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

Mannich reaction mediated derivatization of chromones and their biological evaluations as putative multipotent ligands for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a complex neurological disorder and multiple pathways are associated with its pathology. Currently available single-targeting drugs are found to be ineffective for the treatment of AD, and most of these drugs provide symptomatic relief. The multi-target directed ligand strategy is proposed as an effective approach for the treatment of AD. Herein, we report the design and synthesis of a series of 2-phenyl substituted chromone derivatives and their evaluation against AChE, MAO-B, and β amyloid self-aggregation inhibition. In the series, NS-4 and NS-13 were identified as the potent leads against all the specified targets. NS-4 and NS-13 exhibited balanced multipotent activities against AChE with IC50 values of 3.09 μM, and 0.625 μM and against MAO-B with IC50 values of 19.64 μM and 12.31 μM, respectively. These compounds also displayed 28.5% and 32.2% self-aggregation inhibition potential against Aβ1-42, respectively. All the compounds were found to be selective for AChE over BuChE. Additionally, NS-4 also exhibited potent BuChE inhibition with an IC50 value of 1.95 μM. Moreover, NS-4 and NS-13 reduced intracellular ROS levels up to 65% against SH-SY5Y cells at 25 μM concentration. The lead compounds were found to be neuroprotective and exhibited no cytotoxicity even at 25 μM concentration. In enzyme kinetic inhibition studies, these compounds showed mixed-type inhibition to AChE. In the computational studies, binding interactions, and orientations of the ligands at the active site of the enzymes were analyzed and these lead compounds were found to be thermodynamically stable inside the active cavity for up to 100 ns.

Phenylstyrylpyrimidine derivatives as potential multipotent therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is a multifactorial neurological disorder that affects millions of people worldwide. Despite extensive research efforts, there are currently no effective disease-modifying therapeutics available for the complete cure of AD. In the current study, we have designed and synthesized a series of phenyl-styryl-pyrimidine derivatives as potential multifunctional agents against different targets of AD. The compounds were evaluated for their ability to inhibit acetylcholinesterase (AChE), monoamine oxidase (MAO) and β amyloid aggregation which are associated with the initiation and progression of the disease. Several compounds in the series exhibited potent inhibitory activity against AChE and MAO-B, with IC50 values in the low micromolar range. In particular, two compounds, BV-12 and BV-14, were found to exhibit a multipotent profile and showed non-competitive inhibition against MAO-B with IC50 values of 4.93 ± 0.38 & 7.265 ± 0.82 μM, respectively and AChE inhibition with IC50 values of 7.265 and 9.291 μM, respectively. BV-12 and BV-14 also displayed β amyloid self-aggregation inhibition of 32.98% and 23.25%, respectively. Furthermore, molecular modelling studies revealed that BV-14 displayed a docking score of -11.20 kcal mol-1 with MAO-B & -6.767 kcal mol-1 with AChE, forming a stable complex with both proteins. It was concluded that phenyl-styryl-pyrimidine derivatives have the potential to be developed as multitarget directed ligands for the treatment of AD.

Artificial intelligence assisted identification of potential tau aggregation inhibitors: ligand- and structure-based virtual screening, in silico ADME, and molecular dynamics study

Alzheimer's disease (AD) is a severe, growing, multifactorial disorder affecting millions of people worldwide characterized by cognitive decline and neurodegeneration. The accumulation of tau protein into paired helical filaments is one of the major pathological hallmarks of AD and has gained the interest of researchers as a potential drug target to treat AD. Lately, Artificial Intelligence (AI) has revolutionized the drug discovery process by speeding it up and reducing the overall cost. As a part of our continuous effort to identify potential tau aggregation inhibitors, and leveraging the power of AI, in this study, we used a fully automated AI-assisted ligand-based virtual screening tool, PyRMD to screen a library of 12 million compounds from the ZINC database to identify potential tau aggregation inhibitors. The preliminary hits from virtual screening were filtered for similar compounds and pan-assay interference compounds (the compounds containing reactive functional groups which can interfere with the assays) using RDKit. Further, the selected compounds were prioritized based on their molecular docking score with the binding pocket of tau where the binding pockets were identified using replica exchange molecular dynamics simulation. Thirty-three compounds showing good docking scores for all the tau clusters were selected and were further subjected to in silico pharmacokinetic prediction. Finally, top 10 compounds were selected for molecular dynamics simulation and MMPBSA binding free energy calculations resulting in the identification of UNK_175, UNK_1027, UNK_1172, UNK_1173, UNK_1237, UNK_1518, and UNK_2181 as potential tau aggregation inhibitors.

In Vitro and In Vivo Investigations of Chromone Derivatives as Potential Multitarget-Directed Ligands: Cognitive Amelioration Utilizing a Scopolamine-Induced Zebrafish Model

Alzheimer's disease is a complex neurological disorder linked with multiple pathological hallmarks. The interrelation of therapeutic targets assists in the enhancement of cognitive decline through interference with overall neuronal transmission. We have synthesized and screened various chromone derivatives as potential multitarget-directed ligands for the effective treatment of Alzheimer's disease. The synthesized compounds exhibited multipotent activity against AChE, BuChE, MAO-B, and amyloid β aggregation. Three potent compounds, i.e., VN-3, VN-14, and VN-19 were identified that displayed remarkable activities against different targets. These compounds displayed IC50 values of 80 nM, 2.52 μM, and 140 nM against the AChE enzyme, respectively, and IC50 values of 2.07 μM, 70 nM, and 450 nM against the MAO-B isoform, respectively. VN-3 displayed potent activity against self-induced Aβ1-42 aggregation with inhibition of 58.3%. In the ROS inhibition studies, the most potent compounds reduced the intracellular ROS levels up to 80% in SH-SY5Y cells at 25 μM concentration. The compounds were found to be neuroprotective and noncytotoxic even at a concentration of 25 μM against SH-SY5Y cells. In silico studies showed that the compounds were nicely accommodated in the active sites of the receptors along with thermodynamically stable orientations. Compound VN-19 exhibited a balanced multitargeting profile against AChE, BuChE, MAO-B, and Aβ1-42 enzymes and was further evaluated for in vivo activities on the scopolamine-induced zebrafish model. VN-19 was found to ameliorate the cognitive decline in zebrafish brains by protecting them against scopolamine-induced neurodegeneration. Thus, VN-3, VN-14, and VN-19 were identified as potent multitarget-directed ligands with a balanced activity profile against different targets and can be developed as therapeutics for AD.

Lead optimization based design, synthesis, and pharmacological evaluation of quinazoline derivatives as multi-targeting agents for Alzheimer's disease treatment

The complexity and multifaceted nature of Alzheimer's disease (AD) have driven us to further explore quinazoline scaffolds as multi-targeting agents for AD treatment. The lead optimization strategy was utilized in designing of new series of derivatives (AK-1 to AK-14) followed by synthesis, characterization, and pharmacological evaluation against human cholinesterase's (hChE) and β-secretase (hBACE-1) enzymes. Amongst them, compounds AK-1, AK-2, and AK-3 showed good and significant inhibitory activity against both hAChE and hBACE-1 enzymes with favorable permeation across the blood-brain barrier. The most active compound AK-2 revealed significant propidium iodide (PI) displacement from the AChE-PAS region and was non-neurotoxic against SH-SY5Y cell lines. The lead molecule (AK-2) also showed Aβ aggregation inhibition in a self- and AChE-induced Aβ aggregation, Thioflavin-T assay. Further, compound AK-2 significantly ameliorated Aβ-induced cognitive deficits in the Aβ-induced Morris water maze rat model and demonstrated a significant rescue in eye phenotype in the Aꞵ-phenotypic drosophila model of AD. Ex-vivo immunohistochemistry (IHC) analysis on hippocampal rat brains showed reduced Aβ and BACE-1 protein levels. Compound AK-2 suggested good oral absorption via pharmacokinetic studies and displayed a good and stable ligand-protein interaction in in-silico molecular modeling analysis. Thus, the compound AK-2 can be regarded as a lead molecule and should be investigated further for the treatment of AD.

Identification of potential JNK3 inhibitors through virtual screening, molecular docking and molecular dynamics simulation as therapeutics for Alzheimer's disease

Alzheimer's disease (AD) is a complex neurological disorder and no effective drug is available for its treatment. Numerous pathological conditions are believed to be responsible for the initiation and development of AD including c-Jun N-terminal kinases (JNKs). The JNKs are one of the enzymes from the mitogen-activated protein kinase (MAPK) family that controls the phosphorylation of various transcription factors on serine and threonine residues, and hold significant responsibilities in tasks like gene expression, cell proliferation, differentiation, and apoptosis. Since, JNK3 is primarily expressed in the brain hence its increased levels in the brain are associated with the AD pathology promoting neurofibrillary tangles, senile plaques, neuroinflammation, and nerve cell apoptosis. The current research work is focused on the development of novel JNK inhibitors as therapeutics for AD employing a structure-based virtual screening (SBVS) approach. The ZINC database (14634052 compounds) was investigated after employing pan assay interference (PAINs), drug-likeness, and diversity picking filter to distinguish molecules interacting with JNK3 by following three docking precision criteria: High Throughput Virtual Screening (HTVS), Standard Precision (SP), and Extra Precision (XP) & MMGBSA. Five lead molecules showed a better docking score in the range of -13.091 to -14.051 kcal/mol better than the reference compound (- 11.828 kcal/mol). The lead compounds displayed acceptable pharmacokinetic properties and were subjected to molecular dynamic simulations of 100 ns and binding free energy calculations. All the lead molecules showed stable RMSD and hydrogen bond interactions throughout the trajectory. The ∆GMM/PBSA_total score for the lead compounds ZINC220382956, ZINC147071339, ZINC207081127, ZINC205151456, ZINC1228819126, and CC-930 was calculated and found to be - 31.39, - 42.8, - 37.04, - 39.01, - 36.5, - 34.16 kcal/mol, respectively. Thus, it was concluded that the lead molecules identified in these studies have the potential to be explored as potent JNK3 inhibitors.

A comprehensive review of multi-target directed ligands in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is the most common form of dementia affecting specifically older population. AD is an irreversible neurodegenerative CNS disorder associated with complex pathophysiology. Presently, the USFDA has approved only four drugs viz. Donepezil, Rivastigmine, Memantine, and Galantamine for the treatment of AD. These drugs exhibit their neuroprotective effects either by inhibiting cholinesterase enzyme (ChE) or N-methyl-d-aspartate (NMDA) receptor. However, the conventional therapy "one target, one molecule" has failed to provide promising therapeutic effects due to the multifactorial nature of AD. This triggered the development of a novel strategy called Multi-Target Directed Ligand (MTDL) which involved designing one molecule that acts on multiple targets simultaneously. The present review discusses the detailed pathology involved in AD and the various MTDL design strategies bearing different heterocycles, in vitro and in vivo activities of the compounds, and their corresponding structure-activity relationships. This knowledge will allow us to identify and design more effective MTDLs for the treatment of AD.

Design, Synthesis, and Biological Investigation of Quinazoline Derivatives as Multitargeting Therapeutics in Alzheimer's Disease Therapy

An efficient and promising method of treating complex neurodegenerative diseases like Alzheimer's disease (AD) is the multitarget-directed approach. Here in this work, a series of quinazoline derivatives (AV-1 to AV-21) were rationally designed, synthesized, and biologically evaluated as multitargeted directed ligands against human cholinesterase (hChE) and human β-secretase (hBACE-1) that exhibit moderate to good inhibitory effects. Compounds AV-1, AV-2, and AV-3 from the series demonstrated balanced and significant inhibition against these targets. These compounds also displayed excellent blood-brain barrier permeability via the PAMPA-BBB assay. Compound AV-2 significantly displaced propidium iodide (PI) from the acetylcholinesterase-peripheral anionic site (AChE-PAS) and was found to be non-neurotoxic at the maximum tested concentration (80 μM) against differentiated SH-SY5Y cell lines. Compound AV-2 also prevented AChE- and self-induced Aβ aggregation in the thioflavin T assay. Additionally, compound AV-2 significantly ameliorated scopolamine and Aβ-induced cognitive impairments in the in vivo behavioral Y-maze and Morris water maze studies, respectively. The ex vivo and biochemical analysis further revealed good hippocampal AChE inhibition and the antioxidant potential of the compound AV-2. Western blot and immunohistochemical (IHC) analysis of hippocampal brain revealed reduced Aβ, BACE-1, APP/Aβ, and Tau molecular protein expressions levels. The pharmacokinetic analysis of compound AV-2 demonstrated significant oral absorption with good bioavailability. The in silico molecular modeling studies of lead compound AV-2 moreover demonstrated a reasonable binding profile with AChE and BACE-1 enzymes and stable ligand-protein complexes throughout the 100 ns run. Compound AV-2 can be regarded as the lead candidate and could be explored more for AD therapy.

Calcium channel blockers' contribution to overcoming Current drug discovery challenges in Alzheimer's disease

INTRODUCTION

Alzheimer's disease (AD) is a progressive, irreversible, and multifactorial brain disorder that gradually and insidiously destroys individual's memory, thinking, and other cognitive abilities.

AREAS COVERED

In this perspective, the authors examine the complex and multifactorial nature of Alzheimer's disease and believe that the best approach to develop new drugs is the MTDL strategy, which obviously faces several challenges. These challenges include identifying the key combination of targets and their suitability for coordinated actions, as well as developing an acceptable pharmacokinetic and toxicological profile to deliver a drug candidate.

EXPERT OPINION

Since calcium plays a crucial role in the pathology of AD, a polypharmacological approach with calcium channel blockers reinforced by activities targeting other factors involved in AD is a serious option in our opinion. This is exemplified by a phase III clinical trial using a drug combination approach with Losartan, Amlodipine (a calcium channel blocker), and Atorvastatin, as well as several MTDL-based calcium channel blockade approaches with a promising in vitro and in vivo profile.

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.

Caesium carbonate promoted regioselective O-functionalization of 4,6-diphenylpyrimidin-2(1H)-ones under mild conditions and mechanistic insight

A facile one-step catalyst free methodology has been developed for the regioselective functionalization of 4,6-diphenylpyrimidin-2(1H)-ones under mild conditions. Selectivity towards the O-regioisomer was achieved by using Cs2CO3 in DMF without use of any coupling reagents. A total of 14 regioselective O-alkylated 4,6-diphenylpyrimidines were synthesized in 81-91% yield. In the DFT studies it was observed that the transition state for the formation of the O-regioisomer is more favourable with Cs2CO3 as compared to K2CO3. Furthermore, this methodology was extended to increase the O/N ratio for the alkylation of 2-phenylquinazolin-4(3H)-one derivatives.

Design, synthesis and biological evaluation of oxadiazole clubbed piperazine derivatives as potential antidepressant agents

Piperazine derivatives have been of great interest to medicinal chemists in the development of antidepressant drugs due to their distinct molecular and structural features along with their pharmacological profile. In this study, we have designed and synthesized a series of 10 compounds of piperazine clubbed oxadiazole derivatives (5a-j) and screened for their MAO inhibitory activity. Compound 5f and 5 g were found to be the most potent MAO-A inhibitors of the series with IC₅₀ values of 0.96 ± 0.04 µM µM and 0.81 ± 0.03 µM, respectively with a selectivity index of 18-folds and 9-folds over MAO-B isoform. The compounds were found to be reversible inhibitors of MAO-A with no cytotoxicity against SH-SY5Y neuronal cells. The compounds also displayed good antioxidant activity. Further, in vivo TST studies revealed that both the compounds 5f and 5 g possessed good anti-depressant-like activity and reduced the immobility time significantly although were found inactive in FST studies. The molecular docking studies revealed that both compounds fit well at the active site of MAO-A enzyme as similar to clorgyline and form a stable complex. The results were confirmed via molecular dynamic studies which demonstrate the stable complex formation between MAO-A and 5f & 5 g. The appropriate drug-like characteristics with favourable ADMET profile, these molecules presented this piperazine clubbed oxadiazole structural framework as a key pharmacophore for the development of new antidepressant molecules along with strong candidature for further clinical investigations.

2-Hydroxy-4-benzyloxylimine Resveratrol Derivatives as Potential Multifunctional Agents for the Treatment of Parkinson's Disease

A series of 2-hydroxy-4-benzyloxylimine resveratrol derivatives was designed, synthesized and evaluated as multifunctional agents for the treatment of Parkinson's disease. The results revealed that most derivatives possessed good multifunctional activities. Among them, representative compound (E)-5-[(4-fluorobenzyl)oxy]-2-{[(4-hydroxyphenyl)imino]methyl}phenol (7 h) exhibited excellent MAO-B inhibition (IC₅₀ =8.43×10^-3  μM) and high antioxidant activity (ORAC=3.45 Trolox equivalent). Additionally, 7 h displayed good metal chelating ability, appropriate blood-brain barrier (BBB) permeability, significant neuroprotective effect, and great anti-neuroinflammatory activity. Furthermore, 7 h can also ameliorate 1-methyl-4-phenyl-1,2,3,6-tetrahydropyridine (MPTP)-induced Parkinson's disease symptoms in mice. Therefore, compound 7 h was found to be a promising candidate for further development against PD.

Current Pharmacotherapy and Multi-Target Approaches for Alzheimer's Disease

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by decreased synaptic transmission and cerebral atrophy with appearance of amyloid plaques and neurofibrillary tangles. Cognitive, functional, and behavioral alterations are commonly associated with the disease. Different pathophysiological pathways of AD have been proposed, some of which interact and influence one another. Current treatment for AD mainly involves the use of therapeutic agents to alleviate the symptoms in AD patients. The conventional single-target treatment approaches do not often cause the desired effect in the disease due to its multifactorial origin. Thus, multi-target strategies have since been undertaken, which aim to simultaneously target multiple targets involved in the development of AD. In this review, we provide an overview of the pathogenesis of AD and the current drug therapies for the disease. Additionally, rationales of the multi-target approaches and examples of multi-target drugs with pharmacological actions against AD are also discussed.

Pyrazolines as potential anti-Alzheimer's agents: DFT, molecular docking, enzyme inhibition and pharmacokinetic studies

Alzheimer's disease (AD) is a neurodegenerative disease that is characterized as the main dementia in the elderly. Eighteen pyrazolines were synthesized and evaluated for their inhibitory effects against acetylcholinesterase (AChE) in vitro. Possible interactions between pyrazolines and the enzyme were explored by in silico experiments. Compound 2B of the series was the most active pyrazoline with an IC50 value of 58 nM. Molecular docking studies revealed two important π-π interactions with residues Trp 286 and Tyr 341. A correlation between the HOMO-1 surface and AChE inhibition was observed. ADMET assays demonstrated a good profile for compound 2B. From the abovementioned findings, a new avenue of compound 2B analogues could be explored to develop anti-AD agents.

Design, Synthesis and Assay of Novel Methylxanthine-Alkynylmethylamine Derivatives as Acetylcholinesterase Inhibitors

Xanthine derivatives have been a great area of interest for the development of potent bioactive agents. Thirty-eight methylxanthine derivatives as acetylcholinesterase inhibitors (AChE) were designed and synthesized. Suzuki-Miyaura cross-coupling reactions of 8-chlorocaffeine with aryl(hetaryl)boronic acids, the CuAAC reaction of 8-ethynylcaffeine with several azides, and the copper(I) catalyzed one-pot three-component reaction (A³-coupling) of 8-ethynylcaffeine, 1-(prop-2-ynyl)-, or 7-(prop-2-ynyl)-dimethylxanthines with formaldehyde and secondary amines were the main approaches for the synthesis of substituted methylxanthine derivatives (yield 53-96%). The bioactivity of all new compounds was evaluated by Ellman's method, and the results showed that most of the synthesized compounds displayed good and moderate acetylcholinesterase (AChE) inhibitory activities in vitro. The structure-activity relationships were also discussed. The data revealed that compounds 53, 59, 65, 66, and 69 exhibited the most potent inhibitory activity against AChE with IC₅₀ of 0.25, 0.552, 0.089, 0.746, and 0.121 μM, respectively. The binding conformation and simultaneous interaction modes were further clarified by molecular docking studies.

Design, Synthesis, and Biological Evaluation of Novel Chromanone Derivatives as Multifunctional Agents for the Treatment of Alzheimer's Disease

Based on a multitarget strategy, a series of novel chromanone-1-benzyl-1,2,3,6-tetrahydropyridin hybrids were identified for the potential treatment of Alzheimer's disease (AD). Biological evaluation demonstrated that these hybrids exhibited significant inhibitory activities toward acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B). The optimal compound C10 possessed excellent dual AChE/MAO-B inhibition both in terms of potency and equilibrium (AChE: IC₅₀ = 0.58 ± 0.05 μM; MAO-B: IC₅₀ = 0.41 ± 0.04 μM). Further molecular modeling and kinetic investigations revealed that compound C10 was a dual-binding inhibitor bound to both the catalytic anionic site and peripheral anionic site of AChE. In addition, compound C10 exhibited low neurotoxicity and potently inhibited AChE enzymatic activity. Furthermore, compound C10 more effectively protected against mitochondrial dysfunction and oxidation than donepezil, strongly inhibited AChE-induced amyloid aggregation, and moderately reduced glutaraldehyde-induced phosphorylation of tau protein in SH-SY5Y cells. Moreover, compound C10 displayed largely enhanced improvements in cognitive behaviors and spatial memory in a scopolamine-induced AD mice model with better efficacy than donepezil. Overall, the multifunctional profiles of compound C10 suggest that it deserves further investigation as a promising lead for the prospective treatment of AD.