Cglycosylation

C-glycosylation, or C-glycosylation of flavonoids, is a form of glycosylation in which a sugar moiety is attached to a carbon atom of the aglycone, forming a direct carbon–carbon bond rather than the common O- or N-glycosidic linkage. C-glycosides are widespread in plants, particularly among flavonoids and related phenolics.

In plants, the sugar donor is typically UDP-glucose, and the sugar is transferred by specialized C-glycosyltransferases to form C-glycosides such as isovitexin (apigenin-6-C-glucoside) and vitexin (apigenin-8-C-glucoside). These enzymes are distinct from classical O- and N-glycosyltransferases and often show specific regioselectivity, attaching the sugar at various positions on the aglycone (for example at C-6 or C-8 on flavones).

C-glycosylation yields C-glycosides that are generally more resistant to hydrolysis and enzymatic cleavage, which can influence solubility, stability, and bioactivity compared with O-glycosides. The modification can affect antioxidant activity, metabolite stability, and the pharmacokinetic properties of the compounds, contributing to their function in plant defense and nutrition.

Biological and practical relevance: C-glycosides are of interest in natural product chemistry, plant biochemistry, and pharmacology. They are studied for their biosynthetic pathways, chemotaxonomic value, and potential health-related properties, while also presenting analytical challenges due to their distinct chemical behavior compared with more common glycosides.