Selective Peptide Chain Extension at the N-terminus of Aspartic and Glutamic Acids Utilizing 1-(N-protected-α-aminoacyl)benzotriazoles

Diverse N‐protected di‐(3a–d, 3a + a′, 5a–d, 5d + d′, and 7a–g) and tripeptides (10a–h) were synthesized under mild reaction conditions in good yields (65–97%) by acylation with 1‐(N‐protected‐α‐aminoacyl)benzotriazoles of the amino groups of free aspartic and glutamic acids. Complete retention of chirality was demonstrated by parallel experiments involving d‐Ala, l‐Ala, and dl‐Ala for the preparation of dipeptides and tripeptides, and supported by NMR and HPLC analyses.