Synthesis, Molecular Electron Density Theory Study, Molecular Docking, and Pharmacological Evaluation of New Coumarin-Sulfonamide-Nitroindazolyl-Triazole Hybrids as Monoamine Oxidase Inhibitors

Inhibitors of monoamine oxidases (MAOs) are of interest for the treatment of neurodegenerative disorders and other human pathologies. In this frame, the present work describes different synthetic strategies to obtain MAO inhibitors via the coupling of the aminocoumarin core with arylsulfonyl chlorides followed by copper azide-alkyne cycloaddition, leading to coumarin-sulfonamide-nitroindazolyl-triazole hybrids. The nitration position on the coumarin moiety was confirmed through nuclear magnetic resonance spectroscopy and molecular electron density theory in order to elucidate the molecular mechanism and selectivity of the electrophilic aromatic substitution reaction. The coumarin derivatives were evaluated for their inhibitory potency against monoamine oxidases and cholinesterases. Molecular docking calculations provided a rational binding mode of the best compounds in the series with MAO A and B. The work identified hybrids 14a-c as novel MAO inhibitors, with a selective action against isoform B, of potential interest to combat neurological diseases.

Multi-Target-Directed Cinnamic Acid Hybrids Targeting Alzheimer's Disease

Progressive cognitive decline in Alzheimer's disease (AD) is a growing challenge. Present therapies are based on acetylcholinesterase inhibition providing only temporary relief. Promising alternatives include butyrylcholinesterase (BuChE) inhibitors, multi-target ligands (MTDLs) that address the multi-factorial nature of AD, and compounds that target oxidative stress and inflammation. Cinnamate derivatives, known for their neuroprotective properties, show potential when combined with established AD agents, demonstrating improved efficacy. They are being positioned as potential AD therapeutic leads due to their ability to inhibit Aβ accumulation and provide neuroprotection. This article highlights the remarkable potential of cinnamic acid as a basic structure that is easily adaptable and combinable to different active groups in the struggle against Alzheimer's disease. Compounds with a methoxy substitution at the para-position of cinnamic acid display increased efficacy, whereas electron-withdrawing groups are generally more effective. The effect of the molecular volume is worthy of further investigation.

Latest advances in dual inhibitors of acetylcholinesterase and monoamine oxidase B against Alzheimer's disease

Alzheimer's disease (AD) is a progressive brain disease characterised by progressive memory loss and cognition impairment, ultimately leading to death. There are three FDA-approved acetylcholinesterase inhibitors (donepezil, rivastigmine, and galantamine, AChEIs) for the symptomatic treatment of AD. Monoamine oxidase B (MAO-B) has been considered to contribute to pathologies of AD. Therefore, we reviewed the dual inhibitors of acetylcholinesterase (AChE) and MAO-B developed in the last five years. In this review, these dual-target inhibitors were classified into six groups according to the basic parent structure, including chalcone, coumarin, chromone, benzo-fused five-membered ring, imine and hydrazine, and other scaffolds. Their design strategies, structure-activity relationships (SARs), and molecular docking studies with AChE and MAO-B were analysed and discussed, giving valuable insights for the subsequent development of AChE and MAO-B dual inhibitors. Challenges in the development of balanced and potent AChE and MAO-B dual inhibitors were noted, and corresponding solutions were provided.

Synthesis and Evaluation of Novel S-alkyl Phthalimide- and S-benzyl-oxadiazole-quinoline Hybrids as Inhibitors of Monoamine Oxidase and Acetylcholinesterase

New S-alkyl phthalimide 5a-f and S-benzyl 6a-d analogs of 5-(2-phenylquinolin-4-yl)-1,3,4-oxadiazole-2-thiol (4) were prepared by reacting 4 with N-bromoalkylphthalimide and CF₃-substituted benzyl bromides in excellent yields. Spectroscopic techniques were employed to elucidate the structures of the synthesized molecules. The inhibition activity of newly synthesized molecules toward MAO-A, MAO-B, and AChE enzymes, was also assessed. All these compounds showed activity in the submicromolar range against all enzymes. Compounds 5a and 5f were found to be the most potent compounds against MAO-A (IC₅₀ = 0.91 ± 0.15 nM) and MAO-B (IC₅₀ = 0.84 ± 0.06 nM), while compound 5c showed the most efficient acetylcholinesterase inhibition (IC₅₀ = 1.02± 0.65 μM). Docking predictions disclosed the docking poses of the synthesized molecules with all enzymes and demonstrated the outstanding potency of compounds 5a, 5f, and 5c (docking scores = -11.6, -15.3, and -14.0 kcal/mol against MAO-A, MAO-B, and AChE, respectively). These newly synthesized analogs act as up-and-coming candidates for the creation of safer curative use against Alzheimer's illness.

The Chemotype of Chromanones as a Privileged Scaffold for Multineurotarget Anti-Alzheimer Agents

The multifactorial nature of Alzheimer's disease necessitates the development of agents able to interfere with different relevant targets. A series of 22 tailored chromanones was conceptualized, synthesized, and subjected to biological evaluation. We identified one representative bearing a linker-connected azepane moiety (compound 19) with balanced pharmacological properties. Compound 19 exhibited inhibitory activities against human acetyl-, butyrylcholinesterase and monoamine oxidase-B, as well as high affinity to both the σ1 and σ2 receptors. Our study provides a framework for the development of further chromanone-based multineurotarget agents.

Revealing the role of the benzyloxy pharmacophore in the design of a new class of monoamine oxidase-B inhibitors

The conceptual layout of monoamine oxidase (MAO) inhibitors has been modified to explore their potential biological application in the case of neurological disorders for the time being. The current review article is an effort to display the summation of innovative conceptual prospects of MAO inhibitors and their intriguing chemistry and bioactivity. Based on this scenario, we emphasize the pivotal role of the benzyloxy moiety attached to scaffolds like oxadiazolones, indolalkylamines, safinamide, caffeine, benzofurans, α-tetralones, β-nitrostyrene, benzoquinones, coumarins, indoles, chromones, and chromanone analogs, while acting as an MAO inhibitor.

Design, Synthesis, and Bioevaluation of Indole Core Containing 2-Arylidine Derivatives of Thiazolopyrimidine as Multitarget Inhibitors of Cholinesterases and Monoamine Oxidase A/B for the Treatment of Alzheimer Disease

In continuation of our previous study to identify multitarget inhibitors of cholinesterases (ChEs) and monoamine oxidase (MAOs) isoforms, we synthesized and evaluated 2-arylidine derivatives of thiazolopyrimidine for the treatment of Alzheimer disease. Three series of compounds with different linker size and target-anchoring functional groups were synthesized. Compounds 34-37 showed excellent to good AChE and BChE inhibition potential at nanomolar to low micromolar concentration. While all the compounds showed excellent MAO-B inhibition and selectivity relative to MAO-A, compounds 25 and 36 emerged as the most potent MAO-B inhibitors of all the series of synthesized compounds with IC₅₀ values of 0.13 μM and 0.10 μM, respectively. Furthermore, kinetic studies of inhibitor 35 showed mixed inhibition mode. Exploration of structure activity relationship (SAR) revealed the role of functionalities and length of linkers on potency. Acute toxicity evaluation showed the safety of tested compounds up to 2000 mg/kg dose. PAMPA-BBB evaluation showed BBB permeability of the tested compounds, while MTT assay performed on neuroblastoma SHSY5Y cells showed that all the tested compounds are non-neurotoxic in the tested concentrations. Docking studies showed a strong correlation with experimental in vitro results via binding orientations and interaction patterns of the synthesized compounds into the binding sites of target enzymes. We have successfully identified safe, non-neurotoxic, and blood brain barrier permeable multitarget lead compounds for the treatment of AD.

Fluoxetine and sertraline based multitarget inhibitors of cholinesterases and monoamine oxidase-A/B for the treatment of Alzheimer's disease: Synthesis, pharmacology and molecular modeling studies

For the potential therapy of Alzheimer's disease (AD), cholinesterases (ChE) and monoamine oxidase (MAO) are key enzymes that regulate the level of acetylcholinesterase (AChE)/butyrylcholinesterase (BChE) and monoamines. The aim of current research is the synthesis of multi-target compounds that can concomitantly inhibit ChEs and MAO. A series of fluoxetine and sertraline hybrids was designed and evaluated as multi-target inhibitors of ChEs and hMAO. In-vitro enzyme inhibition studies demonstrated that a number of compounds displayed excellent inhibition in submicromolar to nanomolar range. However, compounds 17, 22, 38-40 possess excellent concomitant inhibitory activity against ChEs and hMAO-A/B enzymes and thus emerged as optimal multi-target hybrids. In-vivo acute toxicity study showed the safety of synthesized compounds up to 2000 mg/kg dose. The examinations of brain tissue in Swiss albino mice suggested that selected most active MAO-B inhibitors 17 and 22 have a propensity to block the MAO-B activity that could be responsible for their neurodegenerative effect in mice. The in-vitro inhibitory manner of interaction of these multipotent compounds on all four targets were confirmed by molecular docking investigations.

Semicarbazones, thiosemicarbazone, thiazole and oxazole analogues as monoamine oxidase inhibitors: Synthesis, characterization, biological evaluation, molecular docking, and kinetic studies

A series of semicarbazone, thiosemicarbazone, thiazole, and oxazole derivatives were designed, synthesized, and examined for monoamine oxidase inhibition using two isoforms, i.e., MAO-A and MAO-B. Among all the analogues, 3c and 3j possessed substantial activity against MAO-A with IC₅₀ values of 5.619 ± 1.04 µM and 0.5781 ± 0.1674 µM, respectively. Whereas 3d and 3j were active against monoamine oxidase B with the IC₅₀ values of 9.952 ± 1.831 µM and 3.5 ± 0.7 µM, respectively. Other derivatives active against MAO-B were 3c and 3g with the IC₅₀ values of 17.67 ± 5.6 µM and 37.18 ± 2.485 µM. Moreover, molecular docking studies were achieved for the most potent compound (3j) contrary to human MAO-A and MAO-B. Kinetic studies were also performed for the most potent analogue to evaluate its mode of interaction with MAO-A and MAO-B.

Natural multi-target modulators of pathological pathways in Alzheimer's disease isolated from the Rhinella arenarum skin

The skin of anuran amphibians is a rich source of compounds with great medicinal potential. Alzheimer's disease (AD) is a complex disease associated with numerous pathological pathways, making their simultaneous modulation necessary. Nowadays the development of anti-AD drugs is focused on a Multi-Target Directed Ligands strategy. Herein we report the bioactivity of the skin extracts of the toad Rhinella arenarum obtained by an invasive and non-invasive methods, against five AD pathological targets (AChE, BChE, MAO-B, antioxidant and chelating activities). The extract derived from the non-invasive technique showed the highest biological activity, being capable of acting on all or almost all the pathological targets of AD, while also avoiding harm to the animal.

Pharmacophore-based drug design of AChE and BChE dual inhibitors as potential anti-Alzheimer's disease agents

For the Alzheimer's disease (AD) with complex pathogenesis, single target drugs represent one of the most effective therapeutic strategies in clinical. However, the traditional concept of "a disease, a target" is difficult to find very effective drugs, and multi-target drugs have already become new hot spot in drug development for this disease. In our present study, our efforts toward discovering new cholinesterase (ChE) inhibitors aided by computational methods will provide useful information as anti-AD agents in the future. The best 3D-QSAR acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitors pharmacophore hypotheses Hypo1 A and Hypo1 B were generated and validated by HypoGen program in Discovery Studio 2016 based on the training set of flavonoids, and then they were used as 3D query for screening the ZINC database. Next, the hit molecules were then subjected to the ADMET and molecular docking study to prioritize the compounds. Finally, 6 compounds showed good estimated activities and promising ADMET properties. The result of best compound ZINC08751495 with AChE estimate activity (0.028), BChE estimate activity (1.55), AChE fit value (9.369), BChE fit value (8.415), AChE -CDOCKER ENERGY (30.22), BChE -CDOCKER ENERGY (33.13) has the potential for further development as a supplement to treat Alzheimer's disease.

New indane derivatives containing 2-hydrazinothiazole as potential acetylcholinesterase and monoamine oxidase-B inhibitors

Although radical treatment of Alzheimer's and Parkinson's disease is not possible yet, it is aimed to slow the course of the disease and increase the life quality of individuals with the drugs used in the clinic at the present time. Successful results have been achieved in the use of cholinesterase inhibitors and monoamine oxidase inhibitors together in these neurodegenerative diseases. In this study, indane ring which are in the structure of anticholinesterase effective molecules and 2-hydrazinothiazole structure whose inhibitory activities reported on monoamine oxidase-B (MAO-B) were combined; 4-(substituted phenyl)-2-[2-(3-phenyl-2,3-dihydro-1H-inden-1-ylidene) hydrazinyl]thiazole derivatives (3a-3i) were synthesized as dual inhibitors. The structures of the compounds were verified by IR, ¹H-NMR, ¹³C-NMR, and HRMS spectroscopy. When enzyme inhibition activities were evaluated, it was determined that the compounds 3a (42.33%) and 3d (42.39%) on acetylcholinesterase (AChE) enzyme; compounds 3g (75.42%) and 3h (60.33%) showed inhibition on MAO-B enzyme at most, at 10^-3 M concentration.

Inhibitors of Cholinesterases in Pharmacology: the Current Trends

Inhibitors of cholinesterases are a wide group of low molecular weight compounds with a significant role in the current pharmacology. Besides the pharmacological importance, they are also known as toxic compounds like military nerve agents. In the pharmacology, drugs for Alzheimer disease, myasthenia gravis and prophylaxis of poisoning by nerve agents can be mentioned as the relevant applications. Besides this, anti-inflammation and antiphrastic drugs are other pharmacological applications of these inhibitors. This review is focused on a survey of cholinesterase inhibitors with known or expected pharmacological impact and indications of their use. Recent literature with comments is provided here as well.

Alterations and interactions of subcortical modulatory systems in Alzheimer's disease

The pathogenesis of Alzheimer's disease (AD) is not fully understood. Here we summarize current knowledge on the involvement of the serotonergic, noradrenergic, dopaminergic, cholinergic, and opioid systems in AD, emphasizing the importance of interactions between the serotonergic and the other subcortical modulatory systems during the progression of AD. In physiological conditions, all neurotransmitter systems function in concert and are interdependent at both the neuroanatomical and molecular levels. Through their early involvement in AD, cognitive and behavioral abilities that rely on their interactions also become disrupted. Considering that serotonin (5HT) regulates the release of noradrenaline (NA), dopamine (DA) and acetylcholine (ACh), any alteration in 5HT levels leads to disturbance of NA, DA, and ACh homeostasis in the brain. One of the earliest pathological changes during the prodromal phase of AD is a decrease of serotonergic transmission throughout the brain, with serotonergic receptors being also affected. Additionally, serotonergic and noradrenergic as well as serotonergic and dopaminergic nuclei are reciprocally interconnected. As the serotonergic dorsal raphe nucleus (DRN) is affected by pathological changes early in AD, and the noradrenergic locus coeruleus (LC) and dopaminergic ventral tegmental area (VTA) exhibit AD-related pathological changes, their connectivity also becomes altered in AD. Such disrupted interactions among neurotransmitter systems in AD can be used in the development of multi-target drugs. Some of the potential AD therapeutics (such as ASS234, RS67333, tropisetron) target multiple neurotransmitter systems to achieve the best possible improvement of cognitive and behavioral deficits observed in AD. Here, we review how serotonergic system interacts with other subcortical modulatory systems (noradrenergic, dopaminergic, cholinergic, and opioid systems) during AD.

4-Oxoquinolines and monoamine oxidase: When tautomerism matters

4-Oxoquinoline derivatives have been often used in drug discovery programs due to their pharmacological properties. Inspired on chromone and 4-oxoquinoline chemical structure similarity, a small series of quinoline-based compounds was obtained and screened, for the first time, toward human monoamine oxidases isoforms. The data showed the N-(3,4-dichlorophenyl)-1-methyl-4-oxo-1,4-dihydroquinoline-3-carboxamide 10 was the most potent and selective MAO-B inhibitor (IC₅₀ = 5.30 ± 0.74 nM and SI: ≥1887). The data analysis showed that prototropic tautomerism markedly influences the biological activity. The unequivocal characterisation of the quinoline tautomers was performed to understand the attained data. To our knowledge, there have been no prior reports on the characterisation of quinolone tautomers by 2D NMR techniques, namely by ¹H-¹⁵N HSQC and ¹H-¹⁵N HMBC, which are proposed as expedite tools for medicinal chemistry campaigns. Computational studies on enzyme-ligand complexes, obtained after MM-GBSA calculations and molecular dynamics simulations, supported the experimental data.

Synthesis of 2′-(1,2,3-triazoyl)-acetophenones: molecular docking and inhibition of in vitro monoamine oxidase activity

The synthesis of 2′-(1,2,3-triazoyl)-acetophenones by a CuAAC using thiourea as a ligand, molecular docking and MAO activity analyses were performed.

Synthesis of Hantzsch Adducts as Cholinesterases and Calcium Flux inhibitors, Antioxidants and Neuroprotectives

We report herein the design, synthesis, biological evaluation, and molecular modelling of new inhibitors of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), able to block Ca⁺² channels also showing antioxidant and neuroprotective activities. The new MTDL, dialkyl 2,6-dimethyl-4-(4-((5-aminoalkyl)oxy)phenyl)-1,4-dihydropyridine-3,5-dicarboxylate 3a-p, have been obtained via Hantzsch reaction from appropriate and commercially available precursors. Pertinent biological analysis has prompted us to identify MTDL 3h [dimethyl-4-(4-((5-(4-benzylpiperidin-1-yl)pentyl)oxy)phenyl)-2,6-dimethyl-1,4-dihydropyridine-3,5-dicarboxylate] as an attractive inhibitor of AChE (1.8 μM) and BuChE (2 μM), Ca⁺² channel antagonist (47.72% at 10 μM), and antioxidant (2.54 TE) agent, showing significant neuroprotection 28.68% and 38.29% against H₂O_2, and O/R, respectively, at 0.3 μM, thus being considered a hit-compound for further investigation in our search for anti-Alzheimer's disease agents.

Selected 1,3-Benzodioxine-Containing Chalcones as Multipotent Oxidase and Acetylcholinesterase Inhibitors

Chalcones are considered effective templates for the development of monoamine oxidase (MAO) and cholinesterase (ChE) inhibitors. The present work describes the syntheses of selected 1,3-benzodioxine-containing chalcones (CD3, CD8 and CD10), and their inhibitory activities against MAO-A, MAO-B, acetylcholinesterase (AChE), and butyrylcholinesterase (BChE). Compound CD8 most potently inhibited MAO-B with an IC₅₀ value of 0.026 μM, followed by CD10 and CD3 (1.54 and 1.68 μM, respectively). CD8 potently and non-selectively inhibited MAO-A (IC₅₀ value of 0.023 μM). On the other hand, CD10 and CD8 inhibited AChE with IC₅₀ values of 5.40 and 9.57 μM, respectively. Kinetics and reversibility experiments showed that all synthesized molecules were competitive and reversible inhibitors, and the K_i values of CD8 for MAO-A and MAO-B were 0.018 and 0.0019 μM, respectively. By in vitro and in silico analyses, all compounds were found to have high passive human gastrointestinal absorptions, blood-brain barrier permeabilities, and non-toxicities. Molecular docking simulations revealed that docking affinity of each compound for MAO-B was higher than that for MAO-A. The results indicate that CD8 is a potent non-selective MAO inhibitor, and CD10 is an effective selective MAO-B inhibitor, and both possess AChE inhibitory activity. Therefore, we suggest that CD8 and CD10 be considered potential dual-targeting inhibitors of MAO and AChE for the treatment of various neurodegenerative disorders.

Ethyl Acetohydroxamate Incorporated Chalcones: Unveiling a Novel Class of Chalcones for Multitarget Monoamine Oxidase-B Inhibitors Against Alzheimer's Disease

BACKGROUND

Chalcones are considered as the selective scaffold for the inhibition of MAO-B.

OBJECTIVES

A previously synthesized ethyl acetohydroxamate-chalcones (L1-L22) were studied for their inhibitory activities against human recombinant monoamine oxidase A and B (hMAO-A and hMAO-B, respectively) and acetylcholinesterase (AChE) as multi-target directed ligands for the treatment of Alzheimer's Disease (AD).

METHODS

Enzyme inhibition studies of MAO-A, MAO-B and AChE is carried out. Computational studies such as Molecular docking, Molecular Mechanics/Generalized Born Surface Area calculations, ADMET prediction, and protein target prediction are also performed.

RESULTS

Among the screened compounds, compound L3 has most potent hMAO-B inhibition with an IC50 value of 0.028 ± 0.0016 µM, and other compounds, L1, L2, L4, L8, L12, and L21 showed significant potent hMAO-B inhibition with IC50 values of 0.051 ± 0.0014, 0.086 ± 0.0035, 0.036 ± 0.0011, 0.096 ± 0.0061, 0.083 ± 0.0016, and 0.038 ± 0.0021 µM, respectively. On the other hand, among the tested compounds, compound L13 showed highest hMAO-A inhibition with an IC50 value of 0.51± 0.051 µM and L9 has a significant value of 1.85 ± 0.045 µM. However, the compounds L3 and L4 only showed high selectivities for hMAO-B with Selectivity Index (SI) values of 621.4 and 416.7, respectively. Among the substituents in ring A of ethyl acetohydroxamate-chalcones (L1-L9), F atom at p-position (L3) showed highest inhibitory effect against hMAO-B. This result supports the uniqness and bizarre behavior of fluorine. Moreover, chalcones L3, L4, L9, L11, and L12 showed potential AChE inhibitory effect with IC50 values of 0.67, 0.85, 0.39, 0.30, and 0.45 µM, respectively. Inhibitions of hMAO-B by L3 or L4 were recovered to the level of the reversible reference (lazabemide), and were competitive with Ki values of 0.0030 ± 0.0002 and 0.0046 ± 0.0005 µM, respectively. Inhibitions of AChE by L3 and L11 were of the competitive and mixed types with Ki values of 0.30 ± 0.044 and 0.14 ± 0.0054 µM, respectively.

CONCLUSION

The studies indicated that L3 and L4 are considered to be promising multitarget drug molecules with potent, selective, and reversible competitive inhibitors of hMAO-B and with highly potent AChE inhibitory effect.

Triazolopyridopyrimidine: A New Scaffold for Dual-Target Small Molecules for Alzheimer's Disease Therapy

Alzheimer’s disease (AD) is multifactorial disease characterized by the accumulation of abnormal extracellular deposits of amyloid-beta (Aβ) peptide, and intracellular neurofibrillary tangles (NFTs), along with dramatic neuronal death and decreased levels of choline acetyltransferase. Given the limited therapeutic success of available drugs, it is urgent to explore all the opportunities available to combat this illness. Among them, the discovery of new heterocyclic scaffolds binding different receptors involved in AD should offer structural diversity and new therapeutic solutions. In this context, this work describes new triazolopyridopyrimidine easily prepared in good yields showing anticholinesterase inhibition and strong antioxidant power, particularly the most balanced: 6-amino-5-(4-methoxyphenyl)-2-phenyl-[1,2,4]triazolo[1′,5′:1,6] pyrido[2,3-d]pyrimidine-4-carbonitrile(3c) with IC₅₀ equal to 1.32 μM against AChE and oxygen radical absorbance capacity (ORAC) value equal to 4.01 Trolox equivalents (TE); thus representing a new and very promising hit-triazolopyridopyrimidine for AD therapy.

An Overview of Coumarin as a Versatile and Readily Accessible Scaffold with Broad-Ranging Biological Activities

Privileged structures have been widely used as an effective template for the research and discovery of high value chemicals. Coumarin is a simple scaffold widespread in Nature and it can be found in a considerable number of plants as well as in some fungi and bacteria. In the last years, these natural compounds have been gaining an increasing attention from the scientific community for their wide range of biological activities, mainly due to their ability to interact with diverse enzymes and receptors in living organisms. In addition, coumarin nucleus has proved to be easily synthetized and decorated, giving the possibility of designing new coumarin-based compounds and investigating their potential in the treatment of various diseases. The versatility of coumarin scaffold finds applications not only in medicinal chemistry but also in the agrochemical field as well as in the cosmetic and fragrances industry. This review is intended to be a critical overview on coumarins, comprehensive of natural sources, metabolites, biological evaluations and synthetic approaches.

N-alkylpiperidine carbamates as potential anti-Alzheimer's agents

Compounds capable of interacting with single or multiple targets involved in Alzheimer's disease (AD) pathogenesis are potential anti-Alzheimer's agents. In our aim to develop new anti-Alzheimer's agents, a series of 36 new N-alkylpiperidine carbamates was designed, synthesized and evaluated for the inhibition of cholinesterases [acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)] and monoamine oxidases [monoamine oxidase A (MAO-A and monoamine oxidase B (MAO-B)]. Four compounds are very promising: multiple AChE (IC₅₀ = 7.31 μM), BChE (IC₅₀ = 0.56 μM) and MAO-B (IC₅₀ = 26.1 μM) inhibitor 10, dual AChE (IC₅₀ = 2.25 μM) and BChE (IC₅₀ = 0.81 μM) inhibitor 22, selective BChE (IC₅₀ = 0.06 μM) inhibitor 13, and selective MAO-B (IC₅₀ = 0.18 μM) inhibitor 16. Results of enzyme kinetics experiments showed that despite the carbamate group in the structure, compounds 10, 13, and 22 are reversible and non-time-dependent inhibitors of AChE and/or BChE. The resolved crystal structure of the complex of BChE with compound 13 confirmed the non-covalent mechanism of inhibition. Additionally, N-propargylpiperidine 16 is an irreversible and time-dependent inhibitor of MAO-B, while N-benzylpiperidine 10 is reversible. Additionally, compounds 10, 13, 16, and 22 should be able to cross the blood-brain barrier and are not cytotoxic to human neuronal-like SH-SY5Y and liver HepG2 cells. Finally, compounds 10 and 16 also prevent amyloid β_1-42 (Aβ_1-42)-induced neuronal cell death. The neuroprotective effects of compound 16 could be the result of its Aβ_1-42 anti-aggregation effects.

Design of enamides as new selective monoamine oxidase-B inhibitors

OBJECTIVES

To develop of new class of selective and reversible MAO-B inhibitors from enamides.

METHODS

Syntheses of the titled derivatives (AD1-AD11) were achieved by reacting cinnamoyl chloride and various primary and secondary amines in basic medium. All eleven compounds were investigated for in vitro inhibitory activities against recombinant human MAO-A and MAO-B. The reversibilities of lead compound inhibitions were analysed by dialysis. MTT assays of lead compounds were performed using normal VERO cell lines.

KEY FINDINGS

Compounds AD3 and AD9 exhibited the greatest inhibitory activity against MAO-B with IC₅₀ values of 0.11 and 0.10 µm, respectively, and were followed by AD2 and AD1 (0.51 and 0.71 µm, respectively). Most of the compounds weakly inhibited MAO-A, with the exceptions AD9 and AD7, which had IC₅₀ values of 4.21 and 5.95 µm, respectively. AD3 had the highest selectivity index (SI) value for MAO-B (>363.6) and was followed by AD9 (SI 42.1). AD3 and AD9 were found to be competitive inhibitors of MAO-B with K_i values of 0.044 ± 0.0036 and 0.039 ± 0.0047 µm, respectively. Reversibility experiments showed AD3 and AD9 were reversible inhibitors of MAO-B; dialysis restored the activity of MAO-B to the reference level. MTT assays revealed AD3 and AD9 were non-toxic to normal VERO cell lines with IC₅₀ values of 153.96 and 194.04 µg/ml, respectively. Computational studies provided hypothetical binding modes for AD3 and AD9 in the binding cavities of MAO-A and MAO-B.

CONCLUSIONS

These results encourage further studies on the enamide scaffold as potential drug candidates for the treatment of Alzheimer's and Parkinson's diseases.

Novel small molecule therapeutic agents for Alzheimer disease: Focusing on BACE1 and multi-target directed ligands

Alzheimer's Disease (AD) is a progressive neurodegenerative disorder that effects 50 million people worldwide. In this review, AD pathology and the development of novel therapeutic agents targeting AD were fully discussed. In particular, common approaches to prevent Aβ production and/or accumulation in the brain including α-secretase activators, specific γ-secretase modulators and small molecules BACE1 inhibitors were reviewed. Additionally, natural-origin bioactive compounds that provide AD therapeutic advances have been introduced. Considering AD is a multifactorial disease, the therapeutic potential of diverse multi target-directed ligands (MTDLs) that combine the efficacy of cholinesterase (ChE) inhibitors, MAO (monoamine oxidase) inhibitors, BACE1 inhibitors, phosphodiesterase 4D (PDE4D) inhibitors, for the treatment of AD are also reviewed. This article also highlights descriptions on the regulator of serotonin receptor (5-HT), metal chelators, anti-aggregants, antioxidants and neuroprotective agents targeting AD. Finally, current computational methods for evaluating the structure-activity relationships (SAR) and virtual screening (VS) of AD drugs are discussed and evaluated.

New flavonoid - N,N-dibenzyl(N-methyl)amine hybrids: Multi-target-directed agents for Alzheimer´s disease endowed with neurogenic properties

The design of multi-target directed ligands (MTDLs) is a valid approach for obtaining effective drugs for complex pathologies. MTDLs that combine neuro-repair properties and block the first steps of neurotoxic cascades could be the so long wanted remedies to treat neurodegenerative diseases (NDs). By linking two privileged scaffolds with well-known activities in ND-targets, the flavonoid and the N,N-dibenzyl(N-methyl)amine (DBMA) fragments, new CNS-permeable flavonoid - DBMA hybrids (1-13) were obtained. They were subjected to biological evaluation in a battery of targets involved in Alzheimer's disease (AD) and other NDs, namely human cholinesterases (hAChE/hBuChE), β-secretase (hBACE-1), monoamine oxidases (hMAO-A/B), lipoxygenase-5 (hLOX-5) and sigma receptors (σ₁R/σ₂R). After a funnel-type screening, 6,7-dimethoxychromone - DBMA (6) was highlighted due to its neurogenic properties and an interesting MTD-profile in hAChE, hLOX-5, hBACE-1 and σ₁R. Molecular dynamic simulations showed the most relevant drug-protein interactions of hybrid 6, which could synergistically contribute to neuronal regeneration and block neurodegeneration.

Chromenones as Multineurotargeting Inhibitors of Human Enzymes

The complex nature of multifactorial diseases, such as Morbus Alzheimer, has produced a strong need to design multitarget-directed ligands to address the involved complementary pathways. We performed a purposive structural modification of a tetratarget small-molecule, that is contilisant, and generated a combinatorial library of 28 substituted chromen-4-ones. The compounds comprise a basic moiety which is linker-connected to the 6-position of the heterocyclic chromenone core. The syntheses were accomplished by Mitsunobu- or Williamson-type ether formations. The resulting library members were evaluated at a panel of seven human enzymes, all of which being involved in the pathophysiology of neurodegeneration. A concomitant inhibition of human acetylcholinesterase and human monoamine oxidase B, with IC₅₀ values of 5.58 and 7.20 μM, respectively, was achieved with the dual-target 6-(4-(piperidin-1-yl)butoxy)-4H-chromen-4-one (7).

Highly Significant Scaffolds to Design and Synthesis Cholinesterase Inhibitors as Anti-Alzheimer Agents

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Alzheimer, a progressive disease, is a common term for memory loss which interferes with daily life through severe influence on cognitive abilities. Based on the cholinergic hypothesis, and Xray crystallographic determination of the structure of acetylcholinesterase (AChE) enzyme, the level of acetylcholine (ACh, an important neurotransmitter associated with memory) in the hippocampus and cortex area of the brain has a direct effect on Alzheimer. This fact encourages scientists to design and synthesize a wide range of acetylcholinesterase inhibitors (AChEIs) to control the level of ACh in the brain, keeping in view the crystallographic structure of AChE enzyme and drugs approved by the Food and Drug Administration (FDA).

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AChEIs have slightly diverse pharmacological properties, but all of them work by inhibiting the segregation of ACh by blocking AChE. We reviewed significant scaffolds introduced as AChEIs. In some studies, the activity against butyrylcholinesterase (BuChE) has been evaluated as well because BuChE is a similar enzyme to neuronal acetylcholinesterase and is capable of hydrolyzing ACh. In order to study AChEIs effectively, we divided them structurally into 12 classes and briefly explained effective AChEIs and compared their activities against AChE enzyme.

A Prospective Repurposing of Dantrolene as a Multitarget Agent for Alzheimer's Disease

The orphan drug dantrolene (DAN) is the only therapeutic treatment for malignant hyperthermia (MH), a pharmacogenetic pathology affecting 0.2 over 10,000 people in the EU. It acts by inhibiting ryanodine receptors, which are responsible for calcium recruitment in striatal muscles and brain. Because of its involvement in calcium homeostasis, DAN has been successfully investigated for its potential as neuroprotecting small molecule in several animal models of Alzheimer’s disease (AD). Nevertheless, its effects at a molecular level, namely on putative targets involved in neurodegeneration, are still scarcely known. Herein, we present a prospective study on repurposing of DAN involving, besides the well-known calcium antagonism, inhibition of monoamine oxidase B and acetylcholinesterase, cytoprotection from oxidative insult, and activation of carnitine/acylcarnitine carrier, as concurring biological activities responsible for neuroprotection.

Emerging therapeutic potentials of dual-acting MAO and AChE inhibitors in Alzheimer's and Parkinson's diseases

No drug has been approved to prevent neuronal cell loss in patients suffering from Parkinson's disease (PD) or Alzheimer's disease (AD); despite increased comprehension of the underlying molecular causes, therapies target cognitive functional improvement and motor fluctuation control. Drug design strategies that adopt the "one protein, one target" philosophy fail to address the multifactorial aetiologies of neurodegenerative disorders such as AD and PD optimally. On the contrary, restoring neurotransmitter levels by combined combinatorial inhibition of cholinesterases, monoamine oxidases, and adenosine A_2A A receptors, in conjunction with strategies to counter oxidative stress and beta-amyloid plaque accumulation, would constitute a therapeutically robust, multitarget approach. This extensive review delineates the therapeutic advantages of combining dual-acting molecules that inhibit monoamine oxidases and cholinesterases and/or adenosine A_2A A receptors, and describes the structure-activity relationships of compound classes that include, but are not limited to, alkaloids, coumarins, chalcones, donepezil-propargylamine conjugates, homoisoflavonoids, resveratrol analogs, hydrazones, and pyrazolines. In the wake of recent advances in network biology, in silico approaches, and omics, this review emphasizes the need to consider conceptually informed research strategies for drug discovery, in the context of the mounting burden posed by chronic neurodegenerative diseases with complex aetiologies and pathophysiologies involving multiple signalling pathways and numerous drug targets.

Amphibian skin extracts as source of bioactive multi-target agents against different pathways of Alzheimer's disease

Natural products represent a rich source of bioactive compounds that have been historically used to obtain substances with great medicinal potential. The skin of anuran amphibians is a rich source of compounds with a wide range of biological activity. Alzheimer's disease (AD) is a complex disease associated with all kind of different pathways, making their simultaneous modulation necessary. Nowadays anti-AD treatments are focused on enzymatic inhibitors. Here in we report the activity of skin extracts from nine species from Argentina, belonging to three anuran families, as inhibitors of AChE, BChE and MAO-B enzymes. The extracts also showed antioxidant activities, acting as multi-target on four important pathways of AD.

Synthesis and biological evaluation of 3-arylcoumarins as potential anti-Alzheimer's disease agents

Alzheimer's disease, a neurodegenerative illness, has the extremely complex pathogenesis. Accumulating evidence indicates there is a close relationship between several enzymes and Alzheimer's disease. Various substituted 3-arylcoumarin derivatives were synthesised, and their in vitro activity, including cholinesterase inhibitory activity, monoamine oxidase inhibitory activity, and antioxidant activity were investigated. Most of the compounds exhibited high activity; therefore 3-arylcoumarin compounds have the potential as drug candidates for the treatment of Alzheimer's disease.

Potent and highly selective dual-targeting monoamine oxidase-B inhibitors: Fluorinated chalcones of morpholine versus imidazole

Two series of fluorinated chalcones containing morpholine and imidazole-based compounds (f1-f8) were synthesized and evaluated for recombinant human monoamine oxidase (MAO)-A and -B as well as acetylcholinesterase inhibitory activities. Our results indicate that morpholine containing chalcones are highly selective MAO-B inhibitors having reversibility properties. All the imidazole-based fluorinated chalcones showed weak MAO inhibitions in both isoforms. Among the tested compounds, (2E)-3-(3-fluorophenyl)-1-[4-(morpholin-4-yl)phenyl]prop-2-en-1-one (f2) showed potent inhibitory activity for recombinant human MAO-B (IC₅₀  = 0.087 μM) with a high selectivity index (SI) of 517.2. In the recovery experiments using dialysis, the residual activity of MAO-B inhibited by f2 was close to that with the reversible reference inhibitor. Inhibition assays revealed that the K_i values of f1 and f2 for MAO-B were 0.027 and 0.020 μM, respectively, with competitive patterns. All the morpholine-based compounds (f1-f4) showed moderate inhibition toward acetylcholinesterase with IC₅₀ values ranging between 24 and 54 μM. All morpholine-containing compounds exhibit good blood-brain barrier permeation in the PAMPA method. The rational approach regarding the highly selective MAO-B inhibitor f2 was further ascertained by induced fit docking and molecular dynamics simulation studies.

Neurogenic and neuroprotective donepezil-flavonoid hybrids with sigma-1 affinity and inhibition of key enzymes in Alzheimer's disease

In this work we describe neurogenic and neuroprotective donepezil-flavonoid hybrids (DFHs), exhibiting nanomolar affinities for the sigma-1 receptor (σ1R) and inhibition of key enzymes in Alzheimer's disease (AD), such as acetylcholinesterase (AChE), 5-lipoxygenase (5-LOX), and monoamine oxidases (MAOs). In general, new compounds scavenge free radical species, are predicted to be brain-permeable, and protect neuronal cells against mitochondrial oxidative stress. N-(2-(1-Benzylpiperidin-4-yl)ethyl)-6,7-dimethoxy-4-oxo-4H-chromene-2-carboxamide (18) is highlighted due to its interesting biological profile in σ1R, AChE, 5-LOX, MAO-A and MAO-B. In phenotypic assays, it protects a neuronal cell line against mitochondrial oxidative stress and promotes maturation of neural stem cells into a neuronal phenotype, which could contribute to the reparation of neuronal tissues. Molecular modelling studies of 18 in AChE, 5-LOX and σ1R revealed the main interactions with these proteins, which will be further exploited in the optimization of new, more efficient DFHs.

Computer-Aided Multi-Target Management of Emergent Alzheimer's Disease

Alzheimer's disease (AD) represents an enormous global health burden in terms of human suffering and economic cost. AD management requires a shift from the prevailing paradigm targeting pathogenesis to design and develop effective drugs with adequate success in clinical trials. Therefore, it is of interest to report a review on amyloid beta (Aβ) effects and other multi-targets including cholinesterase, NFTs, tau protein and TNF associated with brain cell death to be neuro-protective from AD. It should be noted that these molecules have been generated either by target-based or phenotypic methods. Hence, the use of recent advancements in nanomedicine and other natural compounds screening tools as a feasible alternative for circumventing specific liabilities is realized. We review recent developments in the design and identification of neuro-degenerative compounds against AD generated using current advancements in computational multi-target modeling algorithms reflected by theragnosis (combination of diagnostic tests and therapy) concern.