Cytotoxic bromoditerpenes from the red alga Sphaerococcus coronopifolius

Three new brominated diterpenes (1, 2, 8), along with six previously reported metabolites (3–7, 9), were isolated from the organic extract of Sphaerococcus coronopifolius, collected in Palaiokastritsa bay at the west coasts of Corfu Island. The structures of the new natural products, as well as their relative stereochemistry, were established by means of spectral data analyses, including 2D experiments. The absolute stereochemistry of 2 and 4 as well as the structure revision of the previously reported metabolite 3 were established by X-ray crystallographic analyses. The cytotoxicity of the isolated metabolites was evaluated against the NSCLC-N6-L16 and A549 human lung cancer cell lines.