Ophiobolin O and 6-epi-ophiobolin O, two new cytotoxic sesterterpenes from the marine derived fungus Aspergillus sp.

Two new sesterterpenes, ophiobolin O (1) and 6-epi-ophiobolin O (2), together with the known ophiobolins G (3), H (4), and K (5), and 6-epi-ophiobolin K (6) were isolated from the marine derived fungus Aspergillus sp. The structures of these compounds were elucidated based on chemical and physicochemical evidence, including MS, UV, IR and NMR spectra. T h e stereochemistry of 1 was further confirmed by catalytic reaction of 5 with p-TsOH as acatalyst. Compounds 1 to 6 showed cytotoxicity against mouse leukemia cell line P388, with IC50 values of 4.7, 9.3, 24.6, 105.7, 13.3 and 24.9 microM, respectively.