Cyclic Hexapeptides from the Deep South China Sea-Derived Streptomyces scopuliridis SCSIO ZJ46 Active Against Pathogenic Gram-Positive Bacteria

Three new cyclohexapeptides, desotamides B-D (2-4), and the known desotamide (1) were isolated from marine microbe Streptomyces scopuliridis SCSIO ZJ46. The sequences and absolute configurations of 2-4 were elucidated on the basis of high-resolution spectroscopic data, Marfey's method, and chiral-phase HPLC data. Desotamide C (3) contains a unique N-formyl-kynurenine residue, whereas 4 lacks formylation at the same site. Compounds 1 and 2 displayed notable antibacterial activities against strains of Streptococcus pnuemoniae, Staphylococcus aureus, and methicillin-resistant Staphylococcus epidermidis (MRSE), and structure activity relationship studies revealed the indispensability of the Trp component for antibacterial activity within this new scaffold.