Highly efficient stereoconservative amidation and deamidation of alpha-amino acids

[reaction: see text] An overall stereoconservative protection and deprotection method of amino and carboxyl groups is presented. N-Phthaloyl N'-alkyl secondary amides of alpha-amino acids can be generated from corresponding N-phthaloyl amino acids by coupling reaction of N-alkylamines using mixed anhydride method. These secondary amides can be transformed by thermal rearrangement of intermediate nitrosoamides to O-alkyl esters with retention of configuration and excellent yields.