Abstract
Phytochemical investigation on the fermentation broth of the fungus Stereum hirsutum led to the isolation of ten steroids, including two previously unreported ones, namely steresterones A (1) and B (2). The semi-synthesis products 3a and 3b were prepared by reduction of the known compound 3 with NaBH4. Their structures and absolute configurations were established via 1D & 2D NMR spectroscopic analysis, and TDDFT/ECD calculations as well as single crystal X-ray diffraction analysis. The structure of 3 which harbored a 5β-H was confirmed by single crystal X-ray diffraction analysis for the first time. All the compounds reported in this study were evaluated for their cytotoxicity against five human cancer cell lines. Bioassay results revealed that 3, 4, 6―9 displayed significant anti-proliferative effects with IC50 values varying from 2.3 to 34.3 μM. The structure-activity relationships of 3, 3a, 3b were discussed.
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