title: Inhibition of the elastase of Pseudomonas aeruginosa by N alpha-phosphoryl dipeptides and kinetics of spontaneous hydrolysis of the inhibitors.
abstract: The rates of hydrolysis of N-[(alpha-L-rhamnopyranosyloxy)phospho]-L-leucyl-L-tryptophan (phosphoramidon), N alpha-phosphoryl-L-leucyl-L-tryptophan (PO3LeuTrp), N alpha-phosphoryl-L-leucyl-L-phenylalanine (PO3LeuPhe), and N alpha-phosphoryl-L-leucyl-L-phenylalaninamide (PO3LeuPheNH2) were followed by proton nuclear magnetic resonance spectroscopy. The rates of hydrolysis (kobsd) of PO3LeuTrp, PO3LeuPhe, and PO3LeuPheNH2 were all first order in phosphorylamide concentration over the pH range studied (3.8-9.5). The values for kobsd at pH 7.3 and 37 degrees C are as follows: PO3LeuTrp, 0.35 h-1; PO3LeuPhe, 0.63 h-1; PO3LeuPheNH2, 0.73 h-1. The values for kobsd do not significantly change between pH 5 and pH 8 but dramatically decreased with increasing pH. The hydrolysis of PO3LeuPhe and PO3LeuPheNH2 above a pH of approximately 5 was positively correlated with the concentration of monoanionic species (NHRPO3H)1-, and the values for the first-order rate constants for the respective monoanionic species were calculated to be 0.66 +/- 0.03 h-1 and 1.07 +/- 0.10 h-1. Phosphoramidon was not found to hydrolyze after 6 days at 37 degrees C at a pH of 4.6 and 7.7, while the phosphorylamide PO3LeuTrp, synthesized by the removal of L-rhamnose from phosphoramidon by base hydrolysis, was found to rapidly hydrolyze under these conditions. Solvolysis in aqueous methanol of PO3LeuPhe and PO3LeuPheNH2 indicates that the hydrolysis reaction is bimolecular, proceeding by way of direct attack of solvent (H2O, CH3OH) on phosphorus.(ABSTRACT TRUNCATED AT 250 WORDS)
mesh_terms: D004151:Dipeptides / Q000138:chemical synthesis*; D006868:Hydrolysis; D007700:Kinetics; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D010196:Pancreatic Elastase / Q000037:antagonists & inhibitors*; D011550:Pseudomonas aeruginosa / Q000201:enzymology*; D013329:Structure-Activity Relationship
chemical_list: D004151:Dipeptides; D010196:Pancreatic Elastase