Isolation and structure of the unusual Indian Ocean Cephalodiscusgilchristi components, cephalostatins 5 and 6

The Indian Ocean (South African) marine worm Cephalodiscusgilchristi (Hemichordata phylum) has been found to contain a series of unusual disteroidal alkaloids, designated the cephalostatins, that possess exceptionally potent lymphocytic leukemia (murine P388) cell line inhibitory activity (to ED50 10−9 μg/mL). Two of the less prominent members with P388 ED50 10−3–10−2 μg/mL, cephalostatins 5 (2) and 6 (3), were isolated and assigned structures based on rigorous interpretation of two-dimensional 400-MHz 1H and 13C nuclear magnetic resonance.