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is an organic is an organic

compound, usually of plant compound, usually of plant

origin, that is composed of a origin, that is composed of a

sugar portion linked to a non-sugar portion linked to a non-

sugar moiety. The sugar sugar moiety. The sugar

portion is called portion is called glyconeglycone,,

while the non-sugar portion while the non-sugar portion

is called is called aaglycone or glycone or geningenin. .

OCH2OH

OHOH

OH

OH

+ CH3OH

OCH2OH

OH

HO

OH

OCH3

H

+ H2O

-D glucopyranose

Mehtyl -D glucopyranose

OH on the anomeric carbon is replaced by an OR group, such acetal is called glycoside

The linkage between the sugar and The linkage between the sugar and the aglycone is an the aglycone is an acetal acetal linkagelinkage..

Types of GlycosidesTypes of Glycosides: :

II- - According to atoms involved in According to atoms involved in the glycosidic linkagethe glycosidic linkage : :

11 - -O-glycosidesO-glycosides

22 - -C-glycosidesC-glycosides

33 - -S-glycosidesS-glycosides

44 - -N-glycosidesN-glycosides

II- II- According to the configuration of According to the configuration of the glycosidic linkagethe glycosidic linkage::

11 - --glycosides-glycosides::

Here the sugar involved has the Here the sugar involved has the configuration at the hemiacetal configuration at the hemiacetal carboncarbon . .

The majority of plant glycosides The majority of plant glycosides isolated are isolated are -glycosides-glycosides..

22 - - -glycosides -glycosides: :

Here the sugar involved has Here the sugar involved has the the configuration at the configuration at the hemiacetal carbon; the sugar hemiacetal carbon; the sugar is usually of the L-series e.g. is usually of the L-series e.g. L-rhamnose. There are only L-rhamnose. There are only few medicinal few medicinal -glycosides -glycosides known, especially the known, especially the rhamnosidesrhamnosides..

III-III- According to the sugar According to the sugar moietymoiety::

11--GlucosidesGlucosides::22 - -RibosidesRibosides::

33 - -RhamnosidesRhamnosides::

IV-IV- According to the aglyconeAccording to the aglycone:: 11--Cardiac glycosidesCardiac glycosides

22-- Flavonoid glycosidesFlavonoid glycosides 33-- Anthracene glycosidesAnthracene glycosides

44 - -Saponin glycosidesSaponin glycosides

55--ThioglycosidesThioglycosides

66 - -Cyanogenic glycosidesCyanogenic glycosides

77 - -Phenolic glycosides possessing Phenolic glycosides possessing phenolic aglycones e.g. arbutinphenolic aglycones e.g. arbutin..

88 - -Alcohol glycosides, with alcoholic Alcohol glycosides, with alcoholic aglycones e.g. salicinaglycones e.g. salicin..

99--Antibiotic glycosidesAntibiotic glycosides

e.g, e.g, Amino-glycoside antibioticsAmino-glycoside antibiotics

1010 - -Ester glycosides, such as the Ester glycosides, such as the glycosides of methyl salicylate glycosides of methyl salicylate e.g e.g gaultheringaultherin

1111 - -Aldehyde glycosides, with an Aldehyde glycosides, with an aldehyde aglycone e.g. aldehyde aglycone e.g.

glucovanillinglucovanillin . .

1212 - -TerpeneTerpene glycosides glycosides : :

a- Monoterpene glycosides e.g. a- Monoterpene glycosides e.g. gentiopicrin and loganingentiopicrin and loganin . .

b- Triterpene saponin glycosideb- Triterpene saponin glycoside..

1313 - -GlycoalkaloidsGlycoalkaloids::

These are the glycosidal These are the glycosidal alkaloids i.e. They possess a alkaloids i.e. They possess a glycosidicglycosidic

linkage and a cyclic nitrogen in linkage and a cyclic nitrogen in the aglycone. e.g steroidal the aglycone. e.g steroidal alkaloids of Solanum species alkaloids of Solanum species e.ge.g..

solaninesolanine..

1414 - -Complex glycosidesComplex glycosides::

These include a number of These include a number of

complex secondary complex secondary

carbohydrates e.g. gums, carbohydrates e.g. gums,

mucilage & pectin; a number mucilage & pectin; a number

of glycosidal resins e.g. Jalap of glycosidal resins e.g. Jalap

resin as well as aresin as well as a number of number of

glycosidal tannins e.g. glycosidal tannins e.g.

glucogallinglucogallin in Rhubarb in Rhubarb . .

Sugars in glycosidesSugars in glycosides::

The sugar portionThe sugar portion: : 11 - -It may be molecule of a It may be molecule of a

monosaccharide e.g. monosaccharide e.g. D-glucose D-glucose or L-rhamnoseor L-rhamnose..

- - or composed of 2 or more or composed of 2 or more sugars, forming a di-or sugars, forming a di-or oligosaccharide chain e.g. oligosaccharide chain e.g. purpurea glycoside Apurpurea glycoside A has a has a tetrasaccharide attached to tetrasaccharide attached to digitoxigenin e.g. Digitoxigenindigitoxigenin e.g. Digitoxigenin

--O-(digitoxose)3-O-glucoseO-(digitoxose)3-O-glucose. .

OH

O

OO

D-glucose-3 D-digitoxoses

Digitoxin (= digitoxoside = digitalin)

Purpurea glycoside A

22 - -In certain cases, the oligosaccharide In certain cases, the oligosaccharide

portion is branched as in theportion is branched as in the

steroidal saponin,steroidal saponin, digitonin where digitonin where

there is a branched pentasaccharide there is a branched pentasaccharide

chainchain..

33 - -Sometimes, two monosaccharide Sometimes, two monosaccharide

units are attached at two differentunits are attached at two different

positions in the aglycone molecule, so positions in the aglycone molecule, so

we are dealing with a diglycoside e.gwe are dealing with a diglycoside e.g . .

O OH

CO2H

H-D-glc

D glc-

Rheinosides A, B

The sugars involvedThe sugars involved:: 11 - --D-glucose -D-glucose is the most is the most

common sugar in glycosidescommon sugar in glycosides . .

22 - -Other sugars includeOther sugars include : :

i - Other hexoses e.g. i - Other hexoses e.g. galactosegalactose

ii - Pentoses e.g.ii - Pentoses e.g. ribose, ribose, xylose and arabinosexylose and arabinose..

iii - 6-Deoxyhexoses e.g.iii - 6-Deoxyhexoses e.g. rhamnose and digitaloserhamnose and digitalose..

iv - 2,6-Dideoxysugars e.g. iv - 2,6-Dideoxysugars e.g.

sarmentose, digitoxose and sarmentose, digitoxose and

cymarose cymarose (rare sugars)(rare sugars)

The 6-Deoxy sugars and 2,6-The 6-Deoxy sugars and 2,6-

Dideoxy sugar are common in Dideoxy sugar are common in

Cardiac glycosides.Cardiac glycosides.

vi - vi - A uronic acidA uronic acid e.g. e.g.

glucuronic acid found in glucuronic acid found in

glycyrrhizin . glycyrrhizin .

Effect of the sugar portion Effect of the sugar portion on solubility of the on solubility of the glycosideglycoside::

Ex. Ex. salicin,salicin, with one with one glucose unit, is glucose unit, is soluble in ether, soluble in ether, while glycosides while glycosides with a with a larger sugar larger sugar portionportion are more are more soluble in alcohol or soluble in alcohol or aqueous alcoholic aqueous alcoholic

solventssolvents . .

CH2OH

Salicin

O Glc

Effect of the sugar on Effect of the sugar on susceptibility of the glycoside susceptibility of the glycoside

to acid hydrolysisto acid hydrolysis::Generally Generally 2-deoxy2-deoxy sugars can be sugars can be hydrolyzed easier than hydrolyzed easier than 6-6-deoxydeoxysugars, and the latter more sugars, and the latter more easily than easily than normal sugarsnormal sugars . Thus . Thus milder conditions can be chosen milder conditions can be chosen to hydrolyze the glycoside to hydrolyze the glycoside involving 2-deoxysugars, without involving 2-deoxysugars, without

affecting the othersaffecting the others. .

Solubility of glycosidesSolubility of glycosides: :

The presence or absence of The presence or absence of various polarity contributing various polarity contributing functional groups in the functional groups in the structure of the aglycone structure of the aglycone portion, would contribute to the portion, would contribute to the degree of solubility in a given degree of solubility in a given solvent e.g.solvent e.g. thioglycosidesthioglycosides are are soluble in water partly because soluble in water partly because of the ionic sulfate residueof the ionic sulfate residue . .

The number and kind of The number and kind of

monosaccharidemonosaccharide units units

present in the sugar portion present in the sugar portion

would contribute a certain would contribute a certain

polarpolar character and thus character and thus

contributing to the degree of contributing to the degree of

solubility in solubility in polarpolar solvents solvents . .

Hydrolytic cleavage and Hydrolytic cleavage and stabilitystability 1-1-Acid Hydrolysis:Acid Hydrolysis: Glycosides Glycosides can be hydrolyzed can be hydrolyzed

by heating with a dilute acid, by heating with a dilute acid, where by the glycosidic where by the glycosidic linkages are cleaved. linkages are cleaved.

GlycosidicGlycosidic linkages involving linkages involving different kinds of sugars are different kinds of sugars are hydrolyzed with different hydrolyzed with different degrees bydegrees by acid hydrolysis acid hydrolysis

e.g. e.g. 2-deoxy2-deoxysugars are hydrolyzed sugars are hydrolyzed

easier than easier than 6-deoxy6-deoxy-sugars, -sugars,

which is still easier than normal which is still easier than normal

sugarssugars . .

- -If there is a di-or an If there is a di-or an

oligosaccharide unit in the oligosaccharide unit in the

molecule, it is practically molecule, it is practically

impossible to cleave one unit of impossible to cleave one unit of

sugar at a time with acid sugar at a time with acid

hydrolysishydrolysis . .

When stepwise cleavage of When stepwise cleavage of monosaccharide units is monosaccharide units is needed, needed, specific enzyme specific enzyme

hydrolysishydrolysis must be used. must be used.

C-glycosides are more C-glycosides are more resistant resistant to acid hydrolysis to acid hydrolysis than than O-glycosides O-glycosides

i.e. they do require more i.e. they do require more vigorousvigorous conditions. conditions.

22-- Enzymatic HydrolysisEnzymatic Hydrolysis: : Glycosides can be hydrolyzed by Glycosides can be hydrolyzed by

appropriate enzymes, which are appropriate enzymes, which are usually found in the usually found in the same plantsame plant, , in separate compartments. in separate compartments.

The glycosidic linkages involving The glycosidic linkages involving -D-glucose as well as most -D-glucose as well as most --glycosides can be hydrolyzed by glycosides can be hydrolyzed by

variousvarious -glycosidases-glycosidases. .

- - Stepwise hydrolysis of Stepwise hydrolysis of monosaccharide units is possible monosaccharide units is possible using specific enzyme.using specific enzyme.

a- Digitalidase, in a- Digitalidase, in Digitalis Digitalis purpureapurpurea

b- Lanatosidase present in b- Lanatosidase present in D. D. lanatalanata

c-c-StrophanthibiaseStrophanthibiase acts upon K- acts upon K-strophanthoside to give cymarin.strophanthoside to give cymarin.

It is thus clear thatIt is thus clear that enzymatic enzymatic hydrolysis is specific . hydrolysis is specific .

N.BN.B

During extraction or During extraction or

isolation of glycosides isolation of glycosides

appropriate measures should appropriate measures should

be taken to prevent the be taken to prevent the

cleavage of glycosides by the cleavage of glycosides by the

enzymes that may be present enzymes that may be present

in in the same plant. the same plant.

33-- Effect of AlkaliEffect of Alkali:: - -Alkalies do not , generally, Alkalies do not , generally,

cleave cleave glycosidic linkagesglycosidic linkages..

- - Ester groups in the glycosides Ester groups in the glycosides may be cleaved e.g. the acetylmay be cleaved e.g. the acetyl--

group in lanatosides or the group in lanatosides or the sulfate group in thioglycosides sulfate group in thioglycosides ... etc... etc . .

- -Degradation may occur in the Degradation may occur in the aglycone or in the sugar aglycone or in the sugar

portionportion by by alkali alkali . .

The lactone ring at C17, in cardiac The lactone ring at C17, in cardiac

aglycones is aglycones is openedopened by strong by strong

alkalies, with subsequent loss of alkalies, with subsequent loss of

the cardiotonic activity, this the cardiotonic activity, this

change is change is irreversibleirreversible on on

addition of acidsaddition of acids . .O O

OH

HOH

A B

C D

Cardenolides:Digitoxigenin

1

2

3

4 6

7

8

9

10

5

11

1213

14

15

16

17

Extraction and IsolationExtraction and Isolation 11 - -AcidicAcidic conditions should be conditions should be

avoided during extractionavoided during extraction..

22 - -InactivationInactivation of the enzymes of the enzymes::

a- Boiling alcohol for 10-20 a- Boiling alcohol for 10-20 minutesminutes..

b- Boiling with acetoneb- Boiling with acetone . .

c- Low temperature i.e. in the c- Low temperature i.e. in the coldcold..

d- precipitates the enzymes with d- precipitates the enzymes with ammonium sulfateammonium sulfate..

e- Freeze-dryinge- Freeze-drying..

f-A special drying procedure such as a f-A special drying procedure such as a short heat treatmentshort heat treatment..

Extraction ProceduresExtraction Procedures::

Generally, the glycoside is extracted Generally, the glycoside is extracted from the crude drug withfrom the crude drug with::

- Alcohol. Alcohol. -Adding basic -Adding basic lead acetatelead acetate to the to the

alcoholic extract causes the alcoholic extract causes the impurities to precipitate. impurities to precipitate.

After filteration, the alcoholic After filteration, the alcoholic extract is concentrated, and extract is concentrated, and the glycosides may the glycosides may

crystallizecrystallize……

( (oily seeds should be oily seeds should be defatteddefatted.).)

Pharmacological or Pharmacological or Therapeutic ActivityTherapeutic Activity: :

11 - -cardiac glycosides of Digitalis, cardiac glycosides of Digitalis, Strophanthus, and squill are Strophanthus, and squill are cardiotonic agents useful in cardiotonic agents useful in congestive heart failurecongestive heart failure..

22 - -Anthracene glycosides of Anthracene glycosides of cascara, Frangula, senna, cascara, Frangula, senna, Rhuharb, Aloes have a Rhuharb, Aloes have a laxativelaxative effecteffect . .

33 - -Flavonoid glycosides e.g. rutin Flavonoid glycosides e.g. rutin and hesperidin are used to and hesperidin are used to decrease capillary fragilitydecrease capillary fragility and and permeabilitypermeability..

44 - -In case of cyanogenic or In case of cyanogenic or thioglycosides, that the thioglycosides, that the aglycone is the active aglycone is the active component used. The aglycone component used. The aglycone from the former (e.g. HCN & from the former (e.g. HCN & Benzaldehyde) is useful as a Benzaldehyde) is useful as a sedative and flavoring agentsedative and flavoring agent

aglycone from the latter (e.g. aglycone from the latter (e.g.

allyliso- thiocyanate) is useful as allyliso- thiocyanate) is useful as

a a rubifacientrubifacient and and counterirritantcounterirritant . .

Generally the pharmacological Generally the pharmacological

action of the glycoside is due to action of the glycoside is due to

the the aglycone.aglycone. However, the However, the

sugar portion is necessary to sugar portion is necessary to

carry the aglycone to the site of carry the aglycone to the site of

actionaction..

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By : - Jaspreet Rekhi www.rhombnet.com www.ppt.rhombnet.com