Discovery of novel benzimidazole derivatives as selective and reversible monoamine oxidase B inhibitors for Parkinson's disease treatment

Parkinson's disease (PD) is a common neurodegenerative disorder characterized by the loss of dopaminergic neurons in the substantia nigra pars compacta. The development of novel scaffolds for human monoamine oxidase B (hMAO-B) inhibitors with reversible properties represents an important strategy to improve the efficacy and safety for PD treatment. In the current work, we have devised and assessed two innovative derivative series serving as hMAO-B inhibitors. These series have utilized benzimidazole as a scaffold and strategically incorporated a primary amide group, which is recognized as a pivotal pharmacophore in subsequent activity screening and reversible mode of action. Among these compounds, 16d has emerged as the most potent hMAO-B inhibitor with an IC50 value of 67.3 nM, comparable to safinamide (IC50 = 42.6 nM) in vitro. Besides, 16d demonstrated good selectivity towards hMAO-B isoenzyme with a selectivity index over 387. Importantly, in line with the design purpose, 16d inhibited hMAO-B in a competitive and reversible manner (Ki = 82.50 nM). Moreover, 16d exhibited a good safety profile in both cellular and acute toxicity assays in mice. It also displayed ideal pharmacokinetic properties and blood-brain barrier permeability in vivo, essential prerequisites for central nervous system medicines. In the MPTP-induced PD mouse model, 16d significantly alleviated the motor impairment, especially muscle relaxation and motor coordination. Therefore, 16d, serving as a lead compound, holds instructive significance for subsequent investigations regarding its application in the treatment of PD.

Synthesis and biological evaluation of O4'-benzyl-hispidol derivatives and analogs as dual monoamine oxidase-B inhibitors and anti-neuroinflammatory agents

Design, synthesis, and biological evaluation of two series of O4'-benzyl-hispidol derivatives and the analogous corresponding O3'-benzyl derivatives aiming to develop selective monoamine oxidase-B inhibitors endowed with anti-neuroinflammatory activity is reported herein. The first O4'-benzyl-hispidol derivatives series afforded several more potentially active and MAO-B inhibitors than the O3'-benzyl derivatives series. The most potential compound 2e of O4'-benzyl derivatives elicited sub-micromolar MAO-B IC50 of 0.38 µM with a selectivity index >264 whereas most potential compound 3b of O3'-benzyl derivatives showed only 0.95 MAO-B IC50 and a selectivity index >105. Advancement of the most active compounds showing sub-micromolar activities to further cellular evaluations of viability and induced production of pro-neuroinflammatory mediators confirmed compound 2e as a potential lead compound inhibiting the production of the neuroinflammatory mediator nitric oxide significantly by microglial BV2 cells at 3 µM concentration without significant cytotoxicity up to 30 µM. In silico molecular docking study predicted plausible binding modes with MAO enzymes and provided insights at the molecular level. Overall, this report presents compound 2e as a potential lead compound to develop potential multifunctional compounds.

Design, synthesis, and biological evaluation of 1,2,4-oxadiazole-based derivatives as multitarget anti-Alzheimer agents

A series of novel 1,2,4-oxadiazole-based derivatives were synthesized and evaluated for their potential anti-Alzheimer disease activity. The results revealed that compounds 2b, 2c, 2d, 3a, 4a, 6, 9a, 9b, and 13b showed excellent inhibitory activity against acetylcholinesterase (AChE) with IC50 values in the range of 0.0158 to 0.121 μM. They were 1.01 to 7.78 times more potent than donepezil (IC50 = 0.123 μM). The newly synthesized compounds exhibited lower activity towards butyrylcholinesterase (BuChE) when compared to rivastigmine. Compounds 4b and 13b showed the most prominent inhibitory potential against BuChE with IC50 values of 11.50 and 15 μM, respectively. Moreover, 4b, and 9b were found to be more potent antioxidant agents (IC50 values of 59.25, and 56.69 μM, respectively) in comparison with ascorbic acid (IC50 = 74.55 μM). Compounds 2b and 2c exhibited monoamine oxidase-B (MAO-B) inhibitory activity with IC50 values of 74.68 and 225.48 μM, respectively. They were 3.55 and 1.17 times more potent than biperiden (IC50 = 265.85 μM). The prominent interactions of the compounds with the AChE active site can be used to computationally explain the high AChE inhibitory activity. The results unveiled 1,2,4-oxadiazole derivatives 2c and 3a as multitarget anti-AD agents. The predicted ADME properties for compounds 2b and 4a were satisfactory, and 4a had the highest likelihood of crossing the blood-brain barrier (BBB), making it the optimum compound for future optimization.

Probing the inhibition of MAO-B by chalcones: an integrated approach combining molecular docking, ADME analysis, MD simulation, and MM-PBSA calculations

CONTEXT

Monoamine oxidase B (MAO-B), an enzyme of significant relevance in the realm of neurodegenerative disorders, has garnered considerable attention as a potential target for therapeutic intervention. Natural compounds known as chalcones have shown potential as MAO-B inhibitors. In this particular study, we employed a multimodal computational method to evaluate the inhibitory effects of chalcones on MAO-B.

METHODS

Molecular docking methods were used to study and assess the complicated binding interactions that occur between chalcones and MAO-B. This extensive analysis provided a valuable and deep understanding of possible binding methods as well as the key residues implicated in the inhibition process. Furthermore, the ADME investigation gave valuable insights into the pharmacokinetic properties of chalcones. This allowed them to be assessed in terms of drug-like attributes. The use of MD simulations has benefited in the research of ligand-protein interactions' dynamic behaviour and temporal stability. MM-PBSA calculations were also done to estimate the binding free energies and acquire a better knowledge and understanding of the binding affinity between chalcones and MAO-B. Our thorough method gives a thorough knowledge of chalcones' potential as MAO-B inhibitors, which will be useful for future experimental validation and drug development efforts in the context of neurodegenerative illnesses.

Nitrogen-containing heterocyclic compounds: A ray of hope in depression?

Depression is not similar to daily mood fluctuations and temporary emotional responses to day-to-day activities. Depression is not a passing problem; it is an ongoing problem. It deals with different episodes consisting of several symptoms that last for at least 2 weeks. It can be seen for several weeks, months, or years. At its final stage, or can say, in its worst condition, it can lead to suicide. Antidepressants are used to inhibit the reuptake of the neurotransmitters by some selective receptors, which increase the concentration of specific neurotransmitters around the nerves in the brain. Drugs that are currently being used for the management of various types of depression include selective serotonin reuptake inhibitors, tricyclic antidepressants, atypical antidepressants, serotonin, noradrenaline reuptake inhibitors, etc. In this review, we have outlined different symptoms, causes, and recent advancements in nitrogen-containing heterocyclic drug candidates for the management of depression. This article highlights the various structural features along with the structure-activity relationship (SAR) of nitrogen-containing heterocyclics that play a key role in binding at target sites for potential antidepressant action. The in silico studies were carried out to determine the binding interactions of the target ligands with the receptor site to determine the potential role of substitution patterns at core pharmacophoric features. This article will help medicinal chemists, biochemists, and other interested researchers in identifying the potential pharmacophores as lead compounds for further development of new potent antidepressants.

Inhibiting Monoamine Oxidase in CNS and CVS would be a Promising Approach to Mitigating Cardiovascular Complications in Neurodegenerative Disorders

The flavoenzyme monoamine oxidases (MAOs) are present in the mitochondrial outer membrane and are responsible for the metabolism of biogenic amines. MAO deamination of biological amines produces toxic byproducts such as amines, aldehydes, and hydrogen peroxide, which are significant in the pathophysiology of multiple neurodegenerative illnesses. In the cardiovascular system (CVS), these by-products target the mitochondria of cardiac cells leading to their dysfunction and producing redox imbalance in the endothelium of the blood vessels. This brings up the biological relationship between the susceptibility of getting cardiovascular disorders in neural patients. In the current scenario, MAO inhibitors are highly recommended by physicians worldwide for the therapy and management of various neurodegenerative disorders. Many interventional studies reveal the benefit of MAO inhibitors in CVS. Drug candidates who can target both the central and peripheral MAO could be a better to compensate for the cardiovascular comorbidities observed in neurodegenerative patients.

Paradigms and Success Stories of Natural Products in Drug Discovery Against Neurodegenerative Disorders (NDDs)

Neurodegenerative disorders (NDDs) are multifaceted complex disorders that have put a great health and economic burden around the globe nowadays. The multi-factorial nature of NDDs has presented a great challenge in drug discovery and continuous efforts are in progress in search of suitable therapeutic candidates. Nature has a great wealth of active principles in its lap that has cured the human population since ancient times. Natural products have revealed several benefits over conventional synthetic medications and scientists have shifted their vision towards exploring the therapeutic potentials of natural products in the past few years. The structural mimicking of natural compounds to endogenous ligands has presented them as a potential therapeutic candidate to prevent the development of NDDs. In the presented review, authors have summarized demographical facts about various NDDs including Alzheimer's disease (AD), Parkinson's disease (PD), Huntington's disease (HD) and various types of sclerosis in the brain. The significant findings of new active principles of natural origin along with their therapeutic potentials on NDDs have been included. Also, a description of clinical trials and patents on natural products has been enlisted in this compilation. Although natural products have shown promising success in drug discovery against NDDs, still their use is associated with several ethical issues which need to be solved in the upcoming time.

Virtual screening and molecular dynamics simulation approach for the identification of potential multi-target directed ligands for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurological disorder characterized by memory loss and cognitive impairment. The currently available single-targeting drugs have miserably failed in the treatment of AD, and multi-target directed ligands (MTDLs) are being explored as an alternative treatment strategy. Cholinesterase and monoamine oxidase enzymes are reported to play a crucial role in the pathology of AD, and multipotent ligands targeting these two enzymes simultaneously are under various phases of design and development. Recent studies have revealed that computational approaches are robust and trusted tools for identifying novel therapeutics. The current research work is focused on the development of potential multi-target directed ligands that simultaneously inhibit acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B) enzymes employing a structure-based virtual screening (SBVS) approach. The ASINEX database was screened after applying pan assay interference and drug-likeness filter to identify novel molecules using three docking precision criteria; High Throughput Virtual Screening (HTVS), Standard Precision (SP), and Extra Precision (XP). Additionally, binding free energy calculations, ADME, and molecular dynamic simulations were employed to get structural insights into the mechanism of protein-ligand binding and pharmacokinetic properties. Three lead molecules viz. AOP19078710, BAS00314308 and BDD26909696 were successfully identified with binding scores of -10.565, -10.543 & -8.066 kcal/mol against AChE and -11.019, -12.357 & -10.068 kcal/mol against MAO-B, better score as compared to the standard inhibitors. In the near future, these molecules will be synthesized and evaluated through in vitro and in vivo assays for their inhibition potential against AChE and MAO-B enzymes.

"Click Chemistry": An Emerging Tool for Developing a New Class of Structural Motifs against Various Neurodegenerative Disorders

Click chemistry is a set of easy, atom-economical reactions that are often utilized to combine two desired chemical entities. Click chemistry accelerates lead identification and optimization, reduces the complexity of chemical synthesis, and delivers extremely high yields without undesirable byproducts. The most well-known click chemistry reaction is the 1,3-dipolar cycloaddition of azides and alkynes to form 1,2,3-triazoles. The resulting 1,2,3-triazoles can serve as both bioisosteres and linkers, leading to an increase in their use in the field of drug discovery. The current Review focuses on the use of click chemistry to identify new molecules for treating neurodegenerative diseases and in other areas such as peptide targeting and the quantification of biomolecules.

Monoamine oxidase B inhibitors based on natural privileged scaffolds: A review of systematically structural modification

Monoamine oxidase is a flavin enzyme that catalyzes the oxidation of monoamine neurotransmitters in the brain. Various toxic by-products, aldehydes and hydrogen peroxide produced during the catalytic process, can cause oxidative stress and neuronal cell death. Overexpression of MAO-B and insufficient dopamine concentration are recognized as pathological factors in neurodegenerative diseases (NDs) including Parkinson's disease (PD) and Alzheimer's disease (AD). Therefore, the inhibition of MAO-B is an attractive target for the treatment of NDs. Despite significant efforts, few selective and reversible MAO-B inhibitors have been clinically approved. Natural products have emerged as valuable sources of lead compounds in drug discovery. Compounds such as chromone, coumarin, chalcone, caffeine, and aurone, present in natural structures, are considered as privileged scaffolds in the synthesis of MAO-B inhibitors. In this review, we summarized the structure-activity relationship (SAR) of MAO-B inhibitors based on the naturally privileged scaffolds over the past 20 years. Additionally, we proposed a balanced discussion on the advantages and limitations of natural scaffold-based MAO-B inhibitors with providing a future perspective in drug development.

Design, synthesis and biological evaluation of novel indanones derivatives as potent acetylcholinesterase/monoamine oxidase B inhibitors

Aim: Based on a multitarget design strategy, a series of novel indanone-1-benzyl-1,2,3,6-tetrahydropyridin hybrids were identified for the potential treatment of Alzheimer's disease (AD). Results: These compounds exhibited significant inhibitory activities against acetylcholinesterase (AChE) and moderate inhibitory activities toward monoamine oxidase B (MAO-B). The optimal compound A1 possessed excellent dual AChE/MAO-B inhibition both in terms of potency (AChE: IC50 = 0.054 ± 0.004 μM; MAO-B: IC50 = 3.25 ± 0.20 μM), moderate inhibitory effects on self-mediated amyloid-β (Aβ) aggregation and antioxidant activity. In addition, compound A1 exhibited low neurotoxicity. More importantly, compound A1 showed significant cognitive and spatial memory improvements in the scopolamine-induced AD mouse model. Conclusion: All results suggest that compound A1 may become a promising lead of anti-AD drug for further development.

Imidazoles as Serotonin Receptor Modulators for Treatment of Depression: Structural Insights and Structure-Activity Relationship Studies

Serotoninergic signaling is identified as a crucial player in psychiatric disorders (notably depression), presenting it as a significant therapeutic target for treating such conditions. Inhibitors of serotoninergic signaling (especially selective serotonin reuptake inhibitors (SSRI) or serotonin and norepinephrine reuptake inhibitors (SNRI)) are prominently selected as first-line therapy for the treatment of depression, which benefits via increasing low serotonin levels and norepinephrine by blocking serotonin/norepinephrine reuptake and thereby increasing activity. While developing newer heterocyclic scaffolds to target/modulate the serotonergic systems, imidazole-bearing pharmacophores have emerged. The imidazole-derived pharmacophore already demonstrated unique structural characteristics and an electron-rich environment, ultimately resulting in a diverse range of bioactivities. Therefore, the current manuscript discloses such a specific modification and structural activity relationship (SAR) of attempted derivatization in terms of the serotonergic efficacy of the resultant inhibitor. We also featured a landscape of imidazole-based development, focusing on SAR studies against the serotoninergic system to target depression. This study covers the recent advancements in synthetic methodologies for imidazole derivatives and the development of new molecules having antidepressant activity via modulating serotonergic systems, along with their SAR studies. The focus of the study is to provide structural insights into imidazole-based derivatives as serotonergic system modulators for the treatment of depression.

Investigation on Novel E/Z 2-Benzylideneindan-1-One-Based Photoswitches with AChE and MAO-B Dual Inhibitory Activity

The multitarget therapeutic strategy, as opposed to the more traditional 'one disease-one target-one drug', may hold promise in treating multifactorial neurodegenerative syndromes, such as Alzheimer's disease (AD) and related dementias. Recently, combining a photopharmacology approach with the multitarget-directed ligand (MTDL) design strategy, we disclosed a novel donepezil-like compound, namely 2-(4-((diethylamino)methyl)benzylidene)-5-methoxy-2,3-dihydro-1H-inden-1-one (1a), which in the E isomeric form (and about tenfold less in the UV-B photo-induced isomer Z) showed the best activity as dual inhibitor of the AD-related targets acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B). Herein, we investigated further photoisomerizable 2-benzylideneindan-1-one analogs 1b-h with the unconjugated tertiary amino moiety bearing alkyls of different bulkiness and lipophilicity. For each compound, the thermal stable E geometric isomer, along with the E/Z mixture as produced by UV-B light irradiation in the photostationary state (PSS, 75% Z), was investigated for the inhibition of human ChEs and MAOs. The pure E-isomer of the N-benzyl(ethyl)amino analog 1h achieved low nanomolar AChE and high nanomolar MAO-B inhibition potencies (IC50s 39 and 355 nM, respectively), whereas photoisomerization to the Z isomer (75% Z in the PSS mixture) resulted in a decrease (about 30%) of AChE inhibitory potency, and not in the MAO-B one. Molecular docking studies were performed to rationalize the different E/Z selectivity of 1h toward the two target enzymes.

Linezolid-associated serotonin toxicity: a systematic review

PURPOSE

This systematic review aims to evaluate the existing evidence associating linezolid to serotonin toxicity when used as monotherapy or when co-administered with other serotonergic agents.

METHODS

A systematic literature search using PubMed (till March 2023), IDWeek meetings (2003-2023), the European Congress of Clinical Microbiology and Infectious Disease Annual Meetings (2001-2023), and the American College of Clinical Pharmacy (1999-2023) identified studies and abstracts related to linezolid and serotonin toxicity.

RESULTS

A total of 84 studies were included. The data collected in retrospective/observational studies compared the incidence of serotonin toxicity with linezolid monotherapy at 0.0050% and linezolid combination therapy at 0.0134%. All cases which discontinued linezolid and serotonergic agent/s at signs and symptoms of toxicity found symptom resolution; 75% of cases reported serotonin toxicity resolution within 24-48 h after discontinuation.

CONCLUSION

Linezolid therapy when optimal should not be deferred due to the risk of serotonin syndrome. The data collected reveals a low prevalence of serotonin toxicity in both linezolid monotherapy and linezolid concurrent with other serotonergic agents.

Bioisosteric replacement based on 1,2,4-oxadiazoles in the discovery of 1H-indazole-bearing neuroprotective MAO B inhibitors

Following a hybridization strategy, a series of 5-substituted-1H-indazoles were designed and evaluated in vitro as inhibitors of human monoamine oxidase (hMAO) A and B. Among structural modifications, the bioisostere-based introduction of 1,2,4-oxadiazole ring returned the most potent and selective human MAO B inhibitor (compound 20, IC₅₀ = 52 nM, SI > 192). The most promising inhibitors were studied in cell-based neuroprotection models of SH-SY5Y and astrocytes line against H₂O₂. Moreover, preliminary drug-like features (aqueous solubility at pH 7.4; hydrolytic stability at acidic and neutral pH) were assessed for selected 1,2,4-oxadiazoles and compared to amide analogues through RP-HPLC methods. Molecular docking simulations highlighted the crucial role of molecular flexibility in providing a better shape complementarity for compound 20 within MAO B enzymatic cleft than rigid analogue 18. Enzymatic kinetics analysis along with thermal stability curves (T_m shift = +2.9 °C) provided clues of a tight-binding mechanism for hMAO B inhibition by 20.

Design, synthesis, and evaluation of N-methyl-propargylamine derivates as isoform-selective monoamine oxidases inhibitors for the treatment of nervous system diseases

A novel series of N-methyl-propargylamine derivates were designed, synthesized, and evaluated as isoform-selective monoamine oxidases (MAO) inhibitors for the treatment of nervous system diseases. The in vitro studies showed some of the compounds exhibited considerable MAO-A selective inhibitory activity (IC₅₀ of 14.86-17.16 nM), while some of the others exhibited great MAO-B selective inhibitory activity (IC₅₀ of 4.37-17.00 nM). Further studies revealed that compounds A2 （IC₅₀ against MAO-A: 17.16 ± 1.17 nM） and A5 (IC₅₀ against MAO-B: 17.00 ± 1.10 nM) had significant abilities to protect PC12 cells from H₂O₂-induced apoptosis and reactive oxygen species (ROS) production. The parallel artificial membrane permeability assay showed A2 and A5 would be potent to cross the blood-brain barrier. The results indicated that A2 showed potential use in the therapy of MAO-A related diseases, such as depression and anxiety; while A5 exhibited promising ability in the treatment of MAO-B related diseases, such as Alzheimer's disease and Parkinson's disease.

Design, synthesis of 1,2,4-triazine derivatives as antidepressant and antioxidant agents: In vitro, in vivo and in silico studies

The novel series of substituted-N-(5,6-diphenyl-1,2,4-triazin-3-yl) benzamides (R: 1-12) were designed, synthesized and evaluated for in-vitro and in-vivo antidepressant-like activity. In MAO-A inhibition assay, compound R: 5 and R: 9 displayed most potent activity with IC₅₀ = 0.12 and 0.30 µM. R: 5 and R: 9 were also evaluated for in-vivo antidepressant using FST and TST. In both models, the test samples R: 5 and R: 9 showed noteworthy antidepressant effect. R: 5 showed 46.48 % and 45.96 % reduction in immobility in FST and TST respectively at dosage of 30 mg/kg (p.o). Whereas compound R: 9 reduced the immobility time by 52.76 % and 47.14 % as compared to control in FST and TST, respectively at same dosage. Both the compounds were also tested for behavioural study using actophotometer and grip tests. None of compounds exhibited decrease in locomotor activity. Further, these compounds were subjected to in silico studies to determine their ADME properties along with binding energies and binding orientions. In ADME studies none of the compounds violated the Lipinski rule and all other parameters were also within the acceptable ranges. In docking study R: 5 (-10.7) and R: 9 (-10.4) were also displayed highest docking score. These encouraging results present the pharmacophoric features of substituted-N-(5,6-diphenyl-1,2,4-triazin-3-yl) benzamides as interesting lead for further development of new antidepressant drug molecules.

Field and atom-based 3D-QSAR models of chromone (1-benzopyran-4-one) derivatives as MAO inhibitors

Monoamine oxidases (MAOs) are flavo-enzymes that aid in the oxidative deamination of neurotransmitters like dopamine, serotonin, and epinephrine. MAO inhibitors are antidepressants that work by preventing the breakdown of brain neurotransmitters and regulating mood. MAO inhibitors that use the chromone (1-benzopyran-4-one) structure have been found to be quite effective in studies. The current study involves the creation of pharmacophore models, 3-D QSAR, virtual screening, and docking investigations, all of which are evaluated using various criteria. The investigation included 39 ligands that emerged pharmacophore AHRRR_1, as the best pharmacophore model with a survival score of 5.6485. The 3D QSAR investigation revealed a significant model with the values of R2 = 0.9064 and Q2 = 0.8239. Docking study revealed that compound 18 had the highest docking (-10.402 kcal/mol) score in the series and showed interactions with the essential amino acid TYR398 required for MAO inhibitory activity. ZINC compounds were screened using the created pharmacophore model, which was followed up with a virtual screening study. The ZINC compounds with the best XP docking scores are ZINC03113255, ZINC07777127, ZINC05166353 and ZINC09341502 (with docking scores -10.021, -9.486, -8.031 and -7.792 kcal/mol, respectively). ZINC03113255, which showed the best score, has binding interactions with amino acid residues, TYR326, TYR398 and LYS296 of monoamine oxidase B. The ADME analysis demonstrated the compound's drug-like characteristics. The findings of this study may be used in the development of chromone compounds that target the MAO inhibitor.Communicated by Ramaswamy H. Sarma.

3-(3,4-Dichlorophenyl)-5-(1H-indol-5-yl)-1,2,4-oxadiazole

3-(3,4-Dichlorophenyl)-5-(1H-indol-5-yl)-1,2,4-oxadiazole was synthesized via the condensation of 3,4-dichlorobenzamidoxime and methyl 1H-indole-5-carboxylate using a superbasic medium (NaOH/DMSO). The compound was tested as a potential inhibitor of human monoamine oxidase (MAO) A and B. It demonstrated a notable inhibition with an IC50 value of 0.036 μM for the MAO-B and isoform specificity. The product was characterized by 1H-NMR, 13C-NMR, and HRMS. In conclusion, the new active MAO-B inhibitor may serve as a candidate for the future discovery of therapeutic agents for neurodegenerative disorders such as Parkinson’s disease.

Discovery of reversible selective monoamine oxidase B inhibitors with anti-acetylcholinesterase activity derived from 4-oxo-N-4-diphenyl butanamides

Aim: Multitargeted drugs are essential for the treatment of various neurodegenerative disorders, because of their complex nature. This study aimed to develop novel small molecules as selective monoamine oxidase B (MAO-B) inhibitors with cholinesterase inhibition. Materials & methods: With the help of fragment-based drug design, some 4-oxo-N-4-diphenyl butanamides were designed and synthesized as MAO-B inhibitors with anti-acetylcholinesterase (AChE) activity. Results: Compound 6m showed the best neuroprotection, with reversible selective MAO-B inhibition activity (IC₅₀ = 11.54 ± 0.64 nM). Compounds 6b, 6h, 6j, 6n and 6p (IC₅₀ = 20.90 ± 0.50, 17.25 ± 0.90, 15.85 ± 0.16, 16.81 ± 0.85 and 25.19 ± 0.17 nM, respectively) also appeared as potent and selective MAO-B inhibitors with anti-AChE activity. Conclusion: The present study suggests potent, neuroprotective and nontoxic lead compounds as selective MAO-B inhibitors with anti-AChE activity.

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.

Design, Synthesis, and Monoamine Oxidase B Selective Inhibitory Activity of N-Arylated Heliamine Analogues

Monoamine oxidase B (MAO-B) metabolizes monoamines such as dopamine regarding neural transmission and controls its level in the mammalian's brain. When MAO-B metabolizes dopamine abnormally, normal neurotransmission does not occur, and central nervous system disorders such as Parkinson's disease may develop. Although several MAO inhibitors have been developed, most of them have no selectivity between monoamine oxidase A (MAO-A) and MAO-B, or they work irreversibly against the enzyme. This report describes the first case of screening of N-arylated heliamine derivatives to develop novel MAO-B selective inhibitors that can be synthesized concisely by microwave-assisted Pd nanoparticle-catalyzed Buchwald-Hartwig amination. We discovered that the derivatives 4h, 4i, and 4j display inhibitory activity against MAO-B with IC50 values of 1.55, 13.5, and 5.08 μM, respectively.

Design, synthesis, in-vitro, in-vivo and ex-vivo pharmacology of thiazolidine-2,4-dione derivatives as selective and reversible monoamine oxidase-B inhibitors

Neurodegenerative ailments are a diverse set of syndromes distinguished by gradual deterioration of the structure as well as functions of the central nervous system or peripheral nervous system. Alzheimer's disease (AD) and Parkinson's disease (PD) have no cure, common, and are high prevalent neurodegenerative pathologies. In current research, rationally designed thiazolidine-2,4-dione based analogs were synthesized and tested for their inhibition potential against two isoforms of monoamine oxidase (MAO-A / MAO-B). Structure activity relationships were explored. Pyridinyl and thiazolyl hydrazone derivative 43 and 44 with IC₅₀ value of 0.013 µM and 0.008 µM (selectivity 228 / 226 times) exhibited higher potency than reference drug safinamide. Most active compounds showed BBB penetration in PAMPA in-vitro assay. Except nitro derivative 41, all compounds were non-neurotoxic in the studied concentration. Molecular docking studies supported the in-vitro experimental results and the selectivity by comparing the binding energy values against both MAO-A and MAO-B isoforms. All the results of current research suggest compounds 43 and 44 may serve as promising candidates for further research for treatment of neurodegenerative diseases.

Monoamine oxidase inhibitors: A concise review with special emphasis on structure activity relationship studies

Monoamine oxidase enzyme is necessary for the management of brain functions. It oxidatively metabolizes monoamines and produces ammonia, aldehyde and hydrogen peroxide as by-products. Excessive production of by-products of monoamine metabolism generates free radicals which cause cellular apoptosis and several neurodegenerative disorders for example Alzheimer's disease, Parkinson's disease, depression and autism. The inhibition of MAOs is an attractive target for the treatment of neurological disorders. Clinically approved MAO inhibitors for example selegiline, rasagiline, clorgyline, pargyline etc. are irreversible in nature and cause some adverse effects while recently studied reversible MAO inhibitors are devoid of harmful effects of old monoamine oxidase inhibitors. In this review article we have listed various synthesized molecules containing different moieties like coumarin, chalcone, thiazole, thiourea, caffeine, pyrazole, chromone etc. along with their activity, mode of action, structure activity relationship and molecular docking studies.

Calluna vulgaris as a Valuable Source of Bioactive Compounds: Exploring Its Phytochemical Profile, Biological Activities and Apitherapeutic Potential

Calluna vulgaris, belonging to the Ericaceae family, is an invasive plant that has widely spread from Europe all across Asia, North America, Australia and New Zealand. Being able to survive in rigid soil and environmental conditions, it is nowadays considered to be of high nature-conservation value. Known for its nutritional and medicinal properties, C. vulgaris stands out for its varied physiochemical composition, spotlighting a wide range of biological activity. Among the most important bioactive compounds identified in C. vulgaris, the phenolic components found in different parts of this herbaceous plant are the main source of its diverse pro-health properties (antioxidant, anti-inflammatory, antimicrobial, chemoprotective, etc.). Nonetheless, this plant exhibits an excellent nectariferous potential for social insects such as honeybees; therefore, comparing the bioactive compounds observed in the plant and in the final product of the beehive, namely honey, will help us understand and find new insights into the health benefits provided by the consumption of C. vulgaris-related products. Thus, the main interest of this work is to review the nutritional profile, chemical composition and biological activities of the C. vulgaris plant and its related honey in order to encourage the future exploration and use of this health-promoting plant in novel foods, pharmacological products and apitherapy.

Design, synthesis and biological evaluation of light-driven on-off multitarget AChE and MAO-B inhibitors

Neurodegenerative diseases are multifactorial disorders characterized by protein misfolding, oxidative stress, and neuroinflammation, finally resulting in neuronal loss and cognitive dysfunctions. Nowadays, an attractive strategy to improve the classical treatments is the development of multitarget-directed molecules able to synergistically interact with different enzymes and/or receptors. In addition, an interesting tool to refine personalized therapies may arise from the use of bioactive species able to modify their activity as a result of light irradiation. To this aim, we designed and synthesized a small library of cinnamic acid-inspired isomeric compounds with light modulated activity able to inhibit acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B), with remarkable selectivity over butyrylcholinesterase (BChE) and MAO-A, which have been investigated as the enzyme targets related to Alzheimer's disease (AD). The inhibitory activities were evaluated for the pure E-diastereomers and the E/Z-diastereomer mixtures, obtained upon UV irradiation. Molecular docking studies were carried out to rationalize the differences in the inhibition potency of the E and Z diastereomers of the best performing analogue 1c. Our preliminary findings may open-up the way for developing innovative multitarget photo-switch drugs against neurodegenerative diseases.

Design Strategies, Chemistry and Therapeutic Insights of Multi-target Directed Ligands as Antidepressant Agents

Depression is one of the major disorders of the central nervous system worldwide and causes disability and functional impairment. According to the World Health Organization, around 265 million people worldwide are affected by depression. Currently marketed antidepressant drugs take weeks or even months to show anticipated clinical efficacy but remain ineffective in treating suicidal thoughts and cognitive impairment. Due to the multifactorial complexity of the disease, single-target drugs do not always produce satisfactory results and lack the desired level of therapeutic efficacy. Recent literature reports have revealed improved therapeutic potential of multi-target directed ligands due to their synergistic potency and better safety. Medicinal chemists have gone to great extents to design multitarget ligands by generating structural hybrids of different key pharmacophores with improved binding affinities and potency towards different receptors or enzymes. This article has compiled the design strategies of recently published multi-target directed ligands as antidepressant agents. Their biological evaluation, structural-activity relationships, mechanistic and in silico studies have also been described. This article will prove to be highly useful for the researchers to design and develop multi-target ligands as antidepressants with high potency and therapeutic efficacy.

Design, Synthesis, and Pharmacological Evaluation of N-Propargylated Diphenylpyrimidines as Multitarget Directed Ligands for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD), a multifactorial complex neural disorder, is categorized with progressive memory loss and cognitive impairment as main clinical features. The multitarget directed ligand (MTDL) strategy is explored for the treatment of multifactorial diseases such as cancer and AD. Herein, we report the synthesis and screening of 24 N-propargyl-substituted diphenylpyrimidine derivatives as MTDLs against acetylcholine/butyrylcholine esterases and monoamine oxidase enzymes. In this series, VP1 showed the most potent MAO-B inhibitory activity with an IC₅₀ value of 0.04 ± 0.002 μM. VP15 with an IC₅₀ value of 0.04 ± 0.003 μM and a selectivity index of 626 (over BuChE) displayed the most potent AChE inhibitory activity in this series. In the reactive oxygen species (ROS) inhibition studies, VP1 reduced intercellular ROS levels in SH-SY5Y cells by 36%. This series of compounds also exhibited potent neuroprotective potential against 6-hydroxydopamine-induced neuronal damage in SH-SY5Y cells with up to 90% recovery. In the in vivo studies in the rats, the hydrochloride salt of VP15 was orally administered and found to cross the blood-brain barrier and reach the target site. VP15·HCl significantly attenuated the spatial memory impairment and improved the cognitive deficits in the mice. This series of compounds were found to be irreversible inhibitors and showed no cytotoxicity against neuronal cells. In in silico studies, the compounds attained thermodynamically stable orientation with complete occupancy at the active site of the receptors. Thus, N-propargyl-substituted diphenylpyrimidines displayed drug-like characteristics and have the potential to be developed as MTDLs for the effective treatment of AD.

Discovery of 3, 6-disubstituted isobenzofuran-1(3H)-ones as novel inhibitors of monoamine oxidases

Monoamine oxidases A and B (MAO-A and MAO-B) play important roles in biogenic amine metabolism, oxidative stress, and chronic inflammation. Particularly, MAO-B selective inhibitors are promising therapeutic choices for the treatment of neurodegenerative diseases, such as Pakinson's disease and Alzheimer's disease. Herein, novel 3,6-disubstituted isobenzofuran-1(3H)-ones were designed, synthesized and evaluated in vitro as inhibitors of monoamine oxidases A and B. Structure-activity relationships were investigated, and all of the compounds with (R)-3-hydroxy pyrrolidine moiety on the 6-position displayed preferable inhibition toward the MAO-B isoform. Among them, compounds 6c with a 4'-fluorobenzyl ring and 6m bearing a 3',4'-difluorobenzyl ring on the 3-position were the most potent MAO-B inhibitors with IC₅₀ values of 0.35 μM and 0.32 μM, respectively. The binding mode of compound 6m in MAO-B was predicted by CDOCKER program, revealing that (R)-3-hydroxypyrrolidine moiety is a critical structural feature for this series of MAO-B inhibitors. Compound 6m could serve as a new template structure for developing potent and selective MAO-B inhibitors.

Development of a Novel Class of Pyridazinone Derivatives as Selective MAO-B Inhibitors

Sixteen compounds (TR1-TR16) were synthesized and evaluated for their inhibitory activities against monoamine oxidase A and B (MAOs). Most of the derivatives showed potent and highly selective MAO-B inhibition. Compound TR16 was the most potent inhibitor against MAO-B with an IC₅₀ value of 0.17 μM, followed by TR2 (IC₅₀ = 0.27 μM). TR2 and TR16 selectivity index (SI) values for MAO-B versus MAO-A were 84.96 and higher than 235.29, respectively. Compared to the basic structures, the para-chloro substituent in TR2 and TR16 increased the inhibitory activity of MAO-B. TR2 and TR16 were reversible MAO-B inhibitors that were competitive, with K_i values of 0.230 ± 0.004 and 0.149 ± 0.016 µM, respectively. The PAMPA method indicated that compounds TR2 and TR16 had the tendency to traverse the blood-brain barrier. Docking investigations revealed that lead compounds were beneficial for MAO-B inhibition via association with key as well as selective E84 or Y326 residues, but not for MAO-A inhibition via interaction primarily driven by hydrophobic contacts. In conclusion, TR2 and TR16 are therapeutic prospects for the management of multiple neurodegenerative diseases.

Synthesis, In Silico and Pharmacological Evaluation of New Thiazolidine-4-Carboxylic Acid Derivatives Against Ethanol-Induced Neurodegeneration and Memory Impairment

Introduction

Several studies revealed that alcohol utilization impairs memory in adults; however, the underlying mechanism is still unclear. The production of inflammatory markers and reactive oxygen species (ROS) plays a major role in neurodegeneration, which leads to memory impairment. Therefore, targeting neuroinflammation and oxidative distress could be a useful strategy for abrogating the hallmarks of ethanol-induced neurodegeneration. Moreover, several studies have demonstrated multiple biological activities of thiazolidine derivatives including neuroprotection.

Methods

In the current study, we synthesized ten (10) new thiazolidine-4-carboxylic acid derivatives (P1-P10), characterized their synthetic properties using proton nuclear magnetic resonance (¹H-NMR) and carbon-13 NMR, and further investigated the neuroprotective potential of these compounds in an ethanol-induced neuroinflammation model.

Results

Our results suggested altered levels of antioxidant enzymes associated with an elevated level of tumor necrosis factor-alpha (TNF-α), nuclear factor-κB (p-NF-κB), pyrin domain-containing protein 3 (NLRP3), and cyclooxygenase-2 (COX-2) in ethanol-treated animals. Ethanol treatment also led to memory impairment in rats, as assessed by behavioral tests. To further support our notion, we performed molecular docking studies, and all synthetic compounds exhibited a good binding affinity with a fair bond formation with selected targets (NF-κB, TLR4, NLRP3, and COX-2).

Discussion

Overall, our results revealed that these derivatives may be beneficial in reducing neuroinflammation by acting on different stages of inflammation. Moreover, P8 and P9 treatment attenuated the neuroinflammation, oxidative stress, and memory impairment caused by ethanol.

Methylenedioxy Piperamide-Derived Compound D5 Regulates Inflammatory Cytokine Secretion in a Culture of Human Glial Cells

Neuroinflammation is the cornerstone of most neuronal disorders, particularly neurodegenerative diseases. During the inflammatory process, various pro-inflammatory cytokines, chemokines, and enzymes—such as interleukin 1-β (IL1-β), tumor necrosis factor-α (TNF-α), interleukin 6 (IL-6), inducible nitric oxide synthases (iNOS), inhibitory kappa kinase (IKK), and inducible nitric oxide (NO)—are over-expressed in response to every stimulus. Methods: In the present study, we focused on the anti-neuroinflammatory efficacy of (2E,4E)-N,5-bis(benzo[d][1,3]dioxol-5-yl)penta-2,4-dienamide, encoded D5. We investigated the efficacy of D5 on the upstream and downstream products of inflammatory pathways in CHME3 and SVG cell lines corresponding to human microglia and astrocytes, respectively, using various in silico, in vitro, and in situ techniques. Results: The results showed that D5 significantly reduced the level of pro-inflammatory cytokines by up-regulating PPAR-γ expression and suppressing IKK-β, iNOS, NO production, and NF-κB activation in inflamed astrocytes (SVG) and microglia (CHME3) after 24 h of incubation. The data demonstrated remarkably higher efficacy of D5 compared to ASA (Aspirin) in reducing NF-κB-dependent neuroinflammation. Conclusions: We observed that the functional-group alteration had an extreme influence on the levels of druggability and the immunomodulatory properties of two analogs of piperamide, D5, and D4 ((2E,4E)-5-(benzo[d][1,3]dioxol-5-yl)-N-(4-(hydroxymethyl)phenyl)penta-2,4-dienamide)). The present study suggested D5 as a potential anti-neuroinflammatory agent for further in vitro, in vivo, and clinical investigations.

Quantification of tyramine in different types of food using novel green synthesis of ficus carica quantum dots as fluorescent probe

Tyramine (TYM) is catecholamine releasing compound, tyramine rich food causing hypertensive crisis due to combination with monoamine oxidase inhibitor (MAOIs). So, Analysis of TYM in tyramine rich food (old cheese, cured meat, sausage, pickled olive and canned fish) and environment is very essential for hypertensive patients and improvement food industries. In this work, TYM was analyzed in different types of food using novel green synthesis carbon dots from ficus carica (Fig fruits). The gradual addition of TYM to PA@CQDs led to enhancement of the quantum dots fluorescence due to formation of hydrogen bonding between quantum dots and TYM. The calibration graph plotted in the range 5-400 ng mL^-1 . The method was applied to determination of TYM in different types of food as old cheese, cured meat, sausage, pickled olive and canned fish. The lower limit of quantitation (LOQ) was found to be 1.68 ng mL^-1 . The method successfully applied for the quantification of TYM in varying types of food with high sensitivity and high economic effect due to the reusability of the quantum dots. The optical and morphological characters of quantum dots were studied carefully.

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.

A Major Diplotaxis harra-Derived Bioflavonoid Glycoside as a Protective Agent against Chemically Induced Neurotoxicity and Parkinson's Models; In Silico Target Prediction; and Biphasic HPTLC-Based Quantification

Oxidative stress and chronic inflammation have a role in developing neurodegenerative diseases such as Parkinson’s disease (PD) and inflammatory movement disorders such as rheumatoid arthritis that affect millions of populations. In searching for antioxidant and anti-inflammatory molecules from natural sources that can counteract neurodegenerative diseases and arthritis, the flavonoid-rich extract of Diplotaxis harra (DHE) was selected based on its in vitro antioxidant and anti-inflammatory activities. DHE could inhibit the inducible nitric oxide synthase (iNOS) and cyclooxygenase-2 (COX-2) expressions in the lipopolysaccharide (LPS)-stimulated RAW 264.7 macrophages from 100% to the level of 28.51 ± 18.67 and 30.19 ± 5.00% at 20 μg/mL, respectively. A TLC bioautography of DHE fractions using 1,1-diphenyl-2-picryl-hydrazyl radical (DPPH) led to the isolation of a major antioxidant compound which was identified by X-ray diffraction analysis as isorhamnetin-3-O-β-D-glucoside (IR3G). IR3G also exhibited a potent anti-inflammatory activity, particularly by suppressing the upregulation of iNOS expression, similar to that of dexamethasone (DEX) at 10 μM to the level of 35.96 ± 7.80 and 29.34 ± 6.34%, respectively. Moreover, IR3G displayed a strong neuroprotectivity (>60% at 1.0−4−1.0−3 μM) against 6-hydroxydopamine (6-OHDA)-challenged SHSY5Y neuroblastoma, an in vitro model of dopaminergic neurons for Parkinson’s disease (PD) research. Accordingly, the in vivo anti-Parkinson potentiality was evaluated, where it was found that IR3G successfully reversed the 6-OHDA-induced locomotor deficit in a zebrafish model. A study of molecular docking and molecular dynamic (MD) simulation of IR3G and its aglycone isorhamnetin (IR) against human acetylcholine esterase (AChE), monoamine oxidase B (MAO-B), and Polo-like kinase-2 (PLK2) was performed and further outlined a putative mechanism in modulating neurodegenerative diseases such as PD. The free radical scavenging, anti-inflammatory through anti-iNOS and anti-COX-2 expression, and neuroprotective activities assessed in this study would present partial evidence for the potentiality of D. harra-derived IR3G as a promising natural therapeutic agent against neurodegenerative diseases and inflammatory arthritis. Finally, a biphasic HPTLC method was developed to estimate the biomarker IR3G in D. harra quantitatively.

Benzothiazole Pyrazoline: Acid-Switchable Absorption and Fluorescence of Photoinduced Electron Transfer (PET)

Acid-responsive fluorescent compounds were prepared by introducing an ortho-hydroxyphenyl to pyrazoline with a benzothiazole backbone. These compounds demonstrated normal fluorescence photoinduced electron transfer (PET) under neutral conditions but the addition of trifluoroacetic acid showed an arctic blue fluorescence, we verified that a protonation process of nitrogen in the thiazole ring which weakened the ability of thiazole to donate electrons to the pyrazoline and changed the photoinduced electron transfer led to photoinduced electron transfer (PET), which was the mechanism of the fluorescence quenching phenomenon under strongly acidic conditions. The photophysical properties of Benzothiazole pyrazoline exhibited blue emission at 421 nm in aqueous DMSO. The blue shift in the emission was switched by acid in DMSO, showing the compound's distinct fluorescence peak at 554 nm. To investigate solvatochromism, eight different solvents were used. The red-shift emission observed in enhancing the polarity of solvents and emission in DMSO suggested the conformation of the molecule which led to the intramolecular charge transfer by color and emission changes. Furthermore, the probe was also applied using the High-performance liquid chromatography (HPLC) with a UV detector to determine the trifluoroacetic acid in water samples. Interestingly, the method was found to be linear over the range of 10.0 µg L^-1 to 250.0 µg L^-1 (0.999). Under the optimum condition, the separation of trifluoroacetic acid was achieved in 20 min with the LOD of 1.3 µg L^-1 and LOQ of 5.1 µg L^-1. This proposed method also showed satisfactory results when applied for the analysis of trifluoroacetic acid in a water sample.

A Review on the Arylpiperazine Derivatives as Potential Therapeutics for the Treatment of Various Neurological Disorders

Abstract:

Neurological disorders are disease conditions related to the neurons and central nervous system (CNS). Any kind of structural, electrical, biochemical and functional abnormalities in neurons can lead to various types of disorders like Alzheimer’s disease (AD), depression, Parkinson’s disease (PD), epilepsy, stroke, etc. Currently available medicines are symptomatic and do not treat the disease state. Thus, novel CNS active agents with the potential of complete treatment of an illness are highly desired. A range of small organic molecules are being explored as potential drug candidates for the cure of different neurological disorders. In this context, arylpiperazine has been found to be a versatile scaffold and indispensable pharmacophore in many CNS active agents. A number of molecules with arylpiperazine nucleus have been developed as potent leads for the treatment of AD, PD, depression and other disorders. The arylpiperazine nucleus can be optionally substituted at different chemical structures and offer flexibility for the synthesis of large number of derivatives. In the current review article, we have explored the role of various arylpiperazine containing scaffolds against different neurological disorders, including AD, PD, and depression. The structure-activity relationship studies were conducted for recognizing potent lead compounds. This review article may provide important clues on the structural requirements for the design and synthesis of effective molecules as curative agents for different neurological disorders.

Monoamine oxidase A and B inhibitory activities of 3,5-diphenyl-1,2,4-triazole substituted [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives

Monoamine oxidase (EC 1.4.3.4, MAO) is a flavin adenine dinucleotide-containing flavoenzyme located on the outer mitochondrial membrane and catalyzes the oxidative deamination of monoaminergic neurotransmitters and dietary amines. MAO exists in humans as two isoenzymes, hMAO-A and hMAO-B, which are distinguished by their tertiary structures, preferred substrates and inhibitors, and selective inhibition of these isoenzymes are used in the treatment of different diseases such as Alzheimer's, Parkinson's and depression. In the present study, we report the design, synthesis and characterization of 3,5-diphenyl-1,2,4-triazole substituted [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole derivatives as novel and selective inhibitors of hMAO-B. Twenty one compounds (38, 39a-h, 41a-d, 42a-h) were screened for their inhibitory activity against hMAO-A and hMAO-B by using in vitro Amplex Red® reagent based fluorometric method and all compounds were found to be as selective h-MAO-B inhibitors to a different degree. The compound 42e and 42h displayed the highest inhibitory activity against hMAO-B with IC₅₀ values of 2.51 and 2.81 µM, respectively, and more than 25-fold selectivity towards inhibition of hMAO-B. A further kinetic evaluation of the most potent derivative (42e) was also performed and a mixed mode of inhibition of hMAO-B by the compound 42e was determined (K_i = 0,26 µM). According to our findings the [1,2,4]triazolo[3,4-b][1,3,4]thiadiazole emerged as a promising scaffold for the development of novel and selective hMAO-B inhibitors.

Pyridazinones containing dithiocarbamoyl moieties as a new class of selective MAO-B inhibitors

A novel class of potential MAO-B inhibitors was designed and synthesized in good yield by combining the pyridazinone moiety with the dithiocarbamate framework, two relevant pharmacophores for drug discovery. The biological results obtained for the different pyridazinone/dithiocarbamate hybrids (compounds 8-14) indicated that most of them reversibly and selectively inhibit the hMAO-B in vitro with IC₅₀ values in the µM range and exhibit not significant cellular toxicity. The analogues 9a₁, 11a₁, 12a₂, 12b₁ and 12b₂, which present the dithiocarbamate fragment derivatized with a piperidin-1-yl or pyrrolidin-1-yl group and placed at C3 or C4 of the diazine ring, were the most attractive compounds of these series. Molecular modeling studies were performed to analyze the binding mode to the enzyme and the structure activity relationships of the titled compounds, as well as to predict their drug-like properties.

Recent developments in mitogen activated protein kinase inhibitors as potential anticancer agents

The mitogen activated protein kinase (MAPK) belongs to group of kinase that links the extracellular stimuli to intracellular response. The MAPK signalling pathway (RAS-RAF-MEK-ERK) involved in different pathological conditions like cancer, caused due to genetic or any other factor such as physical or environmental. Many studies have been conducted on the pathological view of MAPK cascade and its associated element like RAS, RAF, MEK, ERK or its isoforms, and still the research is going on particularly with respect to its activation, regulation and inhibition. The MAPK signalling pathway has become the area of research to identify new target for the management of cancer. A number of heterocyclics are key to fight with the cancer associated with these enzymes thus give some hope in the management of cancer by inhibiting MAPK cascade. In the present article, we have focussed on MAPK signalling pathway and role of different heterocyclic scaffolds bearing nitrogen, sulphur and oxygen and about their potential to block MAPK signalling pathway. The heterocyclics are gaining importance due to high potency and selectivity with less off-target effects against different targets involved in the MAPK signalling pathway. We have tried to cover recent advancements in the MAPK signalling pathway inhibitors with an aim to get better understanding of the mechanism of action of the compounds. Several compounds in the preclinical and clinical studies have been thoroughly dealt with. In addition to the synthetic compounds, a significant number of natural products containing heterocyclic moieties as MAPK signalling pathway inhibitors have been put together. The structure activity relationship along with docking studies have been discussed to apprehend the mechanistic studies of various compounds that will ultimately help to design and develop more MAPK signalling pathway inhibitors.

Role of Monoamine Oxidase Activity in Alzheimer's Disease: An Insight into the Therapeutic Potential of Inhibitors

Despite not being utilized as considerably as other antidepressants in the therapy of depression, the monoamine oxidase inhibitors (MAOIs) proceed to hold a place in neurodegeneration and to have a somewhat broad spectrum in respect of the treatment of neurological and psychiatric conditions. Preclinical and clinical studies on MAOIs have been developing in recent times, especially on account of rousing discoveries manifesting that these drugs possess neuroprotective activities. The altered brain levels of monoamine neurotransmitters due to monoamine oxidase (MAO) are directly associated with various neuropsychiatric conditions like Alzheimer’s disease (AD). Activated MAO induces the amyloid-beta (Aβ) deposition via abnormal cleavage of the amyloid precursor protein (APP). Additionally, activated MAO contributes to the generation of neurofibrillary tangles and cognitive impairment due to neuronal loss. No matter the attention of researchers on the participation of MAOIs in neuroprotection has been on monoamine oxidase-B (MAO-B) inhibitors, there is a developing frame of proof indicating that monoamine oxidase-A (MAO-A) inhibitors may also play a role in neuroprotection. The therapeutic potential of MAOIs alongside the complete understanding of the enzyme’s physiology may lead to the future advancement of these drugs.

Structural exploration of multifunctional monoamine oxidase B inhibitors as potential drug candidates against Alzheimer's disease

AD is one of the most typical neurodegenerative disorders that suffer many seniors worldwide. Recently, MAO inhibitors have received increasing attention not only for their roles involved in monoamine neurotransmitters metabolism and oxidative stress but also for their additional neuroprotective and neurorescue effects against AD. The curiosity in MAO inhibitors is reviving, and novel MAO-B inhibitors recently developed with ancillary activities (e.g., Aβ aggregation and AChE inhibition, anti-ROS and chelating activities) have been proposed as multitarget drugs foreshadowing a positive outlook for the treatment of AD. The current review describes the recent development of the design, synthesis, and screening of multifunctional ligands based on MAO-B inhibition for AD therapy. Structure-activity relationships and rational design strategies of the synthetic or natural product derivatives (chalcones, coumarins, chromones, and homoisoflavonoids) are discussed.

Development of Halogenated Pyrazolines as Selective Monoamine Oxidase-B Inhibitors: Deciphering via Molecular Dynamics Approach

Halogens have been reported to play a major role in the inhibition of monoamine oxidase (MAO), relating to diverse cognitive functions of the central nervous system. Pyrazoline/halogenated pyrazolines were investigated for their inhibitory activities against human monoamine oxidase-A and -B. Halogen substitutions on the phenyl ring located at the fifth position of pyrazoline showed potent MAO-B inhibition. Compound 3-(4-ethoxyphenyl)-5-(4-fluorophenyl)-4,5-dihydro-1H-pyrazole (EH7) showed the highest potency against MAO-B with an IC₅₀ value of 0.063 µM. The potencies against MAO-B were increased in the order of –F (in EH7) > –Cl (EH6) > –Br (EH8) > –H (EH1). The residual activities of most compounds for MAO-A were > 50% at 10 µM, except for EH7 and EH8 (IC₅₀ = 8.38 and 4.31 µM, respectively). EH7 showed the highest selectivity index (SI) value of 133.0 for MAO-B, followed by EH6 at > 55.8. EH7 was a reversible and competitive inhibitor of MAO-B in kinetic and reversibility experiments with a Ki value of 0.034 ± 0.0067 µM. The molecular dynamics study documented that EH7 had a good binding affinity and motional movement within the active site with high stability. It was observed by MM-PBSA that the chirality had little effect on the overall binding of EH7 to MAO-B. Thus, EH7 can be employed for the development of lead molecules for the treatment of various neurodegenerative disorders.

Multi-Target-Directed Ligands as an Effective Strategy for the Treatment of Alzheimer's Disease

Alzheimer's disease (AD) is a complex neurological disorder, and multiple pathological factors are believed to be involved in the genesis and progression of the disease. A number of hypotheses, including Acetylcholinesterase, Monoamine oxidase, β-Amyloid, Tau protein, etc., have been proposed for the initiation and progression of the disease. At present, acetylcholine esterase inhibitors and memantine (NMDAR antagonist) are the only approved therapies for the symptomatic management of AD. Most of these single-target drugs have miserably failed in the treatment or halting the progression of the disease. Multi-factorial diseases like AD require complex treatment strategies that involve simultaneous modulation of a network of interacting targets. Since the last few years, Multi-Target-Directed Ligands (MTDLs) strategy, drugs that can simultaneously hit multiple targets, is being explored as an effective therapeutic approach for the treatment of AD. In the current review article, the authors have briefly described various pathogenic pathways associated with AD. The importance of Multi-Target-Directed Ligands and their design strategies in recently reported articles have been discussed in detail. Potent leads are identified through various structure-activity relationship studies, and their drug-like characteristics are described. Recently developed promising compounds have been summarized in the article. Some of these MTDLs with balanced activity profiles against different targets have the potential to be developed as drug candidates for the treatment of AD.

Piperazine, a Key Substructure for Antidepressants: Its Role in Developments and Structure-Activity Relationships

Depression is the single largest contributor to global disability with a huge economic and social burden on the world. There are a number of antidepressant drugs on the market, but treatment-resistant depression and relapse of depression in a large number of patients have increased problems for clinicians. One peculiarity observed in most of the marketed antidepressants is the presence of a piperazine substructure. Although piperazine is also used in the optimization of other pharmacological agents, it is almost extensively used for the development of novel antidepressants. One common understanding is that this is due to its favorable CNS pharmacokinetic profile; however, in the case of antidepressants, piperazine plays a much bigger role and is involved in specific binding conformations of these agents. Therefore, in this review, a critical analysis of the significance of the piperazine moiety in the development of antidepressants has been performed. An overview of current developments in the designing and synthesis of piperazine-based antidepressants (2015 onwards) along with SAR studies is also provided. The various piperazine-based therapeutic agents in early- or late-phase human testing for depression are also discussed. The preclinical compounds discussed in this review will help researchers understand how piperazine actually influences the design and development of novel antidepressant compounds. The SAR studies discussed will provide crucial clues about the structural features and optimizations required to enhance the efficacy and potency of piperazine-based antidepressants.

Effect of organic solvents on solvatochromic, fluorescence, and electrochemical properties of synthesized thiazolylcoumarin derivatives

In this present investigation, thiazolylcoumarin derivatives (5a-5k) were synthesized from thiosemicarbazide, ethyl acetoacetate, and naphthaldehyde through a multistep route. The formation of thiazolylcoumarin derivatives with bioactive scaffolds was confirmed through nuclear magnetic resonance spectroscopy. A solvatochromic study of synthesized thiazolylcoumarin derivatives was carried out using ultraviolet-visible methods for dimethylformamide (DMF), ethyl acetate, and ethanol solvents. The redox behaviour of as-synthesized thiazolylcoumarin derivatives (5a-5k) was examined in dimethyl sulphoxide by conducting an electrochemical study. Fluorescence properties of thiazolylcoumarin derivatives were studied in DMF, ethanol, and ethyl acetate to visualize the solvent effect on the emitting ability of thiazolylcoumarin derivatives.