Antiproliferative activity and absolute configuration of zonaquinone acetate from the Jamaican alga Stypopodium zonale.

The chemical investigation of specimens of the Jamaican brown alga Stypopodium zonale led to the isolation of a cytotoxic compound, zonaquinone acetate (1), along with known compounds flabellinone, not previously identified in S. zonale, stypoldione, 5',7'-dihydroxy-2'-pentadecylchromone and sargaol. The structures of the metabolites were established by analysis of the spectral data including 1D and 2D NMR experiments while the stereochemistry of 1 was assessed by VCD measurements. Cytotoxic activity was reported in vitro for 1 against breast cancer and colon cancer cell lines at IC(50) values of 19.22-21.62 μM and 17.11-18.35 μM respectively, comparing favorably with standard treatments tamoxifen (17.22-17.32 μM) and fluorouracil (27.03-31.48 μM). When tested with liver cancer cells (Hep G2), no activity was observed. Weak antioxidant activity was observed with 1 but sargaol exhibited high activity.