Abstract: Dipeptides, their methyl esters, diketopiperazines (DKP), and N-substituted derivatives were racemized at high temperatures (approximately 120" C) in aqueous phosphate buffered solutions at pH values close to the pH of maximum racemization (approximately 8). The racemization of the dipeptides Ala-Gly and Gly-Ala followed reversible first-order kinetics. The initial rate of racemization of DKP was very fast but soon ...