Cglycosidic

C-glycosidic bonds, or C-glycosides, are a class of covalent linkages in which a sugar unit is attached to an aglycone through a carbon–carbon bond rather than through an oxygen atom. In this arrangement, the anomeric carbon (usually C-1) of the sugar forms a direct C–C bond to a carbon on the aglycone, yielding a stable, non-oxygenated linkage that is distinct from the more common O-glycosidic bonds found in many natural products and drugs.

This bond type is found predominantly in plant secondary metabolites, especially flavonoids and related polyphenols. C-glycosides in these systems are typically more resistant to hydrolysis by acids, bases, and enzymatic activity than their O-glycoside counterparts. Consequently, they can exhibit greater chemical and metabolic stability, which can influence their biological activity and bioavailability.

Notable examples include flavonoid C-glycosides such as apigenin-6-C-glucoside, known as isovitexin, and luteolin-6-C-glucoside, known as isoorientin. In these compounds, the glucose moiety is attached to the flavonoid aglycone via a direct C–C bond at specific ring positions, rather than through a glycosidic oxygen.

Biosynthesis and occurrence involve specialized enzymatic processes that form C–C linkages between sugar donors and carbon atoms on the aglycone, often distinct from the conventional O-glycosyltransferases. Research into C-glycosides informs natural product chemistry, plant metabolism, and the design of more stable glycosylated compounds for pharmacological use.