New chloptosins B and C from an Embleya strain exhibit synergistic activity against methicillin-resistant...

Two new dimeric cyclohexapeptides, chloptosins B and C, were discovered from the culture broth of Embleya sp. MM621-AF10 together with the known compounds chloptosin and L-156,602. The structures of the new chloptosins were determined by spectroscopic studies and advanced Marfey's methods. The stereo structure of the constituent isoleucine was determined by C₃ Marfey's analysis. Chloptosins demonstrated potent antimicrobial activity against Gram-positive bacteria including drug-resistant strains of methicillin-resistant Staphylococcus aureus and vancomycin-resistant enterococci with MICs of 0.5-2 µg ml^-1. The antimicrobial activities of chloptosins were enhanced by addition of co-producing compound L-156,602, as shown by checkerboard analysis.