Antibacterial and Cytotoxic Decahydrofluorene-Class Alkaloids from the Marine-Derived Fungus <i>Penicillium</i> sp. SCSIO 41512

Eight new decahydrofluorene-class alkaloids, pyrrospirones R-Y (<b>1</b>-<b>8</b>), together with 13 known analogues (9<b><i>-</i></b>21) were isolated from the marine-derived fungal strain <i>Penicillium</i> 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 <b>1</b> rarely contains an oxime hydroxy with a 6/5/6/5/6/13 polycyclic system. A plausible biosynthetic pathway for <b>1</b> and <b>2</b> was proposed. Biologically, compounds <b>1</b>, <b>4</b>, <b>6</b>, <b>8</b>, <b>10</b>-<b>12</b>, <b>14</b>-<b>15</b>, <b>18</b>-<b>19</b>, and <b>21</b> had cytotoxicity against human cancer cell lines A549 and HCT116 with IC₅₀ values of 7.3-79.3 μM, and <b>1</b>, <b>4</b>, <b>6</b>, <b>11</b>, <b>15</b>, <b>18</b>, and <b>21</b> 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.