A new dimeric (-)-5-methylmellein from cultures of the basidiomycete Inonotus sinensis .

(-)-5-Methylmellein () and its new dimer () were isolated from cultures of the basidiomycete . Their structures were elucidated on the basis of extensive spectroscopic methods including UV, IR, HR-EI-MS, 1D NMR and 2D NMR. The structure of Compound was determined by single-crystal X-ray crystallographic analysis. Compound was tested for the cytotoxicities against five human cancer cell lines.