Pyranopyrazolotacrines as nonneurotoxic, Aβ-anti-aggregating and neuroprotective agents for Alzheimer's disease

Review on advancements of pyranopyrazole: synthetic routes and their medicinal applications

Pyranopyrazoles are among the most distinguished, biologically potent, and exciting scaffolds in medicinal chemistry and drug discovery. Synthesis and design of pyranopyrazoles using functional modifications via multicomponent reactions (MCRs) are thoroughly found in synthetic protocols by forming new C-C, C-N, and C-O bonds. This review aims to focus on the biological importance of pyranopyrazoles as well as on a diverse synthetic approach for their synthesis using various catalytic systems such as acid-catalyzed, base-catalyzed, ionic liquids and green media-catalyzed, nano-particle-catalyzed, metal oxide-supported catalysts, and silica-supported catalysts. In this review, we have summarized data on the advancements in synthesizing pyranopyrazole from the last two decades to the mid-2023 and research papers describing the importance of these scaffolds. This review will be significant for synthetic organic chemists and researchers working in organic chemistry.

1,2,3-Triazolo[4,5-b]aminoquinolines: Design, synthesis, structure, acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory activity, and molecular docking of novel modified tacrines

An efficient [4 + 2] cyclization protocol to synthesize a series of twelve examples of 1,2,3-triazolo[4,5-b]aminoquinolines (5) as novel structurally modified tacrines was obtained by reacting readily accessible precursors (i.e., 3-alky(aryl)-5-amino-1,2,3-triazole-4-carbonitriles (3)) and selected cycloalkanones (4) of five-, six-, and seven-membered rings. We evaluated the AChE and BChE inhibitory activity of the novel modified tacrines 5, and the compound derivatives from cyclohexanone (4b) showed the best AChE and BChE inhibitory activities. Specifically, 1,2,3-triazolo[4,5-b]aminoquinolines 5bb obtained from 3-methyl-carbonitrile (3b) showed the highest AChE (IC50 = 12.01 μM), while 5ib from 3-sulfonamido-carbonitrile (3i) was the most significant inhibitor for BChE (IC50 = 1.78 μM). In general, the inhibitory potency of compound 5 was weaker than the pure tacrine reference, and our findings may help to design and develop novel anticholinesterase drugs based on modified tacrines.

Diastereoselective construction of carbo-bridged polyheterocycles by a three-component tandem annulation reaction

By a hydroamination-induced tandem annulation process, we herein report a new three-component reaction for room temperature construction of carbo-bridged polyheterocycles with exclusive diastereoselectivity, which features readily available feedstocks, catalyst-free conditions, good substrate and functionality compatibility, no need for transition metal catalysts, and high step and atom efficiency. The products are formed via initial formation of 1,2-dihydro-3H-pyrazol-3-one nucleophiles from but-2-ynedioates and hydrazine followed by 2,4-difunctionalization of N-heteroarenium salts. Given that the obtained products possess structurally important tetrahydroquinoline and pyranopyrazole motifs, the developed chemistry is anticipated to be further applied to the discovery of functional molecules including biomedical ones.

Amyloid β, Lipid Metabolism, Basal Cholinergic System, and Therapeutics in Alzheimer’s Disease

The presence of insoluble aggregates of amyloid β (Aβ) in the form of neuritic plaques (NPs) is one of the main features that define Alzheimer’s disease. Studies have suggested that the accumulation of these peptides in the brain significantly contributes to extensive neuronal loss. Furthermore, the content and distribution of cholesterol in the membrane have been shown to have an important effect on the production and subsequent accumulation of Aβ peptides in the plasma membrane, contributing to dysfunction and neuronal death. The monomeric forms of these membrane-bound peptides undergo several conformational changes, ranging from oligomeric forms to beta-sheet structures, each presenting different levels of toxicity. Aβ peptides can be internalized by particular receptors and trigger changes from Tau phosphorylation to alterations in cognitive function, through dysfunction of the cholinergic system. The goal of this review is to summarize the current knowledge on the role of lipids in Alzheimer’s disease and their relationship with the basal cholinergic system, as well as potential disease-modifying therapies.

Five-Membered-Ring-Fused Tacrines as Anti-Alzheimer’s Disease Agents

Our endeavors in the design, synthesis, and biological assessment of five-membered-ring-fused tacrines as potential therapeutic agents for Alzheimer’s disease are summarized. Particularly, we have identified racemic 4-(2-methoxyphenyl)-3-methyl-2,4,6,7,8,9-hexahydropyrazolo[4′,3′:5,6]pyrano[2,3-b]quinolin-5-amine, a pyranopyrazolotacrine, as having the best nontoxic profile at the highest concentrations used (300 μM); this allows cell viability, is less hepatotoxic than tacrine, and is a potent noncompetitive AChE inhibitor (IC50 = 1.52 ± 0.49 μM). It is able to completely inhibit the EeAChE-induced Aβ1–40 aggregation in a statistically significant manner without affecting the Aβ1–40 self-aggregation at 25 μM, and shows strong neuroprotective effects (EC50 = 0.82 ± 0.17 μM).

1 Introduction

2 Furo-, Thieno-, and Pyrrolotacrines

3 Pyrazolo-, Oxazolo-, and Isoxazolotacrines

4 Indolotacrines

5 Pyrano- and Pyridopyrazolotacrines

6 Conclusions and Outlook

Merged Tacrine-Based, Multitarget-Directed Acetylcholinesterase Inhibitors 2015-Present: Synthesis and Biological Activity

Acetylcholinesterase is an important biochemical enzyme in that it controls acetylcholine-mediated neuronal transmission in the central nervous system, contains a unique structure with two binding sites connected by a gorge region, and it has historically been the main pharmacological target for treatment of Alzheimer's disease. Given the large projected increase in Alzheimer's disease cases in the coming decades and its complex, multifactorial nature, new drugs that target multiple aspects of the disease at once are needed. Tacrine, the first acetylcholinesterase inhibitor used clinically but withdrawn due to hepatotoxicity concerns, remains an important starting point in research for the development of multitarget-directed acetylcholinesterase inhibitors. This review highlights tacrine-based, multitarget-directed acetylcholinesterase inhibitors published in the literature since 2015 with a specific focus on merged compounds (i.e., compounds where tacrine and a second pharmacophore show significant overlap in structure). The synthesis of these compounds from readily available starting materials is discussed, along with acetylcholinesterase inhibition data, relative to tacrine, and structure activity relationships. Where applicable, molecular modeling, to elucidate key enzyme-inhibitor interactions, and secondary biological activity is highlighted. Of the numerous compounds identified, there is a subset with promising preliminary screening results, which should inspire further development and future research in this field.

Highly Significant Scaffolds to Design and Synthesis Cholinesterase Inhibitors as Anti-Alzheimer Agents

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Alzheimer, a progressive disease, is a common term for memory loss which interferes with daily life through severe influence on cognitive abilities. Based on the cholinergic hypothesis, and Xray crystallographic determination of the structure of acetylcholinesterase (AChE) enzyme, the level of acetylcholine (ACh, an important neurotransmitter associated with memory) in the hippocampus and cortex area of the brain has a direct effect on Alzheimer. This fact encourages scientists to design and synthesize a wide range of acetylcholinesterase inhibitors (AChEIs) to control the level of ACh in the brain, keeping in view the crystallographic structure of AChE enzyme and drugs approved by the Food and Drug Administration (FDA).

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AChEIs have slightly diverse pharmacological properties, but all of them work by inhibiting the segregation of ACh by blocking AChE. We reviewed significant scaffolds introduced as AChEIs. In some studies, the activity against butyrylcholinesterase (BuChE) has been evaluated as well because BuChE is a similar enzyme to neuronal acetylcholinesterase and is capable of hydrolyzing ACh. In order to study AChEIs effectively, we divided them structurally into 12 classes and briefly explained effective AChEIs and compared their activities against AChE enzyme.

Therapeutic Potential of Multifunctional Tacrine Analogues

Abstract: Tacrine is a potent inhibitor of cholinesterases (acetylcholinesterase and butyrylcholinesterase) that shows limiting clinical application by liver toxicity. In spite of this, analogues of tacrine are considered as a model inhibitor of cholinesterases in the therapy of Alzheimer’s disease. The interest in these compounds is mainly related to a high variety of their structure and biological properties. In the present review, we have described the role of cholinergic transmission and treatment strategies in Alzheimer’s disease as well as the synthesis and biological activity of several recently developed classes of multifunctional tacrine analogues and hybrids, which consist of a new paradigm to treat Alzheimer’s disease. We have also reported potential of these analogues in the treatment of Alzheimer’s diseases in various experimental systems.

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.

New cyclopentaquinoline hybrids with multifunctional capacities for the treatment of Alzheimer's disease

Alzheimer’s disease (AD) is the most common progressive form of brain neurodegeneration and the most prevailing cause of dementia. Unfortunately, the aetiology of AD is not completely studied but different factors are associated with the development of AD such as among others low level of acetylcholine, aggregation of β-amyloid (Aβ), hyperphosphorylated tau protein, oxidative stress, and inflammation. The study encompass organic syntheses of 2,3-dihydro-1H-cyclopenta[b]quinoline with 5,6-dichloronicotinic acid and suitable linkers derivatives as multifunctional agents for AD treatment. Afterwards self-induced amyloid beta aggregation, inhibition studies of acetylcholinesterase and butyrylcholinesterase and molecular docking studies were performed. The results showed that 3b compound exhibited the best acetylcholinesterase inhibitory activity, with IC₅₀ value of 0.052 µM which is lower compared to references. Besides, all synthesised compounds showed good butyrylcholinesterase inhibitory activity with IC₅₀ values from 0.071 to 0.797 µM. Compound 3b exhibited strong Aβ_1–42 aggregation inhibitory effect with 25.7% at 5 µM to 92.8% at 100 µM as well as good anti-inflammatory effect. Thus, new compounds could create new perspectives for further development as a multi-target-directed agent for AD treatment.

Aurone Mannich base derivatives as promising multifunctional agents with acetylcholinesterase inhibition, anti-β-amyloid aggragation and neuroprotective properties for the treatment of Alzheimer's disease

A series of aurone Mannich base 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 were selective AChE inhibitors with good multifunctional properties. Among them, compound 7d exhibited outstanding inhibitory activity for RatAChE, EeAChE and HuAChE (IC₅₀ = 0.00878 ± 0.0002 μM, 0.0212 ± 0.006 μM and 0.0371 ± 0.004 μM, respectively). Moreover, 7d displayed high antioxidant activity and could confer significant neuroprotective effect against H₂O₂-induced PC-12 cell injury. In addition, 7d also showed biometal chelating abilities, good self- and Cu²⁺-induced Aβ_1-42 aggregation inhibitory potency and high BBB permeability. These multifunctional properties highlight 7d as promising candidate for further studies directed to the development of novel drugs against AD.