Cyclization reactions of carotenoids.

ABSTRACT Acetonolysis of the titanium tetrachioride complex of lycopene gives s-carotene and e.carotene. Analogous cyclization reactions have been achieved with y-carotene, rubixanthin esters and f3-zeacarotene. In some typical parasitic plants and semi-parasitic plants, carotenoids with a-structures predominate over those with fl-structures. The formation of carotenoid epoxides is favoured in plants grown at high altitudes. fl-Carotene inhibits the autoxidation of aldehydes. The products include a new type of carotenoid epoxide in which the epoxide group is situated along the polyene chain. Peracid oxidation of canthaxanthin yields the 13,14epoxide. Treatment with lead tetra-acetate constitutes a convenient method for the conversion of carotenoids into their furanoid oxides.