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 14, along with four known compounds 58, 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 14 were established on the basis of extensive spectroscopic analysis. Compounds 18 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.