Antimicrobial activities of chemically modified thiazolyl peptide antibiotic MDL 62,879 (GE2270A).

MDL 62,879 (GE2270A) 1 is a new inhibitor of elongation factor-Tu (EF-Tu) and belongs to the class of thiazolyl peptide antibiotics. Controlled acid hydrolysis of I followed by treatment with base resulted in the lost of the two terminal amino acids and in the formation of water-soluble MDL 62,935 2. Although less active in vitro than its parent compound, 2 was able to inhibit by 50% an Escherichia coli cell-free protein synthesis system at roughly the same concentration of 1. MDL 62.935 2 was subjected to further modification at the β-phenylserine residue. Derivatives obtained from 2 were less active in both antimicrobial (MIC) and enzymatic (IC 50 ) assays. This suggests that β-phenylserine plays an important role for the inhibition of EF-Tu by 1 and 2.