Peniisocoumarins A–J: Isocoumarins from Penicillium commune QQF-3, an Endophytic Fungus of the Mangrove Plant Kandelia candel

Ten new isocoumarins, named peniisocoumarins A–J (1–9 and 11), along with three known analogues (10, 12, and 13) were obtained from the fermentation of an endophytic fungus, Penicillium commune QQF-3, which was isolated from a fresh fruit of the mangrove plant Kandelia candel. Their structures were elucidated through extensive spectroscopic analysis. The absolute configurations of 1–7 were determined by single-crystal X-ray diffraction and modified Mosher’s method, and those of 8, 9, and 11 were assigned on the basis of experimental and calculated electronic circular dichroism data. Compounds 1 and 2 were unusual dimeric isocoumarins with a symmetric four-membered core. These isolated compounds (1–13) were evaluated for their cytotoxicity and enzyme inhibitory activities against α-glucosidase and Mycobacterium tuberculosis protein tyrosine phosphatase B (MptpB). Among them, compounds 3, 7, 9, and 11 exhibited potent inhibitory effects against α-glucosidase with IC50 values ranging from 38.1 to 78.1 μM, and compound 7 was found to inhibit MptpB with an IC50 value of 20.7 μM.