Diversified Polyketides and Nitrogenous Compounds from the Mangrove Endophytic Fungus Penicillium steckiiSCSIO 41025

Main observation and conclusion Four new polyketide decalin derivatives, penicisteck acids A—D (1—4), and three new nitrogenous compounds (7—9), together with eight previously reported compounds, were isolated from the mangrove endophytic fungus Penicillium steckii SCSIO 41025. Their structures and absolute configurations were characterized by analysis of comprehensive spectroscopic data combined with ECD calculations and modified Marfey's method. Structurally, compounds 1—3 were highly oxygenated decalin derivatives harboring an unusual propanoic acid unit at C‐1. Compound 8 was identified as a rare natural alkaloid‐ N ‐oxide confirmed by single crystal X‐ray diffraction analysis. A plausible biogenetic pathway of compounds 1—6 is proposed. Compounds 13 and 15 showed significant anti‐bacterial activity against Staphylococcus aureus with the MIC values of 3.9 and 7.8 μg/mL, respectively. Compounds 10 and 12 exhibited potent α ‐glucosidase inhibitory activity with the IC 50 values of 64.1 and 191.4 μmol/L, respectively.