Secondary Metabolites with Cytotoxic Activities from Streptomyces sp. BM-8 Isolated from the Feces of Equus quagga

A new aliphatic acid, compound 1, together with six known metabolites, including nonactic acid (2), homononactic acid (3), ethyl homononactate (4), homononactylhomononactate (5), valinomycin (6), and cyclo-(Pro-Leu) (7), was isolated from the culture broth of Streptomyces sp. BM-8, an actinobacterial strain isolated from the feces of Equus quagga. The structures of these compounds were established by analyses of spectroscopic data, including 1D and 2D nuclear magnetic resonance spectra (NMR), as well as by HR-ESI-MS spectrometry and chemical derivative analyses. Additionally, a serial analogue of nonactic acid and homononacticacid (8–21) was synthesized. The cytotoxicity of 1–21 wastested against a panel of cancer cell lines, such as HT-29, MCF-7, A375 and K562, with MTT assay. In addition, the cytotoxicity tests revealed that 1 was less cytotoxic toward a panel of cancerous cells, as compared with valinomycin (6).