Neuroprotective Potential of Synthetic Mono-Carbonyl Curcumin Analogs Assessed by Molecular Docking Studies.

Cognitive decline in dementia is associated with deficiency of the cholinergic system. In this study, five mono-carbonyl curcumin analogs were synthesized, and on the basis of their promising in vitro anticholinesterase activities, they were further investigated for in vivo neuroprotective and memory enhancing effects in scopolamine-induced amnesia using elevated plus maze (EPM) and novel object recognition (NOR) behavioral mice models. The effects of the synthesized compounds on the cholinergic system involvement in the brain hippocampus and their binding mode in the active site of cholinesterases were also determined. Compound h2 (p < 0.001) and h3 (p < 0.001) significantly inhibited the cholinesterases and reversed the effects of scopolamine by significantly reducing TLT (p < 0.001) in EPM, while (p < 0.001) increased the time exploring the novel object. The % discrimination index (DI) was significantly increased (p < 0.001) in the novel object recognition test. The mechanism of cholinesterase inhibition was further validated through molecular docking study using MOE software. The results obtained from the in vitro, in vivo and ex vivo studies showed that the synthesized curcumin analogs exhibited significantly higher memory-enhancing potential, and h3 could be an effective neuroprotective agent. However, more study is suggested to explore its exact mechanism of action.

Tacrine - Benzothiazoles: Novel class of potential multitarget anti-Alzheimers drugs dealing with cholinergic, amyloid and mitochondrial systems.

A series of tacrine - benzothiazole hybrids incorporate inhibitors of acetylcholinesterase (AChE), amyloid ß (Aß) aggregation and mitochondrial enzyme ABAD, whose interaction with Aß leads to mitochondrial dysfunction, into a single molecule. In vitro, several of 25 final compounds exerted excellent anti-AChE properties and interesting capabilities to block Aß aggregation. The best derivative of the series could be considered 10w that was found to be highly potent and selective towards AChE with the IC50 value in nanomolar range. Moreover, the same drug candidate exerted absolutely the best results of the series against ABAD, decreasing its activity by 23% at 100 µM concentration. Regarding the cytotoxicity profile of highlighted compound, it roughly matched that of its parent compound - 6-chlorotacrine. Finally, 10w was forwarded for in vivo scopolamine-induced amnesia experiment consisting of Morris Water Maze test, where it demonstrated mild procognitive effect. Taking into account all in vitro and in vivo data, highlighted derivative 10w could be considered as the lead structure worthy of further investigation.

Rapid and efficient synthesis of a novel cholinergic muscarinic M1 receptor positive allosteric modulator using flash chemistry.

Continuous flow-flash synthesis of a 2-bromobenzaldehyde derivative 18 as a key intermediate of a novel cholinergic muscarinic M1 positive allosteric modulator 1 bearing an isoindolin-1-one ring system as a pharmacophore has been achieved using flow microreactors through selective I/Li exchange of 1-bromo-2-iodobenzene derivative 17 with BuLi and subsequent formylation at -40 °C of the highly reactive 2-bromophenyllithium intermediate using DMF, which is difficult to achieve by a conventional batch process due to the conversion of the highly reactive 2-bromophenyllithium intermediate into benzyne even at -78 °C. Late-stage cyclization to give the isoindolin-1-one ring system, through reductive amination of 18 followed by palladium-catalyzed carbonylation with carbon monoxide and intramolecular cyclization, efficiently afforded 1 for its further research and development.

Donepezil-butylated hydroxytoluene (BHT) hybrids as Anti-Alzheimer's disease agents with cholinergic, antioxidant, and neuroprotective properties.

The multifactorial nature of Alzheimer's disease (AD) calls for the development of multitarget agents addressing key pathogenic processes. A novel family of donepezil-butylated hydroxytoluene (BHT) hybrids were designed, synthesized and evaluated as multifunctional ligands against AD. The optimal compound 7d displayed a balanced multifunctional profile covering an intriguing acetylcholinesterase (AChE) inhibition (IC50, 0.075 µM for eeAChE and 0.75 µM for hAChE) and Monoamine oxidase B (MAO-B) inhibition (IC50, 7.4 µM for hMAO-B), excellent antioxidant activity (71.7 µM of IC50 by DPPH method, 0.82 and 1.62 trolox equivalent by ABTS method and ORAC method respectively), and inhibitory effects on self-induced, hAChE-induced Aß aggregation. Moreover, 7d possessed neuroprotective potency against H2O2-induced oxidative damage on PC12 cells and Lipopolysaccharides (LPS)-stimulated inflammation on BV2 cells. Compound 7d was capable of penetrating BBB and presented good liver microsomal metabolic stability. Importantly, compound 7d could dose-dependently reverse scopolamine-induced memory deficit in mice without acute toxicity. Taken together, those outstanding results highlight the donepezil-BHT hybrid 7d as a promising prototype in the research of innovative compound for AD.

Discovery and Optimization of Potent and CNS Penetrant M5-Preferring Positive Allosteric Modulators Derived from a Novel, Chiral N-(Indanyl)piperidine Amide Scaffold.

The pharmacology of the M5 muscarinic acetylcholine receptor (mAChR) is the least understood of the five mAChR subtypes due to a historic lack of selective small molecule tools. To address this shortcoming, we have continued the optimization effort around the prototypical M5 positive allosteric modulator (PAM) ML380 and have discovered and optimized a new series of M5 PAMs based on a chiral N-(indanyl)piperidine amide core with robust SAR, human and rat M5 PAM EC50 values <100 nM and rat brain/plasma Kp values of ∼0.40. Interestingly, unlike M1 and M4 PAMs with unprecedented mAChR subtype selectivity, this series of M5 PAMs displayed varying degrees of PAM activity at the other two natively Gq-coupled mAChRs, M1 and M3, yet were inactive at M2 and M4.

Novel cinnamamide-dibenzylamine hybrids: Potent neurogenic agents with antioxidant, cholinergic, and neuroprotective properties as innovative drugs for Alzheimer's disease.

By using fragments endowed with interesting and complementary properties for the treatment of Alzheimer's disease (AD), a novel series of cinnamamide-dibenzylamine hybrids have been designed, synthesized, and evaluated biologically. In vitro assay indicated that most of the target compounds exhibited a significant ability to inhibit ChEs, strong potency inhibitory of self-induced ß-amyloid (Aß) aggregation and to act as potential antioxidants and biometal chelators. A Lineweaver-Burk plot and molecular modeling study showed that compound 7f targeted both the CAS and PAS of AChE. In addition, compound 7f could chelate metal ions, reduce PC12 cells death induced by oxidative stress and penetrate the blood-brain barrier (BBB). Overall, all of these outstanding in vitro results in combination with promising in vivo outcomes highlighted derivative 7f as the lead structure worthy of further investigation.

One-pot synthesis of tetrazole-1,2,5,6-tetrahydronicotinonitriles and cholinesterase inhibition: Probing the plausible reaction mechanism via computational studies.

In the present study, one-pot synthesis of 1H-tetrazole linked 1,2,5,6-tetrahydronicotinonitriles under solvent-free conditions have been carried out in the presence of tetra-n-butyl ammonium fluoride trihydrated (TBAF) as catalyst and solvent. Computational studies have been conducted to elaborate two plausible mechanistic pathways of this one-pot reaction. Moreover, the synthesized compounds were screened for cholinesterases (acetylcholinesterase and butyrylcholinesterase) inhibition which are consider to be major malefactors of Alzheimer's disease (AD) to find lead compounds for further research in AD therapy.

Selective activation of M4 muscarinic acetylcholine receptors reverses MK-801-induced behavioral impairments and enhances associative learning in rodents.

Positive allosteric modulators (PAMs) of the M4 muscarinic acetylcholine receptor (mAChR) represent a novel approach for the treatment of psychotic symptoms associated with schizophrenia and other neuropsychiatric disorders. We recently reported that the selective M4 PAM VU0152100 produced an antipsychotic drug-like profile in rodents after amphetamine challenge. Previous studies suggest that enhanced cholinergic activity may also improve cognitive function and reverse deficits observed with reduced signaling through the N-methyl-d-aspartate subtype of the glutamate receptor (NMDAR) in the central nervous system. Prior to this study, the M1 mAChR subtype was viewed as the primary candidate for these actions relative to the other mAChR subtypes. Here we describe the discovery of a novel M4 PAM, VU0467154, with enhanced in vitro potency and improved pharmacokinetic properties relative to other M4 PAMs, enabling a more extensive characterization of M4 actions in rodent models. We used VU0467154 to test the hypothesis that selective potentiation of M4 receptor signaling could ameliorate the behavioral, cognitive, and neurochemical impairments induced by the noncompetitive NMDAR antagonist MK-801. VU0467154 produced a robust dose-dependent reversal of MK-801-induced hyperlocomotion and deficits in preclinical models of associative learning and memory functions, including the touchscreen pairwise visual discrimination task in wild-type mice, but failed to reverse these stimulant-induced deficits in M4 KO mice. VU0467154 also enhanced the acquisition of both contextual and cue-mediated fear conditioning when administered alone in wild-type mice. These novel findings suggest that M4 PAMs may provide a strategy for addressing the more complex affective and cognitive disruptions associated with schizophrenia and other neuropsychiatric disorders.

Bioisosteric replacement and related analogs in the design, synthesis and evaluation of ligands for muscarinic acetylcholine receptors.

Previous structure-activity relationship studies involving a series of lactone-based muscarinic ligands identified a lead compound containing a diphenylmethylpiperazine moiety (4; IC50 = 340 nM). The purpose of the present work is to investigate 1,3-benzodioxoles, 4,4-diethyl substituted tetrahydrofurans, 5-substituted oxazolidinones and chromones as bioisosteric replacements for the lactone ring in a novel series of muscarinic ligands. The approach provided compounds with improved % inhibition values and identified a non-selective muscarinic ligand with an IC50 value of 280 nM. The structure-activity relationship for this new series will be discussed. Selected compounds were evaluated in preliminary assays for subtype selectivity and were found to be non-selective.

Generation of candidate ligands for nicotinic acetylcholine receptors via in situ click chemistry with a soluble acetylcholine binding protein template.

Nicotinic acetylcholine receptors (nAChRs), which are responsible for mediating key physiological functions, are ubiquitous in the central and peripheral nervous systems. As members of the Cys loop ligand-gated ion channel family, neuronal nAChRs are pentameric, composed of various permutations of α (α2 to α10) and ß (ß2 to ß4) subunits forming functional heteromeric or homomeric receptors. Diversity in nAChR subunit composition complicates the development of selective ligands for specific subtypes, since the five binding sites reside at the subunit interfaces. The acetylcholine binding protein (AChBP), a soluble extracellular domain homologue secreted by mollusks, serves as a general structural surrogate for the nAChRs. In this work, homomeric AChBPs from Lymnaea and Aplysia snails were used as in situ templates for the generation of novel and potent ligands that selectively bind to these proteins. The cycloaddition reaction between building-block azides and alkynes to form stable 1,2,3-triazoles was used to generate the leads. The extent of triazole formation on the AChBP template correlated with the affinity of the triazole product for the nicotinic ligand binding site. Instead of the in situ protein-templated azide-alkyne cycloaddition reaction occurring at a localized, sequestered enzyme active center as previously shown, we demonstrate that the in situ reaction can take place at the subunit interfaces of an oligomeric protein and can thus be used as a tool for identifying novel candidate nAChR ligands. The crystal structure of one of the in situ-formed triazole-AChBP complexes shows binding poses and molecular determinants of interactions predicted from structures of known agonists and antagonists. Hence, the click chemistry approach with an in situ template of a receptor provides a novel synthetic avenue for generating candidate agonists and antagonists for ligand-gated ion channels.

Synthesis and in vitro evaluation of 7-methoxy-N-(pent-4-enyl)-1,2,3,4-tetrahydroacridin-9-amine-new tacrine derivate with cholinergic properties.

Cholinesterase inhibitors are, so far, the only successful strategy for the symptomatic treatment of Alzheimer's disease. Tacrine (THA) is a potent acetylcholinesterase inhibitor that was used in the treatment of Alzheimer's disease for a long time. However, the clinical use of THA was hampered by its low therapeutic index, short half-life and liver toxicity. 7-Methoxytacrine (7-MEOTA) is equally pharmacological active compound with lower toxicity compared to THA. In this Letter, the synthesis, biological activity and molecular modelling of elimination by-product isolated during synthesis of 7-MEOTA based bis-alkylene linked compound is described.

Discovery of a selective allosteric M1 receptor modulator with suitable development properties based on a quinolizidinone carboxylic acid scaffold.

One approach to ameliorate the cognitive decline in Alzheimer's disease (AD) has been to restore neuronal signaling from the basal forebrain cholinergic system via the activation of the M(1) muscarinic receptor. A number of nonselective M(1) muscarinic agonists have previously shown positive effects on cognitive behaviors in AD patients, but were limited due to cholinergic adverse events thought to be mediated by the activation of the M(2) to M(5) subtypes. One strategy to confer selectivity for M(1) is the identification of positive allosteric modulators, which would target an allosteric site on the M(1) receptor rather than the highly conserved orthosteric acetylcholine binding site. Quinoline carboxylic acids have been previously identified as highly selective M(1) positive allosteric modulators with good pharmacokinetic and in vivo properties. Herein is described the optimization of a novel quinolizidinone carboxylic acid scaffold with 4-cyanopiperidines being a key discovery in terms of enhanced activity. In particular, modulator 4i gave high plasma free fractions, enhanced central nervous system (CNS) exposure, was efficacious in a rodent in vivo model of cognition, and afforded good physicochemical properties suitable for further preclinical evaluation.

DFT calculation of four new potential agents muscarinic of bispyridinium type: structure, synthesis, biological activity, hydration, and relations with the potents W84 and DUO-3O.

Four new potential agents muscarinic (allosteric modulators) were synthesized and studied by using the B3LYP density functional method. The optimum conformation and geometry structure of these compounds were determined and analyzed. Solvent effects were considered including a variable number (1-15) of explicit water molecules surrounding the compound in order to simulate the first hydration shell, as well as using the Tomasi's polarized continuum model (PCM). A similar simultaneous analysis of the potents W84 and DUO-3O allosteric modulator of muscarinic receptors was also carried out. The effect of the hydration on the total atomic charges and several intermolecular distances of interest were also discussed. The biological activity against acetylcholine of our four synthesized bispyridinium salts was determined. Relationships/tendencies structure-activity were established. Several general conclusions were underlined.

A step further towards multitarget drugs for Alzheimer and neuronal vascular diseases: targeting the cholinergic system, amyloid-ß aggregation and Ca(2+) dyshomeostasis.

Alzheimer's disease (AD) is the most common neurodegenerative disease, affecting mainly elderly people. The reasons why AD occurs are complex and multifactorial and several biochemical targets are thought to play a key role in its progress and development. This fact has led to the development of a multitarget-directed ligand strategy as a logical approach for designing a suitable therapy. Currently, most prescribed drugs for treating AD are acetylcholinesterase inhibitors (AChEI), although these inhibitors represent solely palliative treatment. This account will summarize our current therapeutic approach for the design of multitarget drugs primarily aimed at inhibiting AChE using the key features of tacrine, which was the first approved drug for AD treatment. Secondly, as calcium homeostasis is directly related to the cell death-survival equilibrium, suitable therapy might include an action that regulates calcium homeostasis by means of targeting voltage dependent calcium channels. It is, therefore, hoped that targeting calcium homeostasis will lead directly to the development of potential neuroprotective agents. Thus, 1,4-dihydropyridines, well-known voltage-dependent calcium channel (VDCC) ligands, will be incorporated into the new molecules as a second structural feature in order to bring about this action. As a result of this development, herein, we describe the synthetic and pharmacological profile of new [1,8]-naphthyridine analogues, which are hybrids of tacrine and 1,4-dihydropyridines. Some of our molecules have shown improved inhibitory action against cholinesterases, whilst maintaining their VDCC modulating activity, and have good characteristics as neuroprotective agents. Based on kinetic analysis of the AChE inhibition experiments, it has been shown that many of the compounds bind at the peripheral anionic site (PAS). Since the AChE PAS is linked to ß-amyloid aggregation, this would give a third biological target for further preclinical development, making these molecules highly interesting targets in the search to obtain better treatments for AD.

Multipotent drugs with cholinergic and neuroprotective properties for the treatment of Alzheimer and neuronal vascular diseases. I. Synthesis, biological assessment, and molecular modeling of simple and readily available 2-aminopyridine-, and 2-chloropyridine-3,5-dicarbonitriles.

The synthesis, molecular modeling, and pharmacological analysis of new multipotent simple, and readily available 2-aminopyridine-3,5-dicarbonitriles (3-20), and 2-chloropyridine-3,5-dicarbonitriles (21-28), prepared from 2-amino-6-chloropyridine-3,5-dicarbonitrile (1) and 2-amino-6-chloro-4-phenylpyridine-3,5-dicarbonitrile (2) is described. The biological evaluation showed that some of these molecules were modest inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), in the micromolar range. The 2-amino (3, 4), and 2-chloro derivatives 21-23, 25, 26 were AChE selective inhibitors, whereas 2-amino derivatives 5, 14 proved to be selective for BuChE. Only inhibitor 24 was equipotent for both cholinesterases. Kinetic studies on compound 23 showed that this compound is a mixed-type inhibitor of AChE showing a K(i) of 6.33 microM. No clear SAR can be obtained form these data, but apparently, compounds bearing small groups such as the N,N'-dimethylamino or the pyrrolidino, regardless of the presence of a 2-amino, or 6-chloro substituent in the pyridine ring, preferentially inhibit AChE. Molecular modeling on inhibitors 4, 5, 22, and 23 has been carried out to give a better insight into the binding mode on the catalytic active site (CAS), and peripheral anionic site (PAS) of AChE. The most important differences in the observed binding relay on the modifications of the group at C2, as the amino group forms two hydrogen bonds that direct the binding mode, while in the case of compounds with a chlorine atom, this is not possible. The neuroprotective profile of these molecules has been investigated. In the LDH test, only compounds 26, 3, 22, and 24 showed neuroprotection with values in the range 37.8-31.6% in SH-SY5Y neuroblastoma cells stressed with a mixture of oligomycin-A/rotenone, but in the MTT test only compound 17 (32.9%) showed a similar profile. Consequently, these compounds can be considered as attractive multipotent therapeutic molecules on two key pharmacological receptors playing key roles in the progress of Alzheimer, that is, cholinergic dysfunction and oxidative stress, and neuronal vascular diseases.

Peripheral site acetylcholinesterase inhibitors targeting both inflammation and cholinergic dysfunction.

The design and study of two classes of noncompetitive acetylcholinesterase inhibitors (AChEIs) which also function as NSAID prodrugs are reported. The most potent AChEIs disclosed contain an aromatic alkyl-aryl linker between an NSAID and a lipophilic choline mimic and they inhibit acetylcholinesterase (AChE) in the submicromolar range. These agents have the therapeutic potential to dually target inflammation by releasing an NSAID in vivo and activating the cholinergic anti-inflammatory pathway via cholinergic up-regulation.

Tacrine-melatonin hybrids as multifunctional agents for Alzheimer's disease, with cholinergic, antioxidant, and neuroprotective properties.

Tacrine-melatonin hybrids were designed and synthesized as new multifunctional drug candidates for Alzheimer's disease. These compounds may simultaneously palliate intellectual deficits and protect the brain against both beta-amyloid (A beta) peptide and oxidative stress. They show improved cholinergic and antioxidant properties, and are more potent and selective inhibitors of human acetylcholinesterase (hAChE) than tacrine. They also capture free radicals better than melatonin. Molecular modeling studies show that these hybrids target both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE. At sub-micromolar concentrations they efficiently displace the binding of propidium iodide from the PAS and could thus inhibit A beta peptide aggregation promoted by AChE. Moreover, they also inhibit A beta self-aggregation and display neuroprotective properties in a human neuroblastoma line against cell death induced by various toxic insults, such as A beta(25-35), H(2)O(2), and rotenone. Finally, they exhibit low toxicity and may be able to penetrate the central nervous system according to an in vitro parallel artificial membrane permeability assay for the blood-brain barrier (PAMPA-BBB).

Advances in drug discovery to assess cholinergic neurotransmission: a systematic review.

Neurotransmission is essential to physiological processes of cellular communication. The search for new molecules that may influence neurotransmission systems is an open field with possible impact on several pathophysiological conditions or diseases: Alzheimer's disease, Parkinsonism and myasthenia gravis, etc. The present review describes the most important aspects of cholinergic neurotransmission, as well as natural and synthetic compounds that, as clinical or experimental drugs, are able to influence this transmission. The pharmacological effects of substances that bind to muscarinic or nicotinic cholinergic receptors, along with their corresponding affinities will also be presented.

Effect of a M1 allosteric modulator on scopolamine-induced amnesia.

It is well accepted that acetylcholine is involved in memory and learning processes and that loss of memory is characteristic of Alzheimer's disease (AD). Several muscarinic agonists have been shown to be clinically effective in the treatment of AD. However, their use has been limited due to adverse side effects. As a result, more selective M1 agonists are expected to be the next generation of agents for the treatment of AD. One pharmacological approach to evaluate possible cognitive effects of compounds includes their ability to reverse scopolamine-induced amnesia. In the current study the succinamide and succinimide of p-aminophenol, two newly synthesized compounds that were previously designed to be acetylcholine analogues, were evaluated in a Pavlovian/Instrumental autoshaped memory task. Simultaneously, docking studies on the M1 receptor were done. The scopolamine-induced amnesia was reversed by the amide but not the imide. These findings are in line with results derived from the docking simulations, and suggest that at least the succinamide of p-aminophenol could represent a novel candidate for the treatment of AD.