I. Selective Protection of α- or Side-chain Carboxyl Groups of Aspartic and Glutamic Acid. A Facile Synthesis of β-Aspartyl and γ-Glutamyl Peptides

Abstract

(S)-3-Benzyloxycarbonyl-5-oxo-4-oxazolidineacetic acid (IIa) and (S)-3-benzyloxycarbonyl-5-oxo-4-oxazolidinepropionic acid (IIb) were utilized for the selective protection of side-chain carboxyl group of corresponding α-aminodicarboxylic acids and the synthesis of β-aspartyl and γ-glutamyl peptides as an α-carboxyl protected intermediates. It was found that 5-oxazolidinone ring, the α-carboxyl protecting group, was easily removed under not only the condition of alkaline hydrolysis but also catalytic hydrogenolysis. Thus a facile synthesis of β-aspartyl and γ-glutamyl peptides was achieved by the coupling of IIa and IIb with benzyl ester of amino acids and peptides followed by hydrogenolytic removal of all the protecting groups.