Steroids from green alga <Emphasis Type="Italic">Chaetomorpha basiretorsa</Emphasis> Setchell

Six steroids have been isolated from ethanolic extract of green alga Chaetomorpha basiretorsa Setchell by a combination of repeated normal phase silica gel and Sephadex LH-20 gel column chromatography as well as recrystallization. Using spectroscopic methods including MS and NMR, their structures were determined as β-lawsaritol (1), saringosterol (2), 24-hydroperoxy-24-vinyl-cholesterol (3), β-stigmasterol (4), stigmast-4-en-3α, 6β-diol (5), 29-hydroxystigmasta-5, 24 (28)-dien-3β-ol (6). All these compounds were obtained from this genus for the first time and they were inactive (IC₅₀>10 μg /ml) against KB, Bel-7402, PC-3M, Ketr 3 and MCF-7 cell lines. Supported by High Technology Research and Development Program of China (863 Program) (No. 2007AA09Z410 and 2007AA091604), NSFC of China (No.30530080) and the Key Innovative Program, Chinese Academy of Sciences (No. KZCX2-YW-209).