NATURALLY-OCCURRING STEREOISOMERS OF FUCOXANTHIN

Fast and gentle isolation of crude carotenoids from Fucus serratus, Fucus vesiculosus, Ascophyllum nodosum, Pelvetia canaliculata, Laminaria digitata and Laminaria saccharina followed by HPLC examination suggested that all-E (3S,5R,6S,3'S,5'R,6'R)-fucoxanthin is the only naturally occurring stereoisomer in brown algae. Mono-Z isomers (13-Z, 9'-Z and 13'-Z) appeared to be isolation artifacts formed in solution. The 9'Z-6'R isomer, formed during workup procedures, was previously mistaken as the allenic all-E-6'S isomer. The so-called neo B isomer was reisolated and shown to have 13'-Z configuration. It was inferred that neo A represented a mixture of the 13-Z and 9'-Z isomers.