A Novel Synthesis of L-Pyroglutamic Acid Derivatives from L-Proline : Utility of N-Protecting Groups for Ruthenium Tetroxide Oxidation of Cyclic α-Amino Acids

Abstract

The utility of four urethane type N-protecting groups, benzyloxycarbonyl (Z), p-nitro-benzyloxycarbonyl [Z(NO₂)], trichloroethoxycarboyl (Troc) and tert-butoxycarbonyl (Boc) groups, was tested in the ruthenium tetroxide (RuO₄) oxidation of N-protected L-proline esters. Three groups, but not the Z group, which was decomposed by RuO₄, were found to be stable during the oxidation and afforded high yields of the corresponding L-pyroglutamic acid esters. Removal of the protecting groups from the oxidation products was carried out successfully in the usual manner to give N-unsubstituted (NH-type) L-pyroglutamic acid derivatives without racemization. The first transformation of L-proline into L-pyroglutamic acid and its derivatives has been accomplished.