Design, synthesis and evaluation of scutellarein- O -acetamidoalkylbenzylamines as potential multifunctional agents for the treatment of Alzheimer's disease

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

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

A Multilevel Study of Eupatorin and Scutellarein as Anti-Amyloid Agents in Alzheimer's Disease

Today, Alzheimer's disease (AD)-the most common neurodegenerative disorder, which affects 50 million people-remains incurable. Several studies suggest that one of the main pathological hallmarks of AD is the accumulation of abnormal amyloid beta (Aβ) aggregates; therefore, many therapeutic approaches focus on anti-Aβ aggregation inhibitors. Taking into consideration that plant-derived secondary metabolites seem to have neuroprotective effects, we attempted to assess the effects of two flavones-eupatorin and scutellarein-on the amyloidogenesis of Aβ peptides. Biophysical experimental methods were employed to inspect the aggregation process of Aβ after its incubation with each natural product, while we monitored their interactions with the oligomerized Aβ through molecular dynamics simulations. More importantly, we validated our in vitro and in silico results in a multicellular organismal model-namely, Caenorhabditis elegans-and we concluded that eupatorin is indeed able to delay the amyloidogenesis of Aβ peptides in a concentration-dependent manner. Finally, we propose that further investigation could lead to the exploitation of eupatorin or its analogues as potential drug candidates.

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, characterization, molecular docking, dynamics simulations, and in silico absorption, distribution, metabolism, and excretion (ADME) studies of new thiazolylhydrazone derivatives as butyrylcholinesterase inhibitors

In this study, two novel series of thiazolylhydrazone derivatives containing 4-ethylpiperazine (3a–3f) and 4-methoxyphenylpiperazine (3g–3l) side chains were synthesized and their structures were characterized by spectral (1H NMR, 13C NMR, and MS spectra) analyses. In vitro inhibitory activities of synthesized compounds against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) were determined by Ellman method. According to the results, all compounds showed a weak inhibitory effect on AChE, while promising results were obtained on BChE. Among the synthesized compounds, the activities of the derivatives carrying 4-ethylpiperazine (3a–3f) structure were found to be more effective than the compounds carrying 4-methoxyphenyl piperazine (3g–3l) derivatives. Especially, compound 3f bearing the nitro substituent was found to be the most promising compound on BChE in the series. The absorption, distribution, metabolism, and excretion (ADME) parameters of the synthesized compounds were predicted by using the SwissADME server. The potential binding mode and stability of compound 3f with BChE were investigated by the molecular docking and dynamics simulations. The results showed that 3f was strongly bound up with BChE with the optimal conformation; in addition, their binding free energy reached −167.936 ± 13.109 kJ/mol.

Flavones as a Privileged Scaffold in Drug Discovery: Current Developments

BACKGROUND

Flavones are one of the main subclasses of flavonoids with diverse pharmacological properties. They have been reported to possess antimalarial, antimicrobial, anti-tuberculosis, anti-allergic, antioxidant, anti-inflammatory activities, among others.

OBJECTIVE

The present review summarizes the recent information on the pharmacological properties of naturally occurring and synthetic flavones.

METHODS

Scientific publications referring to natural and synthetic flavones in relation to their biological activities were hand-searched in databases such as SciFinder, PubMed (National Library of Medicine), Science Direct, Wiley, ACS, SciELO, Springer, among others.

RESULTS

As per the literature, seventy-five natural flavones were predicted as active compounds with reference to their IC50 (<20 µg/mL) in in vitro studies. Also, synthetic flavones were found active against several diseases.

CONCLUSION

As per the literature, flavones are important sources for the potential treatment of multifactorial diseases. However, efforts toward the development of flavone-based therapeutic agents are still needed. The appearance of new catalysts and chemical transformations is expected to provide avenues for the synthesis of unexplored flavones, leading to the discovery of flavones with new properties and biological activities.

Semi-synthesis and biological evaluation of flavone hybrids as multifunctional agents for the potential treatment of Alzheimer's disease

7-O-galloyltricetiflavan (GTF), a natural flavonoid, is known to exert anti-oxidation and neuroprotective activity, which are related to the prevention of Alzheimer's disease (AD). In this study, three series of GTF hybrids have been designed, synthesized and evaluated as multifunctional agents for treatment AD. The biological assays indicated that most of them showed strong inhibitory effect on self-induced β-amyloid (Aβ) aggregation, and a significant ability to inhibit ChEs. Among them, compound A15 exhibited best inhibition of Aβ aggregation (78.81% at 20 μM), potent AChE inhibitory potencies (IC₅₀, 0.56 μM), and compound C4 presented the highest ability to inhibit BuChE (IC₅₀, 5.77 μM). Furthermore, kinetic, molecular modeling and molecular dynamics studies revealed that A15 and C4 could interact with the catalytic active site of AChE and BuChE, respectively. In addition, compounds A15 and C4 could cross the blood-brain barrier in vitro. More importantly, A15 and C4 also showed excellent neuroprotective activities against H₂O₂-induced human neuroblastoma SH-SY5Y cells damage and nearly no toxicity on SH-SY5Y cells. All of these outstanding in vitro results indicated A15 and C4 as the leading structure worthy of further investigation.

Inhibition of acetylcholinesterase activity and β-amyloid oligomer formation by 6-bromotryptamine A, a multi-target anti-Alzheimer's molecule

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by learning and memory impairments. Recent studies have suggested that AD can be induced by multiple factors, such as cholinergic system dysfunction and β-amyloid (Aβ) neurotoxicity. It was reported that 6-bromo-N-propionyltryptamine could treat neurological diseases, including AD. In the present study, 6-bromotryptamine A, a derivative of 6-bromo-N-propionyltryptamine, was synthesized by the condensation of 2-(6-bromo-1H-indol-3-yl)ethan-1-amine and 2-(4-bromophenyl)acetic acid, and was used as a potential anti-AD molecule. Furthermore, scopolamine can induce impairments of learning and memory, and was widely used to establish AD animal models. The results demonstrated that 6-bromotryptamine A significantly prevented scopolamine-induced short-term cognitive impairments, as revealed by various behavioral tests in mice. Furthermore, an acetylcholinesterase (AChE) activity assay revealed that 6-bromotryptamine A directly inhibited AChE activity. Notably, it was observed that 6-bromotryptamine A blocked the formation of Aβ oligomer, as evaluated by the dot blot assay. All these results suggested that 6-bromotryptamine A may be used to prevent impairments in short-term learning and memory ability possibly via the inhibition of AChE and the blockade of Aβ oligomer formation.

The development of 2-acetylphenol-donepezil hybrids as multifunctional agents for the treatment of Alzheimer's disease

A series of 2-acetylphenol-donepezil hybrids was designed and synthesized based on multi-target-directed ligands strategy. The biological activities were evaluated by AChE/BChE inhibition and MAO-A/MAO-B inhibition. The results revealed that the tertiary amines and methylene chain length significantly affected the eeAChE inhibitory potency, in particular, compound TM-14 showed the best eeAChE inhibitory activity with IC₅₀ value of 2.9 μM, in addition, both kinetic analysis of AChE inhibition and docking study displayed that TM-14 could simultaneously bind to the catalytic active site and peripheral anionic site of AChE. Moreover, compound TM-14 was a selective metal chelator and could form 1:1 TM-14-Cu²⁺ complex. The structure-active-relationship also indicated that the O-alkylamine fragment remarkably decreased hMAO-B inhibitory activity, compound TM-2 exhibited potent hMAO-B inhibitory activity (IC₅₀ = 6.8 μM), which was supported by the molecular docking study. More interestingly, compounds TM-14 and TM-2 could cross the blood-brain barrier in vitro. Therefore, the structure-active-relationship of 2-acetylphenol-donepezil hybrids could encourage the development of multifunction agents with selective AChE inhibition or selective MAO-B inhibition for the treatment of Alzheimer's disease.

Synthesis and AChE Inhibitory Activity of Novel Thiazolylhydrazone Derivatives

Alzheimer’s disease (AD) is the most common of the degenerative brain diseases and is described together with the impairment of cognitive function. Patients with AD lose the capability to code new memories, and life conditions are extremely difficult. The development of new drugs in this area continues at a great pace. A novel series of thiazole-piperazine hybrids, aimed against Alzheimer’s disease (AD), have been synthesized. The structure identification of synthesized compounds was elucidated by ¹HNMR, ¹³C-NMR, and LCMSMS spectroscopic methods. The inhibitory potential of the synthesized compounds on cholinesterase enzymes was investigated. The compounds 3a, 3c and 3i showed significant inhibitory activity on the acetylcholinesterase (AChE) enzyme. On the other hand, none of the compounds showed significant inhibitory activity on the butyrylcholinesterase (BChE) enzyme. In addition to enzyme inhibition studies, enzyme kinetic studies were performed to observe the effects of the most active inhibitor compounds on the substrate–enzyme relationship. In addition to in vitro tests, docking studies also indicated that compound 3c potentially acts as a dual binding site AChE inhibitor.

Discovery of 4'-OH-flurbiprofen Mannich base derivatives as potential Alzheimer's disease treatment with multiple inhibitory activities

A series of 4'-OH flurbiprofen Mannich base derivatives were designed, synthesized and evaluated as potential multifunctional agents for the treatment of Alzheimer's disease. The biological screening results indicated that most of these derivatives exhibited good multifunctional activities. Among them, compound 8n demonstrated the best inhibitory effects on self-induced Aβ_1-42 aggregation (65.03% at 25.0 μM). Moreover, this representative compound also exhibited good antioxidant activity, biometal chelating ability and anti-neuroinflammatory activity in vitro. Furthermore, compound 8n displayed appropriate blood-brain barrier permeability. These multifunctional properties highlight compound 8n as promising candidate for further development of multi-functional drugs against AD.

Novel potential artificial MRSA DNA intercalators: synthesis and biological evaluation of berberine-derived thiazolidinediones

Novel berberine-derived thiazolidinediones as potential artificial DNA intercalators were synthesized, and the preliminary mechanism suggested that active compound 6b could intercalate into MRSA DNA.

Preparation of 4-Flexible Amino-2-Arylethenyl-Quinoline Derivatives as Multi-target Agents for the Treatment of Alzheimer's Disease

Alzheimer’s disease (AD) is a complex and multifactorial neurodegenerative disorder of aged people. The development of multitarget-directed ligands (MTDLs) to act as multifunctional agents to treat this disease is the mainstream of current research. As a continuation of our previous studies, a series of 4-flexible amino-2-arylethenylquinoline derivatives as multi-target agents was efficiently synthesized and evaluated for the treatment of AD. Among these synthesized derivatives, some compounds exhibited strong self-induced Aβ_1–42 aggregation inhibition and antioxidant activity. The structure-activity relationship was summarized, which confirmed that the introduction of a flexible amino group featuring a N,N-dimethylaminoalkylamino moiety at the 4-position increased the Aβ_1–42 aggregation inhibition activity, with an inhibition ratio of 95.3% at 20 μM concentration. Compound 6b₁, the optimal compound, was able to selectively chelate copper (II), and inhibit Cu²⁺-induced Aβ aggregation effectively. It also could disassemble the self-induced Aβ_1–42 aggregation fibrils with a ratio of 64.3% at 20 μM concentration. Moreover, compound 6b₁ showed low toxicity and a good neuroprotective effect against Aβ_1–42-induced toxicity in SH-SY5Y cells. Furthermore, the step-down passive avoidance test indicated compound 6b₁ significantly reversed scopolamine-induced memory deficit in mice. Taken together, these results suggested that compound 6b₁ was a promising multi-target compound worthy of further study for AD.

Discovery of novel 2,5-dihydroxyterephthalamide derivatives as multifunctional agents for the treatment of Alzheimer's disease

A series of 2,5-dihydroxyterephthalamide derivatives were designed, synthesized and evaluated as multifunctional agents for the treatment of Alzheimer's disease. In vitro assays demonstrated that most of the derivatives exhibited good multifunctional activities. Among them, compound 9d showed the best inhibitory activity against both RatAChE and EeAChE (IC₅₀ = 0.56 μM and 5.12 μM, respectively). Moreover, 9d exhibited excellent inhibitory effects on self-induced Aβ_1-42 aggregation (IC₅₀ = 3.05 μM) and Cu²⁺-induced Aβ_1-42 aggregation (71.7% at 25.0 μM), and displayed significant disaggregation ability to self- and Cu²⁺-induced Aβ_1-42 aggregation fibrils (75.2% and 77.2% at 25.0 μM, respectively). Furthermore, 9d also showed biometal chelating abilities, antioxidant activity, anti-neuroinflammatory activities and appropriate BBB permeability. These multifunctional properties highlight 9d as promising candidate for further studies directed to the development of novel drugs against AD.

Anti-Amyloid Aggregation Activity of Black Sesame Pigment: Toward a Novel Alzheimer's Disease Preventive Agent

Black sesame pigment (BSP) represents a low cost, easily accessible material of plant origin exhibiting marked antioxidant and heavy metal-binding properties with potential as a food supplement. We report herein the inhibitory properties of the potentially bioaccessible fraction of BSP following simulated gastrointestinal digestion against key enzymes involved in Alzheimer's disease (AD). HPLC analysis indicated that BSP is transformed under the pH conditions mimicking the intestinal environment and the most abundant of the released compounds was identified as vanillic acid. More than 80% inhibition of acetylcholinesterase-induced aggregation of the β-amyloid Aβ1-40 was observed in the presence of the potentially bioaccessible fraction of BSP, which also efficiently inhibited self-induced Aβ1-42 aggregation and β-secretase (BACE-1) activity, even at high dilution. These properties open new perspectives toward the use of BSP as an ingredient of functional food or as a food supplement for the prevention of AD.

Identification of disulfiram as a secretase-modulating compound with beneficial effects on Alzheimer's disease hallmarks

ADAM10 is a metalloproteinase acting on the amyloid precursor protein (APP) as an alpha-secretase in neurons. Its enzymatic activity results in secretion of a neuroprotective APP cleavage product (sAPP-alpha) and prevents formation of the amyloidogenic A-beta peptides, major hallmarks of Alzheimer’s disease (AD). Elevated ADAM10 levels appeared to contribute to attenuation of A-beta-plaque formation and learning and memory deficits in AD mouse models. Therefore, it has been assumed that ADAM10 might represent a valuable target in AD therapy. Here we screened a FDA-approved drug library and identified disulfiram as a novel ADAM10 gene expression enhancer. Disulfiram increased ADAM10 production as well as sAPP-alpha in SH-SY5Y human neuronal cells and additionally prevented A-beta aggregation in an in vitro assay in a dose-dependent fashion. In addition, acute disulfiram treatment of Alzheimer model mice induced ADAM10 expression in peripheral blood cells, reduced plaque-burden in the dentate gyrus and ameliorated behavioral deficits. Alcohol-dependent patients are subjected to disulfiram-treatment to discourage alcohol-consumption. In such patients, enhancement of ADAM10 by disulfiram-treatment was demonstrated in peripheral blood cells. Our data suggest that disulfiram could be repurposed as an ADAM10 enhancer and AD therapeutic. However, efficacy and safety has to be analyzed in Alzheimer patients in the future.

Synthesis and structure-activity relationship study of multi-target triazine derivatives as innovative candidates for treatment of Alzheimer's disease

The complex pathogenesis of Alzheimer's disease (AD) requires using multi-target ligands (MTLs) for disease management. We synthesized, characterized and evaluated a series of novel triazine analogues as MTLs for AD. The biological screening results indicated that most of our compounds displayed potent inhibitory activities against β-site APP-cleaving enzyme 1 (BACE1) using a FRET-based assay. Compounds 6c and 6m were found to possess significant BACE1 inhibitory properties with IC₅₀ values of 0.91 (±0.25) µM and 0.69 (±0.20) µM, respectively. DPPH radical scavenging activity evaluation showed that compounds with hydroxyl and pyrrole moieties had antioxidant effects. Docking evaluations provided insight into enzyme inhibitory interactions of novel synthesized compounds with the BACE1 active site involving a critical role for Gln73 and/or Phe108 alongside of Asp32. Metal chelation tests confirmed that compound 6m is a chelator for Fe²⁺, Fe³⁺, Zn²⁺, Cu²⁺. Moreover 6m as the most potent BACE1 inhibitor did not show any toxicity against PC12 neuronal cells. These findings demonstrate the high potential of triazine scaffolds in the design of MTLs for treatment of AD.

Piperlongumine B and analogs are promising and selective inhibitors for acetylcholinesterase

Piperlongumine B (19), an alkaloid previously isolated from long pepper (Piper longum) has been synthesized for the first time in a short sequence and in good yield together with 19 analogs. Screening of these compounds in Ellman's assays showed several of them to be good inhibitors of acetylcholinesterase while being less active for butyrylcholinesterase. Activity of the compounds increased with the ring size of the heterocycle, and a maximum of activity was observed for an analog holding 12 methylene groups in the aliphatic side chain. These compounds may be regarded as promising candidates for the development of efficient inhibitors of acetylcholinesterase being useful for the treatment of Alzheimer's disease.

Multifunctional iminochromene-2H-carboxamide derivatives containing different aminomethylene triazole with BACE1 inhibitory, neuroprotective and metal chelating properties targeting Alzheimer's disease

Alzheimer's disease (AD) is a neurodegenerative disorder known for the presence of amyloid beta plaques resulting from the sequential action of β-secretase and γ-secretase on amyloid precursor protein. We developed and synthesized, through click reactions, a new family of iminochromene carboxamides containing different aminomethylene triazole. The BACE1 inhibition, neuroprotective capacity and metal chelation of these derivatives make them ideal candidates against AD. Most of the synthesized compounds were shown to have potent BACE1 inhibitory activity in a FRET assay, with an IC₅₀ value of 2.2 μM for the most potent compound. Moreover, molecular modeling evaluation of these BACE1 inhibitors demonstrates the vital role of the amine and amide linkers through hydrogen bond interactions with key amino acids in the BACE1 active site. Our in vitro neuroprotective evaluations in PC12 neuronal cells of Aβ-induced neuroprotection demonstrated promising activity for most of the compounds as neuroprotective agents. Based on our findings, we propose that introduction of a phthalimide substitute on the triazole ring shown to be interesting multifunctional lead compound worthy of further study.