An Extensive Survey by the Use of High Performance Liquid Chromatography on Racemization during the Coupling of Benzyloxycarbonyl-L-phenylalanyl-L-valine with L-Proline tert-Butyl Ester

Abstract

The extent of racemization and the coupling efficiency during the coupling of benzyloxycarbonyl-L-phenylalanyl-L-valine with L-proline tert-butyl ester were conveniently and rapidly determined by the use of high performance liquid chromatography with high accuracy. An extensive examination of various known coupling methods revealed that the coupling methods using diphenyl phosphorazidate (DPPA) and, especially, diethyl phosphorocyanidate (DEPC) afforded the best results. Reported results using DPPA and DEPC as peptide coupling reagents are also summarized (Table I).