Kinetics and mechanism of succinimide ring formation in the deamidation process of asparagine residues

Abstract

The cyclization of Ac–Gly–Asn–Gly–Gly–NHMe to the succinimide derivative has been studied in the pH range 5.5–10.4 at 37° and µ= 1 mol dm^–3. Kinetic evidence indicates that the reaction is a multistep process with a change in the rate-determining step at pH 6.5–7.0. The suggested mechanism involves the pre-equilibrium deprotonation of the NH group next to the Asn residue, followed by nucleophilic attack of the nitrogen atom on the carbonyl carbon of the Asn side chain giving a cyclic tetrahedral intermediate. At acidic pH the cyclization step is rate determining, whereas, the removal of the leaving group by apparent general-base catalysis is the rate-determining step at neutral and basic pH. The literature data on the deamidation rate are discussed in light of the proposed mechanism.