New Cytotoxic Oxygenated Fucosterols from the Brown Alga Turbinaria conoides

Fucosterol (1), 24ξ-hydroperoxy-24-vinylcholesterol (2), 29-hydroperoxystigmasta-5,24(28)-dien-3β-ol (3), 24-ethylcholesta-4,24(28)-dien-3-one (4), 24ξ-hydroperoxy-24-ethylcholesta-4,28(29)-dien-3-one (5), 24-ethylcholesta-4,24(28)-dien-3,6-dione (6), 24ξ-hydroperoxy-24-ethylcholesta-4,28(29)-dien-3,6-dione (7), 6β-hydroxy-24-ethylcholesta-4,24(28)-dien-3-one (8), and 24ξ-hydroperoxy-6β-hydroxy-24-ethylcholesta-4,28(29)-dien-3-one (9) were isolated from the marine brown alga Turbinaria conoides. The structures of these compounds were established by spectral analysis. Isolated for the first time from a natural source, the oxygenated fucosterols 4−9 exhibit cytotoxicity against various cancer cell lines.