Evaluation of Carbodiimides Using a Competition Method

Abstract

A competitive reaction of activated Boc-Ala-OH and Boc-Phe-OH with H-Leu-resin has been developed for assessing the relative efficiencies of different carbodiimides. This allowed a comparison of the efficiency of the carbodiimides N,N'-dicyclohexylcarbodiimide,N,N'-diisopropylcarbodiimide, N-tert-butyl-N'-methylcarbodiimide and N-tert-butyl-N'-ethylcarbodiimide. Comparable results were obtained when these reagents were used for the preformation of symmetrical anhydrides or of 1-hydroxybenzotriazole esters in situ. Differential incorporation was observed when asymmetrical carbodiimides were used for peptide bond formation by the direct carbodiimide procedure.