Glycoside

Related compounds

Molecules containing an biochemistry call these compounds N-glycosides and group them with the glycosides; this is considered a misnomer and discouraged by IUPAC.)

Chemistry

Much of the chemistry of glycosides is explained in the article on glycosyltransferases. Mutant enzymes termed glycosynthases have been developed that can form glycosidic bonds in excellent yield.

There are a great many ways to chemically synthesize glycosidic bonds. Koenigs-Knorr reaction is the condensation of glycosyl halides and alcohols in the presence of metal salts such as silver carbonate or mercuric oxide.

Classification

We can classify glycosides by the glycone, by the type of glycosidic bond, and by the aglycone.

By glycone

If the glycone group of a glycoside 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.

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 α-amylase can only hydrolize α-linkages; others, such as emulsin, can only affect β-linkages.

By aglycone

Glycosides are also classified according to the chemical nature of the aglycone. For purposes of biochemistry and pharmacology, this is the most useful classification.

Alcoholic glycosides

An example of an alcoholic glycoside is antipyretic and antiinflammatory effects.

Anthraquinone glycosides

These glycosides contain an aglycone group that is a derivative of aloes; they have a laxative effect.

Coumarin glycosides

Here the aglycone is calcium channels.those obtained from dried leaves of Psoralia corylifolia have Main glycosides psoralin and corylifolin.

Cyanogenic glycosides

In this case, the aglycone contains a hydrogen cyanide if acted upon by some enzyme. An example of these is amygdalin from almonds. Cyanogenic glycosides can be found in the fruits (and wilting leaves) of the rose family (including cherries, apples, plums, almonds, peaches, apricots, raspberries, and crabapples). Cassava, an important food plant in Africa and South America, contains cyanogenic glucosides and therefore has to be washed and ground under running water prior to consumption.

Flavonoid glycosides

Here the aglycone is a flavonoid. This is a large group of flavonoid glycosides. Examples include:

• Hesperidin (aglycone: Hesperetin, glycone: Rutinose)
• Naringenin, glycone: Rutinose)
• Quercetin, glycone: Rutinose)
• Quercitrin (aglycone: Rhamnose)

Among the important effects of flavonoids are their antioxidant effect. They are also known to decrease capillary fragility.

Phenolic glycosides (simple)

Here the aglycone is a simple Common Bearberry Arctostaphylos uva-ursi. It has a urinary antiseptic effect. Rutin found in rooibos tea.

Saponins

Main article: Saponin

These compounds give a permanent froth when shaken with water. They also cause hemolysis of red blood cells. Saponin glycosides are found in liquorice. Their medicinal value is due to their expectorant effect.

Steroidal glycosides or cardiac glycosides

Here the aglycone part is a Digitalis, Scilla, and Strophanthus. They are used in the treatment of heart diseases e.g. congestive heart failure (historically as now recognised does not improve survivability; other agents are now preferred] and arrhythmia.

Steviol glycosides

Main article: Steviol glycoside

These sweet glycosides found in the rhamnose-glucose combinations are bound to the ends of the aglycone to form the different compounds.

Thioglycosides

As the name implies, these compounds contain white mustard.

Bond:	N-glycosidic bond
Geometry:	1,6-Glycoside
Glycone:	Glucoside | Fructoside | Glucuronide
Aglycone:	Alcoholic glycoside | Anthraquinone glycoside | Coumarin glycoside | Cardenolide