11

Classification of GlycosidesClassification of Glycosides

A.A. On the basis of sugar moiety such as glucoside , rhamnoside, etc.

A.B. On the basis of therapeutic activity such as - Cardiac glycosides, e.g. Digitalis, Strophenthuss, etc.- Laxative glycosides, e.g. Aloe, Senna, Cascara sagrada, etc.

CH2OH

O C6H11O5

O

OH

O

H

OH

OH

HO

H

CH2OH

HH

OH

Salicin (saligenin + glucose)

Arbutin (hydroquinone + glucose)

22

C. On the basis of linkage of sugar molecule with the aglycon a) O- Glycosides: here the sugar is combined with the

alcoholic or phenolic hydroxyl group of the aglycone.

RO

R = Glucose in daucosterol

ORO

OH O

OCH3

OHR = Rhamnose - glucose

33

b) N- Glycosides: In these glycosides the amino group (-NH2 / -NH-) is condensed with the sugar, e.g. nucleosides, coenzyme, etc.

N

N

N

N

NH2

H

H H

OCH2OH

H

OH OH

N

NN

N

NH2

H

O OH

H HCH2

P

O

O-O

O

PH O-HO

O

PH

CH2

O-HO

CH3C CH3

CHO CH

H

HN

OH

CH

OH

HN

SH

H

O

Adenosine (Adenine + ribose)

Coenzyme A

44

d) C- Glycosides: Condensation of a sugar directly to a carbon atom of the aglycone gives c-glycosides, e.g. aloin, chrysaloin, etc.

OH O OH

H C6H11O5

CH2R

O

CH3

C6H11O5

HO CH3

O

OR = OH, Barbaloin H, Chrysaloin

Aloesin

c) S- Glycosides: These glycosides contain a sugar moiety attached to the sulfur of the aglycone, e.g. isothiocyanate glycosides.

C3H5 C

N

S C6H11O5

O SO3K

Sinigrin

HO CH2 C

S

N O

C6H11O5

SO2-O-K

Sinalbin

55

D) On the basis of the chemical nature of aglycone, the glycosides can be classified into following groups:

HO

H

CH3

CH3

OH

OO

+ digitoxoseDigitoxigenin (cardenolide, C23 steroid)

1. Cardioactive • Digitalis • Strophenthus

RO

H

CH3

CH3

OH

O O

• Squill

R = H, Scillarenin A (bufadienolide, C24 steroid) R = rham – glu, Scillaren A

66

2. Anthraquinone

H C6H11O5

OH O OH

CH2R

• Cascara sagrada• Aloe• Senna• Rhubarb

R = OH, Barbaloin H , Chrysaloin

• Glycyrrhiza• Dioscorea

3. Saponin

HO

CH3

CH3O

O

+ rhamnose, + glucose

Spiroketal steroid nucleus (neutral)

diosgenin

HO

Β – amyrin (aglycone, pentacyclic triterpenoid, acidic)

77

4. Cyanophore C O C6H11O5

H

CN

C OH

H

CNC6H12O6 +

CH OH

H

+ HCN

Mandelonitrile glucoside

Mandelonitrile Benzadehyde

• Wild cherry• Bitter almond

5. Isothiocyanates C3H5 C S

N

C6H11O5

O SO3K

Sinigrin

H2Omyrosin

S C N CH2 CH

CH2 + KHSO4 + C6H12O6

glucoseAllyl isothiocyanate

• Black mustard• White mustard

88

6. Flavanol / flavanoid

OHO

OH O

O

OH

OH

C12H21O9

Rutin

• Citrus fruit

7. Alcohol

+ H2O

CH2OH

OH

+ glucose

Salicin Saligenin

CH2OH

O C6H11O5

• Salix • Populus

99

8. Aldehyde CHO

OCH3

ORR = H, vanillin

R = glu, glucovanillin

• Vanilla

9. Lactone

OHO O

Coumarin

• Cantharide• Tonka beans

1010

11. Tannin HO

OH

OH

COO C6H11O5

Glucogallin (glucoside of gallic acid)

• Nutgall• Hamamelis leaf

10. Phenol OC6H11O5

OH

+ H2O

OH

OH

+ glu

Arbutin Hydroquinine

• Uva ursi

1111

R C O

H

+ ROH R' C OR

H

OH

H+

Hemiacetal

R' C OR

H

OH

+ ROH R' C OR

H

OR

H+

Hemiacetal (an alcohol) acetal

An acetal is a molecule with two single bonded oxygen attached to the same carbon atom.

Hemiacetals and hemiketals are compounds derived from aldehyde and ketones respectively. These compounds are formed by formal addition of an alcohol to the carbonyl group.

1212

H HCOOH

NH2H

H HCOOH

NHOHH

H H

CH

NOH

L-Phenylalamime N-Hydroxy-L-phenylalanine Phenylacetaldoxime

H H

C N

H OH

C N

H O

C N

O

H

HHO

OHH

OH

OH

H

H

Mandelonitrile a-Hydroxymandelonitrile

glucosyl transferase

+ UDP glucose

Prunasin

The biosynthetic pathway for the cyanogenic glycoside, prunasin.