Cytotoxic tremulanes and 5,6-secotremulanes, four new sesquiterpenoids from a plant-associated fungus X1-2.

Two new tremulanes and two new 5,6-secotremulanes, davotremulanes A-D 1-4, along with four known compounds 5-8, were isolated from the culture extract of X1-2, an unidentified plant-associated fungus, which was isolated from the endangered plant, Davidia involucrate Baill. in Shennongjia District. The structures of new compounds 1-4 were established on the basis of extensive spectroscopic analysis. Compounds 1-8 were evaluated for cytotoxic activity to four cancer cell lines, and compounds 1, 2 and 5 displayed selectively moderate activities to A549 cell line with IC50 at 15.3, 25.2, 35.2 μg/mL.