NMR-STUDIES ON NATURAL ALL-TRANS-(9'Z,11'Z)-(3R,3'S,5'R,6'R)-PYRRHOXANTHIN, AN ACETYLENIC-C-37-SKELETAL NOR-CAROTENOID BUTENOLIDE

All-trans-(9'Z,11'Z)-(3R,3'S,5'R,6'R)-pyrrhoxanthin was isolated from a natural bloom of dinoflagellates (mainly Ceratium spp.) and submitted to detailed H-1 NMR and C-13 NMR analysis, including homonuclear COSY (2D), ROESY (1D and 2D), TOCSY (1D) and H-1-detected one-bond and multiple-bond H-1, C-13 COSY. All chemical shifts and coupling constants in the H-1 NMR spectrum and all carbons in the C-13 NMR spectrum were assigned. The result is consistent with the structure, previously deduced, including relative configuration. A recently proposed variant of the ROESY pulse sequence, called T-ROESY, claimed to suppress undesired TOCSY transfer, provided excellent results free of TOCSY artifacts caused by coherent magnetization transfer via J coupling pathways independent of the choice of the position of the carrier frequency.