Inhibition of neurotoxic esterase in vitro by novel carbamates

Carbamyl sulfonate (CS) compounds are a novel class of carbamates derived from amino acid methyl esters. They have the general structure RCH(COOCH3)NH(CO)SO-3K+, where R is the sidechain of the parent amino acid. These compounds were developed as active site-directed inhibitors of human leukocyte elastase (HLE). The purpose of this study was to characterize the inhibition of hen brain neurotoxic esterase (neuropathy target esterase, NTE), horse serum butyrylcholinesterase (BuChE), and bovine erythrocyte acetylcholinesterase (AChE) by CS analogs derived from the methyl esters of L-ala, D-norval, L-norval, L-phe, L-val, L-norleu, D-met, and L-met. Bimolecular rate constants of inhibition (ki) for NTE ranged from 0.571 for L-ala-CS to 17.7 mM-1 min-1 for L-norleu-CS (10-min I50 values of 123 and 3.92 microM, respectively). Potency against NTE increased with chain length for straight-chain R-groups of L-CS compounds. Unlike HLE, NTE was only weakly stereoselective for CS compound enantiomers. The L-isomers were weaker inhibitors of BuChE than NTE (10-min I50 range of 742 to 35.6 microM). In contrast to the L-enantiomers, the I50 plots of D-met-CS and D-norval-CS were not linear for BuChE, suggesting a possible stereospecific mechanistic shift for inhibition of this enzyme, AChE was not effectively inhibited by any of the CS compounds (I50 values > 750 microM). The specificity and charged nature of CS compounds give these unusual NTE inhibitors potential advantages for mechanistic studies of organophosphorus compound-induced delayed neurotoxicity (OPIDN) and its protection or potentiation.