New cytotoxic oxygenated fucosterols from the brown alga Turbinaria conoides

Fucosterol (1), 24 xi-hydroperoxy-24-vinylcholesterol (2), 29-hydroperoxyst igmasta-5,24(28)-dien-3 beta-ol (3), 24-ethylcholesta-4,24(28)-dien-3-one ( 4), 24 xi-hydroperoxy-24-ethylcholesta-4,28(29) (5), 24-ethylcholesta-4,24( 28)-dien-3,6-dione (6), 24 xi-hydroperoxy-24-ethylcholesta-4,28(29)(7), 6 b eta-hydroxy-24-ethylcholesta-4, 24(28)-dien-3-one (8), and 24 xi-hydroperox y-6 beta-hydroxy-24-ethylcholesta-4,-28(29)-dien-3-one (9) were isolated fr om the marine brown alga Turbinaria conoides. The structures of these compo unds were established by spectral analysis. Isolated for the first time fro m a natural source, the oxygenated fucosterols 4-9 exhibit cytotoxicity aga inst various cancer cell lines.