Antimicrobial Activity of Depsidones and Macrocyclic Peptides Isolated from Marine Sponge-Derived Fungus Aspergillus nidulans M256

Chemical study on marine sponge-derivated fungus Aspergillus nidulans resulted in the isolation of seven depsidones (1-7) and two macrocyclic peptides (8 and 9). Their chemical structures were elucidated by extensive analyses of HRESIMS and NMR spectral data, as well as comparison with the literature. Compound 1 was an undescribed depsidone. All compounds exhibited significant antimicrobial activity (MICs: 2-128 mu g/mL) towards at least one of seven microbial strains, including Bacillus cereus, Enterococcus faecalis, Staphylococcus aureus, Escherichia coli, Pseudomonas aeruginosa, Salmonella enterica, and Candida albicans. Of these, chlorinated depsidones (1-3, and 5) displayed potential antimicrobial activity. Nidulin (2) possessed good activity against tested strains except for S. enterica with MIC values in range of 2-16 mu g/mL. Interestingly, undescribed depsidone 1 was selectively bioactive on the Gram-positive bacteria (MICs: 2-4 mu g/mL) and yeast (MIC: 8 mu g/mL) but inactivity on the Gram-negative bacteria (MICs: >256 mu g/mL). Macrocyclic peptides, 8 and 9, displayed modest activity against E. faecalis strain with MIC values of 32 and 128 mu g/mL, respectively.