Graminoides A-D, antibacterial cyclic octaketides from the desert-derived Streptomyces

Four previously unreported cyclic octaketides, designated as graminotides A-D ( 1 – 4 ), along with the known compound GTRI-02 ( 5 ), were isolated from the desert soil-derived actinomycete Streptomyces graminisoli SD11. The planar structures of 1 – 4 were elucidated through comprehensive spectroscopic analysis including 1D, 2D NMR techniques coupled with HR ESI MS measurements. The absolute configurations were established through combination of NOE and coupling constants analysis, and comparison the experimental and calculated ECD spectra. Notably, the biological evaluation revealed that 1 and 2 showed moderate antibacterial activity against Staphylococcus aureus ATCC25923 with MIC of 64 and 32 μg/mL, while 3 displayed activity against Proteus vulgaris CPCC160013 with MIC of 64 μg/mL, respectively. None of the isolated compounds showed antiproliferative effects against HepG2 and MDA-MB-231cells at a tested concentration of 30 μM.