Diverse Meroterpenoids from the Endophytic Fungus Penicillium oxalicum and Their Cytotoxic Activities

The combination of ¹H-nuclear magnetic resonance-based metabolomics tracking coupled with ultraviolet analysis facilitated the targeted isolation of ten meroterpenoids (1-10), including three previously undescribed ones (1, 2, and 5), from the culture broth of an endophytic fungus, Penicillium oxalicum. The chemical structures of these meroterpenoids were elucidated based on comprehensive spectroscopic analysis and mass spectrometry. All isolates were identified as members of the decaturins/oxalicines family, which features a naturally unique pyridinyl-α-pyrone polyketide subunit. To facilitate the development of novel antitumor agents, the in vitro cytotoxic activities of all isolates were evaluated. MTT assay results revealed that compounds 1-5, 9, and 10 exhibited weak to moderate cytotoxic effects against tumor cell lines, with half-maximal inhibitory concentration values from 8.74 ± 1.09 to 39.92 ± 0.47 µM, respectively.