| Summary: | A new thiopeptide (micrococcin P3, <b>1</b>) and a known one (micrococcin P1, <b>2</b>) were isolated from the culture broth of a marine-derived strain of <i>Bacillus stratosphericus</i>. The structures of both compounds were elucidated using spectroscopic methods, including extensive 1D and 2D NMR analysis, high resolution mass spectrometry (HRMS), and tandem mass spectrometry. Both compounds exhibited potent antibacterial activities against Gram-positive strains with minimum inhibitory concentration (MIC) values of 0.05−0.8 μg/mL and did not show cytotoxicity in the MTT assay up to a concentration of 10 μM. This study adds a new promising member, micrococcin P3, to the family of thiopeptide antibiotics, which shows potential for the development of new antibiotics targeting Gram-positive bacteria.
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