A NOVEL ACTIVATED ESTER IN PEPTIDE SYNTHESES Sir : Bodanszky and du Vigneaud1a2 have introduced the p-nitrophenylesters of N-carbobenzoxyaxnino acids for the synthesis of oligopeptides. The ad- vantage of this method is obvious and has been discussed thoroughly by these authors. In extend- ing this conception it seemed of interest to us to study activated esters of the general type (I) for their properties as N-acylating agents. 0 ... I H Z-NH-CC-NH-CC- ...