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 ( 1a and 1b ) and (±)-versilulin B ( 2a and 2b ), and two diphenyl ether derivatives, versilulins C and D ( 3 and 4 ), together with four known compounds ( 5 – 8 ), were isolated from the endophytic fungus Aspergillus versicolor 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 1 and 2 possess an unprecedented 6/5/6/6 tetracyclic polyketide with a unique 1,4-dioxospiro[4.5]decan-8-one core skeleton. Compound 3 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 4 contains a novel 6/8/6/6/6/6 hexacyclic fused ring system. Biological assays revealed that compounds 3 and 5 displayed modest antibacterial activity against Staphylococcus aureus with an equal MIC value of 32 μg/mL.