Solanapyrone analogues from endophytic Nigrospora sphaerica MZW-A associated with the endangered conifer Pinus wangii

Eight previously undescribed solanapyrone analogues, sphasolanapyrones A-H (1-8), together with four structurally related known compounds (9-12) were obtained from the solid fermentation of Nigrospora sphaerica MZW-A, an endophytic fungus isolated from the fresh branches of the endangered conifer Pinus wangii. This study represents the first investigation on the secondary metabolites of endophytic fungus associated with this precious plant. The structures and absolute configurations of compounds 1-8 were elucidated by extensive spectroscopic analysis and electronic circular dichroism (ECD) calculations. 1 and 2 are first examples of 3,4-vic diol solanapyrone analogues, whereas 7 and 8 are rare 17-nor-solanapyrones. Among these isolates, 3, 4, 5, and 11 showed weak inhibitory against Staphylococcus aureus. In addition, compound 5 displayed weak cytotoxic effects against several tumor cell lines.