Quantitative structure‐activity relationships for the pre‐steady state acetylcholinesterase inhibition by carbamates

4‐Nitrophenyl‐ N ‐substituted carbamates (1) are characterized as pseudosubstrate inhibitors of acetylcholinesterase. The first step is formation of the enzyme‐inhibitor tetrahedral intermediate with the inhibition constant ( K i ), the second step is formation of the carbamyl enzyme with the carbamylation constant ( k c ), and the third step is hydrolysis of the carbamyl enzyme with decarbamylation constant ( k d ). According to pre‐steady state kinetics the K i step is divided further into two steps: (1) formation of the enzyme‐inhibitor complex with the dissociation constant ( K S ) and (2) formation of the enzyme‐inhibitor tetrahedral intermediate from the complex with the equilibrium constant ( k 2 / k −2 ). Since the inhibitors are protonated in pH 7.0 buffer solution, the virtual dissociation constant ( K S ′) of the enzyme‐protonated inhibitor complex can be calculated from the equation, ‐log K S ′ = −log K S − p K a + 14. The −log K S , −log K S ′, log k 2 , and log k −2 values are multiply linearly correlated with the Jäve equation (log( k / k 0 ) = ρ*σ* + δ E s + ψ π). For ‐log K S ′ − σ* − E s − π‐correlation, the ρ* value of −0.4 indicates that the enzyme‐protonated inhibitor complexes have more positive charges than the protonated inhibitors, the δ value of 0.44 suggests that the bulkily substituted inhibitors lessen the reaction due to the difficulty of the inhibitors to enter the narrow enzyme active site gorge, and the ψ value of 0.27 implies that the inhibitors with hydrophobic substituents accelerate the inhibitors entering the active site gorge of the enzyme. For log k 2 / k −2 ,− σ* − E s − π‐correlation, the ρ* value of 1.1 indicates that the enzyme‐protonated inhibitor tetrahedral intermediates have more negative charges than the enzyme‐protonated inhibitor complexes, the δ value of 0.15 suggests that the bulkily substituted inhibitors are difficult to bind into a small acyl binding site of the enzyme, and the ψ value of −0.3 implies that the inhibitors with hydrophobic substituents resist binding to the hydrophilic acyl binding site of the enzyme. © 2005 Wiley Periodicals, Inc. J Biochem Mol Toxicol 18:353–360, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/jbt.20045