title: Phosphinic acid inhibitors of D-alanyl-D-alanine ligase.
abstract: We report the synthesis of a series of phosphinic acid dipeptide analogues, NH2CH(R1)PO(OH)CH2CH(R2)CO2H, related to DAla-DAla. The best of these compounds are potent, essentially irreversible inhibitors of DAla-DAla ligase, and their preferred stereochemistry was shown by chiral synthesis of (1(S)-aminoethyl)(2(R)-carboxy-1-n-propyl)phosphinic acid, 12b, and by X-ray crystallography of its derivative benzyl [1(S)-[(benzyloxycarbonyl)-amino]ethyl](2(R)-carbomethoxy-1-propyl) phosphinate, 13, to correspond to the stereochemical configuration of DAla-DAla at both centers. A mechanism for the inhibition of DAla-DAla ligase by these compounds is proposed to involve an ATP-dependent formation of phosphorylated inhibitor within the enzyme's active site. The antibacterial activities of these compounds are modest although their spectra include both Gram-positive and Gram-negative susceptible organisms. The best antibacterial activity was shown by (1(S)-aminoethyl) [2-carboxy-2(R)-(methylthio)-1-ethyl]phosphinic acid, 3e, whose MIC's range from 4-128 micrograms/mL on nine of a panel of 11 bacterial organisms. Combination of one of the more active phosphinic acids 12b with the alanine racemase inhibitor fluoro-D-alanine enhances the antibacterial spectrum of the latter on several strains of bacteria and inhibits fluoro-D-alanine's self-reversal, which normally occurs at concentrations several fold higher than its MIC level. This inhibition of fluoro-D-alanine self-reversal is consistent with an involvement of DAla-DAla ligase inhibition in the antibacterial activity of these compounds.
mesh_terms: D000255:Adenosine Triphosphate / Q000494:pharmacology; D001665:Binding Sites; D055598:Chemical Phenomena; D002621:Chemistry; D003523:Cycloserine / Q000494:pharmacology; D004151:Dipeptides / Q000138:chemical synthesis / Q000494:pharmacology*; D013293:Enterococcus faecalis / Q000187:drug effects / Q000201:enzymology; D008826:Microbial Sensitivity Tests; D010453:Peptide Synthases / Q000037:antagonists & inhibitors*; D010721:Phosphinic Acids / Q000138:chemical synthesis / Q000494:pharmacology*; D010766:Phosphorylation; D011514:Proteus vulgaris / Q000187:drug effects; D011550:Pseudomonas aeruginosa / Q000187:drug effects
chemical_list: D004151:Dipeptides; D010721:Phosphinic Acids; D000255:Adenosine Triphosphate; D003523:Cycloserine; D010453:Peptide Synthases; C019638:D-alanylalanine synthetase