Synthesis and characterization of a series of novel glutamic γ-15N-anilide dipeptides

The preparation of a series of novel Cbz–Gln–Gly dipeptide derivatives is reported, wherein the γ-carboxamide groups of the glutamine side chains have been modified to γ-¹⁵N-anilides which are substituted in the para position with -NO₂, -Cl, -H, -CH₃, -OCH₃, and -N(CH₃)₂. Characterization of the free anilines (pK_a values and ¹⁵N NMR chemical shifts) and corresponding γ-anilides (¹⁵N NMR chemical shifts and FTIR wavenumbers) is also reported. Correlation of these physicochemical data to Hammett substituent parameters (σ_para) is discussed. These novel dipeptide derivatives should prove to be generally useful for structure–function enzymology studies of γ-glutamyl transferring enzymes.