Glykosid

Glykosid, or glycoside in English, is a molecule in which a sugar unit, called the glycone, is covalently bound to a non-sugar moiety, the aglycone, via a glycosidic linkage. The bond typically involves the anomeric carbon of the sugar (C1 in aldoses, C2 in ketoses) and a hydroxyl, amine, or other group on the aglycone, producing O-, N-, or S-glycosidic linkages. O-glycosides are by far the most common in nature. The sugar component can be a simple monosaccharide or a more complex oligosaccharide.

Glycosides are often hydrolyzed by glycosidase enzymes, yielding the sugar (glycone) and the aglycone. The term encompasses a broad class of natural and synthetic compounds whose properties depend on the sugar and the aglycone. The name of a glycoside often reflects its components, with the suffix indicating the sugar portion (for example, glucoside).

Glycosides occur widely in plants, microorganisms, and some animals. In plants they frequently serve defense roles, storage functions, or pigments and aroma compounds. Some glycosides are toxic, such as cyanogenic glycosides which release hydrogen cyanide upon hydrolysis, while others have therapeutic value, including cardiac glycosides like digoxin and digitoxin that affect heart muscle function. Flavonoid and phenolic glycosides also contribute to the solubility, stability, and bioactivity of their aglycones.

Biosynthesis commonly involves glycosyltransferases that transfer sugar residues from activated donors (for example UDP-glucose) to aglycones, producing the glycoside. The sugar moiety can significantly influence solubility, pharmacokinetics, and biological effect of the compound.