A new isochromane derivative from a marine-associated Penicillium sp. and its potential antiviral and antimicrobial activity.

Marine-derived endophytic fungi are a rich source of structurally unique and bioactive natural products. In this study, we isolated a new isochromane derivative, (6S,7R)-7-methoxy-10,11,12,13-tetramethylisochromane-1,3-diol (compound 1), along with seven known compounds (compounds 2-8), from Penicillium sp. Fx1.1.3, an endophyte obtained from the stem of Tetragonia tetragonioides collected in Beigong Island, China. Structural elucidation of compound 1 was performed by 1D and 2D NMR, HR-ESI-MS, and ECD spectral analyses, confirming its absolute configuration as 6S,7R. Antimicrobial screening showed that compound 1 exhibited moderate inhibitory activity 125 μg/mL (494 µM) against Staphylococcus aureus, Escherichia coli, and Candida albicans, while compounds 2 and 4 showed more potent inhibitory activity 31.25 μg/mL or 125 µM and 82 µM, respectively against S. aureus. In addition, compounds 1 and 6 displayed significant antiviral activity against A/Puerto Rico/8/34 (H1N1) virus with IC50 values of 8.99 ± 3.32 and 4.04 ± 1.10 μg/mL (35.52 ± 13.12 and 11.40 ± 3.10 μM), respectively.