1/27/25, 8:26 PM Glycosides 1 and 2des
PHM 4453 8 GLYCOSIDES 1
(Introduction, ald glycs, alc/phenolic glys, Anthraq-intro.)
by
EDITH WAKORI
25th June 2018
1. GLYCOSIDES
1.1 Introduction
Glycosides are (usually) non-reducing compounds, which on hydrolysis by reagents or
enzymes yield one or more reducing sugars among the products of hydrolysis.
A molecule in which a sugar is bound to another functional (non-sugar!) group via a glycosidic
bond/linkage.
The sugar group is known as the glycone and the non-sugar group as the aglycone or genin part
of the glycoside.
The glycone can consist of a single sugar group or several sugar groups.
The sugars involved are glucose, fructose, galactose, mannose, rhamnose, digitoxose,
cymarose, etc
Examples of glycosides; salicin, arbutin, glucovanillin, barbaloin and oleandrin.
Glycosides play numerous important roles in living organisms.
1.2 Role of glycosides in organisms
Many plants store chemicals in the form of inactive glycosides.
These can be activated by enzyme hydrolysis which causes the sugar part to be broken off,
making the chemical available for use.
Many such plant glycosides are used as medications.
In animals and humans, poisons are often bound to sugar molecules as part of their elimination
from the body.
1.3 Medicinal importance of glycosides
Source of analgesics e.g., gaultherin source of methylsalicylate ‘a hydrolytic product
Anti rheumatic: e.g., salicin.
Anti-inflammatory: e.g., the glycoside glycyrrhizin. Also has demulcent, expectorant
and antispasmodic action.
Cardiac drugs: e.g., digitalis glycosides, strophanthus, squill.
Laxatives: e.g., anthraquinone glycosides of senna, aloes, rhubarb, cascara, frangula.
Counter irritants e.g., thioglycosides and their hydrolytic products ‘allylisothio
cyanate’
Reduce the capillary fragility e.g., flavonoidal glycoside rutin.
More recently as an anticancer agent e.g., amygdalin
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,1/27/25, 8:26 PM Glycosides 1 and 2des
1. 4 Sugars in glycosides:
Monosaccharide (glucose in salicin, digitoxose in digoxin, rhamnose in ouabain, ETC)
Disaccharides (gentiobiose in amygdalin).
Trisaccharides (strophanthotriose).
Tetrasaccharides (purpurea glycosides)
Rare sugars (deoxy sugars)
Sugar generally linked in one position to the aglycone, rarely in 2 positions as cascarosides.
1.4 Physical & chemical properties
Structures are diverse, however;
Most glycosides are water soluble and soluble in alcohols.
Either insoluble or less soluble in non polar organic solvents.
More sugar units in a glycoside lead to more solubility in polar solvents.
Glycosides do not reduce Fehling’s solution, but when are susceptible to hydrolysis give
reducing sugars
1.5 Classification
Glycosides can be classified by the glycone (type of sugar), by the type of glycosidic bond,
and by the aglycone.
a).By glycone
If glucose, then the molecule is a glucoside;
If fructose, then the molecule is a fructoside;
If glucuronic acid, then the molecule is a glucuronide; etc. In the body, toxic substances are
often bonded to glucuronic
1.5 Classification
acid to increase their water solubility; the resulting glucuronides are then excreted.
If galactose, galactosides.
If the glycone is mannose, mannosides.
If the glycone is arabinose, arabinosides.
b). By type of glycosidic bond-
Sugars exist in isomeric α and β forms.
All natural glycosides are of the β Type.
Some α linkage exists in sucrose, glycogen and starch. Also,in the glycoside K-
strophanthoside, strophanthidin-linked to cymarose + β-glucose + α- glucose.
The most commonly found glycoside type is β-D-glucose
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, 1/27/25, 8:26 PM Glycosides 1 and 2des
Some enzymes such as α-amylase can only hydrolyze α-linkages; others, such as emulsin, can
only affect β-linkages.
Types of linkages;-
C-linkage/glycosidic bond, where the sugar molecule is linked to carbon atom-
are non-hydrolysable by heating with dilute acids/alkalis.
hydrolyzed by oxidative hydrolysis with FeCl3.
include some anthraquinone glycosides such as cascarosides, aloin and some members of the
flavones type of glycosides.
O-linkage/glycosidic bond. These are very common in higher
plants, e.g senna, rhubarb.
N-linkage/glycosidic bond- glycosylamines, nucleosides.
S-linkage/glycosidic bond- thioglycosides, e.g, sinigrin and sinalbin.
c). By aglycone-
The classification is according to the chemical nature of the aglycone. For purposes of
biochemistry, pharmacognosy and pharmacology, this is the most useful classification.
The following are various groups depending on aglycone type:
i)Aldehyde glycosides- e.g, vanillin
ii)Alcoholic glycosides- e.g, salicin/)Phenolic glycosides- the aglycone is a simple phenolic s
tructure e.g, arbutin.
iii)Anthraquinone glycosides- where aglycone group is a
derivative of anthraquinone.
iv)Cardiac glycosides-aglycone part is a C27 steroidal nucleus.
v)Coumarin and furanocoumarin glycosides- the aglycone is coumarin or its derivative.
vi)Cyanogenic glycosides- the aglycone contains a cyanide group, e.g , amygdalin.
vii)Flavonoid and flavonol glycosides- the aglycone is a flavanoid.
viii) Isothiocyanate glycosides-
x)Saponins glycosides- These compounds give a permanent soapy froth when shaken
with water.
xi)Others e.g Steviol, quassia (under terpenoids) glycosides.
Steviol glycosides have steviol as the aglycone part.
d). By pharmacological action
According to the physiological or pharmacological activity, e.g.
Laxative, Cardiotonic, analgesic, anti-inflammatory glycosides, etc.
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PHM 4453 8 GLYCOSIDES 1
(Introduction, ald glycs, alc/phenolic glys, Anthraq-intro.)
by
EDITH WAKORI
25th June 2018
1. GLYCOSIDES
1.1 Introduction
Glycosides are (usually) non-reducing compounds, which on hydrolysis by reagents or
enzymes yield one or more reducing sugars among the products of hydrolysis.
A molecule in which a sugar is bound to another functional (non-sugar!) group via a glycosidic
bond/linkage.
The sugar group is known as the glycone and the non-sugar group as the aglycone or genin part
of the glycoside.
The glycone can consist of a single sugar group or several sugar groups.
The sugars involved are glucose, fructose, galactose, mannose, rhamnose, digitoxose,
cymarose, etc
Examples of glycosides; salicin, arbutin, glucovanillin, barbaloin and oleandrin.
Glycosides play numerous important roles in living organisms.
1.2 Role of glycosides in organisms
Many plants store chemicals in the form of inactive glycosides.
These can be activated by enzyme hydrolysis which causes the sugar part to be broken off,
making the chemical available for use.
Many such plant glycosides are used as medications.
In animals and humans, poisons are often bound to sugar molecules as part of their elimination
from the body.
1.3 Medicinal importance of glycosides
Source of analgesics e.g., gaultherin source of methylsalicylate ‘a hydrolytic product
Anti rheumatic: e.g., salicin.
Anti-inflammatory: e.g., the glycoside glycyrrhizin. Also has demulcent, expectorant
and antispasmodic action.
Cardiac drugs: e.g., digitalis glycosides, strophanthus, squill.
Laxatives: e.g., anthraquinone glycosides of senna, aloes, rhubarb, cascara, frangula.
Counter irritants e.g., thioglycosides and their hydrolytic products ‘allylisothio
cyanate’
Reduce the capillary fragility e.g., flavonoidal glycoside rutin.
More recently as an anticancer agent e.g., amygdalin
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,1/27/25, 8:26 PM Glycosides 1 and 2des
1. 4 Sugars in glycosides:
Monosaccharide (glucose in salicin, digitoxose in digoxin, rhamnose in ouabain, ETC)
Disaccharides (gentiobiose in amygdalin).
Trisaccharides (strophanthotriose).
Tetrasaccharides (purpurea glycosides)
Rare sugars (deoxy sugars)
Sugar generally linked in one position to the aglycone, rarely in 2 positions as cascarosides.
1.4 Physical & chemical properties
Structures are diverse, however;
Most glycosides are water soluble and soluble in alcohols.
Either insoluble or less soluble in non polar organic solvents.
More sugar units in a glycoside lead to more solubility in polar solvents.
Glycosides do not reduce Fehling’s solution, but when are susceptible to hydrolysis give
reducing sugars
1.5 Classification
Glycosides can be classified by the glycone (type of sugar), by the type of glycosidic bond,
and by the aglycone.
a).By glycone
If glucose, then the molecule is a glucoside;
If fructose, then the molecule is a fructoside;
If glucuronic acid, then the molecule is a glucuronide; etc. In the body, toxic substances are
often bonded to glucuronic
1.5 Classification
acid to increase their water solubility; the resulting glucuronides are then excreted.
If galactose, galactosides.
If the glycone is mannose, mannosides.
If the glycone is arabinose, arabinosides.
b). By type of glycosidic bond-
Sugars exist in isomeric α and β forms.
All natural glycosides are of the β Type.
Some α linkage exists in sucrose, glycogen and starch. Also,in the glycoside K-
strophanthoside, strophanthidin-linked to cymarose + β-glucose + α- glucose.
The most commonly found glycoside type is β-D-glucose
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, 1/27/25, 8:26 PM Glycosides 1 and 2des
Some enzymes such as α-amylase can only hydrolyze α-linkages; others, such as emulsin, can
only affect β-linkages.
Types of linkages;-
C-linkage/glycosidic bond, where the sugar molecule is linked to carbon atom-
are non-hydrolysable by heating with dilute acids/alkalis.
hydrolyzed by oxidative hydrolysis with FeCl3.
include some anthraquinone glycosides such as cascarosides, aloin and some members of the
flavones type of glycosides.
O-linkage/glycosidic bond. These are very common in higher
plants, e.g senna, rhubarb.
N-linkage/glycosidic bond- glycosylamines, nucleosides.
S-linkage/glycosidic bond- thioglycosides, e.g, sinigrin and sinalbin.
c). By aglycone-
The classification is according to the chemical nature of the aglycone. For purposes of
biochemistry, pharmacognosy and pharmacology, this is the most useful classification.
The following are various groups depending on aglycone type:
i)Aldehyde glycosides- e.g, vanillin
ii)Alcoholic glycosides- e.g, salicin/)Phenolic glycosides- the aglycone is a simple phenolic s
tructure e.g, arbutin.
iii)Anthraquinone glycosides- where aglycone group is a
derivative of anthraquinone.
iv)Cardiac glycosides-aglycone part is a C27 steroidal nucleus.
v)Coumarin and furanocoumarin glycosides- the aglycone is coumarin or its derivative.
vi)Cyanogenic glycosides- the aglycone contains a cyanide group, e.g , amygdalin.
vii)Flavonoid and flavonol glycosides- the aglycone is a flavanoid.
viii) Isothiocyanate glycosides-
x)Saponins glycosides- These compounds give a permanent soapy froth when shaken
with water.
xi)Others e.g Steviol, quassia (under terpenoids) glycosides.
Steviol glycosides have steviol as the aglycone part.
d). By pharmacological action
According to the physiological or pharmacological activity, e.g.
Laxative, Cardiotonic, analgesic, anti-inflammatory glycosides, etc.
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