| Solid-state NMR experiments with stable isotope-labeled Staphylococcus aureus have provided insight into the structure of the peptidoglycan binding sites of potent vancomycin derivatives, LY329332, LY309687, and fluoro-biphenyl vancomycin (FBV). LY329332 and LY309687 (Eli Lilly product numbers) are the chemical derivatives of a natural product chloroeremomycin, which differs from vancomycin by an additional vancosamine present in the aglycon structure. LY329332 and LY309687 are formed by the alkylation of an amine-sugar of chloroeremomycin, with 4-flurophenyl-benzaldehyde and 4-trifluoromethoxyl-benzaldehyde respectively. The chemical structure of FBV is identical to LY329332, except for an additional vancosamine. LY329332 is a thousand times more potent than vancomycin in an in vitro assay against vancomycin resistant enterococci. LY309687 and FBV are less potent than LY329332 by factors of 10 and 4 respectively.; Rotational-echo double resonance (REDOR) NMR yielded internuclear distances from the 19F of these glycopeptide antibiotics to natural abundance 31P, and to specific 13C and 15N labels biosynthetically incorporated into the bacteria from labeled alanine, glycine, and lysine in the growth medium. Results from the LY329332 experiments with intact late log-phase bacteria and cell walls show homogeneous drug-peptidoglycan binding. Drug dimers were not detected in situ, and the hydrophobic fluorobiphenyl group was not inserted into the bilayer membrane.; Models of the LY329332, LY309687 and FBV binding sites, consistent with the REDOR results, position the vancomycin cleft around an uncross-linked D-Ala-D-Ala peptide stem. The relative positions of alkylated moieties of the antibiotics to the bridge structure differ due to different interactions of the drug sugars with the peptidoglycan. |
