Design, Synthesis, and Evaluation of γ-Phosphono Diester Analogues of Glutamate as Highly Potent Inhibitors and Active Site Probes of γ-Glutamyl Transpeptidase†

γ-Glutamyl transpeptidase (GGT, EC 2.3.2.2) catalyzes the transfer of the γ-glutamyl group of glutathione and related γ-glutamyl amides to water (hydrolysis) or to amino acids and peptides (transpeptidation) and plays a central role in glutathione metabolism. GGT is involved in a number of biological events, such as drug resistance and metastasis of cancer cells by detoxification of xenobiotics and reactive oxygen species through glutathione metabolism, and is also implicated in physiological disorders, such as Parkinson's disease, neurodegerative disease, diabetes, and cardiovascular diseases. In this study, we designed, synthesized, and evaluated a series of γ-phosphono diester analogues of glutamate as transition-state mimic inhibitors of GGT. The electrophilic phosphonate diesters served as highly potent mechanism-based inhibitors that caused the time-dependent and irreversible inhibition of both the E. coli and human enzymes, probably by phosphonylating the catalytic Thr residue of the enzyme. In par...