OTTELIONE-A AND OTTELIONE-B - POTENTLY CYTOTOXIC 4-METHYLENE-2-CYCLOHEXENONES FROM OTTELIA-ALISMOIDES

Two diastereomeric 4-methylene-2-cyclohexenones, otteliones A and B (1 A and 1B), have been isolated from the freshwater plant Ottelia alismo ides collected in the Nile Delta, Egypt. These natural products show r emarkable in vitro cytotoxicity against various cancer cell lines. Ott elione B proved to have a constitution identical to that of the known (constitution only) ottelione A. The relative configurations of both 1 A and 1B were studied by NOE and by the combination of molecular model ing and H-1 NMR coupling constant analysis. A unique relative configur ational assignment (1 alpha,3 beta,3a beta,7a alpha) was deduced for 1 B; 1A was assigned one of two alternative diastereomers (1 alpha,3 alp ha,3a alpha,7a alpha or 1 alpha,3 alpha,3a beta,7a beta).