A synthesis of N-phthaloyl amino acids and amino acid esters under mild conditions

The racemization-free synthesis of N-phthaloyl amino acids (Pht-amino acids) from amino acid esters, by using o-methoxycarbonylbenzoyl chloride in anhydrous media, is described. The N-phthaloyl amino acids and esters from proteins were obtained in high yields. Three N-phthaloyl amino acids were synthesized for the first time: N-Pht-LTrp, N-Pht-S-Bzl-LCys and N-Pht-Nim-Bzl-LHis. In the case of some sterically hindered amino acids, LIle and α-amino-isobutyric acid, the intermediate N-(o-methoxycarbonylbenzoyl) amino acid derivative could be isolated.