New 3β,6β-dihydroxy and 3β,5α,6β-trihydroxy sterols from marine bryozoan Bugula neritina in South China Sea and their cytotoxicity

•Two new sterols and one sterol never reported from natural sources were isolated.•Seven known sterols or steroid glycoside were also identified from Bugula neritina.•The 3β,6β-dihydroxy Δ4 nucleus in sterols was found firstly from marine bryozoans.•Sterols 1, 2 and 5 showed selective cytotoxicity against HepG2 cancer cell line.

Two new sterols, (22E)-cholest-4,22-diene-3β,6β-diol (1) and (23S,24R)-dimethylcholest-7-ene-3β, 5α,6β-triol (3), a sterol reported for the first time from natural sources, (22E,24S)-24-methylcholest-4,22-diene-3β,6β-diol (2), together with a known steroid glycoside (4) and six known sterols (5-10), were isolated from the marine bryozoan Bugula neritina inhabiting South China Sea. The structures of the new compounds were determined on the basis of extensive spectral analysis, including 1D and 2D NMR, EI-MS, HR-EI/ESI-MS data. Compounds 1-10 were evaluated for their cytotoxicity against human tumor cell lines HepG2, NCI-H460 and SGC7901. Sterols 1, 2 and 5 exhibited selective inhibitions against HepG2 cancer cell line with the IC50 values of 36.6 μM, 52.1 μM and 47.8 μM, respectively, while showed inactivity to NCI-H460 and SGC7901 cell lines. The characteristic 3β,6β-dihydroxy Δ4 nucleus in sterols 1, 2 and 5 was found from marine bryozoans for the first time.

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