A reasonably stereospecific multistep conversion of Boc-protected α-amino acids to Phth-protected β3-amino acids

Abstract

A selenium-mediated protocol for the homologation of N -Boc α-amino acids into the corresponding N -phthaloyl β-amino acids has been developed. A method for the synthesis of β 3 -amino acids starting from α-amino acids is described. This conversion can be effected by an eight-step procedure which involves the transformation of the carboxylic group into an alkyne followed by a selenium-mediated conversion of the carbon–carbon triple bond to a Se -phenyl selenocarboxylate intermediate. The reactive Se -phenyl selenocarboxylate intermediates can be trapped with water, alcohols or the amine of an amino acid derivative to give β 3 -amino acids, β 3 -amino esters or mixed peptides, respectively. The whole transformations of the carboxylic group into an alkyne and of the alkyne group into β 3 -amino acids may not require purification of the intermediate products but a work-up and isolation procedure of crude materials.