CARBOXYL ACTIVATION IN PEPTIDE SYNTHESIS USING 4-OXIMINO-PYRAZOL-5-ONES

4‐Oximino‐pyrazol‐5‐ones 2a, b and their esters with N‐protected amino acids 3a, b have been studied for carboxyl activation in peptide synthesis. 2a, b and 3a, b appear to be diastereoisomeric mixtures whose configurations have been assigned on the basis of spectroscopic and X‐ray data. Some peptides obtained using these pyrazolone derivatives are reported: no racemization was noted by the Weig and test.