Crystallographic and NMR studies on sterols from green alga Chaetomorpha basiretorsa Setchell

Chemical investigation of the ethanol extract of the marine green alga Chaetomorpha basiretorsa Setchell led to the isolation of a new sterol stigmast-4, 28-dien-3α, 6β-diol 1 in addition to the five known sterols of β-lawsaritol 2, saringosterol 3, 24-hydroperoxy-24-vinyl-cholesterol 4, β-stigmasterol 5, 29-hydroxystigmasta-5, 24(28)-dien-3β-ol 6. Compounds were isolated by normal phase silica gel and Sephadex LH-20 gel colum chromatography, reverse phase HPLC and recrystalization. Their structures were elucidated by spectroscopic methods including MS, IR 1D/2D NMR and X-ray analysis. Cytotoxicity of compounds was screened by using the standard MTT method. All these compounds were isolated from the green alga Chaetomorpha basiretorsa Setchell for the first time and they were inactive (50% inhibitory concentration was greater than 10 μg/cm³) against KB, Bel-7402, PC-3M, Ketr 3 and MCF-7 cell lines.