Abstract: To study the bioactive constituents of Streptomyces  sp.strain H41-59 isolated from the sea bed mud at the mangrove district of South China Sea.By using silica gel,Sephadex LH-20 column chromatography and preparative HPLC methods,ten ergosterols were isolated from its ethyl acetate extract.Based on the analysis of NMR and ESIMS spectral data,the structures of these compounds were identified as ergosta-7,22-diene-3β,5α,6β-triol(1),ergosta-7,22-diene-3β,5α,6α-triol(2),ergosta-7,22-diene-3β,5α,6β,9α-tetraol(3),ergosta-7,22-diene-3β,5α,6β,25-tetraol(4),5α,6α-epoxy-ergosta-8(9),22-diene-3β,7α-diol(5),5α,6α-epoxy-ergosta-8(14),22-diene-3β,7α-diol(6),ergosta-8(9),22-diene-3β,5α,6β,7α-tetraol(7),ergosta-8(14),22-diene-3β,5α,6β,7α-tetraol(8),5α,6α-epoxyergosta-8(14),22-diene-3β,7β-diol(9),ergosta-5,7,22-triene-3β-ol(10).Compound 1-10 were isolated from Streptomyces species for the first time. Cytotoxicities of these sterols against three cancer cell lines were evaluated in vitro by MTT method.All of them showed cytotoxic activity to some extent.Among them,compound 5,7 and 8 displayed moderate cytotoxicity,with IC₅₀ values lower than 50 μg/mL.

Key words: Streptomyces, sterols, metabolite, mangrove, cytotoxicity