Structures of five new carotenoids from the oyster Crassostrea gigas.

Five new minor carotenoids, 1-5, were isolated from the oyster Crassostrea gigas. The structure of 1 was determined to be (3S,5R,6R,6'S)-3,5,6'-trihydroxy-3'-oxo-6,7-didehydro-5,6-dihydro-10,11,20-trinor-beta,epsilon-caroten-19',11'-olide 3-acetate by detailed analyses of NMR and CD data. The structures of the other carotenoids, 2-5, were also determined in a similar manner. In the FAB-MS/MS of 2-4, having the 5-hydroxy-3,6-epoxy-5,6-dihydro-beta-carotene moiety, the characteristic product ions resulting from the sequential cleavage of C-C bonds in the polyene chain were observed.