The pH-rate profile for the hydrolysis of O-phenyl N-(glycyl)phosphoramidate (II) reveals intramolecular catalysis by the neighboring carboxylate function which serves to accelerate greatly the rate of P-0 bond cleavage. In fact, P-0 bond fission in the reference compound, O-(phenyl)phosphoramidate (I), is not detected. The catalysis of II is further enhanced (>102) by the addition of Zn2+ or Mg2 + ions, which do not affect the rate of hydrolysis of I. A mechanism is postulated featuring formation of a five-membered cyclic acyl phosphate (product studies in hydroxylamine buffer) which decomposes via water attack on phosphorus rather than carbon (18O tracer experiments). These findings suggest that two types of biologically important catalysis may be incorporated into a model system in order to confer dramatic reactivity on a normally unreactive phosphate diester. These results contrast with the Cu(II)-catalyzed hydrolysis of salicyl phosphate, which apparently is of the general- acid type with carboxylate merely serving as a coordinating ligand.
All Science Journal Classification (ASJC) codes
- Organic Chemistry