Antimicrobial metabolites from a marine-derived Actinomycete Streptomyces sp. G278

Analysis of an antimicrobial extract prepared from culture broth of the marine-derived actinomycete Streptomyces sp. G278 led to the isolation of ten compounds, 1-10. Two compounds, 2,5-Bis(5-tert-butyl-2-benzoxazolyl)thiophene (1), and 3-hydroxyl-2-methylpyridine (2) were isolated from a natural source for the first time. The structures of the isolated compounds were established by their spectral data analysis, including mass spectrometry, 1D-NMR, 2D-NMR, and X-ray crystallographic analysis in case of compound 3. All isolated compounds were evaluated for their antimicrobial activity against a panel of clinically significant microorganisms. Compounds 1 and 3 selectively inhibited Enterococcus faecalis (MIC: 256 μg/mL). Compound 2 was found to have antibacterial and antifungal activity against Escherichia coli (MIC: 64 μg/mL), Salmonella enterica (MIC: 256 μg/mL), Staphylococcus aureus (MIC: 256 μg/mL), Enterococcus faecalis (MIC: 256 μg/mL), and Candida albicans (MIC: 64 μg/mL). Except for compounds 9 and 10, the other known metabolites (4-8) also exhibited antimicrobial activity.