Synthesis and characterization of intermediate and transition-state analogue inhibitors of gamma-glutamyl peptide ligases

The phosphonodifluoromethyl ketone and phosphonofluoridate derivatives of L-glutamic acid were synthesized and characterized as analogues of the gamma-glutamyl phosphate intermediate and the tetrahedral transition state, respectively, for the inhibition of gamma-glutamylcysteine synthetase and glutamine synthetase. The former served as a poor inhibitor of both enzymes, but the latter inhibited glutamine synthetase with a Ki of 59 microM and partially inactivated the enzyme in an NH3- and ATP-dependent manner.