Acetylcholinesterase inhibitors with a thiazolium scaffold: structural features and binding modes

Abstract

Aim. To assess the structural features of substituents and the role of a thiazolium scaffold in mechanisms of acetylcholinesterase inhibition by thiazolium salts. Results and discussion. On the basis of activities of model compounds at pH 6.5 and pH 8.0 and the results of molecular docking the binding modes of quaternized derivatives of 5-(2-hydroxyethyl)-4-methylthiazole with different substituents in position 3 and 5 were analyzed. The presence of (N)3-benzyl substituent provides the inhibitor fixation in the catalytic anionic site, whereas acyl fragments of substituents in position 5 are situated in the peripheral anionic site. Logarithms of ІС50 values of the thiazolium inhibitors, except for the compounds containing O-acyl carbocyclic groups, linearly depend on the calculated docking energies in case of a thiazolium, ion as well as a neutral tetrahedral intermediate of the thiazolium ring opening. Experimental part. Thiazolium salts were synthesized by the known methods. The activity of acetylcholinesterase was studied by Ellman’s method. Molecular docking to the active site of acetylcholinesterase was performed using an AutoDock 4.2 program. Conclusions. Structural fragments of substituents in positions 3 and 5 of the heterocyclic scaffold provide binding of the inhibitor in the catalytic anionic site and the peripheral anionic site of acetylcholinesterase, respectively. The heterocyclic scaffold can be bound to the enzyme as a thiazolium ion or a neutral tetrahedral intermediate of the ring opening reaction.

Keywords

• thiazolium salts
• acetylcholinesterase
• molecular docking