Bioactive Isocoumarin Derivatives from the Endophytic Fungus Paraconiothyrium bonneyae NS16 of Pteris multifida

An endophytic fungus isolated from the roots of Pteris multifida was identified as Paraconiothyrium bonneyae NS16 based on morphology combined with multigene phylogenetic analysis (ITS, LSU, SSU, TUB2, and TEF1-α). Rice-fermented cultures of P. bonneyae NS16 yielded three new isocoumarin derivatives (1-3) together with three known compounds (4-6). Their chemical structures were elucidated by high-resolution electrospray ionization mass spectrometry, nuclear magnetic resonance, and single-crystal X-ray diffraction. In bioactivity evaluations, compounds 1-6 exhibited notable antioxidant activity, with oxygen radical absorbance capacity values ranging from 0.27 ± 0.02 to 4.94 ± 0.17 (µmol TE)/µmol. In addition, compound 1 showed inhibitory activity against α-glucosidase and protein tyrosine phosphatase 1B, with 50% inhibitory concentration values of 353.5 and 27.15 µmol/L, respectively. These results highlight P. bonneyae as a productive source of bioactive isocoumarins and support their potential as antioxidant and antidiabetic leads.