Discussion A distinction between the 5 (4H)-oxazolone and the enolization mechanism of racemization of C-activated peptide derivatives is the following: in the 5 (4H)-oxazolone formation the rate-determining step does not involve the breaking of an a-carbon-hydrogen bond, while in the enolization mechanism the slow step is the removal of cy-hydrogen.+" An earlier report12 demonstrated that the deuterium isotope effect can be used to distinguish ...