Production of New Antibacterial 4-Hydroxy-α-Pyrones by a Marine Fungus Aspergillus niger Cultivated in Solid Medium

Four 4-hydroxy-alpha -pyrones including three new ones named nipyrones A-C (1-3) together with one known analogue germicidin C (4) were discovered from a marine sponge-derived fungus Aspergillus niger cultivated in a solid rice culture. Their structures and absolute configurations were elucidated through a combination of spectroscopic data and electronic circular dichroism (ECD) calculations as well as comparison with literature data. Compounds 1-4 were evaluated for their antibacterial activities against five pathogenic bacteria (Staphylococcus aureus, Escherichia coli, Bacillus subtilis, methicillin-resistant Staphylococcus aureus, and Mycobacterium tuberculosis). Compound 3 showed promising activity against S. aureus and B. subtilis, with minimum inhibitory concentration (MIC) values of 8 mu g/mL and 16 mu g/mL, respectively, and displayed weak antitubercular activities against M. tuberculosis, with MIC value of 64 mu g/mL, while compounds 1 and 2 exhibited moderate antibacterial efficacy against four pathogenic bacteria with MIC values of 32-64 mu g/mL.