Diacarnusins A-F, nor-Terpene Endoperoxides of the Red Sea Sponge Diacarnus erythraeanus.

Six new nor-terpene endoperoxides, diacarnusins A-F (1-6), along with five known ones (7-11), were isolated from the extract of the Red Sea sponge Diacarnus erythraeanus, which presented cytotoxic activity against the colon carcinoma cell line. The structure elucidation was performed by analysis of mass spectrometric and 1D and 2D NMR data. The relative and absolute configurations of the stereocenters of the compounds were deduced based on the Capon and Macleod empirical rule and comparison of the sign of their specific rotations with those of endoperoxides with proven absolute configurations. The cytotoxicity of the pure compounds was evaluated against a panel of cancer cell lines. The structure elucidation and biological activity of the compounds are discussed.