Flurbiprofen-chalcone hybrid Mannich base derivatives as balanced multifunctional agents against Alzheimer's disease: Design, synthesis and biological evaluation

A Promising Drug Candidate as Potent Therapeutic Approach for Neuroinflammation and Its In Silico Justification of Chalcone Congeners: a Comprehensive Review

Multiple genetic, environmental, and immunological variables cause neuropsychiatric disorders (NPDs). The induced inflammatory immune response is also connected to the severity and treatment outcomes of various NPDs. These reactions also significantly impact numerous brain functions such as GABAergic signaling and neurotransmitter synthesis through inflammatory cytokines and chemokines. Chalcones (1,3-diaryl-2-propen-1-ones) and their heterocyclic counterparts are flavonoids with various biological characteristics including anti-inflammatory activity. Several pure chalcones have been clinically authorized or studied in humans. Chalcones are favored for their diagnostic and therapeutic efficacy in neuroinflammation due to their tiny molecular size, easy manufacturing, and flexibility for changes to adjust lipophilicity ideal for BBB penetrability. These compounds reached an acceptable plasma concentration and were well-tolerated in clinical testing. As a result, they are attracting increasing attention from scientists. However, chalcones' therapeutic potential remains largely untapped. This paper is aimed at highlighting the causes of neuroinflammation, more potent chalcone congeners, their mechanisms of action, and relevant structure-activity relationships.

A Comprehensive Review of the Docking Studies of Chalcone for the Development of Selective MAO-B Inhibitors

Monoamine oxidase B is a crucial therapeutic target for neurodegenerative disorders like Alzheimer's and Parkinson's since they assist in disintegrating neurotransmitters such as dopamine in the brain. Pursuing efficacious monoamine oxidase B inhibitors is a hot topic, as contemporary therapeutic interventions have many shortcomings. Currently available FDA-approved monoamine oxidase inhibitors like safinamide, selegiline and rasagiline also have a variety of side effects like depression and insomnia. In the quest for a potent monoamine oxidase B inhibitor, sizeable, diverse chemical entities have been uncovered, including chalcones. Chalcone is a renowned structural framework that has been intensively explored for its monoamine oxidase B inhibitory activity.The structural resemblance of chalcone (1,3-diphenyl-2-propen-1-one) based compounds and 1,4-diphenyl- 2-butene, a recognized MAO-B inhibitor, accounts for their MAO-B inhibitory activity. Therefore, multiple revisions to the chalcone scaffold have been attempted by the researchers to scrutinize the implications of substitutions onthe molecule's potency. In this work, we outline the docking investigation results of various chalcone analogues with monoamine oxidase B available in the literature until now to understand the interaction modes and influence of substituents. Here we focused on the interactions between reported chalcone derivatives and the active site of monoamine oxidase B and the influence of substitutions on those interactions. Detailed images illustrating the interactions and impact of the substituents or structural modifications on these interactions were used to support the docking results.

Application of the Mannich reaction in the structural modification of natural products

The Mannich reaction is commonly used to introduce N atoms into compound molecules and is thus widely applied in drug synthesis. The Mannich reaction accounts for a certain proportion of structural modifications of natural products. The introduction of Mannich bases can significantly improve the activity, hydrophilicity, and medicinal properties of compounds; therefore, the Mannich reaction is widely used for the structural modification of natural products. In this paper, the application of the Mannich reaction to the structural modification of natural products is reviewed, providing a method for the structural modification of natural products.

Development of novel salicylic acid-donepezil-rivastigmine hybrids as multifunctional agents for the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a chronic, progressive brain degenerative disease that is common in the elderly. So far, there is no effective treatment. The multi-target-directed ligands (MTDLs) strategy has been recognised as the most promising approach due to the complexity of the pathogenesis of AD. Herein, novel salicylic acid-donepezil-rivastigmine hybrids were designed and synthesised. The bioactivity results exhibited that 5a was a reversible and selective eqBChE inhibitor (IC₅₀ = 0.53 μM), and the docking provided the possible mechanism. Compound 5a also displayed potential anti-inflammatory effects and significant neuroprotective effect. Moreover, 5a exhibited favourable stabilities in artificial gastrointestinal solution and plasma. Finally, 5a demonstrated potential cognitive improvement in scopolamine-induced cognitive dysfunction. Hence, 5a was a potential multifunctional lead compound against AD.

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

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

Design, synthesis and evaluation of quinoline-O-carbamate derivatives as multifunctional agents for the treatment of Alzheimer's disease

A series of novel quinoline-O-carbamate derivatives was rationally designed for treating Alzheimer's disease (AD) by multi-target-directed ligands (MTDLs) strategy. The target compounds were synthesised and evaluated by AChE/BuChE inhibition and anti-inflammatory property. The in vitro activities showed that compound 3f was a reversible dual eeAChE/eqBuChE inhibitor with IC₅₀ values of 1.3 µM and 0.81 µM, respectively. Moreover, compound 3f displayed good anti-inflammatory property by decreasing the production of IL-6, IL-1β and NO. In addition, compound 3f presented significant neuroprotective effect on Aβ_25-35-induced PC12 cell injury. Furthermore, compound 3f presented good stabilities in artificial gastrointestinal fluids, liver microsomes in vitro and plasma. Furthermore, compound 3f could improve AlCl₃-induced zebrafish AD model by increasing the level of ACh. Therefore, compound 3f was a promising multifunctional agent for the treatment of AD.

An ongoing journey of chalcone analogues as single and multi-target ligands in the field of Alzheimer's disease: A review with structural aspects

Alzheimer's disease (AD) is a chronic and irreversible neurodegenerative disorder with progressive dementia and cognitive impairment. AD poses severe health challenge in elderly people and become one of the leading causes of death worldwide. It possesses complex pathophysiology with several hypotheses (cholinergic hypothesis, amyloid hypothesis, tau hypothesis, oxidative stress, mitochondrial dysfunction etc.). Several attempts have been made for the management of multifactorial AD. Acetylcholinesterase is the only target has been widely explored in the management of AD to the date. The current review set forth the chalcone based natural, semi-synthetic and synthetic compounds in the search of potential anti-Alzheimer's agents. The main highlights of current review emphasizes on chalcone target different enzymes and pathways like Acetylcholinesterase, β-secretase (BACE1), tau proteins, MAO, free radicals, Advanced glycation end Products (AGEs) etc. and their structure activity relationships contributing in the inhibition of above mentioned various targets of AD.

Development of the "hidden" multi-target-directed ligands by AChE/BuChE for the treatment of Alzheimer's disease

Accumulation of evidences suggested that excessive amounts of AChE and BuChE in the brain of AD patients at the different stage of AD, which could hydrolyze ACh and accelerated Aβ aggregation. To develop new "hidden" multifunctional agents through AChE/BuChE would be a promising strategy to treat AD. To this end, firstly, a series of chalcone derivatives with chelating property was designed and synthesized. The in vitro results showed that compound 3f indicated significant selective MAO-B inhibitory activity (IC₅₀ = 0.67 μM) and remarkable anti-inflammatory property. It also significantly inhibited self-induced Aβ_1-42 aggregation and showed remarkable neuroprotective effects on Aβ_25-35-induced PC12 cell injury. Furthermore, compound 3f was a selective metal chelator and could inhibit Cu²⁺-induced Aβ_1-42 aggregation. Based on this, the carbamate fragment was introduced to compound 3f to obtain carbamate derivatives. The biological activity results exhibited that compound 4b showed good BBB permeability, good AChE inhibitory potency (IC₅₀ = 5.3 μM), moderate BuChE inhibitory potency (IC₅₀ = 12.4 μM), significant MAO-B inhibitory potency, anti-inflammation potency on LPS-induced BV-2 cells and neuroprotective effects on Aβ_25-35-induced PC12 cell injury. Compared with 3f, compound 4b did not show obvious chelation property. Significantly, compound 4b could be activated by AChE/BuChE following inhibition of AChE/BuChE to liberate an active multifunctional chelator 3f, which was consistent with our original intention. More importantly, compounds 3f and 4b presented favorable ADME properties and good stability in artificial gastrointestinal fluid, blood plasma and rat liver microsomes. The in vivo results suggested that compound 4b (0.0195 μg/mL) could significantly improve dyskinesia and reaction capacity of the AlCl₃-induced zebrafish AD model by increasing the level of ACh. Together our data suggest that compound 4b was a promising "hidden" multifunctional agent by AChE/BuChE, and this strategy deserved further development for the treatment of AD.

Synthesis and characterization of biologically active flurbiprofen amide derivatives as selective prostaglandin-endoperoxide synthase II inhibitors: In vivo anti-inflammatory activity and molecular docking

A novel series of twenty two flurbiprofen amides (1-22) were designed and synthesized in good to excellent yields by reacting flurbiprofen acid with various aromatic/aliphatic primary amines in the presence of 1,1‑carbonyldiimidazole (CDI) in basic medium using acetonitrile as solvent. Structures of the synthesized derivatives were elucidated with the help of HR-ESI-MS, ¹H-, and ¹³C NMR spectroscopy and finally screened them for their in-vivo anti-inflammatory potential using carrageenan induced mice paw oedema assay. Among the series, four compounds (8, 14, 15, and 20) displayed excellent activity ranging from 59.0 to 77.7 % decrease, while eight compounds (1, 3, 7, 10, 12, 13, 17, and 18) exhibited good activity in the decrease range of 37.0-50.0 %. Additionally, four compounds (2, 6, 16, and 22) attributed less activity, while the remaining six compounds (4, 5, 9, 11, 19, and 21) were found to be inactive. Furthermore, the In-silico studies were executed on the synthesized derivatives in order to explain the binding interface of compounds with the active sites of prostaglandin endoperoxide-synthase II enzyme.

Identification of New N-methyl-piperazine Chalcones as Dual MAO-B/AChE Inhibitors

Monoamine oxidase-B (MAO-B), acetylcholinesterase (AChE), and butyrylcholinesterase (BChE) have been considered target enzymes of depression and neurodegenerative diseases, including Alzheimer's disease (AD). In this study, seventeen N-methyl-piperazine chalcones were synthesized, and their inhibitory activities were evaluated against the target enzymes. Compound 2k (3-trifluoromethyl-4-fluorinated derivative) showed the highest selective inhibition against MAO-B with an IC₅₀ of 0.71 μM and selectivity index (SI) of 56.34, followed by 2n (2-fluoro-5-bromophenyl derivative) (IC₅₀ = 1.11 μM, SI = 16.04). Compounds 2k and 2n were reversible competitive MAO-B inhibitors with K_i values of 0.21 and 0.28 μM, respectively. Moreover, 2k and 2n effectively inhibited AChE with IC₅₀ of 8.10 and 4.32 μM, which underscored their multi-target inhibitory modes. Interestingly, compound 2o elicited remarkable inhibitions over MAO-B, AChE, and BChE with IC₅₀ of 1.19-3.87 μM. A cell-based assay of compounds 2k and 2n against Vero normal cells pointed out their low cytotoxicity. In a docking simulation, 2k showed the lowest energy for MAO-B (-11.6 kcal/mol) with four hydrogen bonds and two π-π interactions. Furthermore, in silico studies were conducted, and disclosed that 2k and 2n are expected to possess favorable pharmacokinetic properties, such as the ability to penetrate the blood-brain barrier (BBB). In view of these findings, compounds 2k and 2n could serve as promising potential candidates for the treatment of neurodegenerative diseases.

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.

Synthetic Transformation of 2-{2-Fluoro[1,1'-biphenyl]-4-yl} Propanoic Acid into Hydrazide-Hydrazone Derivatives: In Vitro Urease Inhibition and In Silico Study

In the present study, 28 acyl hydrazones (4-31) of flurbiprofen were synthesized in good to excellent yield by reacting different aromatic aldehydes with the commercially available drug flurbiprofen. The compounds were deduced with the help of different spectroscopic techniques like ¹H-NMR and HREI-MS and finally evaluated for in vitro urease inhibitory activity. All of the synthesized products demonstrated good inhibitory activities in the range of IC₅₀ = 18.92 ± 0.61 to 90.75 ± 7.71 μM as compared to standard thiourea (IC₅₀ = 21.14 ± 0.42 μM). Compound 30 was found to be the most active among the series better than the standard thiourea. A structure-activity relationship (SAR) study revealed that the presence of electron-donating groups on the phenyl ring plays a prominent role in the inhibition of the urease enzyme. Moreover, in silico molecular modeling analysis was carried out to study the effect of substituents in synthesized derivatives on the binding interactions with the urease enzyme.

Design, synthesis, and evaluation of novel O-alkyl ferulamide derivatives as multifunctional ligands for treating Alzheimer's disease

Herein, a series of novel O-alkyl ferulamide derivatives were designed and synthesised through the multi-target-directed ligands (MTDLs) strategy. The biological activities in vitro showed that compounds 5a, 5d, 5e, 5f, and 5h indicated significantly selective MAO-B inhibitory potency (IC50 = 0.32, 0.56, 0.54, 0.73, and 0.86 μM, respectively) and moderate antioxidant activity. Moreover, compounds 5a, 5d, 5e, 5f, and 5h showed potent anti-inflammatory properties, remarkable effects on self-induced Aβ1-42 aggregation, and potent neuroprotective effect on Aβ1-42-induced PC12 cell injury. Furthermore, compounds 5a, 5d, 5e, 5f, and 5h presented good blood-brain barrier permeation in vitro and drug-like properties. More interesting, the PET/CT images with [11C]5f demonstrated that [11C]5f could penetrate the BBB with a high brain uptake and exhibited good brain clearance kinetic property. Therefore, compound 5f would be a promising multi-functional agent for the treatment of AD.

The relationships between neuroglial and neuronal changes in Alzheimer's disease, and the related controversies II:

Since the original description of Alzheimer´s disease (AD), research into this condition has mainly focused on assessing the alterations to neurons associated with dementia, and those to the circuits in which they are involved. In most of the studies on human brains and in many models of AD, the glial cells accompanying these neurons undergo concomitant alterations that aggravate the course of neurodegeneration. As a result, these changes to neuroglial cells are now included in all the "pathogenic cascades" described in AD. Accordingly, astrogliosis and microgliosis, the main components of neuroinflammation, have been integrated into all the pathogenic theories of this disease, as discussed in this part of the two-part monograph that follows an accompanying article on gliopathogenesis and glioprotection. This initial reflection verified the implication of alterations to the neuroglia in AD, suggesting that these cells may also represent therapeutic targets to prevent neurodegeneration. In this second part of the monograph, we will analyze the possibilities of acting on glial cells to prevent or treat the neurodegeneration that is the hallmark of AD and other pathologies. Evidence of the potential of different pharmacological, non-pharmacological, cell and gene therapies (widely treated) to prevent or treat this disease is now forthcoming, in most cases as adjuncts to other therapies. A comprehensive AD multimodal therapy is proposed in which neuronal and neuroglial pharmacological treatments are jointly considered, as well as the use of new cell and gene therapies and non-pharmacological therapies that tend to slow down the progress of dementia.

Recent advance on pleiotropic cholinesterase inhibitors bearing amyloid modulation efficacy

Due to the hugely important roles of neurotransmitter acetylcholine (ACh) and amyloid-β (Aβ) in the pathogenesis of Alzheimer's disease (AD), the development of multi-target directed ligands (MTDLs) focused on cholinesterase (ChE) and Aβ becomes one of the most attractive strategies for combating AD. To date, numerous preclinical studies toward multifunctional conjugates bearing ChE inhibition and anti-Aβ aggregation have been reported. Noteworthily, most of the reported multifunctional cholinesterase inhibitors are carbamate-based compounds due to the initial properties of carbamate moiety. However, because their easy hydrolysis in vivo and the instability of the compound-enzyme conjugate, the mechanism of action of these compounds is rare. Thus, non-carbamate compounds are of great need for developing novel cholinesterase inhibitors. Besides, given that Aβ accumulation begins to occur 10-15 years before AD onset, modulating Aβ is ineffective only in inhibiting its aggregation but not eliminate the already accumulated Aβ if treatment is started when the patient has been diagnosed as AD. Considering the limitation of current Aβ accumulation modulators in ameliorating cognitive deficits and ineffectiveness of ChE inhibitors in blocking disease progression, the development of a practically valuable strategy with multiple pharmaceutical properties including ChE inhibition and Aβ modulation for treating AD is indispensable. In this review, we focus on summarizing the scaffold characteristics of reported non-carbamate cholinesterase inhibitors with Aβ modulation since 2020, and understanding the ingenious multifunctional drug design ideas to accelerate the pace of obtaining more efficient anti-AD drugs in the future.

Bio-Oriented Synthesis of Novel (S)-Flurbiprofen Clubbed Hydrazone Schiff’s Bases for Diabetic Management: In Vitro and In Silico Studies

A new series of (S)-flurbiprofen derivatives 4a–4p and 5a–5n were synthesized with different aromatic or aliphatic aldehydes and ketones to produce Schiff’s bases and their structures were confirmed through HR-ESI-MS, ¹H, and ¹³C-NMR spectroscopy. The α-glucosidase inhibitory activities of the newly synthesized compounds were scrutinized, in which six compounds 5k, 4h, 5h, 4d, 4b, and 5i showed potent inhibition in the range of 0.93 to 10.26 µM, respectively, whereas fifteen compounds 4c, 4g, 4i, 4j, 4l, 4m, 4o, 4p, 5c, 5d, 5j, 5l, 5m, 5n and 1 exhibited significant inhibitory activity with IC₅₀ in range of = 11.42 to 48.39 µM. In addition, compounds 5g, 5f, 4k, 4n, and 4f displayed moderate-to-low activities. The modes of binding of all the active compounds were determined through the molecular docking approach, which revealed that two residues, specifically Glu277 and His351 are important in the stabilization of the active compounds in the active site of α-glucosidase. Furthermore, these compounds block the active site with high binding energies (−7.51 to −3.36 kcal/mol) thereby inhibiting the function of the enzyme.

Structural Modifications on Chalcone Framework for Developing New Class of Cholinesterase Inhibitors

Due to the multifaceted pharmacological activities of chalcones, these scaffolds have been considered one of the most privileged frameworks in the drug discovery process. Structurally, chalcones are α, β-unsaturated carbonyl functionalities with two aryl or heteroaryl units. Amongst the numerous pharmacological activities explored for chalcone derivatives, the development of novel chalcone analogs for the treatment of Alzheimer's disease (AD) is among the research topics of most interest. Chalcones possess numerous advantages, such as smaller molecular size, opportunities for further structural modification thereby altering the physicochemical properties, cost-effectiveness, and convenient synthetic methodology. The present review highlights the recent evidence of chalcones as a privileged structure in AD drug development processes. Different classes of chalcone-derived analogs are summarized for the easy understanding of the previously reported analogs as well as the importance of certain functionalities in exhibiting cholinesterase inhibition. In this way, this review will shed light on the medicinal chemistry fraternity for the design and development of novel promising chalcone candidates for the treatment of AD.

Conjugated Dienones from Differently Substituted Cinnamaldehyde as Highly Potent Monoamine Oxidase-B Inhibitors: Synthesis, Biochemistry, and Computational Chemistry

Fifteen multiconjugated dienones (MK1-MK15) were synthesized and evaluated to determine their inhibitory activities against monoamine oxidases (MAOs) A and B. All derivatives were found to be potent and highly selective MAO-B inhibitors. Compound MK6, with an IC₅₀ value of 2.82 nM, most effectively inhibited MAO-B, like MK12 (IC₅₀ = 3.22 nM), followed by MK5, MK13, and MK14 (IC₅₀ = 4.02, 4.24, and 4.89 nM, respectively). The selectivity index values of MK6 and MK12 for MAO-B over MAO-A were 7361.5 and 1780.5, respectively. Compounds MK6 and MK12 were competitive reversible inhibitors of MAO-B, with K _i values of 1.10 ± 0.20 and 3.0 ± 0.27 nM, respectively. Cytotoxic studies showed that MK5, MK6, MK12, and MK14 exhibited low toxicities on Vero cells, with IC₅₀ values of 218.4, 149.1, 99.96, and 162.3 μg/mL, respectively, which were much higher than those for their effective nanomolar-level concentrations. Also, MK5, MK6, MK12, and MK14 decreased cell damage in H₂O₂-induced cells via a significant scavenging effect of reactive oxygen species. Molecular modeling was performed to rationalize the potential inhibitory activities of MK5, MK6, MK12, and MK14 toward MAO-B and their possible binding mechanisms, showing high-affinity binding pocket interactions and conformation perturbations of the compounds with MAO-B, which were interpreted as the conformational dynamics of MAO-B. This study concluded that all the compounds tested were more potent MAO-B inhibitors than the reference drugs, and leading compounds could be further explored for their effectiveness in various kinds of neurodegenerative disorders.

Development of naringenin-O-alkylamine derivatives as multifunctional agents for the treatment of Alzheimer's disease

In this study, a series of naringenin-O-alkylamine derivatives were designed and obtained by introducing an alkylamine fragment into the naringenin skeleton. The in vitro biological activity results revealed that compounds 5f and 7k showed good antioxidant activity with ORAC values of 2.3eq and 1.2eq, respectively. Compounds 5f and 7k were reversible and excellent huAChE inhibitors with IC₅₀ values of 0.91 μM and 0.57 μM, respectively. Moreover, compounds 5f and 7k could inhibit self-induced Aβ_1–42 aggregation with 62.1% and 43.8% inhibition rate, respectively, and significantly inhibited huAChE-Aβ_1–40 aggregation with 51.7% and 43.4% inhibition rate, respectively. In addition, compounds 5f and 7k were selective metal chelators and remarkably inhibited Cu²⁺-induced Aβ_1–42 aggregation with 73.5% and 68.7% inhibition rates, respectively. Furthermore, compounds 5f and 7k could cross the blood-brain barrier in vitro and displayed good neuroprotective effects and anti-inflammatory properties. Further investigation showed that compound 5f did not show obvious hepatotoxicity and displayed a good hepatoprotective effect by its antioxidant activity. The in vivo study displayed that compound 5f significantly improved scopolamine-induced mice memory impairment. Therefore, compound 5f was a potential multifunctional candidate for the treatment of AD.

Development of novel 2-aminoalkyl-6-(2-hydroxyphenyl)pyridazin-3(2H)-one derivatives as balanced multifunctional agents against Alzheimer's disease

Based on multitarget-directed ligands approach, through two rounds of screening, a series of 2-aminoalkyl-6-(2-hydroxyphenyl)pyridazin-3(2H)-one derivatives were designed, synthesized and evaluated as innovative multifunctional agents against Alzheimer's disease. In vitro biological assays indicated that most of the hybrids were endowed with great AChE inhibitory activity, excellent antioxidant activity and moderate Aβ_1-42 aggregation inhibition. Taken both efficacy and balance into account, 12a was identified as the optimal multifunctional ligand with significant inhibition of AChE (EeAChE, IC₅₀ = 0.20 μM; HuAChE, IC₅₀ = 37.02 nM) and anti-Aβ activity (IC₅₀ = 1.92 μM for self-induced Aβ_1-42 aggregation; IC₅₀ = 1.80 μM for disaggregation of Aβ_1-42 fibrils; IC₅₀ = 2.18 μM for Cu²⁺-induced Aβ_1-42 aggregation; IC₅₀ = 1.17 μM for disaggregation of Cu²⁺-induced Aβ_1-42 fibrils; 81.7% for HuAChE-induced Aβ_1-40 aggregation). Moreover, it was equipped with the potential to serve as antioxidant (3.03 Trolox equivalents), metals chelator and anti-neuroinflammation agent for synergetic treatment. Finally, in vivo study demonstrated that 12a, with suitable BBB permeability (log BB = -0.61), could efficaciously ameliorate cognitive dysfunction on scopolamine-treated mice by regulating cholinergic system and oxidative stress simultaneously. Altogether, these results highlight the potential of 12a as an innovative balanced multifunctional candidate for Alzheimer's disease treatment.

The molecular mechanism, targets, and novel molecules in the treatment of Alzheimer's disease

Alzheimer's disease (AD) is a progressive neurological illness that causes dementia mainly in the elderly. The challenging obstacles related to AD has freaked global healthcare system to encourage scientists in developing novel therapeutic startegies to overcome with the fatal disease. The current treatment therapy of AD provides only symptomatic relief and to some extent disease-modifying effects. The current approach for AD treatment involves designing of cholinergic inhibitors, Aβ disaggregation inducing agents, tau inhibitors and several antioxidants. Hence, extensive research on AD therapy urgently requires a deep understanding of its pathophysiology and exploration of various chemical scaffolds to design and develop a potential drug candidate for the treatment. Various issues linked between disease and therapy need to be considered such as BBB penetration capability, clinical failure and multifaceted pathophisiology requires a proper attention to develop a lead candidate. This review article covers all probable mechanisms including one of the recent areas for investigation i.e., lipid dyshomeostasis, pathogenic involvement of P. gingivalis and neurovascular dysfunction, recently reported molecules and drugs under clinical investigations and approved by FDA for AD treatment. Our summarized information on AD will attract the researchers to understand and explore current status and structural modifications of the recently reported heterocyclic derivatives in drug development for AD therapy.

Design and synthesis of novel chalcone derivatives and evaluation of their inhibitory activities against acetylcholinesterase

According to the cholinergic hypothesis, an increase in the acetylcholine level in Alzheimer's disease patients relatively slows down the symptoms of the disease. The most commonly used drug, donepezil, is a cholinesterase inhibitor. In this study, 12 new chalcones (2a-l) were designed and synthesized. In biological activity studies, the acetylcholinesterase (AChE) and butyrylcholinesterase inhibitory potentials of all compounds were evaluated using the in vitro Ellman method. The biological evaluation showed that compounds 2d, 2f, 2j, and 2l displayed significant activity against AChE. The compounds 2d, 2f, 2j, and 2l displayed IC₅₀ values of 0.042, 0.024, 0.053, and 0.033 µM against AChE, respectively. The reference drug donepezil (IC₅₀  = 0.021 µM) also displayed significant inhibition of AChE. The inhibitory activities of these compounds for β-amyloid plaque aggregation were investigated. The enzyme kinetic study was performed to observe the effect of the most active compound 2f on the substrate-enzyme relationship, and a mixed-type inhibition of AchE was determined. Further, docking simulation also revealed that these compounds (2d, 2f, 2j, and 2l) interacted with the enzyme active site in a similar manner to donepezil. The most active derivative, compound 2f, interacted with the amino acids Trp286, Phe295, Tyr341, Trp86, and Glu202.

Synthesis, Spectroscopic Analysis, and in Vitro/in Silico Biological Studies of Novel Piperidine Derivatives Heterocyclic Schiff-Mannich Base Compounds

In the present study, 3-substitued-4-(4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (S1-8) were synthesized by treating 4-hydroxybenzaldehyde (B) with eight different 3-substitued-4-amino-4,5-dihydro-1H-1,2,4-triazole-5-ones (T1-8) in acetic acid medium, separately. The synthesized Schiff bases (S) were reacted with formaldehyde and secondary amine such as 4-piperidinecarboxyamide to afford novel heterocyclic bases. 3-Substitued-4-(4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (T) were treated with 4-piperidinecarboxyamide in the presence of formaldehyde to synthesize eight new 1-(4-piperidinecarboxyamide-1-yl-methyl)-3-substitued-4-(4-hydroxybenzylidenamino)-4,5-dihydro-1H-1,2,4-triazol-5-ones (M1-8). The structure characterization of compounds was carried out using ¹ H-NMR, IR, HR-MS, and ¹³ C-NMR spectroscopic methods. The inhibitory properties of the newly synthesized compounds were calculated against the acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and glutathione S-transferase (GST) enzymes. Ki values were calculated in the range of 20.06±3.11-36.86±6.17 μM for GST, 17.87±2.91-30.53±4.25 μM for AChE, 9.08±0.69-20.02±2.88 μM for BChE, respectively, Besides, IC₅₀ values were also calculated. Best binding scores of -inhibitors against used enzymes were calculated as -12.095 kcal/mol, -12.775 kcal/mol, and -9.336 kcal/mol, respectively. While 5-oxo-triazole piperidine-4-carboxamide moieties have a critical role in the inhibition of AChE and GST enzymes, hydroxy benzyl moiety is important for BChE enzyme inhibition.

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.

Morpholine-based chalcones as dual-acting monoamine oxidase-B and acetylcholinesterase inhibitors: synthesis and biochemical investigations

Nine compounds (MO1–MO9) containing the morpholine moiety were assessed for their inhibitory activities against monoamine oxidases (MAOs) and acetylcholinesterase (AChE). Most of the compounds potently inhibited MAO-B; MO1 most potently inhibited with an IC₅₀ value of 0.030 µM, followed by MO7 (0.25 µM). MO5 most potently inhibited AChE (IC₅₀ = 6.1 µM), followed by MO9 (IC₅₀ = 12.01 µM) and MO7 most potently inhibited MAO-A (IC₅₀ = 7.1 µM). MO1 was a reversible mixed-type inhibitor of MAO-B (K_i = 0.018 µM); MO5 reversibly competitively inhibited AChE (K_i = 2.52 µM); and MO9 reversibly noncompetitively inhibited AChE (K_i = 7.04 µM). MO1, MO5 and MO9 crossed the blood–brain barrier, and were non-toxic to normal VERO cells. These results show that MO1 is a selective inhibitor of MAO-B and that MO5 is a dual-acting inhibitor of AChE and MAO-B, and that both should be considered candidates for the treatment of Alzheimer’s disease.

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

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

Trimethoxy Crown Chalcones as Multifunctional Class of Monoamine Oxidase Enzyme Inhibitors

BACKGROUND

Chalcones with methoxy substituents are considered as a promising framework for the inhibition of monoamine oxidase (MAO) enzymes.

METHODS

A series of nine trimethoxy substituted chalcones (TMa-TMi) was synthesized and evaluated as a multifunctional class of MAO inhibitors. All the synthesized compounds were investigated for their in vitro MAO inhibition, kinetics, reversibility, blood-brain barrier (BBB) permeation, and cytotoxicity and antioxidant potentials.

RESULTS

In the present study, compound (2E)-3-(4-nitrophenyl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (TMf) was provided with an MAO-A inhibition constant value equal to 3.47±0.09 μM and with a selectivity of 0.008. Thus, it was comparable to that of moclobemide, a well known potent hMAO-A inhibitor (SI=0.010). Compound (2E)-3-(4-bromophenyl)-1-(3,4,5-trimethoxyphenyl)prop-2-en-1-one (TMh) showed good MAO-B inhibition, with an inhibition constant of 0.46±0.009 μM. The PAMPA assay demonstrated that all the synthesized derivatives can cross the BBB successfully. The cytotoxicity studies revealed that TMf and TMh have 88.22 and 80.18 % cell viability at 25 µM. Compound TMf appeared as the most promising antioxidant molecule with IC₅₀ values, relative to DPPH and H₂O₂ radical activities, equal to 6.02±0.17 and 7.25±0.07 μM. To shed light on the molecular interactions of TMf and TMh towards MAO-A and MAO-B, molecular docking simulations and MM/GBSA calculations have been carried out.

CONCLUSION

The lead molecules TMf and TMh with multi-functional nature can be further employed for the treatment of various neurodegenerative disorders and depressive states.

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

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

Chalcone and its analogs: Therapeutic and diagnostic applications in Alzheimer's disease

Chalcone [(E)-1,3-diphenyl-2-propene-1-one], a small molecule with α, β unsaturated carbonyl group is a precursor or component of many natural flavonoids and isoflavonoids. It is one of the privileged structures in medicinal chemistry. It possesses a wide range of biological activities encouraging many medicinal chemists to study this scaffold for its usefulness to oncology, infectious diseases, virology and neurodegenerative diseases including Alzheimer's disease (AD). Small molecular size, convenient and cost-effective synthesis, and flexibility for modifications to modulate lipophilicity suitable for blood brain barrier (BBB) permeability make chalcones a preferred candidate for their therapeutic and diagnostic potential in AD. This review summarizes and highlights the importance of chalcone and its analogs as single target small therapeutic agents, multi-target directed ligands (MTDLs) as well as molecular imaging agents for AD. The information summarized here will guide many medicinal chemist and researchers involved in drug discovery to consider chalcone as a potential scaffold for the development of anti-AD agents including theranostics.

Aminoalkylated Phenolic Chalcones: Investigation of Biological Effects on Acetylcholinesterase and Carbonic Anhydrase I and II as Potential Lead Enzyme Inhibitors

Background:

Phenolic Mannich bases have been reported as acetylcholinesterase (AChE) inhibitors for the medication of Alzheimer's disease. Carbonic Anhydrases (CAs) are molecular targets for anticonvulsant, diuretic and antiglaucoma drugs in the clinic. Phenolic compounds have also been mentioned as CA inhibitors. The importance of Mannich bases in drug design inspired our research group to design novel phenolic Mannic bases as potent enzyme inhibitors.

Objective:

In this study, novel Mannich bases, 1-(3,5-bis-aminomethyl-4-hydroxyphenyl)-3-(4- substitutedphenyl)-2-propen-1-ones (1-9), were designed to discover new and potent AChE inhibitors for the treatment of Alzheimer's disease and also to report their carbonic anhydrase inhibitory potency against the most studied hCA I and hCA II isoenzymes with the hope to find out promising enzyme inhibitors.

Methods:

Mannich bases were synthesized by the Mannich reaction. The structures of the compounds were elucidated by 1H NMR, 13C NMR, and HRMS. Enzyme inhibitory potency of the compounds was evaluated spectrophotometrically towards AChE, hCA I and hCA II enzymes.

Results and Discussion:

The compounds showed inhibition potency in nanomolar concentrations against AChE with Ki values ranging from 20.44±3.17 nM to 43.25±6.28 nM. They also showed CAs inhibition potency with Ki values in the range of 11.76±1.29-31.09±2.7 nM (hCA I) and 6.08 ± 1.18-23.12±4.26 nM (hCA II). Compounds 1 (hCA I), 5 (hCA II), and 4 (AChE) showed significant inhibitory potency against the enzymes targeted.

Conclusion:

Enzyme assays showed that Mannich derivatives might be considered as lead enzyme inhibitors to design more selective and potent compounds targeting enzyme-based diseases.

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.