Page 124 - Medicinal Plants_PharmD general

IV. Glycosides

Definition:
A glycoside is an organic compound, usually of plant origin and

consisting of a sugar portion linked to a non-sugar part in a particular way.
The non-sugar part is known as aglycone or genin. When the sugar portion
of a glycoside is glucose, the glycoside is known as a glucoside. Glycosides
can be hydrolysed either by acids or enzymes. The enzyme emulsin
hydrolyses most naturally occurring glycosides.

The aglycones of the glycosides differ in their chemical nature;, they
may be alcoholic, phenolic, anthracene derivatives, flavonooid and
steroidal.

Properties of glycosides:
- Glycosides are colourless, solid, non volatile, generally crystalline
compounds
- Most glycosides are bitter in taste, although some are not bitter (e.g.
populin has a sweet taste).
- They do not reduce Fehling’s solution except after hydrolysis

- Glycosides are generally very slightly soluble in water, but are more
soluble in ethyl, methyl alcohol or mixture of water with ethanol or
methanol. A number of steroidal glycosides are soluble in chloroform,
ether, acetone.

Types of glycosidic Linkage:
The usual linkage between the sugar and aglycone is an oxygen

linkage such glycosides called O-glycosides and are the most numerous
ones found in nature

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