Two cytotoxic sterols from the soft coral Nephthea sp.

Two cytotoxic sterols have been isolated from Nephthea sp. collected from Xisha islands of the South China Sea by bioassay-guided isolation. Their structures were established as 24-methylcholestan-5-ene-3 beta,8 beta-diol (1) and 24-methylenecholestan-4-ene-3 beta,6 beta-diol (2) by MS, IR, H-1 NMR, C-13 NMR (DEPT), HSQC and HMBC analysis. Sterol 1 is a previously unknown compound and the stereochemistry of sterol 2 has been validated by X-ray diffraction analysis for the first time. Sterol 1 exhibited cytotoxicity against BEL-7402, P-388 and LOVO cells (IC50 18.0, 25.5 and 20.6 mu g/mL, respectively). Sterol 2 also showed significant cytotoxicity against P388 and MCF cells (IC50 1.0 and 2.5 mu g/mL, respectively).