Pyrrospirones R-Y, antibacterial decahydrofluorene-class alkaloids from the marine-derived fungus Penicillium sp. SCSIO 41512

Eight new decahydrofluorene-class alkaloids, pyrrospirones R-Y (1-8), together with 13 known analogues (9-21) were isolated from the marine-derived fungal strain Penicillium sp. SCSIO 41512. Their structures were determined by extensive spectroscopic analysis, and their absolute configurations were established by quantum chemical calculations of electronic circular dichroism (ECD) spectra or comparison of experimental ECD spectra or single crystal X-ray diffraction analysis. Compound 1 rarely contains an oxime hydroxyl with a 6/5/6/5/6/13 polycyclic system. Biologically, compounds 1, 4, 6, 8, 10-12, 14-15, 18-19, and 21 had cytotoxicity against human cancer cell lines A549 and HCT116 with IC₅₀ values of 7.3-79.3 μM, and 1, 4, 6, 11, 15, 18, and 21 also showed significant inhibitory activity against six pathogenic bacteria with MIC values of 1.6-13.0 μg/mL. Their structure-bioactivity relationship was also discussed.