DESIGN, SYNTHESIS AND EVALUATION OF TRANSITION-STATE ANALOG INHIBITORS OF ESCHERICHIA-COLI GAMMA-GLUTAMYLCYSTEINE SYNTHETASE

Phosphinic acid-, sulfoximine- and sulfone-based transition-state anal ogues were synthesized and evaluated as inhibitors of Escherichia coli gamma-glutamylcysteine synthetase. These compounds have a carboxyl fu nction at the beta-carbon to the tetrahedral central hetero atom so as to mimic the carboxyl group of the attacking cysteine in the transiti on state. The phosphinic acid- and the sulfoximine-based compounds wer e found to be potent ATP-dependent inactivators, both showing a slow-b inding kinetics with overall affinities and second-order inactivation rates of one to two orders of magnitude greater than those of L-buthio nine (SR)-sulfoximine (L-BSO). The sulfone was a simple reversible inh ibitor without causing ATP-dependent enzyme inactivation, but its affi nity toward the enzyme was still five times greater than that of L-BSO , indicating that the beta-carboxyl function plays a key role in the r ecognition of the inhibitors by the enzyme. The sulfoximine with (S)-b eta-carbon to the sulfur was synthesized stereoselectively, and the tw o diastereomers with respect to the chiral sulfur atom were separated as a cyclic sulfoximine derivative. The sulfoximine with R-configurati on around the sulfur served as an extremely powerful ATP-dependent ina ctivator with an overall inhibition constant of 39 nM and an inactivat ion rate of 6750 M-1 s(-1), which correspond to 1260-fold higher affin ity and almost 1400-fold greater inactivation rate as compared with L- BSO. The sulfoximine with (S)-sulfur was a simple reversible inhibitor with an inhibition potency comparable to that of the sulfone. The syn thesis and inhibition profile of the N-phosphoryl sulfoximine is also described. (C) 1998 Elsevier Science Ltd. All rights reserved.