The extremely low efficiency during the α-chymotrypsin-catalyzed coupling of an inherently poor amino acid substrate, e.g., alanine, using the methyl ester as an acyl donor was significantly improved using esters such as the 2,2,2-trifluoroethyl or carbamoylmethyl ester. The ameliorating effect of the latter ester was especially significant.
The coupling efficiency in alpha-chymotrypsin-catalysed peptide synthesis is greatly improved by the use of activated esters such as the 2,2,2-trifluoroethyl ester as acyl donor instead of the conventional methyl ester; this approach Is useful for the incorporation of non-protein amino acids into peptides.