Carotenes are polyunsaturated hydrocarbons formed biochemically from polymerization of isoprendoid compounds. They are yellow, orange, or red, depending on their chemical structures. Carotenoids are soluble in fats, whereas anthocyanins and flavonols are water-soluble compounds because of their attached sugar groups.
Geranylgeranyl pyrophosphate is the precursor. Two molecules of this compound are condensed into cis-Phytoene, a hydrocarbon with 40 carbon atoms.
Phytoene is converted to Lycopene, a C40 polyunsaturated hydrocarbon.
Lycopene is converted to beta-Carotene, still a C40 polyunsaturated hydrocarbon, by cyclization to form a cyclohexene ring at each end of the chain.
Beta-Carotene is oxidized on one of the cyclohexene rings to form Zeaxanthin.
Epoxidation of Zeaxanthin on each ring leads to violaxanthin.