New methods in peptide synthesis. Part V. On α- and γ-diphenylmethyl and phenacyl esters of L-glutamic acid

Abstract

Several diphenylmethyl and phenacyl esters of monocarboxylic acids (L-proline, S-trityl-L-cysteine, L-glutamine, and L-asparagine) as well as α- and γ-esters of L-glutamic acid are described. The structures of the α-and γ-esters have been established by conversion of the α-esters into derivatives of L-glutamine. All these esters should prove to be useful in peptide synthesis, since the carboxy protecting groups can be selectively removed; the diphenylmethyl group by hydrogen chloride in certain non-polar solvents, and the phenacyl group by the action of sodium phenyl sulphide. Furthermore, both protecting groups can be removed by hydrogenolysis. An explanation for the unexpected hydrogenolysis of the phenacyl esters is presented.