Isolation of 24‐Hydroperoxy‐24‐Vinylcholesterol and Fucosterol from the Brown Alga Turbinaria Conoides

A highly cytotoxic hydroperoxysterol 24‐hydroperoxy‐24‐vinylcholesterol (1) and fucosterol (2) were isolated from the brown alga Turbinaria conoides. Compound (1) was transformed into 29‐hydroperoxystigmasta‐5, 24(28)‐dien‐3β3‐ol 3 in chloroform solution at −5–0°C in quantitative yield. The latter compound has been shown to exhibit much stronger cytotoxicity toward cultured spleen lymphocytes stimulated by mitogen concanavalin A than toward normal spleen lymphocytes.