New Derivatives of Eremomycin Containing 15N or F Atoms for NMR Study

New semisynthetic derivatives of eremomycin containing N-15 or F atoms were obtained for studying the antibiotic-target interaction in intact cells of Gram-positive bacteria by REDOR NMR method. Interaction of the terminal carboxyl group of amino acid 7 (AA7) of eremomycin with amines in the presence of PyBOP and TBTU reagents resulted in the corresponding [N-15]-amide, p-fluorobenzylamide, p-fluorophenylpiperazide, and 6-N-(p-fluorobenzyl)aminohexylamide. A selective method of [N-15]-amidation of carboxyl group of amino acid 3 (AA3) of carboxyeremomycin was developed, and the amide of eremomycin containing [N-15] in AA3 amide group near the antibiotic binding pocket was obtained. Carboxyeremomycin bisamides substituted at AA3 and AA7 and containing two atoms of [N-15] or F were obtained from carboxyeremomycin and [N-15]NH4Cl or the corresponding p-fluorobenzylamine hydrochloride in the presence of PyBOP at pH similar to 8. The Edman degradation of eremomycin p-fluorobenzylamide gave de-(D-MeLeu)-eremomycin p-fluorobenzylamide, a hexapeptide derivative incapable of the antibiotic binding with -D-Ala-D-Ala fragment of growing cell wall peptidoglycan. Among the compounds studied, carboxyeremomycin bis-p-fluorobenzylamide showed the best activity against both the glycopeptides-sensitive and glycopeptides-resistant strains of staphylococci and enterococci.