The N-.gamma.-glutamyl derivatives of L-thiazolidine-4-carboxylic acid, 4-aminobutyric acid, 1-aminocyclopentanecarboxylic acid, 2-aminophenol and p-fluoro-L-phenylalanine (compounds 6, 8, 9, 10 and 12, respectively) were synthesized using the synthon phthaloylglutamic anhydride. Their relative rates of cleavage by the enzyme .gamma.-glutamyl transpeptidase (.gamma.-GT) were determined to evaluate the possibility for their selective release by this enzyme which is elevated in certain pathological conditions. Compounds 6, 8 and 9 were not readily solvolyzed by .gamma.-GT, but compounds 10 and 12, as well as the N-.gamma.-glutamylated derivatives of 3- and 4-aminophenol, were readily cleaved.