Classification based on Linkages
Classification of glycoside
1. By glycone:
If the glycone group of a glycoside is glucose, then the molecule is a glucoside;
if it is fructose, then the molecule is a fructoside;
if it is glucuronic acid, then the molecule is a glucuronide; etc.
In the body, toxic substances are often bonded to glucuronic acid to increase their water solubility; the resulting glucuronides are then excreted.
2. By type of glycosidic bond:
Depending on whether the glycosidic bond lies “above” or “below” the plane of the cyclic sugar molecule, glycosides are classified as α-glycosides or β- glycosides.
Some enzymes such as α-amylase can only hydrolyzed α-linkages; others, such as emulsin, can only affect β-linkages.
Stereochemically these considered as a theoretical aspect, because the plants contain only β- glycosides.
3. By aglycone:
i. Steroidal glycosides or cardiac glycosides:
Here the aglycone part is a steroidal nucleus.
These glycosides are found in the plant genera Digitalis, Scilla, and Strophanthus.
They are used in the treatment of heart diseases e.g. congestive heart failure and arrhythmia.
ii. Alcoholic glycosides:
An example of an alcoholic glycoside is salicin which is found in the genus salix.
Salicin is converted in the body into salicylic acid, which is closely related to aspirin and has analgesic, antipyretic and antiinflammatory effects. Example: Salicin
iii. Anthraquinone glycosides:
These glycosides contain an aglycone group that is a derivative of anthraquinone.
They are present in senna, rhubarb and aloes; they have a laxative effect. E.g. Barbaloin.
iv. Coumarin glycosides:
Here the aglycone is coumarin.
An example is apterin which is reported to dilate the coronary arteries as well as block channels those obtained from dried leaves of Psoralia corylifolia have Main glycosides psoralin and corylifolin. [Coumarin (benzopyrone)] [Apterin]
v. Cyanogenic glycosides:
In this case, the aglycone contains a cyanide group and the glycoside can release the poisonous hydrogen cyanide if acted upon by some enzyme.
An example of these is amygdalin from almonds.
vi. Flavonoids glycosides:
Here the aglycone is a flavonoid.
This is a large group of flavonoid glycosides. E.g. – Hesperidin (aglycone: Hesperetin, glycone: Rutinose).
Here, the aglycone is a flavonoid. Examples of this large group of glycosides include:
Hesperidin (aglycone: Hesperetin, glycone: Rutinose),
Naringin (aglycone: Naringenin, glycone: Rutinose) Rutin (aglycone: Quercetin, glycone: Rutinose) Quercitrin (aglycone: Quercetin, glycone: Rhamnose)
These compounds give a permanent froth when shaken with water.
They also cause hemolysis of red blood cells.
Soponins glycosides are found in liquorice (Glycyrrhizin).
Their medicinal value is due to their expectorant effect. [Glycyrrhizin]
As the name implies, these compounds contain sulfur. E.g.- sinigrin, found in black mustard, and sinalbin, found in white mustard. Example: Sinigrin
ix. Phenolic glycosides:
Here the aglycone is a simple Phenolic structure. E.g. – arbutin found in the Common Bearberry Arctostaphylos uva-ursi.
It has a urinary antiseptic effect.