Antibacterial and Cytotoxic 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, by a comparison of experimental ECD spectra, or by single-crystal X-ray diffraction analysis. Compound 1 rarely contains an oxime hydroxy with a 6/5/6/5/6/13 polycyclic system. A plausible biosynthetic pathway for 1 and 2 was proposed. 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.