Novel donepezil-like N -benzylpyridinium salt derivatives as AChE inhibitors and their corresponding dihydropyridine “bio-oxidizable” prodrugs: Synthesis, biological evaluation and structure-activity relationship

Synthesis and evaluation of lipoic acid - donepezil hybrids for Alzheimer's disease using a straightforward strategy

Alzheimer's disease is associated with a progressive loss of neurons and synaptic connections in the cholinergic system. Oxidative stress contributes to neuronal damages and to the development of amyloid plaques and neurofibrillary tangles. Therefore, antioxidants have been widely studied to mitigate the progression of Alzheimer's disease, and among these, lipoic acid has demonstrated a neuroprotective effect. Here, we present the synthesis, the molecular modelling, and the evaluation of lipoic acid-donepezil hybrids based on O-desmethyldonepezil. As compounds 5 and 6 display a high inhibition of acetylcholinesterase (IC50 = 7.6 nM and 9.1 nM, respectively), selective against butyrylcholinesterase, and a notable neuroprotective effect, slightly better than that of lipoic acid, the present study suggests that O-desmethyldonepezil could serve as a platform for the straightforward design of donepezil hybrids.

Synthesis of 4-Alkylated 1,4-Dihydropyridines: Fe(II)-Mediated Oxidative Cascade Cyclization Reaction of Cyclic Ethers with Enaminones

Syntheses of highly functionalized 4-alkylated 1,4-dihydropyridines (1,4-DHPs) from cyclic ethers and enaminones via iron(II)-mediated oxidative free radical cascade C(sp3)-H bond functionalization/C(sp3)-O bond cleavage/cyclization reaction have been first developed. This novel synthetic strategy offers an alternative method for the construction of 1,4-DHPs by using esters as the C4 sources, as well as expands the application of ethers in heterocycle synthesis.

Recent advance on carbamate-based cholinesterase inhibitors as potential multifunctional agents against Alzheimer's disease

Alzheimer's disease (AD), as the fourth leading cause of death among the elderly worldwide, has brought enormous challenge to the society. Due to its extremely complex pathogeneses, the development of multi-target directed ligands (MTDLs) becomes the major strategy for combating AD. Carbamate moiety, as an essential building block in the development of MTDLs, exhibits structural similarity to neurotransmitter acetylcholine (ACh) and has piqued extensive attention in discovering multifunctional cholinesterase inhibitors. To date, numerous preclinical studies demonstrate that carbamate-based cholinesterase inhibitors can prominently increase the level of ACh and improve cognition impairments and behavioral deficits, providing a privileged strategy for the treatment of AD. Based on the recent research focus on the novel cholinesterase inhibitors with multiple biofunctions, this review aims at summarizing and discussing the most recent studies excavating the potential carbamate-based MTDLs with cholinesterase inhibition efficacy, to accelerate the pace of pleiotropic cholinesterase inhibitors for coping AD.

Advances in prodrug design for Alzheimer's Disease: the state of the art

INTRODUCTION

: Alzheimer's disease (AD) is the most common cause of dementia with a memory loss and other cognitive abilities and is a complex and multifactorial neurodegenerative disease that remains today a challenge for drug discovery. Like many pathologies of the central nervous system, one of the first hurdles is the development of a compound with a sufficient brain exposure to ensure a potential therapeutic benefit. In this direction, the development of prodrugs has been an intense field of research in the last years.

AREAS COVERED

: Two main strategies of prodrugs development are analysed in this review. First, the application of the classical modulation of an active compound to incorporate a drug carrier or to prepare bioprecursor has been exemplified in the field of AD. This approach has led to several examples engaged in the clinical trials. In a second chapter, a series of innovative prodrugs based on a polypharmacological approach is described to take into account the complexity of AD.

EXPERT OPINION

: In the past 10 years, at least 6 prodrugs have been approved by the FDA for the treatment of central nervous system pathologies. Most of them have been developed in order to improve membrane permeability of the parent drugs. Facing the limitation of Alzheimer's disease drug discovery, the development of prodrugs will likely play a central role in the next years. Indeed, beside addressing the challenge of distribution, prodrug could also tackle the complex multifactorial origin of the disease with the rise of innovative pleiotropic prodrugs.

Synthesis, kinetic evaluation and molecular docking studies of donepezil-based acetylcholinesterase inhibitors

In an effort to develop new therapeutic agents to treat Alzheimer's disease, a series of donepezil-based analogs were designed, synthesized using an environmentally friendly route, and biologically evaluated for their inhibitory activity against electric eel acetylcholinesterase (AChE) enzyme. In vitro studies revealed that the phenyl moiety of donepezil can be successfully replaced with a pyridine ring leading to equally potent inhibitors of electric eel AChE. Further kinetic evaluations of the most potent inhibitor showed a dual-binding (mixed inhibition) mode, similar to donepezil. Molecular modeling studies suggest that several additional residues could be involved in the binding of this inhibitor in the human AChE enzyme active site compared to donepezil.

Interest of novel N-alkylpyridinium-indolizine hybrids in the field of Alzheimer's disease: Synthesis, characterization and evaluation of antioxidant activity, cholinesterase inhibition, and amyloid fibrillation interference

A small library of molecules combining indolizine and N-alkyl pyridinium was synthesized and evaluated in a multi-target-directed-ligand strategy for Alzheimer's disease (AD) treatment. The new compounds were classified in three series depending on the number of methylene residues linking the two heterocycles (Ind-PyCx with x = 0, 2 or 3). The molecules were synthesized from the corresponding bis-pyridines by two-step formation of the indolizine core including mono-alkylation of pyridine and 1,3-dipolar cycloaddition with an alkylpropiolate. Their activities against AD's key-targets were evaluated in vitro: acetyl- and butyrylcholinesterase (AChE and BChE) inhibition, antioxidant properties and inhibition of amyloid fibril formation. None of the three series showed significant activities against all the targets. The Ind-PyC2 and Ind-PyC3 series are active on eeAChE and hAChE (µM IC₅₀ values). Most of the positively charged molecules from these two series also appeared active against eqBChE, however they lost their activity on hBChE. Comparative molecular modeling of 13 and 15 docked in hAChE and hBChE highlighted the importance of the substituent (p-methoxybenzoyl or methyloxycarbonyl, respectively) located on the indolizine C-3 for the binding. The larger molecule 13 fits more tightly at the active site of the two enzymes than 15 that shows a larger degree of freedom. The Ind-PyC2 and Ind-PyC3 hybrids displayed some antioxidant activity when tested at 750 µg/mL (up to 95% inhibition of DPPH radical scavenging for 10). In both series, most hybrids were also able to interact with amyloid fibers, even if the inhibitory effect was observed at a high 100 µM concentration. The Ind-PyC0 molecules stand out completely due to their spectroscopic properties which prevent their evaluation by Ellman's and ThT assays. However, these molecules showed interesting features in the presence of preformed fibers. In particular, the strong increase in fluorescence of 3 in the presence of amyloid fibers is very promising for its use as a fibrillation fluorescent reporter dye.

Investigation of Experimental and In Silico Physicochemical Properties of Thiazole-Pyridinium Anti-Acetylcholinesterase Derivatives with Potential Anti-Alzheimer’s Activity

Background: Physicochemical properties play important role in fundamental issues like absorption and distribution of pharmaceuticals to the target tissue. This is particularly importantfor drugs acting in central nervous system (CNS). In this study, physicochemical properties of previously synthesized thiazole-pyridinium derivatives with anti-acetylcholinesterase activity and possible anti-Alzheimer effect were studied. Methods: Partition coefficient (n-octanol/water) and chromatographic Rf values for the studied compounds were determined using shake flask and high performance thin layer chromatography(HPTLC) methods, respectively. Different druglikeness properties of the compounds were also calculated using available software and web-servers. Results: The experimentally determined logarithm of partition coefficients (log P) for the studied compounds were in the range of -1.00 to -0.38. The Rf values for the studied compounds under the applied chromatographic condition ranged between 0.38 to 0.58. Moreover, calculated physicochemical properties, and druglikeness scores of the studied thiazole-pyridiniumderivatives and matching piperidine analogues were predicted. Furthermore, some ADMETfeatures of studied compounds like toxicity and metabolism by CYP450 (2C9, 2D6, 3A4, 1A2and 2C19) enzymes were predicted. Conclusion: The ranges of experimental and calculated LogP values for the studied thiazolepyridinumswere close. However, the determined Rf values showed relatively better correlation to the predicted LogP values indicating the suitability of used chromatographic method for comparing the lipophilicity of the positively charged pyridinium derivatives. The studied compounds were predicted to pass GI membrane and reach the CNS where they can exert their effects. In silico studies indicate that the piperidine counterparts of the studied thiazolepyridiniumsmay represent anti-Alzheimer agents with improved druglikeness properties.

Design, synthesis and biological evaluation of 2,3-dihydro-5,6-dimethoxy-1H-inden-1-one and piperazinium salt hybrid derivatives as hAChE and hBuChE enzyme inhibitors

2,3-Dihydro-5,6-dimethoxy-2-[4-(4-alkyl-4-methylpiperazinium-1-yl)benzylidine]-1H-inden-1-one halide salt derivatives as a novel donepezil hybrid analogs with the property of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzyme inhibition were designed and synthesized via N-alkylation reaction of 2,3-dihydro-5,6-dimethoxy-2-[4-(4-methylpiperazin-1-yl)benzylidene]-1H-inden-1-one with some alkyl halides. Biological tests demonstrated that most of the synthesized compounds have moderate to good inhibitory activities effect on cholinesterase enzymes. Among them, 10e showed the best profile as a selected compound for inhibition of hAChE (IC50 = 0.32) and hBuChE (IC50 = 0.43 μM) enzymes. Kinetic analysis and molecular docking led to a better understanding of this compound. Kinetic studies disclosed that 10e inhibited acetylcholinesterase in mixed-type and butyrylcholinesterase in non-competitive type. The toxicity results showed that 10e is less toxic than donepezil and has better inhibitory activity against hBuChE when compared to donepezil or Galantamine. Other performed experiments revealed that 10e has an anti-β amyloid effect which is capable of reducing ROS, LDH and MDA also possing positive effect on TAC. On the other hand, it has shown a good anti-inflammation effect.

Four-Component Fusion Protocol with NiO/ZrO2 as a Robust Recyclable Catalyst for Novel 1,4-Dihydropyridines

Nickel oxide loaded on zirconia (NiO/ZrO₂) as an expedient catalyst is reported for the synthesis of 18 unsymmetrical 1,4-dihydropyridine derivatives. The Lewis acidic nature of the catalyst proved an excellent choice for the one-pot, four-component fusion reaction with excellent yields of 89-98% and a completion time of 20-45 min. Mechanistic studies show that enamine and imine functionalities are the two possible pathways for the formation of 1,4-dihydropyridines with high selectivity. Crystal structures of two novel compounds (5a, 5c) were reported. The catalyst demonstrated reusability up to six cycles. The reaction at room temperature and ethanol as a solvent make this protocol green and economical.

Overview of Recent Strategic Advances in Medicinal Chemistry

Introducing novel strategies, concepts, and technologies that speed up drug discovery and the drug development cycle is of great importance both in the highly competitive pharmaceutical industry as well as in academia. This Perspective aims to present a "big-picture" overview of recent strategic innovations in medicinal chemistry and drug discovery.

Design, Synthesis, and In Vitro Biological Activities of a Bio-Oxidizable Prodrug to Deliver Both ChEs and DYRK1A Inhibitors for AD Therapy

Despite their side effects, cholinesterase (ChE) inhibitors remain the only approved drugs to treat Alzheimer's disease patients, along with the N-methyl-d-aspartate (NMDA) receptor antagonist memantine. In the last few years, the dual-specificity tyrosine phosphorylation-regulated kinase 1A (DYRK1A) has also been studied as a promising target for the development of new drugs for this pathology. In this context, and based on our previous characterization of bio-oxidizable prodrugs of potent acetylcholinesterase (AChE) inhibitors, we envisioned a strategy involving the synthesis of a bio-oxidizable prodrug of both ChE and DYRK1A inhibitors. To this end, we fixed our interest on a known potent inhibitor of DYRK1A, namely INDY. The designed prodrug of both ChE and DYRK1A inhibitors was successfully synthesized, connecting both inhibitors by a carbonate link. This prodrug and its corresponding drug were then evaluated as ChEs and DYRK1A inhibitors. Remarkably, in vitro results were in accordance with the starting hypothesis, showing a relative inactivity of the prodrug against DYRK1A and ChEs and a potent inhibition of ChEs by the oxidized form. Molecular docking and kinetic studies of ChE inhibition by the active compound are also discussed in this report.

Access to Highly Enantioenriched Donepezil-like 1,4-Dihydropyridines as Promising Anti-Alzheimer Prodrug Candidates via Enantioselective Tsuji Allylation and Organocatalytic Aza-Ene-Type Domino Reactions

This work aims at exploiting both the enantioselective Tsuji allylation of allyl carbonate 6 and an organocatalytic aza-ene-type domino reaction between enal 3a and β-enaminone 4a to develop a straightforward access to all of the four possible stereoisomers of a donepezil-like 1,4-dihydropyridine 1a (er up to 99.5:0.5; overall yield up 64%), an anti-Alzheimer's prodrug candidate. This strategy was extended to the preparation of other enantioenriched 1,4-dihydropyridines 1b-i (eight examples), highlighting its potential in the development of these chiral AChE inhibitors.

Structure-based design, synthesis, and evaluation of structurally rigid donepezil analogues as dual AChE and BACE-1 inhibitors

A new series of structurally rigid donepezil analogues was designed, synthesized and evaluated as potential multi-target-directed ligands (MTDLs) against neurodegenerative diseases. The investigated compounds 10-13 displayed dual AChE and BACE-1 inhibitory activities in comparison to donepezil, the FDA-approved drug. The hybrid compound 13 bearing 2-aminoquinoline scaffold exhibited potent AChE inhibition (IC₅₀ value of 14.7 nM) and BACE-1 inhibition (IC₅₀ value of 13.1 nM). Molecular modeling studies were employed to reveal potential dual binding mode of 13 to AChE and BACE-1. The effect of the investigated compounds on the viability of SH-SY5Y neuroblastoma cells and their ability to cross the blood-brain barrier (BBB) in PAMPA-BBB assay were further studied.

Design and synthesis of donepezil analogues as dual AChE and BACE-1 inhibitors

Multi-target-directed ligands (MTDLs) centered on β-secretase 1 (BACE-1) inhibition are emerging as innovative therapeutics in addressing the complexity of neurodegenerative diseases. A new series of donepezil analogues was designed, synthesized and evaluated as MTDLs against neurodegenerative diseases. Profiling of donepezil, a potent acetylcholinesterase (hAChE) inhibitor, into BACE-1 inhibition was achieved through introduction of backbone amide linkers to the designed compounds which are capable of hydrogen-bonding with BACE-1 catalytic site. In vitro assays and molecular modeling studies revealed the dual mode of action of compounds 4-6 against hAChE and BACE-1. Notably, compound 4 displayed potent hAChE inhibition (IC₅₀ value of 4.11 nM) and BACE-1 inhibition (IC₅₀ value of 18.3 nM) in comparison to donepezil (IC₅₀ values of 6.21 and 194 nM against hAChE and BACE-1, respectively). Moreover, 4 revealed potential metal chelating property, low toxicity on SH-SY5Y neuroblastoma cells and ability to cross the blood-brain barrier (BBB) in PAMPA-BBB assay which renders 4 a potential lead for further optimization of novel small ligands for the treatment of Alzheimer's disease.

Kinetic and structural studies on the interactions of Torpedo californica acetylcholinesterase with two donepezil-like rigid analogues

Acetylcholinesterase inhibitors were introduced for the symptomatic treatment of Alzheimer’s disease (AD). Among the currently approved inhibitors, donepezil (DNP) is one of the most preferred choices in AD therapy. The X-ray crystal structures of Torpedo californica AChE in complex with two novel rigid DNP-like analogs, compounds 1 and 2, have been determined. Kinetic studies indicated that compounds 1 and 2 show a mixed-type inhibition against TcAChE, with K_i values of 11.12 ± 2.88 and 29.86 ± 1.12 nM, respectively. The DNP rigidification results in a likely entropy-enthalpy compensation with solvation effects contributing primarily to AChE binding affinity. Molecular docking evidenced the molecular basis for the binding of compounds 1 and 2 to the active site of β-secretase-1. Overall, these simplified DNP derivatives may represent new structural templates for the design of lead compounds for a more effective therapeutic strategy against AD by foreseeing a dual AChE and BACE-1 inhibitory activity.