Design, Synthesis, and Biological Evaluation of Coumarin Derivatives Tethered to an Edrophonium-like Fragment as Highly Potent and Selective Dual Binding Site Acetylcholinesterase Inhibitors

A large series of substituted coumarins linked through an appropriate spacer to 3-hydroxy-N,N-dimethylanilino or 3-hydroxy-N, N,N-trialkylbenzaminium moieties were synthesized and evaluated as acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitors. The highest AChE inhibitory potency in the 3-hydroxy-N, N-dimethylanilino series was observed with a 6,7-dimethoxy-3-substituted coumarin derivative, which, along with an outstanding affinity (IC50 = 0.236 nm) exhibits excellent AChE/BChE selectivity (SI > 300 000). Most of the synthesized 3-hydroxy-N, N, N-trialkylbenzaminium salts display an AChE affinity in the sub-nanomolar to picomolar range along with excellent AChE/BChE selectivities (SI values up to 138 333). The combined use of docking and molecular dynamics simulations permitted us to shed light on the observed structure-affinity and structure-selectivity relationships, to detect two possible alternative binding modes, and to assess the critical role of pi-pi stacking interactions in the AChE peripheral binding site.