Eudistamides A and B, novel cyclic depsipeptides from a marine-derived Streptomyces sp.

Addressing antibiotic resistance represents a significant challenge. Methods for rapid structure determination of bacterially produced antibiotics would help streamline discovery pipelines. Therefore, we evaluated application of biomolecular NMR strategies for rapid structure elucidation of peptide-based natural product antibiotics. Two novel peptides eudistamides A and B (1 and 2), were isolated from a marine Streptomyces sp. Both compounds 1 and 2 contain a unique 3-(2-Methylphenyl)acrylic acid moiety, which was assigned by 1D and 2D NMR experiments. The sequences of the amino residues in 1 and 2 were elucidated on the basis of 3D NMR experiments, and further confirmed by HRESIMS and 1D and 2D NMR data. The absolute configurations were determined by advanced Marfey's method after acid hydrolysis. Compound 2 displays antibacterial activities against strains of Methicillin-resistant Staphylococcus aureus (MRSA), E. coli and Bacillus subtilis.