Aglycons

Aglycons, more commonly called aglycones, are the non-sugar components of glycosides. In a glycoside molecule, a sugar moiety (the glycone) is bound to a non-sugar moiety (the aglycone) through a glycosidic bond. When the glycoside is hydrolyzed, either chemically or enzymatically, the glycone and aglycone are liberated. The term aglycone is sometimes abbreviated as aglycon in older literature.

Aglycones are typically more lipophilic than their sugar-containing counterparts, and they largely determine the biological activity and pharmacokinetic properties of the glycoside. They span a wide range of chemical classes, including flavonoids, anthraquinones, alkaloids, and steroidal compounds. Common examples include flavonoid aglycones such as quercetin and kaempferol, anthraquinone aglycones like emodin, and steroidal aglycones found in certain cardiac glycosides where the aglycone portion may be digitoxigenin or digoxigenin.

In plants, glycosides often serve as storage forms or defense compounds. Hydrolysis within the plant, in the gut after ingestion, or by environmental factors releases the aglycone, which can have distinct ecological roles or be more readily absorbed by organisms. In medicine and pharmacology, the aglycone frequently contributes the essential pharmacological activity; the sugar moiety can modulate solubility, stability, and bioavailability. For analytical and preparative purposes, researchers may hydrolyze glycosides to quantify or identify the aglycone component.

The term aglycon is used synonymously with aglycone in many sources, though modern terminology tends to prefer aglycone.