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A new 5α,8α-epidioxysterol, namely yalongsterol A (1), along with two known related steroids 5α,8α-epidioxy-24-methyl-cholesta-6,24(28)-dien-3β-ol (2) and (22E,24S)-5α,8α-epidioxy-24-methyl-cholesta-6,22-dien-3β-ol (3), were isolated from the South China Sea soft coral Sinularia sp. Their structures were established by extensive spectroscopic analyses and comparisons of the spectral data with those reported in the literature. In bioassay, compounds 1-3 showed moderate immunosuppressive activities against T and/or B lymphocyte cells with IC50 values ranging from 19.30 to 59.49 μM, and low cytotoxicity on murine splenocytes with CC50 values ranging from 40.88 to 62.29 μM.[Formula: see text].

A new sterol, (22R,23R,24R)-5α,8α-epidioxy-22,23-methylene-24-methyl-cholest-6,9(11)-dien-3β-ol (1), and two known sterols, (22R,23R,24R)-5α,8α-epidioxy-22,23-methylene-24-methylcholest-6-en-3β-ol (2) and 24-methylenecholestane-1α,3β,5α, 6β,11α-pentol (3), were isolated from the soft coral Sinularia gaweli. The structure of sterol 1 was established by spectroscopic methods and by comparison of the spectral data with those of known analogues. The cytotoxicity of sterols 1–3 towards various tumor cells is reported.