A glycoside is any molecule in which a sugar group is bonded through its anomeric carbon to another group via glycosidic bond. A glycosidic bond is a certain type of chemical bond that joins a sugar molecule to another molecule. Specifically, a glycosidic bond is formed between the hemiacetal group of a saccharide (or a molecule derived from a saccharide) and the hydroxyl group of an alcohol.
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Containing Glycosides
INTRODUCTION
A glycoside is any molecule in which a sugar group is bonded
through its anomeric carbon to another group via glycosidic bond. A glycosidic
bond is a certain type of chemical bond that joins a sugar molecule to another
mol-ecule. Specifically, a glycosidic bond is formed between the hemiacetal
group of a saccharide (or a molecule derived from a saccharide) and the
hydroxyl group of an alcohol. A substance containing a glycosidic bond is a
glycoside. The glycone and aglycone portions can be chemically separated by
hydrolysis in the presence of acid. There are also numerous enzymes that can
form and break glycosidic bonds.
The sugar group is known as the glycone and the nonsugar
group as the aglycone or genin part of the glycoside. The glycone can consist
of a single sugar group (monosaccharide) or several sugar groups
(oligosaccharide). The sugars found in glycosides may be glucose and rhamnose
(monosaccharides) or, more rarely, deoxysugars such as the cymarose found in
cardiac glycosides.
In plants glycosides are both synthesized and hydrolysed
under the influence of more or less specific enzymes. They are crystalline or
amorphous substances that are soluble in water or alcohols and insoluble in
organic solvents like benzene and ether. The aglycone part is soluble in
organic solvents like benzene or ether. They are hydrolysed by water, enzymes
and mineral acids. They are optically active. While glycosides do not
themselves reduce Fehling’s solution, the simple sugars which they produce on
hydrolysis will do so with precipitation of red cuprous oxide. The sugars
present in glycoside are of two isomeric forms, that is, α form and β form, but all the natural
glycosides contain β-type of sugar.
The term ‘glycoside’ is a very general one which embraces
all the many and varied combinations of sugars and aglycones.
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