title: Mechanism of racemisation of histidine derivatives in peptide synthesis.
abstract: Evidence is presented to show that the racemisation of N(alpha)-benzyloxycarbonyl-N(pi)-phenacyl-L-histidine which occurs on activation with dicyclohexylcarbodiimide in dimethylformamide takes place by action of the pi-nitrogen as an intramolecular base catalyst in the O-acylisourea adduct which is in reversible equilibrium with the reactants, rather than by formation of an optically labile heterocyclic intermediate.
mesh_terms: D055598:Chemical Phenomena; D002621:Chemistry; D004024:Dicyclohexylcarbodiimide; D004126:Dimethylformamide; D006639:Histidine / Q000031:analogs & derivatives*; D010455:Peptides / Q000138:chemical synthesis*
chemical_list: D010455:Peptides; D006639:Histidine; D004024:Dicyclohexylcarbodiimide; D004126:Dimethylformamide