Proansamycin B derivatives from the post-PKS modification gene deletion mutant of Amycolatopsis mediterranei S699

Ten new proansamycin B congeners ( 1 – 10 ) together with one known ( 11 ) were isolated and characterized on the basis of 1D and 2D NMR spectroscopic and HRESIMS data from the Amycolatopsis mediterranei S699 Δ PM :: rifR + rif-orf19 mutant. Compounds 8 and 9 featured with six-membered ring and five-membered ring hemiketal, respectively. Compounds 1 , 2 , and 9 displayed antibacterial activity against MRSA (methicillin-resistant Staphylococcus aureus ), with the MIC (minimal inhibitory concentration) values of 64, 8, and 128 µg/mL, respectively. Compound 1 showed significant cytotoxicity against MDA-MB-231, HepG2 and Panc-1 cell lines with IC 50 (half maximal inhibitory concentration) values of 2.3 ± 0.2, 2.5 ± 0.3 and 3.8 ± 0.5 μM, respectively.