Design and synthesis of novel anti-Alzheimer’s agents: Acridine-chromenone and quinoline-chromenone hybrids

Discovery of novel thiosemicarbazone-acridine targeting butyrylcholinesterase with antioxidant, metal complexing and neuroprotector abilities as potential treatment of Alzheimer's disease: In vitro, in vivo, and in silico studies

Inhibition of cholinesterases, combined with antioxidant activity, metal-chelating capacity, and neuroprotection, is recognized as an effective multitarget therapy for the treatment of Alzheimer's disease (AD). Based on our in-house thiosemicarbazone-acridine compounds, this study recognized these derivatives as possible multi-target-directed ligand (MTDL). Initial screening against cholinesterases identified CL-01, which exhibited a promising IC50 value of 0.71 μM against butyrylcholinesterase (BChE). Twelve new derivatives were designed based on CL-01 aiming to retain the BChE inhibitory activity while incorporating a MTDL profile, including antioxidant properties and metal-complexing abilities. Among the new derivatives, CL-13 maintained a good BChE inhibition (IC50 = 1.15 μM) with improved selective index against acetylcholinesterase (SI = 9.2). The acridine nucleus was important for the activity, as its saturated tetrahydroacridine analogue (TA-01) showed a decrease in cholinesterases inhibition potencies and altered the mode of inhibition, revealing for the first time distinct functional roles for the two nuclei. Moreover, CL-13 emerged as a promising lead compound, demonstrating interesting antioxidant activity (DPPH EC50 = 47.01 μM), chelating capacity of biometals involved in Aβ aggregation and/or oxidative stress, and a lack of neurotoxicity at 50 μM in SH-SY5Y cells. It also exhibited neuroprotective effects in an in vitro oxidative stress model induced by H2O2. Finally, in vivo experiments confirmed that CL-13 effectively reversed scopolamine-induced cognitive impairment, without affecting locomotor activity in the mice.

Recent advancements in the therapeutic approaches for Alzheimer's disease treatment: current and future perspective

Alzheimer's disease (AD) is a complex, incurable neurological condition characterized by cognitive decline, cholinergic neuron reduction, and neuronal loss. Its exact pathology remains uncertain, but multiple treatment hypotheses have emerged. The current treatments, single or combined, alleviate only symptoms and struggle to manage AD due to its multifaceted pathology. The developmental drugs target pivotal disease factors involved in the envisaged hypotheses and include targets such as amyloid aggregation, hyperphosphorylated tau proteins, and receptors like cholinergic, adrenergic, etc. Present-day research focuses on multi-target directed ligands (MTDLs), which inhibit multiple factors simultaneously, helping slow the disease's progression. This review attempts to collate the recent information related to proposed hypotheses for AD etiology. It systematically organizes the advances in various therapeutic options for AD, with a particular emphasis on clinical candidates. Also, it is expected to help medicinal chemists design novel AD treatments based on available information, which could be helpful to AD patients.

Chromenone: An emerging scaffold in anti-Alzheimer drug discovery

Alzheimer's disease (AD) presents a growing global health concern. In recent decades, natural and synthetic chromenone have emerged as promising drug candidates due to their multi-target potential. Natural chromenone, quercetin, scopoletin, esculetin, coumestrol, umbelliferone, bergapten, and methoxsalen (xanthotoxin), and synthetic chromenone hybrids comprising structures like acridine, 4-aminophenyl, 3-arylcoumarins, quinoline, 1,3,4-oxadiazole, 1,2,3-triazole, and tacrine, have been explored for their potential to combat AD. Key reactions used for synthesis of chromenone hybrids include Perkin and Pechmann condensation. The activity of chromenone hybrids has been reported against several drug targets, including AChE, BuChE, BACE-1, and MAO-A/B. This review comprehensively explores natural, semisynthetic, and synthetic chromenone, elucidating their synthetic routes, possible mode of action/drug targets and structure-activity relationships (SAR). The acquired knowledge provides valuable insights for the development of new chromenone hybrids against AD.

Quinoline as a Privileged Structure: A Recent Update on Synthesis and Biological Activities

Among heterocyclic compounds, quinoline is one of the best ubiquitous heterocyclic rings for medicinal chemistry purposes. Quinoline appears to be a powerful chemical structure to develop new drug entities. The quinoline derivatives own a wide array of biological activities such as anticancer, antimalarial, antimicrobial, anti-inflammatory, anti-leishmanial, etc. Because of the wide spectrum of bioactivities, the scientific communities are still looking for more efficient synthetic routes to form quinoline derivatives. Therefore, the primary focus of this review is to provide a thorough and inclusive, updated report on quinoline analogs that may pave the way for more efficient drug development.

Investigation of biological activities of two cultivars of Cicer arietinum proteins mass associated with Alzheimer's disease

Alzheimer's disease (AD) is the most common cause of dementia in the elderly, with some known classical factors. Cicer arietinum (Leguminosae) is a source of protein for humans and contains albumin, globulin, glutelin, and prolamin. The protein content of two cultivars of C. arietinum, Hashem and Mansour, was isolated to evaluate their inhibition activity against acetylcholinesterase (AChE), butyrylcholine esterase (BChE), and β-amyloid peptide (βA) aggregation. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and molecular docking were also applied to evaluate the content and determine the potential of each chickpea protein to interact with AChE, respectively. Obtained data showed that proteins from both cultivars could inhibit AChE with IC50 of 17.73 (0.03) and 22.20 (0.06) μg/mL, respectively, with no activity on BChE. The 50 μg/mL protein concentration of each cultivar suppressed βA accumulation (Mansour: 25.66% and Hashem: 21.69%) and showed biometal chelating activity. SDS-PAGE analysis revealed relatively different protein patterns, though the Mansour cultivar contained some protein bands with molecular weights of 18, 24, and 70 kDa were estimated to belong to vicilin and legumin, which were absent in the Hashem protein mass. Molecular docking showed that legumin and especially vicilin have good potential to interact with AChE. The chickpea proteins showed inhibitory activity against AChE, which might be due to the vicilin and legumin fractions. The characterization of the inhibitory effect of each protein band could be promising in finding new therapeutic peptide candidates to treat Alzheimer's in the future, although more experimental work is needed in this issue.

Ultrasound-assisted synthesis of kojic acid-1,2,3-triazole based dihydropyrano[3,2-b]pyran derivatives using Fe3O4@CQD@CuI as a novel nanomagnetic catalyst

The magnetic nanoparticles coated with carbon quantum dot and copper (I) iodide (Fe₃O₄@CQD@CuI) were used as eco-friendly heterogeneous Lewis / Brønsted acid sites and Cu (I) nanocatalysts. In the first step, it was applied in the synthesis of kojic acid-based dihydropyrano[3,2-b]pyran derivatives in a three-component reaction and in the second step, as a recyclable catalyst for the synthesis of kojic acid-1,2,3-triazole based dihydropyrano[3,2-b]pyran derivatives in the CuI-catalyzed azide/alkyne cycloaddition (CuAAC) reaction. The catalyst was characterized fully by using the different techniques including fourier transform infrared spectroscopy (FT-IR), elemental mapping analysis, X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray spectroscopy (EDX), transmission electron microscopy (TEM), thermal gravimetric (TG) and value-stream mapping (VSM) methods. The final synthesized derivatives were identified by ¹H- and ¹³C-NMR spectroscopy.

Cyclometalated iridium complexes-catalyzed acceptorless dehydrogenative coupling reaction: construction of quinoline derivatives and evaluation of their antimicrobial activities

The acceptorless dehydrogenative coupling (ADC) reaction is an efficient method for synthesizing quinoline and its derivatives. In this paper, various substituted quinolines were synthesized from 2-aminobenzyl alcohols and aryl/heteroaryl/alkyl secondary alcohols in one pot via a cyclometalated iridium-catalyzed ADC reaction. This method has some advantages, such as easy availability of raw materials, mild reaction conditions, wide range of substrates, and environmental friendliness which conforms to the principles of green chemistry. Furthermore, a gram-scale experiment with low catalyst loading offers the potential to access the aryl/heteroaryl quinolones in suitable amounts. In addition, the antibacterial and antifungal activities of the synthesized quinolines were evaluated in vitro, and the experimental results showed that the antibacterial activities of compounds 3ab, 3ad, and 3ah against Gram-positive bacteria and compound 3ck against C. albicans were better than the reference drug norfloxacin.

Inhibitory potential of nitrogen, oxygen and sulfur containing heterocyclic scaffolds against acetylcholinesterase and butyrylcholinesterase

Heterocycles are the key structures in organic chemistry owing to their immense applications in the biological, chemical, and pharmaceutical fields. Heterocyclic compounds perform various noteworthy functions in nature, medication, innovation etc. Most frequently, pure nitrogen heterocycles or various positional combinations of nitrogen, oxygen, and sulfur atoms in five or six-membered rings can be found. Inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) enzymes is a popular strategy for the management of numerous mental diseases. In this context, cholinesterase inhibitors are utilized to relieve the symptoms of neurological illnesses like dementia and Alzheimer's disease (AD). The present review focuses on various heterocyclic scaffolds and their role in designing and developing new potential AChE and BChE inhibitors to treat AD. Moreover, a detailed structure-activity relationship (SAR) has been established for the future discovery of novel drugs for the treatment of AD. Most of the heterocyclic motifs have been used in the design of new potent cholinesterase inhibitors. In this regard, this review is an endeavor to summarize the biological and chemical studies over the past decade (2010-2022) describing the pursuit of new N, O and S containing heterocycles which can offer a rich supply of promising AChE and BChE inhibitory activities.

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 novel cinnamic acid-tryptamine hybrid for inhibition of acetylcholinesterase and butyrylcholinesterase

BACKGROUND

Acetylcholine deficiencies in hippocampus and cortex, aggregation of β-amyloid, and β-secretase over activity have been introduced as main reasons in pathogenesis of Alzheimer's disease.

METHODS

Colorimetric Ellman's method was used for determination of IC50 value in AChE and BChE inhibitory activity. The kinetic studies, neuroprotective and β-secretase inhibitory activities, evaluation of inhibitory potency on β-amyloid (Aβ) aggregations induced by AChE, and docking study were performed for prediction of the mechanism of action.

RESULT AND DISCUSSION

A new series of cinnamic acids-tryptamine hybrid was designed, synthesized, and evaluated as dual cholinesterase inhibitors. These compounds demonstrated in-vitro inhibitory activities against acetyl cholinesterase (AChE) and butyryl cholinesterase (BChE). Among of these synthesized compounds, (E)-N-(2-(1H-indol-3-yl)ethyl)-3-(3,4-dimethoxyphenyl)acrylamide (5q) demonstrated the most potent AChE inhibitory activity (IC50 = 11.51 μM) and (E)-N-(2-(1H-indol-3-yl)ethyl)-3-(2-chlorophenyl)acrylamide (5b) were the best anti-BChE (IC50 = 1.95 μM) compounds. In addition, the molecular modeling and kinetic studies depicted 5q and 5b were mixed type inhibitor and bound with both the peripheral anionic site (PAS) and catalytic sites (CAS) of AChE and BChE. Moreover, compound 5q showed mild neuroprotective in PC12 cell line and weak β-secretase inhibitory activities. This compound also inhibited aggregation of β-amyloid (Aβ) in self-induced peptide aggregation test at concentration of 10 μM.

CONCLUSION

It is worth noting that both the kinetic study and the molecular modeling of 5q and 5b depicted that these compounds simultaneously interacted with both the catalytic active site and the peripheral anionic site of AChE and BChE. These findings match with those resulted data from the enzyme inhibition assay. Graphical abstract A new series of cinnamic-derived acids-tryptamine hybrid derivatives were designed, synthesized and evaluated as butyrylcholinesterase (BChE) and acetylcholinesterase (AChE) inhibitors and neuroprotective agents. Compound 5b and 5q, as the more potent compounds, interacted with both the peripheral site and the choline binding site having mixed type inhibition. Results suggested that derivatives have a therapeutic potential for the treatment of AD.

Novel N-benzylpiperidine derivatives of 5-arylisoxazole-3-carboxamides as anti-Alzheimer's agents

The complex pathophysiology of Alzheimer's disease (AD) has prompted researchers to develop multitarget-directed molecules to find an effective therapy against the disease. In this context, a novel series of N-(1-benzylpiperidin-4-yl)-5-arylisoxazole-3-carboxamide derivatives were designed, synthesized, and evaluated against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). In vitro biological evaluation demonstrated that compound 4e was the best AChE (IC₅₀  = 16.07 μM) and BuChE inhibitor (IC₅₀  = 15.16 μM). A kinetic study of 4e was also conducted, which presented a mixed-type inhibition for both enzymes. Molecular docking studies revealed that compound 4e fitted well into the active sites of AChE and BuChE, forming stable and strong interactions with key residues Glu199, Trp84, Asp72, Tyr121, and Phe288 in AChE and His438, Trp82, Ala328, Tyr332, Phe329, Thr120, and Pro285 in BuChE. Besides, the inhibition of BACE1 by 4e and the biometal chelation activity of 4e were measured. The neuroprotective assessment revealed that 4e exhibited 23.2% protection at 50 µM toward amyloid-beta-induced PC12 neuronal cells. Overall, this study exhibited that compound 4e was a promising compound targeting multiple factors associated with AD.

Design and Synthesis of New Benzo[d]oxazole-Based Derivatives and Their Neuroprotective Effects on β-Amyloid-Induced PC12 Cells

A series of novel synthetic substituted benzo[d]oxazole-based derivatives (5a-5v) exerted neuroprotective effects on β-amyloid (Aβ)-induced PC12 cells as a potential approach for the treatment of Alzheimer's disease (AD). In vitro studies show that most of the synthesized compounds were potent in reducing the neurotoxicity of Aβ25-35-induced PC12 cells at 5 μg/mL. We found that compound 5c was non-neurotoxic at 30 μg/mL and significantly increased the viability of Aβ25-35-induced PC12 cells at 1.25, 2.5 and 5 μg/mL. Western blot analysis showed that compound 5c promoted the phosphorylation of Akt and glycogen synthase kinase (GSK-3β) and decreased the expression of nuclear factor-κB (NF-κB) in Aβ25-35-induced PC12 cells. In addition, our findings demonstrated that compound 5c protected PC12 cells from Aβ25-35-induced apoptosis and reduced the hyperphosphorylation of tau protein, and decreased the expression of receptor for AGE (RAGE), β-site amyloid precursor protein (APP)-cleaving enzyme 1 (BACE1), inducible nitric oxide synthase (iNOS) and Bcl-2-associated X protein/B-cell lymphoma 2 (Bax/Bcl-2) via Akt/GSK-3β/NF-κB signaling pathway. In vivo studies suggest that compound 5c shows less toxicity than donepezil in the heart and nervous system of zebrafish.

Network Pharmacology-Based and Experimental Identification of the Effects of Quercetin on Alzheimer's Disease

Alzheimer’s disease (AD) is one of the neurodegenerative brain disorders inducing nearly half of dementia cases, and the diagnosis and treatment of AD are the primary issues clinically. However, there is a lack of effective biomarkers and drugs for AD diagnosis and therapeutics so far. In this study, bioinformatics analysis combined with an experimental verification strategy was used to identify the biomarkers and the quercetin targets for AD diagnosis and treatment. First, differentially expressed genes in the AD brain were identified by microarray data analysis. Second, quercetin, a predominant flavonoid, was used to screen the target genes. Third, the drug–disease network was determined, and the target genes of quercetin treatment were obtained in AD-related HT-22 cell-based assay. Six genes, including MAPT, PIK3R1, CASP8, DAPK1, MAPK1, and CYCS, were validated by the system pharmacology analysis in the hippocampus samples of AD patients. The results suggested that MAPT, PIK3R1, CASP8, and DAPK1 were significantly increased, but MAPK1 and CYCS were significantly decreased in HT-22 cells after Aβ1-42 treatment. Moreover, MAPK1 and CYCS were markedly increased, but MAPT, PIK3R1, CASP8, and DAPK1 were markedly decreased after quercetin treatment in these HT-22 cells. Altogether, MAPT, PIK3R1, CASP8, DAPK1, MAPK1, and CYCS are all the biomarkers for AD diagnosis and the targets of quercetin treatment, and our findings may provide valuable biomarkers for AD diagnosis and treatment.

Diaryl Ether: A Privileged Scaffold for Drug and Agrochemical Discovery

Diaryl ether (DE) is a functional scaffold existing widely both in natural products (NPs) and synthetic organic compounds. Statistically, DE is the second most popular and enduring scaffold within the numerous medicinal chemistry and agrochemical reports. Given its unique physicochemical properties and potential biological activities, DE nucleus is recognized as a fundamental element of medicinal and agrochemical agents aimed at different biological targets. Its drug-like derivatives have been extensively synthesized with interesting biological features including anticancer, anti-inflammatory, antiviral, antibacterial, antimalarial, herbicidal, fungicidal, insecticidal, and so on. In this review, we highlight the medicinal and agrochemical versatility of the DE motif according to the published information in the past decade and comprehensively give a summary of the target recognition, structure-activity relationship (SAR), and mechanism of action of its analogues. It is expected that this profile may provide valuable guidance for the discovery of new active ingredients both in drug and pesticide research.

Chromene- and Quinoline-3-Carbaldehydes: Useful Intermediates in the Synthesis of Heterocyclic Scaffolds

Chromenes and quinolines are recognized as important scaffolds in medicinal chemistry. Herein, the efficient use of chromene- and quinoline-3-carbaldehydes to synthesize other valuable heterocycles is described. These carbaldehydes are obtained in excellent yields through the Vilsmeyer-Haack reaction of flavanones and azaflavanones. Protocols towards the synthesis of new heterocycles, such as 3H-chromeno[3–c]quinolines, (Z/E)-2-aryl-4-chloro-3-styryl-2H-chromenes, and (E)-2-aryl-4-chloro-3-styrylquinoline-1(2H)-carbaldehydes were established. Altogether, we demonstrate the value of chromene- and quinoline-3-carbaldehydes as building blocks.

In silico modeling for dual inhibition of acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzymes in Alzheimer's disease

In this research, we have implemented two-dimensional quantitative structure-activity relationship (2D-QSAR) modeling using two different datasets, namely, acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) enzyme inhibitors. A third dataset has been derived based on their selectivity and used for the development of partial least squares (PLS) based regression models. The developed models were extensively validated using various internal and external validation parameters. The features appearing in the model against AChE enzyme suggest that a small ring size, higher number of -CH2- groups, higher number of secondary aromatic amines and higher number of aromatic ketone groups may contribute to the inhibitory activity. The features obtained from the model against BuChE enzyme suggest that the sum of topological distances between two nitrogen atoms, higher number of fragments X-C(=X)-X, higher number of secondary aromatic amides, fragment R--CR-X may be more favorable for inhibition. The features obtained from selectivity based model suggest that the number of aromatic ethers, unsaturation content relative to the molecular size and molecular shape may be more specific for the inhibition of the AChE enzyme in comparison to the BuChE enzyme. Moreover, we have implemented the molecular docking studies using the most and least active molecules from the datasets in order to identify the binding pattern between ligand and target enzyme. The obtained information is then correlated with the essential structural features associated with the 2D-QSAR models.

Anticholinesterase Activity of Cinnamic Acids Derivatives: In Vitro, In Vivo Biological Evaluation, and Docking Study

Background:

Acetylcholine deficiency in the hippocampus and cortex, aggregation of amyloid-beta, and beta-secretase overactivity have been introduced as the main reasons in the formation of Alzheimer’s disease.

Objective:

A new series of cinnamic derived acids linked to 1-benzyl-1,2,3-triazole moiety were designed, synthesized, and evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities.

Methods:

Colorimetric Ellman’s method was used for the determination of IC50% of AchE and BuChE inhibitory activity. The kinetic studies, neuroprotective activity, BACE1 inhibitory activity, evaluation of inhibitory potency on Aβ1-42 self-aggregation induced by AchE, and docking study were performed for studying the mechanism of action.

Results:

Some of the synthesized compounds, compound 7b-4 ((E)-3-(3,4-dimethoxyphenyl)-N-((1- (4-fluorobenzyl)-1H-1,2,3-triazole-4-yl) methyl) acrylamide) depicted the most potent acetylcholinesterase inhibitory activities ( IC50 = 5.27 μM ) and compound 7a-1 (N- ( (1- benzyl- 1H- 1, 2, 3- triazole - 4-yl) methyl) cinnamamide) demonstrated the most potent butyrylcholinesterase inhibitory activities (IC50 = 1.75 μM). Compound 7b-4 showed neuroprotective and β-secretase (BACE1) inhibitory activitiy. In vivo studies of compound 7b-4 in Scopolamine-induced dysfunction confirmed memory improvement.

Conculusion:

It should be noted that molecular modeling (compounds 7b-4 and 7a-1) and kinetic studies (compounds 7a-1 and 7b-4) showed that these synthesis compounds interacted simultaneously with both the catalytic site (CS) and peripheral anionic site (PAS) of AChE and BuChE.

Thieno[2,3-b]pyridine amines: Synthesis and evaluation of tacrine analogs against biological activities related to Alzheimer's disease

In search of safer tacrine analogs, various thieno[2,3-b]pyridine amine derivatives were synthesized and evaluated for their inhibitory activity against cholinesterases (ChEs). Among the synthesized compounds, compounds 5e and 5d showed the highest activity towards acetylcholinesterase and butyrylcholinesterase, with IC₅₀ values of 1.55 and 0.23 µM, respectively. The most active ChE inhibitors (5e and 5d) were also candidates for further complementary assays, such as kinetic and molecular docking studies as well as studies on inhibitory activity towards amyloid-beta (βA) aggregation and β-secretase 1, neuroprotectivity, and cytotoxicity against HepG2 cells. Our results indicated efficient anti-Alzheimer's activity of the synthesized compounds.

Design and Synthesis of Novel Arylisoxazole-Chromenone Carboxamides: Investigation of Biological Activities Associated with Alzheimer's Disease

A novel series of hybrid arylisoxazole-chromenone carboxamides were designed, synthesized, and evaluated for their cholinesterase (ChE) inhibitory activity based on the modified Ellman's method. Among synthesized compounds, 5-(3-nitrophenyl)-N-{4-[(2-oxo-2H-1-benzopyran-7-yl)oxy]phenyl}-1,2-oxazole-3-carboxamide depicted the most acetylcholinesterase (AChE) inhibitory activity (IC₅₀ =1.23 μm) and 5-(3-chlorophenyl)-N-{4-[(2-oxo-2H-1-benzopyran-7-yl)oxy]phenyl}-1,2-oxazole-3-carboxamide was found to be the most potent butyrylcholinesterase (BChE) inhibitor (IC₅₀ =9.71 μm). 5-(3-Nitrophenyl)-N-{4-[(2-oxo-2H-1-benzopyran-7-yl)oxy]phenyl}-1,2-oxazole-3-carboxamide was further investigated for its BACE1 inhibitory activity as well as neuroprotectivity and metal chelating ability as important factors involved in onset and progress of Alzheimer's disease. It could inhibit BACE1 by 48.46 % at 50 μm. It also showed 6.4 % protection at 25 μm and satisfactory chelating ability toward Zn²⁺ , Fe²⁺ , and Cu²⁺ ions. Docking studies of 5-(3-nitrophenyl)-N-{4-[(2-oxo-2H-1-benzopyran-7-yl)oxy]phenyl}-1,2-oxazole-3-carboxamide and 5-(3-chlorophenyl)-N-{4-[(2-oxo-2H-1-benzopyran-7-yl)oxy]phenyl}-1,2-oxazole-3-carboxamide confirmed desired interactions with those amino acid residues of the AChE and BChE, respectively.

Novel N-benzylpyridinium moiety linked to arylisoxazole derivatives as selective butyrylcholinesterase inhibitors: Synthesis, biological evaluation, and docking study

A novel series of N-benzylpyridinium moiety linked to arylisoxazole ring were designed, synthesized, and evaluated for their in vitro acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activities. Synthesized compounds were classified into two series of 5a-i and 5j-q considering the position of positively charged nitrogen of pyridinium moiety (3- or 4- position, respectively) connected to isoxazole carboxamide group. Among the synthesized compounds, compound 5n from the second series of compounds possessing 2,4-dichloroaryl group connected to isoxazole ring was found to be the most potent AChE inhibitor (IC₅₀ = 5.96 µM) and compound 5j also from the same series of compounds containing phenyl group connected to isoxazole ring demonstrated the most promising inhibitory activity against BChE (IC₅₀ = 0.32 µM). Also, kinetic study demonstrated competitive inhibition mode for both AChE and BChE inhibitory activity. Docking study was also performed for those compounds and desired interactions with those active site amino acid residues were confirmed through hydrogen bonding as well as π-π and π-anion interactions. In addition, the most potent compounds were tested against BACE1 and their neuroprotectivity on Aβ-treated neurotoxicity in PC12 cells which depicted negligible activity. It should be noted that most of the synthesized compounds from both categories 5a-i and 5j-q showed a significant selectivity toward BChE. However, series 5j-q were more active toward AChE than series 5a-i.

Design, Synthesis and Cytotoxicity of Novel Coumarin-1,2,3-triazole-1,2,4- Oxadiazole Hybrids as Potent Anti-breast Cancer Agents

Background:

This work reports design, synthesis, and in vitro cytotoxicity of novel coumarin-1,2,3-triazole-1,2,4-oxadiazole hybrids against three breast cancer cell lines MCF-7, MDA-MB-231, and T-47D.

Methods:

Synthetic procedure for the preparation of desired compounds was started from the reaction of coumarins or with propargyl bromide to give O-propargylated coumarins or 5. Then, click reaction between the later compounds and 3-aryl-5-(chloromethyl)-1,2,4-oxadiazoles afforded the desired products in good yields.

Results:

Among the synthesized compounds, 4-((1-((3-(4-chlorophenyl)-1,2,4-oxadiazol-5- yl)methyl)-1H-1,2,3-triazol-4-yl)methoxy)-2H-chromen-2-one (9a) showed the best cytotoxicity against breast cancer cell lines.

Conclusion:

Compound 9a depicted the most activity toward MDA-MB-231 and T-47D cells while compounds 8a and 8c were the most potent compounds against MCF-7.

Design, synthesis and biological activity of novel tacrine-isatin Schiff base hybrid derivatives

A series of novel tacrine-isatin Schiff base hybrid derivatives (7a-p) were designed, synthesized and evaluated as multi-target candidates against Alzheimer's disease (AD). The biological assays indicated that most of these compounds displayed potent inhibitory activity toward acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) and specific selectivity for AChE over BuChE. It was also found that they act as excellent metal chelators. The compounds 7k and 7m were found to be good inhibitors of AChE-induced amyloid-beta (Aβ) aggregation. Most of the compounds inhibited AChE with the IC₅₀ values, ranging from 0.42 nM to 79.66 nM. Amongst them, 7k, 7m and 7p, all with a 6 carbon linker between tacrine and isatin Schiff base exhibited the strongest inhibitory activity against AChE with IC₅₀ values of 0.42 nM, 0.62 nM and 0.95 nM, respectively. They were 92-, 62- and 41-fold more active than tacrine (IC₅₀ = 38.72 nM) toward AChE. Most of the compounds also showed a potent BuChE inhibition among which 7d with an IC₅₀ value of 0.11 nM for BuChE is the most potent one (56-fold more potent than that of tacrine (IC₅₀ = 6.21 nM)). In addition, most compounds exhibited the highest metal chelating property. Kinetic and molecular modeling studies revealed that 7k is a mixed-type inhibitor, capable of binding to catalytic and peripheral site of AChE. Our findings make this hybrid scaffold an excellent candidate to modify current drugs in treating Alzheimer's disease (AD).

Experimental and Theoretical Approaches in the Study of Phenanthroline-Tetrahydroquinolines for Alzheimer's Disease

The imino-Diels-Alder reaction is one of the most common strategies in organic chemistry and is an important tool for providing a broad spectrum of biologically active heterocyclic systems. A combined theoretical and experimental study of the imino-Diels-Alder reaction is described. The new phenanthroline-tetrahydroquinolines were evaluated as cholinesterase inhibitors. Their cytotoxicity in human neuroblastoma SH-SY5Y cells was also evaluated. The theoretical results suggest that compounds formation in stages can be explained by endo cycloadducts under the established reaction conditions, thereby confirming experimental results obtained for percentage yield. These results allowed us to establish that pyridine substituent remarkably influences activation energy and reaction yield, as well as in acetylcholinesterase (AChE) activity. Among these derivatives, compounds with 4-pyridyl and 4-nitrophenyl showed favorable AChE activity and proved to be non-cytotoxic.

Bennett acceptance ratio method to calculate the binding free energy of BACE1 inhibitors: Theoretical model and design of new ligands of the enzyme

In recent years, the design, development, and evaluation of several inhibitors of the BACE1 enzyme, as part of Alzheimer's treatment, have gathered the scientific community's interest. Here, a linear regression model was built using binding free energy calculations through the Bennett acceptance ratio method for 20 known inhibitors of the BACE1 enzyme, with a Pearson coefficient of R = 0.88 and R²  = 0.78. The validation of this model was verified employing eight additional random inhibitors, which also gave a linear correlation with R = 0.97 and R²  = 0.93. Furthermore, this linear regression model was also used for proposing the structure of four potential BACE1 inhibitors, and the most active of them gave a theoretical K_d  = 10 nM. However, these molecules have not been synthesized yet. Our team used a total time of more than 800 ns for the Molecular Dynamics to carry out this study, and all the software used were freely available.

Synthesis, biological evaluations and computational studies of N-(3-(-2-(7-Chloroquinolin-2-yl)vinyl) benzylidene)anilines as fungal biofilm inhibitors

In the present investigation, new chloroquinoline derivatives bearing vinyl benzylidene aniline substituents at 2nd position were synthesized and screed for biofilm inhibitory, antifungal and antibacterial activity. The result of biofilm inhibition of C. albicans suggested that compounds 5j (IC₅₀ value = 51.2 μM) and 5a (IC₅₀ value = 66.2 μM) possess promising antibiofilm inhibition when compared with the standard antifungal drug fluconazole (IC₅₀ = 40.0 μM). Two compounds 5a (MIC = 94.2 μg/mL) and 5f (MIC = 98.8 μg/mL) also exhibited good antifungal activity comparable to standard drug fluconazole (MIC = 50.0 μg/mL). The antibacterial screening against four strains of bacteria viz. E. coli, P. aeruginosa, B. subtilis, and S. aureus suggested their potential antibacterial activity and especially all the compounds except 5g were found more active than the standard drug ciprofloxacin against B. subtilis. To further gain insights into the possible mechanism of these compounds in biofilm inhibition through the agglutinin like protein (Als), molecular docking and molecular dynamics simulation studies were carried out. Molecular modeling studies suggested the clear role in inhibition of this protein and the resulting biofilm inhibitory activity.

Design, synthesis and anti-Alzheimer's activity of novel 1,2,3-triazole-chromenone carboxamide derivatives

Alzheimer's disease (AD) is a well-known neurodegenerative disorder affecting millions of old people worldwide and the corresponding epidemiological data highlights the significance of the disease. As AD is a multifactorial illness, various single-target directed drugs that have reached clinical trials have failed. Therefore, various factors associated with outset of AD have been considered in targeted drug discovery and development. In this work, a wide range of 1,2,3-triazole-chromenone carboxamides were designed, synthesized, and evaluated for their cholinesterase inhibitory activity. Among them, N-(1-benzylpiperidin-4-yl)-7-((1-(3,4-dimethylbenzyl)-1H-1,2,3-triazol-4-yl)methoxy)-2-oxo-2H-chromene-3-carboxamide (11b) showed the best acetylcholinesterase inhibitory activity (IC₅₀ = 1.80 µM), however, it was inactive toward butyrylcholinesterase. It should be noted that compound 11b was evaluated for its BACE1 inhibitory activity and calculated IC₅₀ = 21.13 µM confirmed desired inhibitory activity. Also, this compound revealed satisfactory neuroprotective effect against H₂O₂-induced cell death in PC12 neurons at 50 µM as well as metal chelating ability toward Fe²⁺, Cu²⁺, and Zn²⁺ ions.

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.

Effect of the oral administration of nanoencapsulated quercetin on a mouse model of Alzheimer's disease

Quercetin has been identified as a promising compound with a neuroprotective potential against age-related neurodegenerative diseases such as Alzheimer's disease (AD). Nevertheless, the clinical application of quercetin is hampered by its low oral bioavailability. The aim of this work was to evaluate the capability of nanoencapsulated quercetin in zein nanoparticles (NPQ), that significantly improves the oral absorption and bioavailability of the flavonoid, as potential oral treatment for AD. For this purpose, SAMP8 mice were orally treated for two months with either NPQ (25mg/kg every 48h) or a solution of quercetin (Q; 25mg/kg daily). NPQ displayed a size of 260nm and a payload of about 70μg/mg. For Q, no significant effects were observed in animals. On the contrary, the oral administration of NPQ improved the cognition and memory impairments characteristics of SAMP8 mice. These observations appeared to be related with a decreased expression of the hippocampal astrocyte marker GFAP. Furthermore, significant levels of quercetin were quantified in the brain of mice treated with nanoparticles. These findings highlight the potential of zein nanoparticles to promote the oral absorption of quercetin as well as the therapeutic potential of this flavonoid in AD pathogenesis.

Synthesis of novel chromenones linked to 1,2,3-triazole ring system: Investigation of biological activities against Alzheimer's disease

In this work, novel chromenones linked to 1,2,3-triazole ring system were synthesized and evaluated for their anti-ChE activity. Among them, N-((1-(2-chlorobenzyl)-1H-1,2,3-triazol-5-yl)methyl)-8-methoxy-2-oxo-2H-chromene-3-carboxamide (6m) showed good anti-acetylcholinesterase activity (IC₅₀=15.42μM). Also, compound 6m demonstrated neuroprotective effect against H₂O₂-induced cell death in PC12 neurons, however, it showed no beta-secretase (BACE1) inhibitory activity. Docking and kinetic studies separately confirmed dual binding activity of compound 6m since it targeted both the catalytic active site (CAS) and the peripheral anionic site (PAS) of AChE.

Novel tacrine-1,2,3-triazole hybrids: In vitro, in vivo biological evaluation and docking study of cholinesterase inhibitors

A new series of tacrine-1,2,3-triazole hybrids were designed, synthesized, and evaluated as potent dual cholinesterase inhibitors. Most of synthesized compounds showed good in vitro inhibitory activities toward both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Among them, 7-chloro-N-((1-(4-methoxybenzyl)-1H-1,2,3-triazol-4-yl)methyl)-1,2,3,4-tetrahydroacridin-9-amine (5l) was found to be the most potent anti-AChE derivative (IC₅₀ = 0.521 μM) and N-((1-(4-methoxybenzyl)-1H-1,2,3-triazol-4-yl)methyl)-1,2,3,4-tetrahydroacridin-9-amine (5j) demonstrated the best anti-BChE activity (IC₅₀ = 0.055 μM). In vivo studies of compound 5l in Morris water maze task confirmed memory improvement in scopolamine-induced impairment. Also, molecular modeling and kinetic studies showed that compounds 5l and 5j bound simultaneously to the peripheral anionic site (PAS) and catalytic sites (CS) of the AChE and BChE.

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

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