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Evaluation of Carbodiimides Using a Competition Method

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. © 1997 European Peptide Society and John Wiley & Sons, Ltd.