PREPARATION OF (R)-2-AZIDOESTERS FROM 2-((PARA-NITROBENZENE)SULFONYL)OXY ESTERS AND THEIR USE AS PROTECTED AMINO-ACID EQUIVALENTS FOR THE SYNTHESIS OF DIPEPTIDES AND TRIPEPTIDES CONTAINING D-AMINO-ACID CONSTITUENTS

(R)-2-Azidoesters and their derived (R)-2-azido acids are readily prepared from common amino acids by an inversion methodology that employs (S)-2-nosyloxyesters as key intermediates. The (R)-2-azidoesters can be used as protected amino acid equivalents in peptide synthesis. Basic hydrolysis frees the carboxyl group. Triphenylphosphine/water is used to free the amine group. By these reactions a variety of L-D and D-L dipeptides, L-D-L tripeptides, and depsipeptides can be prepared easily in good yields, and without detectable epimerization.