Antibiotic Metabolites from the Coral-Associated Actinomycete Streptomyces sp OUCMDZ-1703

From the oligotrophic culture of a soft coral-associated actinomycetes strain, Streptomyces sp. OUCMDZ-1703, we isolated and identified two new chlorinated polyketides that we named strepchloritides A and B (1 and 2), three thiazole derivatives known as watasemycin A (3), pulicatin G (4) and aerugine (5), along with pyrrole-2-carboxamide, furan-2-carboxamide and 1-(3,5-dihydroxyphenyl)ethanone. The new structures of 1 and 2 were determined by spectroscopic studies such as 1D- and 2D-NMR and MS analyses, while the known compounds were identified by comparison of the NMR data with those in literatures. The results showed that actinomycete strain OUCMDZ-1703 could use the relative high ratio of chlorine in the oligotrophic medium to synthesize chlorinated natural products. New compounds 1 and 2 displayed cytotoxicity against the MCF-7 cells with IC50 values of 9.9 and 20.2 mu mol.L-1, respectively. Thiazole derivatives 3 and 5 were first found to be active against three clinical strains of methicillin-resistant Staphylococcus aureus (MRSA082, MRSA111 and MRSA234) with the same MIC/MBC values of 7.81/7.81 mu g.mL-1.