aglycon

An aglycon, also spelled aglycone, is the non-sugar moiety of a glycoside. In glycoside chemistry, the molecule consists of a glycone (the sugar portion) linked to an aglycone. Hydrolysis—by acids, enzymes, or gut microbiota—splits the glycoside into its sugar and aglycone. The aglycone often carries most of the compound’s biological activity, while the glycone influences solubility and stability.

The term reflects the functional role of the non-sugar residue. Aglycones are commonly phenolic, steroidal, or terpenoid structures and help determine pharmacological properties. Examples include digitoxin and digoxin, cardiac glycosides whose aglycones are digitoxigenin and digoxigenin, respectively. Salicin, a glucoside of salicyl alcohol, yields saligenin as its aglycone upon hydrolysis. Emodin glycosides release aglycones such as emodin. Plant glycosides with diverse aglycones are widespread in nature and can be used in chemotaxonomy and pharmacology.

Enzymatic hydrolysis by beta-glucosidases or acid hydrolysis are common methods to release the aglycone, enabling identification and activity testing. In pharmacology, the distinction between glycone and aglycone is important for understanding a compound’s absorption, distribution, and effects.

See also: glycone, glycoside.