Diverse ansamycin derivatives from the marine-derived Streptomyces sp. ZYX-F-97 and their antibacterial activities.

Four new ansamycin derivatives, named 1,19-epithio-geldanamycin A (1), 17-demethoxylherbimycin H (2), herbimycin M (3), and seco-geldanamycin B (4), together with eight known ansamycin analogues (5-12) were isolated from the solid fermentation of marine-derived actinomycete Streptomyces sp. ZYX-F-97. The structures of new compounds were elucidated by extensive spectroscopic analysis as well as nuclear magnetic resonance (NMR) and electronic circular dichroism (ECD) calculations. All the compounds were assayed for their antibacterial activity. Among them, compounds 4, 8, and 12 exhibited remarkable inhibition against Listeria monocytogenes with minimum inhibitory concentrations (MIC) values ranging from 8 μg·mL to 64 μg·mL, and displayed moderate inhibition against methicillin-resistant Staphylococcus aureus (MRSA) with MIC value of 64 μg·mL. Compounds 4, 8, 9, and 12 showed moderate inhibition activities against both Staphylococcus aureus and Bacillus subtilis with MIC values ranging from 32 μg·mL to 128 μg·mL.