Pharmacophore-Based 3D-QSAR Analysis of Thienyl Chalcones as a New Class of Human MAO-B Inhibitors: Investigation of Combined Quantum Chemical and Molecular Dynamics Approach

High-throughput discovery of highly selective reversible hMAO-B inhibitors based on at-line nanofractionation

Human monoamine oxidase B (hMAO-B) has emerged as a pivotal therapeutic target for Parkinson's disease. Due to adverse effects and shortage of commercial drugs, there is a need for novel, highly selective, and reversible hMAO-B inhibitors with good blood-brain barrier permeability. In this study, a high-throughput at-line nanofractionation screening platform was established with extracts from Chuanxiong Rhizoma, which resulted in the discovery of 75 active compounds, including phenolic acids, volatile oils, and phthalides, two of which were highly selective novel natural phthalide hMAO-B inhibitors that were potent, selective, reversible and had good blood‒brain permeability. Molecular docking and molecular dynamics simulations elucidated the inhibition mechanism. Sedanolide (IC50 = 103 nmol/L; SI = 645) and neocnidilide (IC50 = 131 nmol/L; SI = 207) demonstrated their excellent potential as hMAO-B inhibitors. They offset the limitations of deactivating enzymes associated with irreversible hMAO-B inhibitors such as rasagiline. In SH-SY5Y cell assays, sedanolide (EC50 = 0.962 μmol/L) and neocnidilide (EC50 = 1.161 μmol/L) exhibited significant neuroprotective effects, comparable to the positive drugs rasagiline (EC50 = 0.896 μmol/L) and safinamide (EC50 = 1.079 μmol/L). These findings underscore the potential of sedanolide as a novel natural hMAO-B inhibitor that warrants further development as a promising drug candidate.

Two dimensional-QSAR and molecular dynamics studies of a selected class of aldoxime- and hydroxy-functionalized chalcones as monoamine oxidase-B inhibitors

Candidates generated from unsaturated ketone (chalcone) demonstrated as strong, reversible and specific monoamine oxidase-B (MAO-B) inhibitory activity. For the research on MAO-B inhibition, our team has synthesized and evaluated a panel of aldoxime-chalcone ethers (ACE) and hydroxylchalcones (HC). The MAO-B inhibitory activity of several candidates is in the micro- to nanomolar range in these series. The purpose of this research was to develop predictive QSAR models and look into the relation between MAO-B inhibition by aldoxime and hydroxyl-functionalized chalcones. It was shown that the molecular descriptors ETA Shape P, MDEO-12, ETA dBetaP, SpMax1 Bhi and ETA EtaP B are significant in the inhibitory action of the MAO-B target. Using the current 2D QSAR models, potential chalcone-based MAO-B inhibitors might be created. The lead molecules were further analyzed by the detailed molecular dynamics study to establish the stability of the ligand-enzyme complex.Communicated by Ramaswamy H. Sarma.

Computational Chemistry and Molecular Modeling of Reversible MAO Inhibitors

Proper elucidation of drug-target interaction is one of the most significant steps at the early stages of the drug development research. Computer-aided drug design tools have substantial contribution to this stage. In this chapter, we specifically concentrate on the computational methods widely used to develop reversible inhibitors for monoamine oxidase (MAO) isozymes. In this context, current computational techniques in identifying the best drug candidates showing high potency are discussed. The protocols of structure-based drug design methodologies, namely, molecular docking, in silico screening, and molecular dynamics simulations, are presented. Employing case studies of safinamide binding to MAO B, we demonstrate how to use AutoDock 4.2.6 and NAMD software packages.

Hansch-Type QSAR Models for the Rational Design of MAO Inhibitors: Basic Principles and Methodology

Hansch-type regression analysis enables the derivation of quantitative structure-activity relationship (QSAR) equations correlating bioactivity data with physicochemical parameters accounting for hydrophobicity, electronic properties, and steric effects of molecules or functional groups (substituents). Two datasets of MAO A and B inhibitors were enrolled in prototypical workflows employing multiparametric stepwise regression analysis, which includes linear and nonlinear (generally quadratic) terms. The optimal choice of variables (and/or combinations thereof) along with statistical validation yielded two robust equations describing MAO B potency and B/A selectivity, which included three and one parameter(s), respectively, and explained more than 80% of y-variance (r²) with low standard deviation (s) and good statistical significance (F, Fisher value).

Development of 2D, 3D-QSAR and Pharmacophore Modeling of Chalcones for the Inhibition of Monoamine Oxidase B

BACKGROUND

Selective and reversible types of MAO-B inhibitors have emerged as promising candidates for the management of neurodegenerative diseases. Several functionalized chalcone derivatives were shown to have potential reversible MAO-B inhibitory activity, which have recently been reported from our laboratory.

METHODS

With the experimental results of about 70 chalcone derivatives, we further developed a pharmacophore modelling, and 2D and 3D- QSAR analyses of these reported chalcones for MAO-B inhibition.

RESULTS

The 2D-QSAR model presented four variables (MATS7v, GATS 1i and 3i, and C-006) from 143 Dragon 7 molecular descriptors, with a r2 value of 0.76 and a Q2cv for cross-validation equal to 0.72. An external validation also was performed using 11 chalcones, obtaining a Q2ext value of 0.74. The second 3D-QSAR model using MLR (multiple linear regression) was built starting from 128 Volsurf+ molecular descriptors, being identified as 4 variables (Molecular descriptors): D3, CW1 and LgS11, and L2LGS. Adetermination coefficient (r2) value of 0.76 and a Q2cv for cross-validation equal to 0.72 were obtained for this model. An external validation also was performed using 11 chalcones and a Q2ext value of 0.74 was found.

CONCLUSION

This report exhibited a good correlation and satisfactory agreement between experiment and theory.

Privileged Pharmacophore of FDA Approved Drugs in Combination with Chalcone Framework: A New Hope for Alzheimer's Treatment

Multi-functional design of ligands emerged as a new drug design paradigm of Alzheimer's disease (AD). Given the complexity of AD, the molecules showing dual inhibition of monoamine oxidase (MAO) and acetylcholinesterase (AChE) with neuroprotective properties could prevent the progressive neural degeneration effectively. Numerous studies documented that chalcone is a privileged structural framework for the inhibition of both MAO and AChE. The recent studies suggested that the development of chalcone candidates endowed with pharmacophores of FDA approved drugs may become an active molecules in the field of current AD research. The current perspective described the recent updates of chalcone moiety linked with the pharmacophores of flurbiprofen and rivastigmine hybrids as selective ChE/MAO-B inhibitors for the prophylactic agents for AD.

Developing a Multi-target Model to Predict the Activity of Monoamine Oxidase A and B Drugs

INTRODUCTION

Monoamine oxidase inhibitors (MAOIs) are compounds largely used in the treatment of Parkinson's disease (PD), Alzheimer's disease and other neuropsychiatric disorders since they are closely related to the MAO enzymes activity. The two isoforms of the MAO enzymes, MAO-A and MAO-B, are responsible for the degradation of monoamine neurotransmitters and due to this, relevant efforts have been devoted to finding new compounds with more selectivity and less side effects. One of the most used approaches is based on the use of computational approaches since they are time and money-saving and may allow us to find a more relevant structure-activity relationship.

OBJECTIVE

In this manuscript, we will review the most relevant computational approaches aimed at the prediction and development of new MAO inhibitors. Subsequently, we will also introduce a new multitask model aimed at predicting MAO-A and MAO-B inhibitors.

METHODS

The QSAR multi-task model herein developed was based on the use of the linear discriminant analysis. This model was developed gathering 5,759 compounds from the public dataset Chembl. The molecular descriptors used was calculated using the Dragon software. Classical statistical tests were performed to check the validity and robustness of the model.

RESULTS

The herein proposed model is able to correctly classify all the 5,759 compounds. All the statistical performed tests indicated that this model is robust and reproducible.

CONCLUSION

MAOIs are compounds of large interest since they are largely used in the treatment of very serious illness. These inhibitors may lose efficacy and produce severe side effects. Due to this, the development of selective MAO-A or MAO-B inhibitors is crucial for the treatment of these diseases and their effects. The herein proposed multi-target QSAR model may be a relevant tool in the development of new and more selective MAO inhibitors.

E-pharmacophore based screening to identify potential HIV-1 gp120 and CD4 interaction blockers for wild and mutant types

HIV-1 gp120 provides a multistage viral entry process through the conserved CD4 binding site. Hunting of potential blockers can diminish the interaction of gp120 with the CD4 host receptor leading to the suppression of HIV-1 infection. Structure-based pharmacophore virtual screening followed by binding free energy calculation, molecular dynamics (MD) simulation and density functional theory (DFT) calculation is applied to discriminate the potential blockers from six small molecule databases. Five compounds from six databases exhibited vital interactions with key residues ASP368, GLU370, ASN425, MET426, TRP427 and GLY473 of gp120, involved in the binding with CD4, host receptor. Most importantly, compound NCI-254200 displayed strong communication with key residues of wild type and drug resistance single mutant gp120 (M426L and W427V) even in the dynamic condition, evidenced from MD simulation. This investigation provided a potential compound NCI-254200 which may show inhibitory activity against HIV-1 gp120 variant interactions with CD4 host cell receptors.

New Aspects of Monoamine Oxidase B Inhibitors: The Key Role of Halogens to Open the Golden Door

A large plethora of drugs and promising lead compounds contain halogens in their structures. The introduction of such moieties strongly modulates their physical-chemical features as well as pharmacokinetic and pharmacodynamic profile. The most important outcome was shown to be the ability of these halogens to favourably influence the drug-target interaction and energetic stability within the active site by the establishment of halogen bonds. This review attempted to demonstrate the key role exerted by these versatile moieties when correctly located in an organic scaffold to display Monoamine Oxidase (MAO) inhibition and selectivity towards the B isoform of this important enzyme. Human MAOs are well-recognized as therapeutic targets for mood disorders and neurodegenerative diseases and medicinal chemists were prompted to discover the structural requirements crucial to discriminate the slight differences between the active sits of the two isoforms (MAO-A and MAOB). The analysis of the structure-activity relationships of the most important scaffolds (hydrazothiazoles, coumarins, chromones, chalcones, pyrazolines) and the impact of halogen (F, Cl, Br and I) insertion on this biological activity and isozyme selectivity have been reported being a source of inspiration for the medicinal chemists.

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.

Perspective Design of Chalcones for the Management of CNS Disorders: A Mini-Review

The development of chalcone-based compounds for CNS disorders has been explored by many research groups. Chalcones are being considered as a potent organic scaffold with widespread applications in the field of drug discovery and medicinal chemistry. The planar or semi-planar geometry of chalcones with various functionalities impinged on the terminal aromatic systems renders the molecule its bio-activity including anti-cancer, anti-malarial, anti-microbial, anti-fungal, antileishmanial, anti-viral, anti-diabetic, anti-hypertensive properties, etc. Moreover, cutting-edge research has been executed in the domain of Central Nervous System (CNS) based scheme, further, their identification and classifications also remain of high interest in the field of medicinal chemistry but the specific reviews are limited. Hence, the present review highlights the significance of chalcones toward their CNS activities (up to 2019), which include anti-depressant activity, anxiolytic activity, activity with GABA receptors, acetylcholinesterase (AChE) and butyryl cholinesterase (BChE) inhibitions, activity as adenosine receptor antagonists anti-Alzheimer's agents, β-amyloid plaques imaging agents, monoamine oxidase inhibition. To our knowledge, this is the first review exclusively for CNS activity profile of chalcones.

Aptamers in Drug Design: An Emerging Weapon to Fight a Losing Battle

Implementation of novel and biocompatible polymers in drug design is an emerging and rapidly growing area of research. Even though we have a large number of polymer materials for various applications, the biocompatibility of these materials remains as a herculean task for researchers. Aptamers provide a vital and efficient solution to this problem. They are usually small (ranging from 20 to 60 nucleotides, single-stranded DNA or RNA oligonucleotides which are capable of binding to molecules possessing high affinity and other properties like specificity. This review focuses on different aspects of Aptamers in drug discovery, starting from its preparation methods and covering the recent scenario reported in the literature regarding their use in drug discovery. We address the limitations of Aptamers and provide valuable insights into their future potential in the areas regarding drug discovery research. Finally, we explained the major role of Aptamers like medical imaging techniques, application as synthetic antibodies, and the most recent application, which is in combination with nanomedicines.

Revealing the role of fluorine pharmacophore in chalcone scaffold for shifting the MAO-B selectivity: investigation of a detailed molecular dynamics and quantum chemical study

The development of highly selective monoamine oxidase-B (MAO-B) inhibitors has great therapeutic benefit in treatment of various neurodegenerative disorders. Recent study documented that shifting of fluorine atom from para to ortho position on the phenyl B ring of heteroaryl chalcones shown a remarkable shift in the selectivity and potency between MAO-A and MAO-B isoforms. Despite the large plethora of the design of new selective MAO-B inhibitors, the current paper illustrates the role and orientation of fluorine atom with remarkable MAO-B selectivity of three compounds (O23, O24 and O25), which differ from all other substituents encountered in the chalcone scaffolds is recently reported by our group. Conformational analyses of differential inhibitory effects of O23, O24 and O25 on MAO-A and MAO-B, differential analyses of complementary interactions at MAO-A/-B active sites and differential analysis of affinity binding and per-residue energy contributions are calculated by molecular dynamics study. Density functional theory based electronic structure calculations were employed with special emphasis to electrostatic potential and frontier molecular orbitals. Results of the current study can be used for lead modification and a new insight for the development of novel fluorinated chalcones for the treatment of various neurodegenerative disorders. Communicated by Ramaswamy H. Sarma.

Chalcones: Unearthing their therapeutic possibility as monoamine oxidase B inhibitors

In the last years the continuous efforts in the development of novel and effective inhibitors of human monoamine oxidases (hMAOs) promoted the discovery of new agents able to effectively and selectively bound one of the two isoforms (hMAO-A and hMAO-B). However, the parent chalcone scaffold still covers an important role in hMAOs inhibition. In the present work, we focused our attention on the researches performed in the last five years, involving chalcones or compounds that can be correlated to them. We classified the chalcones into different groups depending on their structural characteristics or common molecular properties. In this regard, we also considered chalcones based on heterocycles and compounds endowed with scaffolds containing a masked chalcone motif. When structural attributes could not be used, we took advantage of enzymatic activity to arrange compounds in a group. We followed this approach for the multitarget agents. Finally, we also analysed the naturally occurring chalcones. All the sections were discussed exhaustively and the structure-activity relationship (SAR) analyses were sustained by means of detailed images describing the effects related to the substituents or structural changes.

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.

Quantitative Structure-Activity Relationship (QSAR) Studies for the Inhibition of MAOs

Monoamine oxidases are the crucial drug targets for the treatment of neurodegenerative disorders like depression, Parkinson's disease, and Alzheimer's disease. The enzymes catalyze the oxidative deamination of several monoamine containing neurotransmitters, i.e. serotonin (5-HT), melatonin, epinephrine, norepinephrine, phenylethylamine, benzylamine, dopamine, tyramine, etc. The oxidative reaction of monoamine oxidases results in the production of hydrogen peroxide that leads to the neurodegeneration process. Therefore, the inhibition of monoamine oxidases has shown a profound effect against neurodegenerative diseases. At present, the design and development of newer lead molecules for the inhibition of monoamine oxidases are under intensive research in the field of medicinal chemistry. Recently, the advancement in QSAR methodologies has shown considerable interest in the development of monoamine oxidase inhibitors. The present review describes the development of QSAR methodologies, and their role in the design of newer monoamine oxidase inhibitors. It will assist the medicinal chemist in the identification of selective and potent monoamine oxidase inhibitors from various chemical scaffolds.

Target Molecular-Based Neuroactivity Screening and Analysis of Panax ginseng by Affinity Ultrafiltration, UPLC-QTOF-MS and Molecular Docking

Panax ginseng exerts good neuroprotective activity at the cell and animal level, but the specific bioactive compounds and action mechanism are needed to be investigated, verified, and confirmed. In this work, affinity ultrafiltration (AUF), UPLC-QTOF-MS, and molecular docking were integrated into one strategy to screen, identify, and evaluate the bioactive compounds in ginseng at the molecular level. Three biological macromolecules (AChE, MAO-B, and NMDA receptor) were selected as the target protein for AUF-MS screening for the first time, and 16 potential neuroactive compounds were found with suitable binding degree. Then, the bioactivity of ginseng and its components were evaluated by AChE-inhibitory test and DPPH assay, and the data indicate that ginseng extract and the screened compounds have good neuroactivity. The interaction between the three targets and the screened compounds was further analyzed by molecular docking, and the results were consistent with a few discrepancies in comparison with the AUF results. Finally, according to the corresponding relation between component-target-pathway, the action mechanism of ginseng elucidated that ginseng exerts a therapeutic effect on AD through multiple relations of components, targets, and pathways, which is in good accordance with the TCM theory.

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.

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.

Monoamine oxidase-B inhibitors as potential neurotherapeutic agents: An overview and update

Monoamine oxidase (MAO) inhibitors have made significant contributions and remain an indispensable approach of molecular and mechanistic diversity for the discovery of antineurodegenerative drugs. However, their usage has been hampered by nonselective and/or irreversible action which resulted in drawbacks like liver toxicity, cheese effect, and so forth. Hence, the search for selective MAO inhibitors (MAOIs) has become a substantial focus in current drug discovery. This review summarizes our current understanding on MAO-A/MAO-B including their structure, catalytic mechanism, and biological functions with emphases on the role of MAO-B as a potential therapeutic target for the development of medications treating neurodegenerative disorders. It also highlights the recent developments in the discovery of potential MAO-B inhibitors (MAO-BIs) belonging to diverse chemical scaffolds, arising from intensive chemical-mechanistic and computational studies documented during past 3 years (2015-2018), with emphases on their potency and selectivity. Importantly, readers will gain knowledge of various newly established MAO-BI scaffolds and their development potentials. The comprehensive information provided herein will hopefully accelerate ideas for designing novel selective MAO-BIs with superior activity profiles and critical discussions will inflict more caution in the decision-making process in the MAOIs discovery.

Cholinesterase Inhibitory Activities of Selected Halogenated Thiophene Chalcones

BACKGROUND

Dual-acting human monoamine oxidase B (hMAO-B) and cholinesterase (ChE) inhibitors are more effective than the classic one-drug one-target therapy for Alzheimer's disease (AD).

METHODS

The ChE inhibitory ability of some halogenated thiophene chalcone-based molecules known to be selective hMAO-B inhibitors was evaluated.

RESULTS

Based on the IC50 values, the selected compounds were found to moderately inhibit ChE, with IC50 values in the range of 14-70 µM. Among the synthesised molecules, T8 and T6 showed the most potent inhibitory activity against AChE and BChE, respectively.

CONCLUSION

Taken together, the data revealed that T8 could be further optimized to enhance its AChE inhibitory activity.

Selected aryl thiosemicarbazones as a new class of multi-targeted monoamine oxidase inhibitors

A series of 13 phenyl substituted thiosemicarbazones (SB1-SB13) were synthesized and evaluated for their inhibitory potential towards human recombinant monoamine oxidase A and B (MAO-A and MAO-B, respectively) and acetylcholinesterase. The solid state structure of SB4 was ascertained by the single X-ray diffraction technique. Compounds SB5 and SB11 were potent for MAO-A (IC₅₀ 1.82 ± 0.14) and MAO-B (IC₅₀ 0.27 ± 0.015 μM), respectively. Furthermore, SB11 showed a high selectivity index (SI > 37.0) for MAO-B. The effects of fluorine orientation revealed that SB11 (m-fluorine) showed 28.2 times higher inhibitory activity than SB12 (o-fluorine) against MAO-B. Furthermore, inhibitions by SB5 and SB11 against MAO-A and MAO-B, respectively, were recovered to near reference levels in reversibility experiments. Both SB5 and SB11 showed competitive inhibition modes, with K _i values of 0.97 ± 0.042 and 0.12 ± 0.006 μM, respectively. These results indicate that SB5 and SB11 are selective, reversible and competitive inhibitors of MAO-A and MAO-B, respectively. Compounds SB5, SB7 and SB11 showed moderate inhibition against acetylcholinesterase with IC₅₀ values of 35.35 ± 0.47, 15.61 ± 0.057 and 26.61 ± 0.338 μM, respectively. Blood-brain barrier (BBB) permeation was studied using the parallel artificial membrane permeation assay (PAMPA) method. Molecular docking studies were carried out using AutoDock 4.2.

Structural and optical profile of a multifunctionalized 2-pyridone derivative in a crystal engineering perspective

The supramolecular structural features of organic molecules are very important with regard to their widespread properties in both solids and solutions. Herein, we describe the synthesis of a novel multifunctional 2-pyridone derivative, namely 6-(4-chlorophenyl)-5-formyl-4-methylsulfanyl-2-oxo-1,2-dihydropyridine-3-carbonitrile, C₁₄H₉ClN₂O₂S, denoted P1, and its structural features were established through X-ray crystallography. A Hirshfeld surface analysis followed by a two-dimensional fingerprint plot analysis was carried out. A frontier molecular orbital investigation and natural bond orbital (NBO) calculations explored the charge-transfer interactions associated with the molecular system. The optical properties of the 2-pyridone derivative were elucidated through UV-Vis absorption and emission spectroscopy, indicating a strong blue emissive nature with a colour purity of 82.5%, a short-lived lifetime and a large Stokes shift. Time-dependent density functional theory (TD-DFT) was used to gain some insight into the absorption behaviour and emissive characteristics of P1.

Imidazole bearing chalcones as a new class of monoamine oxidase inhibitors

In the present study, series of eleven (2E)-1-[4-(1H-imidazol-1-yl)substituted phenyl]-3-phenylprop-2-en-1-one (IM1-IM11) derivatives were synthesized and evaluated as inhibitors of recombinant human monoamine oxidase (MAO) A and B. The results indicate that (2E)-3-[4-(dimethylamino) phenyl]-1-[4-(1H-imidazol-1-yl) phenyl] prop-2-en-1-one (IM5) is a nonselective and reversible competitive inhibitor of MAO-A and MAO-B with IC₅₀ values of 0.30 ± 0.010 and 0.40 ± 0.017 μM, respectively ; those of (2E)-1-[4-(1H-imidazol-1-yl) phenyl]-3-(4-methylphenyl) prop-2-en-1-one (IM4) were 1.06 ± 0.090 and 0.32 ± 0.021 μM, respectively. Kinetic studies document that both IM5 and IM4 are competitive inhibitors of MAO-A and MAO-B with Ki value of 0.11 ± 0.0085 and 0.085 ± 0.0064 μM, respectively. Molecular docking studies of lead compounds further explained the binding modes in the inhibitor binding cavity of both MAO-A and MAO-B.

Discovery of potent and reversible MAO-B inhibitors as furanochalcones

A series of twelve furanochalcones (F1-F12) was synthesized and investigated for their human monoamine oxidase inhibitory activities. Among the series, compound (2E, 4E)-1-(furan-2-yl)-5-phenylpenta-2, 4-dien-1-one (F1), which was analyzed by single-crystal X-ray diffraction, showed potent and selective MAO-B inhibitory activity with an inhibition constant (K_i) value of 0.0041 μM and selectivity index of (SI) 172.4, and exhibited competitive inhibition. Introduction of a cinnamyl group to the furanochalcone significantly increased the inhibitory activity. In the dilution-recovery experiments, the residual activities of MAO-A and MAO-B by F1 under the diluted condition fully recovered as compared with the undiluted condition, indicating F1 is a reversible inhibitor. The K_i value of F1 is the lowest among the values of chalcone derivatives and furthermore lower than that (0.0079 μM) of the reversible MAO-B inhibitor, lazabemide, a marketed drug. Molecular docking study against hMAO-B provided the binding site interactions of the lead compound, including strong π-π stacking between the phenyl system and FAD nucleus.