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

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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.