Development of chalcone-O-alkylamine derivatives as multifunctional agents against Alzheimer's disease

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.

Research progress of natural products and their derivatives against Alzheimer's disease

Alzheimer's disease (AD), a persistent neurological dysfunction, has an increasing prevalence with the aging of the world and seriously threatens the health of the elderly. Although there is currently no effective treatment for AD, researchers have not given up, and are committed to exploring the pathogenesis of AD and possible therapeutic drugs. Natural products have attracted considerable attention owing to their unique advantages. One molecule can interact with multiple AD-related targets, thus having the potential to be developed in a multi-target drug. In addition, they are amenable to structural modifications to increase interaction and decrease toxicity. Therefore, natural products and their derivatives that ameliorate pathological changes in AD should be intensively and extensively studied. This review mainly presents research on natural products and their derivatives for the treatment of 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 anti-inflammatory activity characterization of novel brain-permeable HDAC6 inhibitors

Targeting histone deacetylase 6 (HDAC6) has emerged as a promising therapeutic approach for anti-inflammation and related biological pathways, including inflammatory events associated with the brain. In this study, in order to develop brain-permeable HDAC6 inhibitors for anti-neuroinflammation, we report here the design, synthesis, and characterization of a number of N-heterobicyclic analogues that can inhibit HDAC6 with high specificity and strong potency. Among our analogues, PB131 exhibits potent binding affinity and selectivity against HDAC6, with an IC50 value of 1.8 nM and more than 116-fold selectivity over other HDAC isoforms. In addition, PB131 shows good brain penetration, binding specificity, and reasonable biodistribution through our positron emission tomography (PET) imaging studies of [18F]PB131 in mice. Furthermore, we characterized the efficacy of PB131 on regulating neuroinflammation using the mouse microglia model BV2 cells in vitro and the LPS-induced inflammation mouse model in vivo. These data not only indicate the anti-inflammatory activity of our novel HDAC6 inhibitor PB131, but also strengthen the biological functions of HDAC6 and further extend the therapeutic approach inhibiting HDAC6. Our findings show that PB131 displays good brain permeability, high specificity, and strong potency toward inhibiting HDAC6 and is a potential HDAC6 inhibitor for inflammation-related disease treatment, especially neuroinflammation.

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.

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.

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.

Chalcone: A Promising Bioactive Scaffold in Medicinal Chemistry

Chalcones are a class of privileged scaffolds with high medicinal significance due to the presence of an α,β-unsaturated ketone functionality. Numerous functional modifications of chalcones have been reported, along with their pharmacological behavior. The present review aims to summarize the structures from natural sources, synthesis methods, biological characteristics against infectious and non-infectious diseases, and uses of chalcones over the past decade, and their structure–activity relationship studies are detailed in depth. This critical review provides guidelines for the future design and synthesis of various chalcones. In addition, this could be highly supportive for medicinal chemists to develop more promising candidates for various infectious and non-infectious diseases.

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.

A Novel Multifunctional 5,6-Dimethoxy-Indanone-Chalcone-Carbamate Hybrids Alleviates Cognitive Decline in Alzheimer’s Disease by Dual Inhibition of Acetylcholinesterase and Inflammation

Backgrounds

Alzheimer’s disease (AD) is a multifactorial neurodegenerative disease. The treatment of AD through multiple pathological targets may generate therapeutic efficacy better. The multifunctional molecules that simultaneously hit several pathological targets have been of great interest in the intervention of AD.

Methods

Here, we combined the chalcone scaffold with carbamate moiety and 5,6-dimethoxy-indanone moiety to generate a novel multi-target-directed ligand (MTDL) molecule (E)-3-((5,6-dimethoxy-1-oxo-1,3-dihydro-2H-inden-2-ylidene)-methyl)phenylethyl(methyl) carbamate (named AP5). In silico approaches were used to virtually predict the binding interaction of AP5 with AChE, the drug-likeness, and BBB penetrance, and later validated by evaluation of pharmacokinetics (PK) in vivo by LC-MS/MS. Moreover, studies were conducted to examine the potential of AP5 for inhibiting AChE and AChE-induced amyloid-β (Aβ) aggregation, attenuating neuroinflammation, and providing neuroprotection in the APP/PS1 model of AD.

Results

We found that AP5 can simultaneously bind to the peripheral and catalytic sites of AChE by molecular docking. AP5 exhibited desirable pharmacokinetic (PK) characteristics including oral bioavailability (67.2%), >10% brain penetrance, and favorable drug-likeness. AP5 inhibited AChE activity and AChE-induced Aβ aggregation in vivo and in vitro. Further, AP5 lowered Aβ plaque deposition and insoluble Aβ levels in APP/PS1 mice. Moreover, AP5 exerted anti-inflammatory responses by switching microglia to a disease-associated microglia (DAM) phenotype and preventing A1 astrocytes formation. The phagocytic activity of microglial cells to Aβ was recovered upon AP5 treatment. Importantly, chronic AP5 treatment significantly prevented neuronal and synaptic damage and memory deficits in AD mice.

Conclusion

Together, our work demonstrated that AP5 inhibited the AChE activity, decreased Aβ plaque deposition by interfering Aβ aggregation and promoting microglial Aβ phagocytosis, and suppressed inflammation, thereby rescuing neuronal and synaptic damage and relieving cognitive decline. Thus, AP5 can be a new promising candidate for the treatment of AD.

Chalcone Scaffolds Exhibiting Acetylcholinesterase Enzyme Inhibition: Mechanistic and Computational Investigations

This study was aimed to perform the mechanistic investigations of chalcone scaffold as inhibitors of acetylcholinesterase (AChE) enzyme using molecular docking and molecular dynamics simulation tools. Basic chalcones (C1–C5) were synthesized and their in vitro AChE inhibition was tested. Binding interactions were studied using AutoDock and Surflex-Dock programs, whereas the molecular dynamics simulation studies were performed to check the stability of the ligand–protein complex. Good AChE inhibition (IC₅₀ = 22 ± 2.8 to 37.6 ± 0.75 μM) in correlation with the in silico results (binding energies = −8.55 to −8.14 Kcal/mol) were obtained. The mechanistic studies showed that all of the functionalities present in the chalcone scaffold were involved in binding with the amino acid residues at the binding site through hydrogen bonding, π–π, π–cation, π–sigma, and hydrophobic interactions. Molecular dynamics simulation studies showed the formation of stable complex between the AChE enzyme and C4 ligand.

Recent Advances Towards Diagnosis and Therapeutic Fingerprinting for Alzheimer's Disease

Since the report of "a peculiar severe disease process of the cerebral cortex" by Alois Alzheimer in 1906, it was considered to be a rare condition characterized by loss of cognition, memory impairment, and pathological markers such as senile plaques or neurofibrillary tangles (NFTs). Later on, the report was published in the textbook "Psychiatrie" and the disease was named as Alzheimer's disease (AD) and was known to be the consequences of aging; however, owing to its complex etiology, there is no cure for the progressive neurodegenerative disorder. Our current understanding of the mechanisms involved in the pathogenesis of AD is still at the mechanistic level. The treatment strategies applied currently only alleviate the symptoms and co-morbidities. For instance, the available treatments such as the usage of acetylcholinesterase inhibitors and N-methyl D-aspartate antagonists have minimal impact on the disease progression and target the later aspects of the disease. The recent advancements in the last two decades have made us more clearly understand the pathophysiology of the disease which has led to the development of novel therapeutic strategies. This review gives a brief idea about the various facets of AD pathophysiology and its management through modern investigational therapies to give a new direction for development of targeted therapeutic measures.

Development of a potential PET probe for HDAC6 imaging in Alzheimer’s disease

Although the epigenetic regulatory protein histone deacetylase 6 (HDAC6) has been recently implicated in the etiology of Alzheimer's disease (AD), little is known about the role of HDAC6 in the etiopathogenesis of AD and whether HDAC6 can be a potential therapeutic target for AD. Here, we performed positron emission tomography (PET) imaging in combination with histopathological analysis to better understand the underlying pathomechanisms of HDAC6 in AD. We first developed [¹⁸F]PB118 which was demonstrated as a valid HDAC6 radioligand with excellent brain penetration and high specificity to HDAC6. PET studies of [¹⁸F]PB118 in 5xFAD mice showed significantly increased radioactivity in the brain compared to WT animals, with more pronounced changes identified in the cortex and hippocampus. The translatability of this radiotracer for AD in a potential human use was supported by additional studies, including similar uptake profiles in non-human primates, an increase of HDAC6 in AD-related human postmortem hippocampal tissues by Western blotting protein analysis, and our ex vivo histopathological analysis of HDAC6 in postmortem brain tissues of our animals. Collectively, our findings show that HDAC6 may lead to AD by mechanisms that tend to affect brain regions particularly susceptible to AD through an association with amyloid pathology.

An approach to pharmacological targets of pyrrole family from a medicinal chemistry viewpoint

Pyrrole is one of the most widely used heterocycles in the pharmaceutical industry. Due to the importance of pyrrole structure in drug design and development, herein, we tried to conduct an extensive review of the bioactive pyrrole based compounds reported recently. The bioactivity of pyrrole derivatives varies, so in the review, we categorized them based on their direct pharmacologic targets. Therefore, readers are able to find the variety of biologic targets for pyrrole containing compounds easily. This review explains around seventy different biologic targets for pyrrole based derivatives, so, it is helpful for medicinal chemists in design and development novel bioactive compounds for different diseases. This review presents an extensive meaningful structure activity relationship for each reported structure as much as possible. The review focuses on papers published between 2018 and 2020.

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.

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.

Promising heterocycle-based scaffolds in recent (2019-2021) anti-Alzheimer's drug design and discovery

Alzheimer's disease (AD) is one of the neurodegenerative diseases that led to morbidity and mortality world-wide. It is a complex disease whose etiology is not completely known that leads to difficulty in prevent or cure of the AD. Also, there are only few approved drugs for AD treatment. Apart from deaths due to AD, expenditure of treatment and care of AD patients is higher than that of treatment of HIV and cancer diseases combined. Hence, it leads to an economic burden also. Although research is being carried out on designing drugs for AD, most of them have ended up in poor inhibitors with high toxicity. Hence, researchers should shoulder a great responsibility of discovery of efficient drugs for AD treatment. In the field of drug discovery, heterocycles played an important role. Also, most of the heterocyclic scaffolds have been used in design of potent anti-AD agents. In view of this, heterocyclic molecules reported recently are compiled and evaluated comprehensively. Especially, the molecules which exhibited pronounced activity are emphasized and described with respect to structure-activity relationship (SAR) in brief.

Design, synthesis, and evaluation of chalcone-Vitamin E-donepezil hybrids as multi-target-directed ligands for the treatment of Alzheimer's disease

A novel series of chalcone-Vitamin E-donepezil hybrids was designed and developed based on multitarget-directed ligands (MTDLs) strategy for treating Alzheimer’s disease (AD). The biological results revealed that compound 17f showed good AChE inhibitory potency (ratAChE IC₅₀ = 0.41 µM; eeAChE IC₅₀ = 1.88 µM). Both the kinetic analysis and docking study revealed that 17f was a mixed type AChE inhibitor. 17f was also a good antioxidant (ORAC = 3.3 eq), selective metal chelator and huMAO-B inhibitor (IC₅₀ = 8.8 µM). Moreover, it showed remarkable inhibition of self- and Cu²⁺-induced Aβ_1–42 aggregation with a 78.0 and 93.5% percentage rate at 25 µM, respectively, and disassembled self-induced and Cu²⁺-induced aggregation of the accumulated Aβ_1–42 fibrils with 72.3 and 84.5% disaggregation rate, respectively. More importantly, 17f exhibited a good neuroprotective effect on H₂O₂-induced PC12 cell injury and presented good blood-brain barrier permeability in vitro. Thus, 17f was a promising multi-target-directed ligand for treating AD.

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.

Halogenated Coumarin-Chalcones as Multifunctional Monoamine Oxidase-B and Butyrylcholinesterase Inhibitors

A series of halogenated coumarin-chalcones were synthesized, characterized, and their inhibitory activities against monoamine oxidases (MAOs), acetylcholinesterase (AChE), butyrylcholinesterase (BChE), and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) were evaluated. Compound CC2 most potently inhibited MAO-B with an IC₅₀ value of 0.51 μM, followed by CC1 (IC₅₀ = 0.69 μM), with a selectivity index (SI) of >78.4 and >58.0, respectively, over MAO-A. However, none of the compounds effectively inhibited MAO-A, AChE, and BChE, except for CC2 and CC3 inhibiting BChE with IC₅₀ values of 7.00 (SI > 5.73 over AChE) and 11.8 μM, respectively. CC1 and CC2 were found to be reversible and competitive inhibitors of MAO-B, with K _i values of 0.50 ± 0.06 and 0.53 ± 0.04 μM, respectively, and CC2 was also a reversible and competitive inhibitor of BChE, with a K _i value of 2.84 ± 0.09 μM. The parallel artificial membrane permeability assay (PAMPA) method showed that lead candidates can cross the blood-brain barrier (BBB). The in vitro toxicity analysis on the Vero cell line (Normal African green monkey kidney epithelial cells) by MTT confirmed that both CC1 and CC2 were nontoxic up to 100 μg/mL, which is almost equivalent to 100 times of their effective concentration used in biological studies. In addition, CC1 and CC2 attenuated H₂O₂-induced cellular damage via their reactive oxygen species (ROS) scavenging effect. These results suggest that CC1 and CC2 are selective and competitive inhibitors of MAO-B, and that CC2 is a selective and competitive inhibitor of BChE. Molecular docking studies of lead compounds provided the possible type of interactions in the targeted enzymes. Based on the findings, both compounds, CC1 and CC2, can be considered plausible drug candidates against neurodegenerative disorders.

Design, synthesis and biological evaluation of naringenin carbamate derivatives as potential multifunctional agents for the treatment of Alzheimer's disease

A series of naringenin derivatives were designed and synthesized as multifunctional anti-Alzheimer's disease (AD) agents. The results showed that these derivatives displayed moderate-to-good acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities at the micromolar range (IC₅₀, 12.91 ~ 62.52 μM for AChE and 0.094 ~ 13.72 μM for BuChE). Specifically, compound 1 showed the highest inhibitory activity against BuChE with the IC₅₀ value of (0.094 ± 0.0054) μM. A Lineweaver-Burk plot and molecular docking studies demonstrated that 1 targeted both the catalytically active site (CAS) and the peripheral anion site (PAS) of BuChE. Besides, all derivatives showed excellent hydroxyl free radicals (·OH) scavenging ability than vitamin C and cyclic voltammetry results displayed that 1 could effectively scavenge superoxide anion radical (·O₂^-). In addition, compound 1 displayed good metal chelating properties and had anti-Aβ aggregation activities. Therefore, compound 1 might be the potential anti-AD agent for further developments.

Piperazine-substituted chalcones: a new class of MAO-B, AChE, and BACE-1 inhibitors for the treatment of neurological disorders

Eleven piperazine-containing 1,3-diphenylprop-2-en-1-one derivatives (PC1-PC11) were evaluated for their inhibitory activities against monoamine oxidases (MAOs), cholinesterases (ChEs), and β-site amyloid precursor protein cleaving enzyme 1 (BACE-1) with a view toward developing new treatments for neurological disorders. Compounds PC10 and PC11 remarkably inhibited MAO-B with IC₅₀ values of 0.65 and 0.71 μM, respectively. Ten of the eleven compounds weakly inhibited AChE and BChE with > 50% of residual activities at 10 μM, although PC4 inhibited AChE by 56.6% (IC₅₀ = 8.77 μM). Compound PC3 effectively inhibited BACE-1 (IC₅₀ = 6.72 μM), and PC10 and PC11 moderately inhibited BACE-1 (IC₅₀ =14.9 and 15.3 μM, respectively). Reversibility and kinetic studies showed that PC10 and PC11 were reversible and competitive inhibitors of MAO-B with K_i values of 0.63 ± 0.13 and 0.53 ± 0.068 μM, respectively. ADME predictions for lead compounds revealed that PC10 and PC11 have central nervous system (CNS) drug-likeness. Molecular docking simulations showed that fluorine atom and trifluoromethyl group on PC10 and PC11, respectively, interacted with the substrate cavity of the MAO-B active site. Our results suggested that PC10 and PC11 can be considered potential candidates for the treatment of neurological disorders such as Alzheimer's disease and Parkinson's disease.

Synthesis and Characterization of a Positron Emission Tomography Imaging Probe Selectively Targeting the Second Bromodomain of Bromodomain Protein BRD4

Two tandem bromodomains (BD1 and BD2) of bromodomain and extraterminal domain (BET) family proteins have shown distinct roles in mediating gene transcription and expression. Inhibitors that interact with a specific bromodomain may contribute to a specific therapeutic potential with fewer side effects. However, little is known about this disease-related target. Positron emission tomography (PET) imaging could allow us to achieve in-depth knowledge of the BD2 bromodomain. Herein we describe the radiosynthesis and evaluation of [¹¹C]1 as a BRD4 BD2 bromodomain PET imaging radioligand. Our preliminary PET imaging results in rodents demonstrated that [¹¹C]1 had suitable biodistribution in peripheral organs and tissues. Further blocking studies indicated that [¹¹C]1 had good binding specificity toward the BD2 bromodomain. This study may pave the way for the development of a PET radioligand specifically targeting BD1/2 bromodomains as well as for the biological mechanism investigation of BD1/2 bromodomains.

Trimethoxylated Halogenated Chalcones as Dual Inhibitors of MAO-B and BACE-1 for the Treatment of Neurodegenerative Disorders

Six halogenated trimethoxy chalcone derivatives (CH1-CH6) were synthesized and spectrally characterized. The compounds were further evaluated for their inhibitory potential against monoamine oxidases (MAOs) and β-secretase (BACE-1). Six compounds inhibited MAO-B more effectively than MAO-A, and the 2',3',4'-methoxy moiety in CH4-CH6 was more effective for MAO-B inhibition than the 2',4',6'-methoxy moiety in CH1-CH3. Compound CH5 most potently inhibited MAO-B, with an IC₅₀ value of 0.46 µM, followed by CH4 (IC₅₀ = 0.84 µM). In 2',3',4'-methoxy derivatives (CH4-CH6), the order of inhibition was -Br in CH5 > -Cl in CH4 > -F in CH6 at the para-position in ring B of chalcone. CH4 and CH5 were selective for MAO-B, with selectivity index (SI) values of 15.1 and 31.3, respectively, over MAO-A. CH4 and CH5 moderately inhibited BACE-1 with IC₅₀ values of 13.6 and 19.8 µM, respectively. When CH4 and CH5 were assessed for their cell viability studies on the normal African Green Monkey kidney cell line (VERO) using MTT assays, it was noted that both compounds were found to be safe, and only a slightly toxic effect was observed in concentrations above 200 µg/mL. CH4 and CH5 decreased reactive oxygen species (ROS) levels of VERO cells treated with H₂O₂, indicating both compounds retained protective effects on the cells by antioxidant activities. All compounds showed high blood brain barrier permeabilities analyzed by a parallel artificial membrane permeability assay (PAMPA). Molecular docking and ADME prediction of the lead compounds provided more insights into the rationale behind the binding and the CNS drug likeness. From non-test mutagenicity and cardiotoxicity studies, CH4 and CH5 were non-mutagenic and non-/weak-cardiotoxic. These results suggest that CH4 and CH5 could be considered candidates for the cure of neurological dysfunctions.

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.

Multitarget Effect of 2-(4-(Methylthio)phenyl)-3-(3-(piperidin-1-yl)propyl)thiazolidin-4-one in a Scopolamine-Induced Amnesic Rat Model

Cholinergic system dysfunction, oxidative damage, and alterations in ion pump activity have been associated with memory loss and cognitive deficits in Alzheimer's disease. 1,3-thiazolidin-4-ones have emerged as a class of compounds with potential therapeutic effects due to their potent anticholinesterase activity. Accordingly, this study investigated the effect of the 2-(4-(methylthio)phenyl)-3-(3-(piperidin-1-yl)propyl)thiazolidin-4-one (DS12) compound on memory, cholinergic and oxidative stress parameters, ion pump activity, and serum biochemical markers in a scopolamine-induced memory deficit model. Male Wistar rats were divided into four groups: I-Control; II-Scopolamine; III-DS12 (5 mg/kg) + scopolamine; and IV-DS12 (10 mg/kg) + scopolamine. The animals from groups III and IV received DS12 diluted in canola oil and administered for 7 days by gavage. On the last day of treatment, scopolamine (1 mg/kg) was administered intraperitoneally (i.p.) 30 min after training in an inhibitory avoidance apparatus. Twenty-four hours after scopolamine administration, the animals were subjected to an inhibitory avoidance test and were thereafter euthanized. Scopolamine induced memory deficits, increased acetylcholinesterase activity and oxidative damage, and decreased Na+/K+-ATPase activity in cerebral cortex and hippocampus. Pretreatment with DS12 prevented these brain alterations. Scopolamine also induced an increase in acetylcholinesterase activity in lymphocytes and whereas butyrylcholinesterase in serum and treatment with DS12 prevented these changes. In animals treated with DS12, no changes were observed in renal and hepatic parameters when compared to the control group. In conclusion, DS12 emerged as an important multitarget compound capable of preventing neurochemical changes associated with memory deficits.

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.

Synthesis and biological evaluation of 2'-Aminochalcone: A multi-target approach to find drug candidates to treat Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative process that compromises cognitive functions. The physiopathology of AD is multifactorial and is mainly supported by the cholinergic and amyloid hypotheses, which allows the identification the fundamental role of some markers, such as the enzymes acetylcholinesterase (AChE) and β-secretase (BACE-1), and the β-amyloid peptide (Aβ). In this work, we prepared a series of chalcones and 2'-aminochalcones, which were tested against AChE and BACE-1 enzymes and on the aggregation of Aβ. All compounds inhibited AChE activity with different potencies. We have found that the majority of chalcones having the amino group are able to inhibit BACE-1, which was not observed for chalcones without this group. The most active compound is the one derived from 2,3-dichlorobenzaldeyde, having an IC₅₀ value of 2.71 μM. A molecular docking study supported this result, showing a good interaction of the amino group with aspartic acid residues of the catalytic diade of BACE-1. Thioflavin-T fluorescence emission is reduced in 30 - 40%, when Aβ₄₂ is incubated in the presence of some chalcones under aggregation conditions. In vitro cytotoxicity and in silico prediction of pharmacokinetic properties were also conducted in this study.

The Emerging Therapeutic Potential of Nitro Fatty Acids and Other Michael Acceptor-Containing Drugs for the Treatment of Inflammation and Cancer

Nitro fatty acids (NFAs) are endogenously generated lipid mediators deriving from reactions of unsaturated electrophilic fatty acids with reactive nitrogen species. Furthermore, Mediterranean diets can be a source of NFA. These highly electrophilic fatty acids can undergo Michael addition reaction with cysteine residues, leading to post-translational modifications (PTM) of selected regulatory proteins. Such modifications are capable of changing target protein function during cell signaling or in biosynthetic pathways. NFA target proteins include the peroxisome proliferator-activated receptor γ (PPAR-γ), the pro-inflammatory and tumorigenic nuclear factor-κB (NF-κB) signaling pathway, the pro-inflammatory 5-lipoxygenases (5-LO) biosynthesis pathway as well as soluble epoxide hydrolase (sEH), which is essentially involved in the regulation of vascular tone. In several animal models of inflammation and cancer, the therapeutic efficacy of well-tolerated NFA has been demonstrated. This has already led to clinical phase II studies investigating possible therapeutic effects of NFA in subjects with pulmonary arterial hypertension. Albeit Michael acceptors feature a broad spectrum of bioactivity, they have for a rather long time been avoided as drug candidates owing to their presumed unselective reactivity and toxicity. However, targeted covalent modification of regulatory proteins by Michael acceptors became recognized as a promising approach to drug discovery with the recent FDA approvals of the cancer therapeutics, afatanib (2013), ibrutinib (2013), and osimertinib (2015). Furthermore, the Michael acceptor, neratinib, a dual inhibitor of the human epidermal growth factor receptor 2 and epidermal growth factor receptor, was recently approved by the FDA (2017) and by the EMA (2018) for the treatment of breast cancer. Finally, a number of further Michael acceptor drug candidates are currently under clinical investigation for pharmacotherapy of inflammation and cancer. In this review, we focus on the pharmacology of NFA and other Michael acceptor drugs, summarizing their potential as an emerging class of future antiphlogistics and adjuvant in tumor therapeutics.

Metabolic Impact of Flavonoids Consumption in Obesity: From Central to Peripheral

The prevention and treatment of obesity is primary based on the follow-up of a healthy lifestyle, which includes a healthy diet with an important presence of bioactive compounds such as polyphenols. For many years, the health benefits of polyphenols have been attributed to their anti-oxidant capacity as free radical scavengers. More recently it has been described that polyphenols activate other cell-signaling pathways that are not related to ROS production but rather involved in metabolic regulation. In this review, we have summarized the current knowledge in this field by focusing on the metabolic effects of flavonoids. Flavonoids are widely distributed in the plant kingdom where they are used for growing and defensing. They are structurally characterized by two benzene rings and a heterocyclic pyrone ring and based on the oxidation and saturation status of the heterocyclic ring flavonoids are grouped in seven different subclasses. The present work is focused on describing the molecular mechanisms underlying the metabolic impact of flavonoids in obesity and obesity-related diseases. We described the effects of each group of flavonoids in liver, white and brown adipose tissue and central nervous system and the metabolic and signaling pathways involved on them.

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.

Cognitive Facilitation and Antioxidant Effects of an Essential Oil Mix on Scopolamine-Induced Amnesia in Rats: Molecular Modeling of In Vitro and In Vivo Approaches

The present study investigated the capability of an essential oil mix (MO: 1% and 3%) in ameliorating amnesia and brain oxidative stress in a rat model of scopolamine (Sco) and tried to explore the underlying mechanism. The MO was administered by inhalation to rats once daily for 21 days, while Sco (0.7 mg/kg) treatment was delivered 30 min before behavioral tests. Donepezil (DP: 5 mg/kg) was used as a positive reference drug. The cognitive-enhancing effects of the MO in the Sco rat model were assessed in the Y-maze, radial arm maze (RAM), and novel object recognition (NOR) tests. As identified by gas chromatography–mass spectrometry (GC–MS), the chemical composition of the MO is comprised by limonene (91.11%), followed by γ-terpinene (2.02%), β-myrcene (1.92%), β-pinene (1.76%), α-pinene (1.01%), sabinene (0.67%), linalool (0.55%), cymene (0.53%), and valencene (0.43%). Molecular interactions of limonene as the major compound in MO with the active site of butyrylcholinesterase (BChE) was explored via molecular docking experiments, and Van der Waals (vdW) contacts were observed between limonene and the active site residues SER198, HIS438, LEU286, VAL288, and PHE329. The brain oxidative status and acetylcholinesterase (AChE) and BChE inhibitory activities were also determined. MO reversed Sco-induced memory deficits and brain oxidative stress, along with cholinesterase inhibitory effects, which is an important mechanism in the anti-amnesia effect. Our present findings suggest that MO ameliorated memory impairment induced by Sco via restoration of the cholinergic system activity and brain antioxidant status.