Phenoxyethyl Piperidine/Morpholine Derivatives as PAS and CAS Inhibitors of Cholinesterases: Insights for Future Drug Design

Yaghoub Pourshojaei,Zahra Haghighijoo,Ardavan Abiri,Najmeh Edraki,Khalil Eskandari,Ali Asadipour

doi:10.1038/s41598-019-56463-2

Yaghoub Pourshojaei, Zahra Haghighijoo + Show 4 more

Open Access

https://doi.org/10.1038/s41598-019-56463-2

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Abstract

Acetylcholinesterase (AChE) catalyzes the conversion of Aβ peptide to its aggregated form and the peripheral anionic site (PAS) of AChE is mainly involved in this phenomenon. Also catalytic active site (CAS) of donepezil stimulates the break-down of acetylcholine (ACh) and depletion of ACh in cholinergic synapses are well established in brains of patients with AD. In this study, a set of compounds bearing phenoxyethyl amines were synthesized and their inhibitory activity toward electric eel AChE (eeAChE) and equine butyrylcholinesterase (eqBuChE) were evaluated. Molecular dynamics (MD) was employed to record the binding interactions of best compounds against human cholinesterases (hAChE and hBuChE) as well as donepezil as reference drug. In vitro results revealed that compound 5c is capable of inhibiting eeAChE activity at IC50 of 0.50 µM while no inhibitory activity was found for eqBuChE for up to 100 µM concentrations. Compound 5c, also due to its facile synthesis, small structure and high selectivity for eeAChE would be very interesting candidate in forthcoming studies. The main interacting parts of compound 5c and compound 7c (most potent eeAChE and eqBuChE inhibitors respectively) with receptors which confer selectivity for AChE and BuChE inhibition were identified, discussed, and compared with donepezil’s interactions. Also during MD simulation it was discovered for the first time that binding of substrates like donepezil to dual CAS and PAS or solely CAS region might have a suppressive impact on 4-α-helical bundles near the tryptophan amphiphilic tetramerization (WAT) domain of AChE and residues which are far away from AChE active site. The results proposed that residues involved in donepezil interactions (Trp86 and Phe295) which are located in CAS and mid-gorge are the mediator of conformational changes in whole protein structure.

Highlights

Acetylcholinesterase (AChE) catalyzes the conversion of Aβ peptide to its aggregated form and the peripheral anionic site (PAS) of AChE is mainly involved in this phenomenon
The results of our in vitro studies were significant considering that we identified a small molecule lead-like structure for eel AChE (eeAChE), which was highly selective for eeAChE and was capable of undergoing further chemical reactions with other nucleophiles to provide a more diverse set of chemicals
Even though compound 5c indicated an IC50 comparable with some mixed-type inhibitors discovered previously, its 53 nM Ki value, introduced this compound as one of the most potent mixed-type inhibitors discovered for AChE

Summary

Introduction

Acetylcholinesterase (AChE) catalyzes the conversion of Aβ peptide to its aggregated form and the peripheral anionic site (PAS) of AChE is mainly involved in this phenomenon. Catalytic active site (CAS) of donepezil stimulates the break-down of acetylcholine (ACh) and depletion of ACh in cholinergic synapses are well established in brains of patients with AD. It is suggested that PAS can facilitate the movement of ACh toward CAS, and leads to boost the catalytic performance of AChE. Dual inhibition of PAS and CAS of cholinesterases, restrain the rate-limiting step (diffusion of ACh to CAS), and reduce the turnover number (Kcat) of enzymes[13]. The behavior of AChE and BuChE is more perplexing when previous surveys suggest that binding of some substrates to PAS at low pH might activate the function of cholinesterases via a PAS-induced conformational change[15]. Molecular dynamics studies with sufficient simulation time have been recommended as reliable tools in assessment of these strange or obscure conformational changes[16,17,18]

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