Synthesis and anti-cholinesterase activity of new 7-hydroxycoumarin derivatives

Umbelliferone and Its Synthetic Derivatives as Suitable Molecules for the Development of Agents with Biological Activities: A Review of Their Pharmacological and Therapeutic Potential

Umbelliferone (UMB), known as 7-hydroxycoumarin, hydrangine, or skimmetine, is a naturally occurring coumarin in the plant kingdom, mainly from the Umbelliferae family that possesses a wide variety of pharmacological properties. In addition, the use of nanoparticles containing umbelliferone may improve anti-inflammatory or anticancer therapy. Also, its derivatives are endowed with great potential for therapeutic applications due to their broad spectrum of biological activities such as anti-inflammatory, antioxidant, neuroprotective, antipsychotic, antiepileptic, antidiabetic, antimicrobial, antiviral, and antiproliferative effects. Moreover, 7-hydroxycoumarin ligands have been implemented to develop 7-hydroxycoumarin-based metal complexes with improved pharmacological activity. Besides therapeutic applications, umbelliferone analogues have been designed as fluorescent probes for the detection of biologically important species, such as enzymes, lysosomes, and endosomes, or for monitoring cell processes and protein functions as well various diseases caused by an excess of hydrogen peroxide. Furthermore, 7-hydroxy-based chemosensors may serve as a highly selective tool for Al3+ and Hg2+ detection in biological systems. This review is devoted to a summary of the research on umbelliferone and its synthetic derivatives in terms of biological and pharmaceutical properties, especially those reported in the literature during the period of 2017-2023. Future potential applications of umbelliferone and its synthetic derivatives are presented.

Development of quinazolinone and vanillin acrylamide hybrids as multi-target directed ligands against Alzheimer's disease and mechanistic insights into their binding with acetylcholinesterase

In view of Multi-Target Directed Ligand (MTDL) approach in treating Alzheimer's Disease (AD), a series of novel quinazolinone and vanillin cyanoacetamide based acrylamide derivatives (9a-z) were designed, synthesized, and assessed for their activity against a panel of selected AD targets including acetylcholinesterase (AChE), butyrylcholinesterase (BChE), amyloid β protein (Aβ), and also 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging and neuroprotective activities. Five of the target analogs 9e, 9h, 9 l, 9t and 9z showed elevated AChE inhibitory activity with IC50 values of 1.058 ± 0.06, 1.362 ± 0.09, 1.434 ± 0.10, 1.015 ± 0.10, 1.035 ± 0.02 µM respectively, high inhibition selectivity against AChE over BChE and good DPPH radical scavenging activity. Enzyme kinetic studies of the potent hybrids in the series disclosed their mixed inhibition approach. Active analogs were found to be non-toxic on SK-N-SH cell lines and have excellent neuroprotective effects against H2O2-induced cell death. Strong modulating affinities on Aβ aggregation process were observed for most active compounds since; they irretrievably interrupted the morphology of Aβ42 fibrils, increased the aggregates and declined the Aβ-induced toxicity in neurons. From the fluorescence emission studies, the binding constants (K) were determined as 2.5 ± 0.021x103, 2.7 ± 0.015x103, 3.7 ± 0.020x103, 2.4 ± 0.013x104, and 5.0 ± 0.033x103 M-1 and binding free energies as -5.82 ± 0.033, -6.07 ± 0.042, -6.26 ± 0.015, -7.71 ± 0.024, and -6.29 ± 0.026 kcal M-1 for complexes of AChE-9e, 9h, 9 l, 9t and 9z, respectively. Moreover, the CD analysis inferred the limited modifications in the AChE secondary structure when it binds to 9e, 9h, 9 l, 9t and 9z. On the basis of docking studies against AChE, the most active congeners were well oriented in the enzyme's active site by interacting with both catalytic active site (CAS) and peripheral anionic site (PAS). In summary, these quinazolinone and vanillin acrylamide hybrid analogs can be used as promising molecular template to further explore their in vivo efficiency in the development of lead compound to treat AD.Communicated by Ramaswamy H. Sarma.

Pathogenesis of Alzheimer's Disease and Diversity of 1,2,3-Triazole Scaffold in Drug Development: Design Strategies, Structural Insights, and Therapeutic Potential

Alzheimer's disease is a most prevalent form of dementia all around the globe and currently poses a significant challenge to the healthcare system. Currently available drugs only slow the progression of this disease rather than provide proper containment. Identification of multiple targets responsible for this disease in the last three decades established it as a multifactorial neurodegenerative disorder that needs novel multifunctional agents for its management and the possible reason for the failure of currently available single target clinical drugs. 1,2,3-Triazole is a miraculous nucleus in medicinal chemistry and the first choice for development of multifunctional hybrid molecules. Apart from that, it is an integral component of various drugs in clinical trials as well as in clinical practice. This review is focused on the pathogenesis of Alzheimer's disease and 1,2,3-triazole containing derivatives developed in recent decades as potential anti-Alzheimer's agents. The review will provide (A) precise insight of various established targets of Alzheimer's disease including cholinergic, amyloid, tau, monoamine oxidases, glutamate, calcium, and reactive oxygen species hypothesis and (B) design hypothesis, structure-activity relationships, and pharmacological outcomes of 1,2,3-triazole containing multifunctional anti-Alzheimer's agents. This review will provide a baseline for various research groups working on Alzheimer's drug development in designing potent, safer, and effective multifunctional anti-Alzheimer's candidates of the future.

Review of triazole scaffolds for treatment and diagnosis of Alzheimer's disease

Triazole scaffolds, a series of 5-membered heterocycles, are well known for their high efficacy, low toxicity, and superior pharmacokinetics. Alzheimer's disease (AD) is the first neurodegenerative disorder with complex pathological mechanisms. Triazole, as an aromatic group with three nitrogen atoms, forms polar and non-polar interactions with diverse key residues in the receptor-ligand binding procedure, and has been widely used in the molecular design in the development of anti-AD agents. Moreover, considering the simple synthesis approaches, triazole scaffolds are commonly used to link two pharmacodynamic groups in one chemical molecule, forming multi-target directed ligands (MTDLs). Furthermore, the click reaction between azide- and cyano-modified enzyme and ligand provides feasibility for the new modulator discovery, compound tissue distribution evaluation, enzyme localization, and pharmacological mechanism study, promoting the diagnosis of AD course.

Synthesis of water-soluble novel bioactive pyridine-based azo coumarin derivative and competitive cytotoxicity, DNA binding, BSA binding study, and in silico analysis with coumarin

The diazo coupliling reaction of 3- amino pyridine with coumarin in water medium produces water soluble 6-[3-pyridyl]azocoumarin. The synthesised compound has been fully charecterised by IR, NMR, and Mass spectroscopy. The frontier molecular orbital calculations reveal that 6-[3-pyridyl]azocoumarin is more biologically and chemically active in comparison to coumarin. The cytotoxicity evaluation confirms that 6-[3-pyridyl]azocoumarin is more active than coumarin against human brain glioblastoma cell lines, LN-229 with IC50 value 9.09 μM (IC50 value for coumarin is 9.9 μM). The compound (I) has been synthesized by coupling of diazotized solution of 3-aminopyridine with coumarin in an aqueous medium at ∼ pH 10. The structure of the compound (I) has been characterized using UV-vis, IR, NMR, and Mass spectral studies. Frontier molecular orbital calculations reveal that 6-[3-pyridyl]azocoumarin (I) is more active chemically and biologically in comparison to coumarin. IC50 value 9.09 and 9.9 μM of 6-[3-pyridyl]azocoumarin and coumarin respectively obtained in cytotoxicity evaluation confirms the enhanced activity of the synthesized compound against human brain glioblastoma cell lines, LN-229. The synthesized compound also shows strong binding interactions with DNA and BSA in comparison with coumarin. The DNA binding study shows groove binding interaction of the synthesized compound with CT-DNA. The nature of interaction, binding parameters and structural variations of BSA in the presence of the synthesized compound and coumarin have been evaluated using several usefull spectroscopy approaches such as UV -Vis, time resolved and stady state flurescence. The molecular docking interaction has been carried out to justify the experimental binding interaction with DNA and BSA.

An overview of structure-based activity outcomes of pyran derivatives against Alzheimer's disease

Pyran is a heterocyclic group containing oxygen that possesses a variety of pharmacological effects. Pyran is also one of the most prevalent structural subunits in natural products, such as xanthones, coumarins, flavonoids, benzopyrans, etc. Additionally demonstrating the neuroprotective properties of pyrans is the fact that this heterocycle has recently attracted the attention of scientists worldwide. Alzheimer's Disease (AD) treatment and diagnosis are two of the most critical research objectives worldwide. Increased amounts of extracellular senile plaques, intracellular neurofibrillary tangles, and a progressive shutdown of cholinergic basal forebrain neuron transmission are often related with cognitive impairment. This review highlights the various pyran scaffolds of natural and synthetic origin that are effective in the treatment of AD. For better understanding synthetic compounds are categorized as different types of pyran derivatives like chromene, flavone, xanthone, xanthene, etc. The discussion encompasses both the structure-activity correlations of these compounds as well as their activity against AD. Because of the intriguing actions that were uncovered by these pyran-based scaffolds, there is no question that they are at the forefront of the search for potential medication candidates that could treat Alzheimer's disease.

The cellular model for Alzheimer's disease research: PC12 cells

Alzheimer's disease (AD) is a common age-related neurodegenerative disease characterized by progressive cognitive decline and irreversible memory impairment. Currently, several studies have failed to fully elucidate AD's cellular and molecular mechanisms. For this purpose, research on related cellular models may propose potential predictive models for the drug development of AD. Therefore, many cells characterized by neuronal properties are widely used to mimic the pathological process of AD, such as PC12, SH-SY5Y, and N2a, especially the PC12 pheochromocytoma cell line. Thus, this review covers the most systematic essay that used PC12 cells to study AD. We depict the cellular source, culture condition, differentiation methods, transfection methods, drugs inducing AD, general approaches (evaluation methods and metrics), and in vitro cellular models used in parallel with PC12 cells.

Design, synthesis and biological evaluation of substituted pyrazoles endowed with brominated 4-methyl 7-hydroxy coumarin as new scaffolds against Alzheimer’s disease

Background

The study aimed to design, synthesize and evaluate various brominated derivatives of 7-hydroxy coumarin as a new scaffold against Alzheimer’s disease by in vivo and in vitro models. A group of three novel pyrazoles endowed with brominated 7-hydroxy 4-methyl coumarin derivatives were designed. Among the designed compounds, a single entity (D1) was selected based on the docking score, which could be considered mainly for the treatment of Alzheimer’s disease. Three novel pyrazoles endowed with brominated 7-hydroxy 4-methyl coumarin derivatives were designed and docking studies of these compounds were carried out using Argus lab4.0.1 version. According to the docking score, a single entity of compound (D1) was selected for further study. The structure of the compound (D1) was explored by spectral analysis. The anti-Alzheimer’s activity was evaluated by in vivo and in vitro methods. All results were compared statistically by one-way ANOVA using GraphPad Prism.

Results

Molecular docking studies revealed that the compound D1 was able to bind simultaneously to the amino acid and in the active sites of the acetylcholine esterase enzyme. In acetylcholine esterase inhibition assay, the compound shows a significant increase in acetylcholine esterase level. The MAO inhibitory activities were in the nanomole range (human MAO-A IC50 = 3.9, human MAO-B IC 50 = 4.4). DPPH (2,2-diphenyl-1-picryl-hydrazyl-hydrate) assay showed that the compound shows a promising antioxidant property. In the evaluation of learning and memory of compound D1 using elevated plus maze, the compound D1-pretreated group showed a significant increase in memory and learning when compared with donepezil.

Conclusions

Among the designed series of pyrazole endowed with brominated 7-hydroxyl 4-methyl coumarin derivatives, compound D1 showed good antioxidant property and acetylcholine esterase and MAO inhibitory activity; based on this property, the synthesized compound D1 can be considered a new scaffold on Alzheimer’s disease.

Application of NMI-TfCl-mediated amide bond formation in the synthesis of biologically relevant oxadiazole derivatives employing less basic (hetero)aryl amines

We herein report a modified methodology for the synthesis of some oxadiazoles linked to amides under mild conditions. The developed protocol using NMI-TfCl has been found to be effective and tolerant for the amide bond formation reaction of a series of electronically deactivating and sterically challenging amines. The antioxidant potential of the newly synthesized compounds has been evaluated at the later stage.

Efficacy of acetylcholinesterase inhibitors in Alzheimer's disease

Alzheimer's disease (AD), the most common cause of adult-onset dementia is characterized by a progressive decline of cognitive functions accompanied by behavioral manifestations. The main class of drugs currently used for the treatment of AD are acetylcholinesterase/cholinesterase inhibitors (ChE-Is). The first ChE-I licensed for symptomatic treatment of AD was tacrine. The ChE-Is currently available in the market are donepezil, rivastigmine and galantamine as tacrine is no longer in use, due to its hepatotoxicity. According to mechanism of action the ChE-Is are classified as short-acting or reversible agents such as tacrine, donepezil, and galantamine, as intermediate-acting or pseudo-irreversible agent such as rivastigmine. Overall, the efficacy of the three ChE-Is available in the market is similar and the benefit of administration of these compounds is mild and may not be clinically significant. Due to gastrointestinal side effects of these drugs, medicinal chemistry and pharmaceutical delivery studies have investigated solutions to improve the pharmacological activity of these compounds. In spite of the limited activity of ChE-Is, waiting for more effective approaches, these drugs still represent a pharmacotherapeutic resource for the treatment of AD. Other approaches in which ChE-Is were investigated is in their use in combination with other classes of drugs such as cholinergic precursors, N-methyl-d-aspartate (NMDA) receptor antagonists and antioxidant agents. After many years from the introduction in therapy of ChE-Is, the combination with other classes of drugs may represent the chance for a renewed interest of ChE-Is in the treatment of adult-onset dementia disorders.

Donepezil Derivatives Targeting Amyloid-β Cascade in Alzheimer's Disease

Alzheimer's Disease (AD) is a neurodegenerative disorder with an increasing impact on society. Because currently available therapy has only a short-term effect, a huge number of novel compounds are developed every year exploiting knowledge of the various aspects of AD pathophysiology. To better address the pathological complexity of AD, one of the most extensively pursued strategies by medicinal chemists is based on Multi-target-directed Ligands (MTDLs). Donepezil is one of the currently approved drugs for AD therapy acting as an acetylcholinesterase inhibitor. In this review, we have made an extensive literature survey focusing on donepezil-derived MTDL hybrids primarily targeting on different levels cholinesterases and amyloid beta (Aβ) peptide. The targeting includes direct interaction of the compounds with Aβ, AChE-induced Aβ aggregation, inhibition of BACE-1 enzyme, and modulation of biometal balance thus impeding Aβ assembly.

In Silico ADME and QSAR Studies on a Set of Coumarin Derivatives As Acetylcholinesterase Inhibitors Against Alzheimer’s Disease: CoMFA, CoMSIA, Topomer CoMFA, and HQSAR

Background:

Alzheimer’s disease (AD) is increasingly being recognized as one of the lethal diseases in older people. Acetylcholinesterase (AChE) has proven to be the most promising target in AD, used for designing drugs against AD.

Methods:

In silico studies, 2D- or 3D-QSAR like hologram QSAR (HQSAR), Topomer comparative molecular field analysis (Topomer CoMFA), comparative molecular field analysis (CoMFA), and comparative molecular similarity indices analysis (CoMSIA) methods were used to generate QSAR models for acetylcholinesterase inhibitors.

Results:

Acetylcholinesterase inhibitors used for the present study contain a series of 7- hydroxycoumarin derivatives connected by piperidine, piperazine, tacrine, triazole, or benzyl fragments through alkyl or amide spacer training set compounds were used to generate best model with a HQSAR q2 value of 0.916 and r2 value of 0.940; a Topomer CoMFA q2 value of 0.907 and r2 value of 0.959, CoMFA q2 value of 0.880 and r2 value of 0.960; and a CoMSIA q2 value of 0.865 and r2 value of 0.941. In addition, contour plots obtained from QSAR models suggested the significant regions that influenced the AChE inhibitory activity.

Conclusion:

In light of these results, this study provides knowledge about the structural requirements for the development of more active acetylcholinesterase inhibitors. In addition, the predicted ADME profile helps us to find CNS active molecules, the obtained prediction compared with well-known AChE inhibitors viz., ensaculin, tacrine, galantamine, rivastigmine, and donepezil. Based on the knowledge obtained from these studies, the hybridization approach is one of the best ways to find lead compounds and these findings can be useful in the treatment of Alzheimer's disease.

New phosphazine and phosphazide derivatives as multifunctional ligands targeting acetylcholinesterase and β-Amyloid aggregation for treatment of Alzheimer's disease

Phosphazine and phosphazide derivatives are described herein as a new class of selective and potent acetylcholinesterase (AChE) inhibitors and β-amyloid aggregation inhibitors. Phosphazines (5-7) were synthesized smoothly via a redox-condensation reaction of 1,2-bis(diphenylphosphino)ethane with different amines derivatives in the presence of dialkyl azodicarboxylate (Staudinger reaction) while phosphazides (8) via electrophilic attack of azido derivatives. Structures of the synthesized compounds were justified on the basis of compatible elementary and spectroscopic analyses. All the compounds were evaluated for their acetylcholinesterase inhibitory activity. The most three potent compounds (5b-c and 8b) showing AChE IC₅₀ values (29.85-34.96 nM) comparable to that of donepezil (34.42 nM) were subjected to further investigation by testing their butyrylcholinesterase, MMP-2 and self-induced Aβ aggregation inhibition activity. Especially, the coumarin phosphazide derivative (8b) presented the best AChE inhibition selectivity index (IC₅₀ = 34.96 nM, AChE/BuChE; 3.81) together with good inhibition ability against MMP-2 (IC₅₀ = 441.33 nM) and self-induced Aβ_1-42 aggregation (IC₅₀ = 337.77 nM). In addition, the inhibition of metal-induced Aβ aggregation by 8b was confirmed by thioflavine T fluorescence. The most potent effect of 8b was observed on the Zn²⁺-induced Aβ₄₂ aggregation. Kinetic study of compound 8b suggested it to be a competitive AChE inhibitor. Also, it specifically chelates metal and is predicted to be permeable to BBB. It also possesses low toxicity on SH-SY5Y neuroblastoma cells with a safety index of 15.37. In addition, it was demonstrated that compound 8b can improve the cognitive impairment of scopolamine-induced model in mice with % alternations and transfer latency time comparable to that of donepezil. Also, a docking study was carried out and it was in accordance with the in vitro results. These promising in vitro and in vivo findings highlight compound 8b as a possible drug candidate in searching for new multifunctional AD drugs.

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

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

:

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

Recent Advances in Multi-target Anti-Alzheimer Disease Compounds (2013 Up to the Present)

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Since the last century, when scientists proposed the lock-and-key model, the discovery of drugs has focused on the development of drugs acting on single target. However, single-target drug therapies are not effective to complex diseases with multi-factorial pathogenesis. Moreover, the combination of single-target drugs readily causes drug resistance and side effects. In recent years, multi-target drugs have increasingly been represented among FDA-approved drugs. Alzheimer’s Disease (AD) is a complex and multi-factorial disease for which the precise molecular mechanisms are still not fully understood. In recent years, rational multi-target drug design methods, which combine the pharmacophores of multiple drugs, have been increasingly applied in the development of anti-AD drugs. In this review, we give a brief description of the pathogenesis of AD and provide detailed discussions about the recent development of chemical structures of anti-AD agents (2013 up to present) that have multiple targets, such as amyloid-β peptide, Tau protein, cholinesterases, monoamine oxidase, β-site amyloid-precursor protein-cleaving enzyme 1, free radicals, metal ions (Fe2+, Cu2+, Zn2+) and so on. In this paper, we also added some novel targets or possible pathogenesis which have been reported in recent years for AD therapy. We hope that these findings may provide new perspectives for the pharmacological treatment of AD.

Synthesis of 2-(2-oxo-2H-chromen-4-yl)acetamides as potent acetylcholinesterase inhibitors and molecular insights into binding interactions

Sixteen novel coumarin-based compounds are reported as potent acetylcholinesterase (AChE) inhibitors. The most active compound in this series, 5a (IC₅₀ 0.04 ± 0.01 µM), noncompetitively inhibited AChE with a higher potency than tacrine and galantamine. Compounds 5d, 5j, and 5 m showed a moderate antilipid peroxidation activity. The compounds showed cytotoxicity in the same range as the standard drugs in HEK-293 cells. Molecular docking demonstrated that 5a acted as a dual binding site inhibitor. The coumarin moiety occupied the peripheral anionic site and showed π-π interaction with Trp278. The tertiary amino group displayed significant cation-π interaction with Phe329. The aromatic group showed π-π interaction with Trp83 at the catalytic anionic site. The long chain of methylene lay along the gorge interacting with Phe330 via hydrophobic interaction. Molecular docking was applied to postulate the selectivity toward AChE of 5a in comparison with donepezil and tacrine. Structural insights into the selectivity of the coumarin derivatives toward huAChE were explored by molecular docking and 3D QSAR and molecular dynamics simulation for 20 ns. ADMET analysis suggested that the 2-(2-oxo-2H-chromen-4-yl)acetamides showed a good pharmacokinetic profile and no hepatotoxicity. These coumarin derivatives showed high potential for further development as anti-Alzheimer agents.

Profiling Auspicious Butyrylcholinesterase Inhibitory Activity of Two Herbal Molecules: Hyperforin and Hyuganin C

Cholinergic therapy based on cholinesterase (ChE) inhibitory drugs is the mainstay for the treatment of Alzheimer's disease. Therefore, an extensive research has been continuing for the discovery of drug candidates as inhibitors of acetyl- and butyrylcholinesterase. In this study, two natural molecules, e. g. hyperforin and hyuganin C were tested in vitro for their AChE and BChE inhibitory activity. Both of the compounds were ineffective against AChE, whereas hyperforin (IC₅₀ =141.60±3.39 μm) and hyuganin C (IC₅₀ =38.86±1.69 μm) were found to be the highly active inhibitors of BChE as compared to galantamine (IC₅₀ =46.58±0.91 μm) which was used as the reference. Then, these molecules were further proceeded to molecular docking experiments in order to establish their interactions at the active site of BChE. The molecular docking results indicated that both of them are able to block the access to key residues in the catalytic triad of the enzyme, while they complement some of the hydrophobic residues of the cavity, what is consistent with our in vitro data. While both compounds were predicted as mutagenic, only hyuganin C showed hepatotoxicity in in silico analysis. According to whole outcomes that we obtained, particularly hyuganin C besides hyperforin are the promising BChE inhibitors, which can be the promising compounds for AD therapy.

Synthesis, anticholinesterase activity and molecular modeling studies of novel carvacrol-substituted amide derivatives

In the present study, 23 novel carvacrol derivatives involving the amide moiety as a linker between the alkyl chains and/or the heterocycle nucleus were synthesized and tested in vitro as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors. 2-(5-Isopropyl-2-methylphenoxy)-N-(quinolin-8-yl)acetamide (5v) revealed the highest inhibition properties against AChE and BuChE with the IC₅₀ values of 1.93 and 0.05 µM, respectively. The blood-brain barrier (BBB) permeability of the potent inhibitor (5v) was also assessed by the widely used parallel artificial membrane permeability assay (PAMPA-BBB). The results showed that 5v is capable of crossing the BBB. Pharmacokinetic and toxicity profiles of the studied molecule predictions were investigated by MetaCore/MetaDrug comprehensive systems biology analysis suite. Bioactive conformations of the synthesized molecules, their predicted binding energies as well as structural and dynamical profiles of molecules at the binding pockets of AChE and BuChE targets were also investigated using different docking algorithms and molecular dynamics (MD) simulations.Communicated by Ramaswamy H. Sarma.

Molecular docking studies of coumarin hybrids as potential acetylcholinesterase, butyrylcholinesterase, monoamine oxidase A/B and β-amyloid inhibitors for Alzheimer's disease

Coumarins are the phytochemicals, which belong to the family of benzopyrone, that display interesting pharmacological properties. Several natural, synthetic and semisynthetic coumarin derivatives have been discovered in decades for their applicability as lead structures as drugs. Coumarin based conjugates have been described as potential AChE, BuChE, MAO and β-amyloid inhibitors. Therefore, the objective of this review is to focus on the construction of these pharmacologically important coumarin analogues with anti-Alzheimer’s activities, highlight their docking studies and structure–activity relationships based on their substitution pattern with respect to the selected positions on the chromen ring by emphasising on the research reports conducted in between year 1968 to 2017.

A review on flavonoid-based scaffolds as multi-target-directed ligands (MTDLs) for Alzheimer's disease

Alzheimer's disease (AD), the most common form of dementia, is a multifactorial neurodegenerative disease. The target enzymes inhibition including cholinesterase, beta-secretase, monoamine oxidase and inhibition of amyloid-β aggregation as well as oxidative stress and metal chelation play an important role in the pathogenesis of AD. Chroman-4-one scaffold with benzo-γ-pyrone network is a privileged structure in organic synthesis and drug design. A large number of research has been carried out on modified naturally occurring chromanone scaffolds and/or synthesized new analogues, to obtain effective drugs for AD management. The present review summarizes aspects related to the multi-target-directed ligands (MTDLs) strategy in enzyme targets modulation performed with natural and synthesized chroman-4-one-based structures to look at their potential in the management of multifactorial Alzheimer's disease.

Coumarin derivatives bearing benzoheterocycle moiety: synthesis, cholinesterase inhibitory, and docking simulation study

Objective(s):

To investigate the efficiency of a novel series of coumarin derivatives bearing benzoheterocycle moiety as novel cholinesterase inhibitors.

Materials and Methods:

Different 7-hydroxycoumarin derivatives were synthesized via Pechmann or Knoevenagel condensation and conjugated to different benzoheterocycle (8-hydroxyquinoline, 2-mercaptobenzoxazole or 2-mercaptobenzimidazole) using dibromoalkanes 3a-m: Final compounds were evaluated against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) by Ellman’s method. Kinetic study of AChE inhibition and ligand-protein docking simulation were also carried out for the most potent compound 3b.

Results:

Some of the compounds revealed potent and selective activity against AChE. Compound 3b containing the quinoline group showed the best activity with an IC₅₀ value of 8.80 μM against AChE. Kinetic study of AChE inhibition revealed the mixed-type inhibition of the enzyme by compound 3b. Ligand-protein docking simulation also showed that the flexibility of the hydrophobic five carbons linker allows the quinoline ring to form π-π interaction with Trp279 in the PAS.

Conclusion:

We suggest these synthesized compounds could become potential leads for AChE inhibition and prevention of AD symptoms.

Acetamide Derivatives of Chromen-2-ones as Potent Cholinesterase Inhibitors

Alzheimer's disease (AD), a neurodegenerative disorder, is a serious medical issue worldwide with drastic social consequences. Inhibition of cholinesterase is one of the rational and effective approaches to retard the symptoms of AD and, hence, consistent efforts are being made to develop efficient anti-cholinesterase agents. In pursuit of this, a series of 19 acetamide derivatives of chromen-2-ones were synthesized and evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory potential. All the synthesized compounds exhibited significant anti-AChE and anti-BChE activity, with IC₅₀ values in the range of 0.24-10.19 μM and 0.64-30.08 μM, respectively, using donepezil hydrochloride as the standard. Out of 19 compounds screened, 3 compounds, viz. 22, 40, and 43, caused 50% inhibition of AChE at 0.24, 0.25, and 0.25 μM, respectively. A kinetic study revealed them to be mixed-type inhibitors, binding with both the CAS and PAS sites of AChE. The above-selected compounds were found to be effective inhibitors of AChE-induced and self-mediated Aβ_1-42 aggregation. ADMET predictions demonstrated that these compounds may possess suitable blood-brain barrier (BBB) permeability. Hemolytic assay results revealed that these compounds did not lyse human RBCs up to a thousand times of their IC₅₀ value. MTT assays performed for the shortlisted compounds showed them to be negligibly toxic after 24 h of treatment with the SH-SY5Y neuroblastoma cells. These results provide insights for further optimization of the scaffolds for designing the next generation of compounds as lead cholinesterase inhibitors.

Synthesis of umbelliferone derivatives in Escherichia coli and their biological activities

BACKGROUND

Umbelliferone, also known as 7-hydroxycoumarin, is a phenolic metabolite found in many familiar plants. Its derivatives have been shown to have various pharmacological and chemo-preventive effects on human health. A uridine diphosphate glycosyltransferase YjiC from Bacillus licheniformis DSM 13, a cytochrome P450BM3 (CYP450 BM3) variant namely mutant 13 (M13) from Bacillus megaterium, and an O-methyltransferase from Streptomyces avermitilis (SaOMT2) were used for modifications of umbelliferone.

RESULTS

Three umbelliferone derivatives (esculetin, skimmin, and herniarin) were generated through enzymatic and whole cell catalysis. To improve the efficiencies of biotransformation, different media, incubation time and concentration of substrate were optimized and the production was scaled up using a 3-L fermentor. The maximum yields of esculetin, skimmin, and herniarin were 337.10 μM (67.62%), 995.43 μM (99.54%), and 37.13 μM (37.13%), respectively. The water solubility of esculetin and skimmin were 1.28-folds and 3.98-folds as high as umbelliferone, respectively, whereas herniarin was 1.89-folds less soluble than umbelliferone. Moreover, the antibacterial and anticancer activities of herniarin showed higher than umbelliferone, esculetin and skimmin.

CONCLUSIONS

This study proves that both native and engineered enzymes could be employed for the production of precious compounds via whole cell biocatalysis. We successfully produced three molecules herniarin, esculetin and skimmin in practical amounts and their antibacterial and anticancer properties were accessed. One of the newly synthesized molecules the present research suggests that the combinatorial biosynthesis of different biosynthetic enzymes could rapidly promote to a novel secondary metabolite.

Pteryxin - A promising butyrylcholinesterase-inhibiting coumarin derivative from Mutellina purpurea

Pteryxin is a dihydropyranocoumarin derivative found in Apiaceae family. In this study, pteryxin, which was previously isolated from the fruits of Mutellina purpurea, was investigated for its inhibitory potential against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), which are the key enzymes in the pathology of Alzheimer's disease (AD). The compound was tested in vitro using ELISA microplate reader at 100 μg/ml and found to cause 9.30 ± 1.86% and 91.62 ± 1.53% inhibition against AChE and BChE, respectively. According to our results, pteryxin (IC₅₀ = 12.96 ± 0.70 μg/ml) was found to be a more active inhibitor of BChE than galanthamine (IC₅₀ = 22.16 ± 0.91 μg/ml; 81.93± 2.52% of inhibition at 100 μg/ml). Further study on pteryxin using molecular docking experiments revealed different possible binding modes with both polar and hydrophobic interactions inside the binding pocket of BChE. Top docking solution points out to the formation of two hydrogen bonds with the catalytic residues S198 and H438 of BChE as well as a strong π - π stacking with W231. Therefore, pteryxin as a natural coumarin seems to be a strong BChE inhibitor, which could be considered as a lead compound to develop novel BChE inhibitors for AD treatment.

Synthesis and Anti-Acetylcholinesterase Activity of N-[(indolyl)ethyl)-coumarin-yloxy)]Alkanamides

Novel coumarin–tryptamine systems attached through a linker were synthesised and evaluated in vitro against acetylcholinesterase by the classical Ellman's test.

The effect of chalcogen substitution on the structure and spectroscopy of 4,7-dimethyl-2H-chromen-2-one/thione analogues

The structural and spectroscopic properties of the 1-benzopyran-2-one/thione moiety.

A review on tacrine-based scaffolds as multi-target drugs (MTDLs) for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurological disorder among elderly people and combinatorial factors such as genetic, lifestyle, and environmental are involved in onset and disease progression. It has been demonstrated that loss of cholinergic transmission is one of the most significant causes of AD. One strategy currently being investigated for the development of new therapeutics relates to the enhancement of cholinergic system through several ways. At this juncture, anticholinesterase inhibitors have absorbed lots of attention and different marketed drugs such as donepezil, rivastigmine, tacrine, and galantamine have been developed. 9-Amino-1,2,3,4-tetrahydroacridine known as tacrine was introduced in 1945 as an efficient anticholinesterase agent. The mechanism of action of tacrine was proved to inhibit the metabolism of acetylcholine and therefore extending its activity and raising levels in the cerebral cortex. However, extensive use of tacrine was limited since it showed various side effects and toxicity. Thus, lots of efforts were carried out to prepare tacrine analogues to overcome the related adverse effects. This review describes differently synthesized tacrine-based scaffolds as cholinesterase inhibitors to manage Alzheimer's disease (AD).