Versilulins A–D, Spiroketals, and Diphenyl Ether Derivatives from Marine-Derived <i>Aspergillus versicolor</i> 347 with Antibacterial Activity

Four unreported compounds, including two pairs of spiroketal racemates, (±)-versilulin A (<b>1a</b> and <b>1b</b>) and (±)-versilulin B (<b>2a</b> and <b>2b</b>), and two diphenyl ether derivatives, versilulins C and D (<b>3</b> and <b>4</b>), together with four known compounds (<b>5</b>-<b>8</b>), were isolated from the endophytic fungus <i>Aspergillus versicolor</i> 347. The assignment of their structures was accomplished by spectroscopic analysis, including HRESIMS, NMR, chiral analysis, ECD calculation, and X-ray diffraction. Among them, compounds <b>1</b> and <b>2</b> possess an unprecedented 6/5/6/6 tetracyclic polyketide with a unique 1,4-dioxospiro[4.5]decan-8-one core skeleton. Compound <b>3</b> was characterized by an unusual 6/6/6/6/6/6 hexacyclic ring system featuring a rare 9-oxospiro[5.5]undecan-3-one. Compound <b>4</b> contains a novel 6/8/6/6/6/6 hexacyclic fused ring system. Biological assays revealed that compounds <b>3</b> and <b>5</b> displayed modest antibacterial activity against <i>Staphylococcus aureus</i> with an equal MIC value of 32 μg/mL.