C − − O bond is formed at eachO bond is formed at each

carboncarbon..

C

C

OH

OH

H(O/ 2 C

O

H(O/ H2O



4hen three or more $CHOH "roups are4hen three or more $CHOH "roups are

conti"uous- the internal ones are obtained asconti"uous- the internal ones are obtained as

formic acid formic acid . %or e&ample- "lycerol. %or e&ample- "lycerol

H

C

C

C

H

H

H

H OH

OH

OH

Glycerol

2 O/

C

H H

O

C

H OH

O

C

H H

O

(ormalde#yde)

(ormalde#yde)

(ormic acid)



O&idatie cleaa"e also taes place !hen an $OHO&idatie cleaa"e also taes place !hen an $OH

"roup is adBacent to the carbonyl "roup of an"roup is adBacent to the carbonyl "roup of an

aldehyde or etone (but not that of an acid or analdehyde or etone (but not that of an acid or an

ester). %or e&ample- "lyceraldehydeester). %or e&ample- "lyceraldehyde

O

C

C

C

H

H

H OH

OH

H

Glyceralde#yde

2 O/

C

H OH

O

C

H OH

O

C

H H

O

(ormic acid)

(ormalde#yde)

(ormic acid)



Geriodic acid does not cleae compounds in !hichGeriodic acid does not cleae compounds in !hichthe hydro&yl "roups are separated by anthe hydro&yl "roups are separated by aninterenin" $CHinterenin" $CH22 $ "roup- nor those in !hich a $ "roup- nor those in !hich a

hydro&yl "roup is adBacent to an ether or acetalhydro&yl "roup is adBacent to an ether or acetalfunction.function.

H2C

CH2

H2C OH

OH

O/ no clea0age

H2C

HC

H2C >

OH

OCH*

O/ no clea0age



7. >eduction of ,onosaccharides' 5lditols7. >eduction of ,onosaccharides' 5lditols

(CHOH)n

CHO

CH2OH

(CHOH)n

CH2OH

CH2OH

Aldose Alditol

.aH/

5ldoses (and etoses) can be reduced !ith sodium 5ldoses (and etoses) can be reduced !ith sodiumborohydride to compounds calledborohydride to compounds called alditolsalditols. %or. %or

e&ample- ;:"lucitol (or ;:sorbitol)e&ample- ;:"lucitol (or ;:sorbitol)



DisaccharidesDisaccharides

;isaccharides are carbohydrates that yield;isaccharides are carbohydrates that yield

t!o monosaccharide molecules on hydrolysis.t!o monosaccharide molecules on hydrolysis.

e.". sucrose- lactose- maltosee.". sucrose- lactose- maltose

Structurally- disaccharides areStructurally- disaccharides are glycosidesglycosides inin

!hich the alo&y "roup attached to the!hich the alo&y "roup attached to theanomeric carbon is deried from a secondanomeric carbon is deried from a second

su"ar molecule.su"ar molecule.



)%crose)%croseHHOH2C

HO H

H OH

O

CH2OHO

α −lucosidic

lina"eβ −%ructosidic

lina"e

1

2

$ /

,

O

H

HO

H

HO

H

H

OH

OH

H1

2$

/,

Ordinary table su"ar (C2H22O)

5cid hydrolysis yields ;:"lucose and ;:fructose.

Sucrose is a nonreducin" su"ar6 it "ies ne"atietests !ith %ehlin"Ds solution because neither the"lucose nor the fructose portion of sucrose has ahemiacetal "roup (both carbonyl "roups are

present as full acetals (i.e. as "lycosides).



PolysaccharidesPolysaccharides

Golysaccharides- also no!n as glycans- consist ofmonosaccharides Boined to"ether by "lycosidic

lina"es.

Golysaccharides that are polymers of a sin"le

monosaccharide are called homopolysaccharides6those made up of more than one type of

monosaccharide are called heteropolysaccharides.

Homopolysaccharides are also classified on the

basis of their monosaccharide units. 5

homopolysaccharide consistin" of "lucose

monomeric unit is called a glucan- one consistin" of

"alactose units is a galactan- and so on.



PolysaccharidesPolysaccharides

3hree important polysaccharides- all of !hich3hree important polysaccharides- all of !hich

are "lucans- are starch- "lyco"en- andare "lucans- are starch- "lyco"en- and

cellulose.cellulose.

StarchStarch is the principle food resere of plant.is the principle food resere of plant.

GlycogenGlycogen functions as a carbohydratefunctions as a carbohydrateresere for animals.resere for animals.

CelluloseCellulose seres as structural material inseres as structural material in

plants.plants.



Carbohydrate 5ntibioticsCarbohydrate 5ntibiotics

One of the importantdiscoeries in

carbohydrate chemistry

!as the isolation of the

carbohydrate antibiotic

called streptomycin.

Streptomycin is made

up of three unusual

components.

3he "lycosidic lina"e is

nearly al!ays

OH

H<

<H

OH

<H2

<H

<H

H2<

OH

O

CHO

HO

H*C

O

>?>

HO

HO

> <HCH*

>? CH2OH

O

O

Streptomycin

Streptidine

#:Streptose

2:;eo&y:2:methylamino:α−#:"lucopyranose

pharmacognosy i (part 5)

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