Secondary metabolites from the endolichenic fungus Ophiosphaerella korrae

The isolation of the cytotoxic fractions from the endolichenic fungus Ophiosphaerella korrae yielded six new metabolites, including five polyketides (ophiofuranones A (1) and B (2), with unusual furopyran-3,4-dione-fused heterocyclic skeletons, ophiochromanone (3), ophiolactone (4), and ophioisocoumarin (5)), one sesquiterpenoid ophiokorrin (10), and nine known compounds. Their structures were established on the basis of the analysis of HRESIMS and NMR spectroscopic data. ECD calculations, GIAO NMR shift calculations and single-crystal X-ray diffraction were employed for the stereo-structure determination. A plausible biogenetic pathway for the ophiofuranones A (1) and B (2) was proposed. The cytotoxic assay suggested that the five known perylenequinones mainly contributed to the cytoxicity of the extract. Further phytotoxic studies indicated that ophiokorrin inhibited root elongation in the germination of Arabidopsis thaliana with an IC₅₀ value of 18.06 μg mL^-1.