Recent progress in carotenoid and retinoid synthesis
Photoisomerization of peridinin and its related sulfone gave the novel 6s allenic isomers. (6s)-Peridinin was synthesized in an optically active form. The first total synthesis of optically active fucoxanthin was accomplished starting from the readily available (4R,6R)-4-hydroxy-2,2,6-trimethylcyclohexanone by the application of the rearrangement of a-acetylenic alcohols to a,P-unsaturated carbonyl compounds by silylvanadate catalyst followed by iodine-catalyzed isomerization. Recent work on the synthesis of bicyclic retinal analogues is also described. In connection with studies on photosynthesis, further interest has again been centered around the two major allenic carotenoids, fucoxanthin 1. and peridinin 2 (Scheme 1) (ref. l), which function as light-harvesting pigments for photosynthesis in the sea and have, in vivo, anti-tumor or anti-cancer-promoting activity (ref. 2). Scheme 1