Comparative Sensitivity of Human Acetylcholinesterase to in vitro Inhibition by Synthetic Analogues of Phosphoramidate Compounds

Abstract

Using phosphoryl chloride as a substrate, some phosphoramidate derivatives with the general formula (R₁)(O)PCl(R₂); [R₁ = NMe₂, OC₆H₅, OC₆H₄CH₃ and R₂ = N(CH₂C₆H₅)(CH₃), N(CH₂C₆H₅)(C₂H₅)] was prepared and characterized by ¹H, ³¹P and ¹³C NMR and IR spectroscopy and elemental analysis. Biochemical studies conducted to evaluation of sensitivities of human acetylcholinesterase to inhibition of these compounds. Determination of human erythrocyte acetylcholinesterase (hAChE) activity was carried out according to the Ellman’s modified kinetic method. Biomolecular rate constant (k_i) of the selected compounds towards the active site of hAChE ranged between 2.4 × 10^-3 and 5.23 × 10^-1 M^-1 min^-1 and their IC₅₀ values varied from 2.33 × 10^-1 to 1.99 × 10^-3 mM. The difference in the inhibitory potency of these compounds is discussed with respect to their hydrophobicity. A comparison of the k_i and IC₅₀ values for inhibition of hAChE by these inhibitors revealed that hydrophobic, steric and electronic factor of phosphorus substituents are important in potency of inhibitory on hAChE.