Abstract
A new test for racemization was developed and used to assess known coupling reagents and procedures. The procedure consists of coupling between BOC-Ala-Met-Leu-OH and tert-butyl ester of amino acid [Leu, Ile or Asp (OBut)], cleaving of the resulting peptide by cyanogen bromide to form dipeptide diastereomers, and analyzing both isomers with an amino acid analyzer. The following results were obtained : 1) The DCC-additive (Eintopf) method, especially the HONB-DCC procedure, was somewhat superior to the standard azide method. 2) Even in the azide method, epimerization during peptide bond formation considerably increased in the presence of excess base. 3) Significant racemization was observed in some of the known coupling methods which have been shown, by the Young or Anderson test, to be free from racemization.
