Studies on the diastereoisomeric and conformational aspects of benzoyl dipeptide esters, as a means of assessing racemisation using nuclear magnetic resonance spectroscopy

Abstract

Distinct methyl ester signals in the ¹H n.m.r. spectra of diastereoisomeric forms of benzoyl dipeptide methyl esters provide a means of estimating the isomer composition of diastereoisomeric mixtures. Analysis of the mixture derived from peptide-coupling reactions using this n.m.r. technique provides a convenient means of comparing the racemisation potential of a series of coupling reagents. Significant asymmetric induction accompanies racemisation during the model peptide couplings. Conformational effects have been studied using ¹³C n.m.r. spectroscopy and the structural criteria for observing diastereoisomeric ester signals in the ¹H n.m.r. spectra have been rationalised.