Antimicrobial metabolites from the endophytic fungus Aspergillus versicolor

Two new diaryl ether derivatives [aspergillethers A (4) and B (5)] and five known metabolites [(22E,24R)-stigmasta-5,7,22 trien 3-beta-ol (1), stigmasta-4,6,8(14),22-tetraen-3-one (2), orcinol (3), and butyrolactones I (6) and VI (7)] were separated from the endophytic fungus Aspergillus versicolor (Aspergillaceae) isolated from the roots of Pulicaria crispa Forssk (Asteraceae) growing in Saudi Arabia. The structures of these compounds were determined by various spectral techniques (e.g., UV, IR, NMR, and HRESIMS) and by comparison with the literature data. Compounds 4 and 5 were evaluated for their antimicrobial properties towards different microorganisms using a disc diffusion assay. Compound 5 exhibited significant antibacterial capacity towards Staphylococcus aureus, Bacillus cereus, and Escherichia coli with inhibition zone diameters (IZDs) of 14.3, 19.8, and 24.5 mm, respectively, and MICs values of 4.3, 3.7, and 3.9 mu g/mL, respectively, compared to ciprofloxacin (MICs 3.1, 2.8, and 3.5 mu g/mL, respectively). In addition, compound 5 exhibited prominent antifungal activity towards Candida albicans and Geotrichium candidum (IZDs 15.8 mm and 17.5 mm, respectively) in comparison to that of clotrimazole (IZDs 17.2 mm and 21.4 mm, respectively).