Preparation of γ-glutamyl dipeptides of sulphur-containing amino-acids

γ-L-Glutamyl-L-methionine, -S-methyl-, S-propyl-, -S-allyl-, and -S-benzyl-L-cysteine were prepared by condensation of α-ethyl N-trifluoroacetyl-L-glutamate dicyclohexylammonium salt with the corresponding amino-acid ethyl ester hydrochloride followed by alkaline hydrolysis of the intermediate N-trifluoroacetyl dipeptide diethyl esters. The peptides containing S-substituted cysteine were difficult to crystallize but were more easily obtained as the crystalline ammonium salts.