Antioxidant Benzophenones and Biphenyls from an Endophytic Fungus Penicillium sp. QM-4

The endophytic fungi from plants are recognized as a valuable source of structurally diverse secondary metabolites with intriguing bioactivities. Three previously undescribed compounds, including two benzophenones, 2-(2,6-dihydroxy-4-methylbenzoyl)benzoic acid (1) and 2-(2,6-dihydroxy-4-(hydroxymethyl)benzoyl)benzoic acid (2), one biphenyl, 4′,5,5′-trihydroxy-3-methoxy-2′-methyl-(1,1′-biphenyl)-2-carbaldehyde (4), along with two known compounds (3 and 5), were isolated from the endophytic fungus Penicillium sp. QM-4 associated with Pteris cretica. Their structures were established by extensive spectroscopic analysis of HRESIMS, UV, IR, and 1D and 2D NMR data. Free radical scavenging activity of compounds 1–5 was assessed, and compound 3 displayed a significant antioxidant effect in the DPPH assay. Structure–activity relationships of compounds 1–3 were also discussed. These findings enrich the structural diversity and bioactivities of benzophenones and biphenyls derived from fungal source.