Elimination–addition mechanisms of acyl group transfer: transcarbamoylation in aminoalkylimidazoles carbamoylated on the heterocyclic nitrogen

Abstract

Histamine and histidine are carbamoylated on the ring nitrogen (probably N^π) in aqueous solutions of cyanic acid from pH 3 to 11. A further reaction occurs where the carbamoyl group is transferred from the ring to the amino nitrogen to form a urea; the major part of the reaction flux for this reaction passes through an intermolecular E–A process involving cyanate ion as an intermediate and not through intramolecular nucleophilic attack by amine on the N^π-carbamoylimidazolyl function.