Cytotoxic bicyclic diterpene from the brown alga Sargassum crispum.

Study of the brown alga Sargassum crispum collected from Red Sea resulted in the isolation of new diterpene with hydroazulene skeleton, Sargassinone (6), some fatty acids ethyl ester andsome fatty acids. The identification of the isolated metabolites was established mainly by spectral methods and chemical transformation of sargassinone (6) to its acetate (7). The two diterpens (6, 7) exhibited substantial cytotoxic activities, as indicated by their IC50 values at the dose of 10 micrograms/ml or less.