Isolation, structure elucidation and antibacterial activities of streptothricin acids

Five streptothricin acids (compounds 1–5) were isolated by ion-exchange resin chromatography and preparative RP-HPLC from the fermentation broth of Streptomyces qinlingensis. Their structures were elucidated mainly by analyses of the IR, HR-EIS-MS and NMR spectral data. They were deduced as two known compounds, streptothricin F acid (1) and streptothricin D acid (2), and three new compounds, 12-carbamoylstreptothricin E acid (3), 12-carbamoylstreptothricin D acid (4) and N-acetyl-streptothricin D acid (5), respectively. The antibacterial activities of 1–5 against Escherichia coli, Bacillus subtilis, Staphylococcus aureus, Bacillus cereus and Pseudomonas aeruginosa were assayed by micro-broth dilution. Comparison of the MICs with streptothricin F and D showed that the antimicrobial activities of 1–5 were decreased significantly but varied with the structures.