Astaxanthin is a keto-
carotenoid. It belongs to a larger class of chemical compounds known as
terpenes, which are built from five carbon precursors;
isopentenyl diphosphate (or IPP) and
dimethylallyl diphosphate (or DMAPP). Astaxanthin is classified as a
xanthophyll (originally derived from a word meaning "yellow leaves" since yellow plant leaf pigments were the first recognized of the xanthophyll family of carotenoids), but currently employed to describe carotenoid compounds that have oxygen-containing moities, hydroxyl (-OH) or ketone (C=O), such as
zeaxanthin and
canthaxanthin. Indeed, astaxanthin is a metabolite of zeaxanthin and/or canthaxanthin, containing both hydroxyl and ketone functional groups. Like many carotenoids, astaxanthin is a colorful,
lipid-soluble
pigment. This colour is due to the extended chain of conjugated (alternating double and single) double bonds at the centre of the compound. This chain of conjugated double bonds is also responsible for the antioxidant function of astaxanthin (as well as other carotenoids) as it results in a region of decentralized electrons that can be donated to reduce a reactive oxidizing molecule.