Algal carotenoids. Part 64. Structure and chemistry of 4-keto-19'-hexanoyloxyfucoxanthin with a novel carotenoid end group

8 pages, 2 figures, 5 schemes.The structural elucidation of a new carotenoid 4-keto-19-hexanoyloxyfucoxanthin 5 from Emiliania huxleyi is documented by chromatographic (HPLC, TLC), spectroscopic (VIS, EIMS, FABMS, FABMSMS, 2D 1H NMR) and chemical evidence. The novel carotenoid end group exhibits particular spectroscopic and chemical properties. In particular the reactions with base and acid are investigated.Due to a very weak molecular ion upon electron impact and facile cleavage to paracentrone 20 related fragments, the new carotenoid was previously misidentified as 19-hexanoyloxyparacentrone 3-acetate 8, also found in other prymnesiophytes (haptophytes).This novel carotenoid readily undergoes cleavage to a C31-skeletal paracentrone 20 related product upon storage, preferably in methanol solution.The new end group represents a plausible precursor for C31-skeletal methyl ketone apocarotenoid metabolites in animals, and differs from the previously suggested precursor.E. S. E. was supported by a research grant from Hoffmann- La Roche, Basel, to S. L.-J.Peer reviewe