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

Abstract

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 (IC(50)=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.

Discovery of a Potent and Selective Hetero‐Bivalent AChE Inhibitor via Bioisosteric Replacement

“…Preliminary results confirmed [12] the tetramethylene linker as the optimal spacer between the two moieties interacting at the catalytic and the peripheral binding site (PAS) of AChE. Then, our attention was focused on the 7-substituted-1,4-dimethylquinolin-2(1H)-one derivatives 1 and 2 ( Figure 3) as they returned the highest rank in docking experiments conducted on the five virtual candidates substituted at the positions 3-, 5-, 6-, 7-and 8-of the 1,4-dimethylquinolin-2(1H)-one scaffold.…”

“…The obtained binding mode matched nicely the one already described in our recent investigations on the corresponding series of coumarin derivatives. [12] Very similar considerations can be extended also to the corresponding QAS candidate compound 2.…”

“…[11] The reference molecular series for the development of the present work was constituted by a number of novel, highly potent AChE inhibitors with a potency reaching the sub-nanomolar range and an excellent selectivity over butyrylcholinesterase (BChE). [12] As described in the literature, [12] a brick-based approach was undertaken for assembling, via a proper sized linker, two weak AChE bioactive fragments (i.e., an edrophonium-like and a coumarin moiety) addressing the catalytic and peripheral AChE binding sites, respectively. The fundamental structural difference between AChE and BChE enzymes is that in the latter the peripheral anionic site (PAS) is missing and this proved to be relevant for the modulation of molecular selectivity.…”

“…[15] This rational design led to the synthesis of the 3-[4-(3-dimethylamino-5-hydroxy-phenoxy)-butoxy]-6,7-dimethoxy-chromen-2-one that along with a very high affinity toward AChE (IC 50 = 0.23 nM) exhibited also an excellent selectivity over BChE (309 000-fold). [12] Interestingly, a recent study [12] based on molecular dynamics elucidated the reason of such an impressive potency and selectivity and, more importantly, indicated a key role of the two methoxy groups at positions 6-and 7-of the coumarin ring for an efficient interaction at the PAS of AChE.…”

“…Inhibition data of the 1,4-dimethylquinolin-2(1H)-one derivatives 1 and 2 and, in parenthesis, of the corresponding 4-methylcoumarin analogues. [12] Inhibition data are expressed as IC 50 (nM) or as percentage of inhibition at 10 mM (relative SEM < 10 %, experiments in triplicate). …”