9H-Carbazole Derivatives Containing theN-Benzyl-1,2,3-triazole Moiety as New Acetylcholinesterase Inhibitors

Pathogenesis of Alzheimer's Disease and Diversity of 1,2,3-Triazole Scaffold in Drug Development: Design Strategies, Structural Insights, and Therapeutic Potential

Alzheimer's disease is a most prevalent form of dementia all around the globe and currently poses a significant challenge to the healthcare system. Currently available drugs only slow the progression of this disease rather than provide proper containment. Identification of multiple targets responsible for this disease in the last three decades established it as a multifactorial neurodegenerative disorder that needs novel multifunctional agents for its management and the possible reason for the failure of currently available single target clinical drugs. 1,2,3-Triazole is a miraculous nucleus in medicinal chemistry and the first choice for development of multifunctional hybrid molecules. Apart from that, it is an integral component of various drugs in clinical trials as well as in clinical practice. This review is focused on the pathogenesis of Alzheimer's disease and 1,2,3-triazole containing derivatives developed in recent decades as potential anti-Alzheimer's agents. The review will provide (A) precise insight of various established targets of Alzheimer's disease including cholinergic, amyloid, tau, monoamine oxidases, glutamate, calcium, and reactive oxygen species hypothesis and (B) design hypothesis, structure-activity relationships, and pharmacological outcomes of 1,2,3-triazole containing multifunctional anti-Alzheimer's agents. This review will provide a baseline for various research groups working on Alzheimer's drug development in designing potent, safer, and effective multifunctional anti-Alzheimer's candidates of the future.

An Overview of 1,2,3-triazole-Containing Hybrids and Their Potential Anticholinesterase Activities

Acetylcholine (ACh) neurotransmitter of the cholinergic system in the brain is involved in learning, memory, stress responses, and cognitive functioning. It is hydrolyzed into choline and acetic acid by two key cholinesterase enzymes, viz., acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE). A loss or degeneration of cholinergic neurons that leads to a reduction in ACh levels is considered a significant contributing factor in the development of neurodegenerative diseases (NDs) such as Alzheimer's disease (AD). Numerous studies have shown that cholinesterase inhibitors can raise the level of ACh and, therefore, enhance people's quality of life, and, at the very least, it can temporarily lessen the symptoms of NDs. 1,2,3-triazole, a five-membered heterocyclic ring, is a privileged moiety, that is, a central scaffold, and is capable of interacting with a variety of receptors and enzymes to exhibit a broad range of important biological activities. Recently, it has been clubbed with other pharmacophoric fragments/molecules in hope of obtaining potent and selective AChE and/or BuChE inhibitors. The present updated review succinctly summarizes the different synthetic strategies used to synthesize the 1,2,3-triazole moiety. It also highlights the anticholinesterase potential of various 1,2,3-triazole di/trihybrids reported in the past seven years (2015-2022), including a rationale for hybridization and with an emphasis on their structural features for the development and optimization of cholinesterase inhibitors to treat NDs.

Critical evaluation of current Alzheimer's drug discovery (2018-19) & futuristic Alzheimer drug model approach

Alzheimer's disease (AD), a neurodegenerative disease responsible for death of millions of people worldwide is a progressive clinical disorder which causes neurons to degenerate and ultimately die. It is one of the common causes of dementia wherein a person's incapability to independently think, behave and decline in social skills can be quoted as major symptoms. However the early signs include the simple non-clinical symptoms such as forgetting recent events and conversations. Onset of these symptoms leads to worsened conditions wherein the AD patient suffers severe memory impairment and eventually becomes unable to work out everyday tasks. Even though there is no complete cure for AD, rigorous research has been going on to reduce the progress of AD. Currently, a very few clinical drugs are prevailing for AD treatment. So this is the need of hour to design, develop and discovery of novel anti-AD drugs. The main factors for the cause of AD according to scientific research reveals structural changes in brain proteins such as beta amyloid, tau proteins into plaques and tangles respectively. The abnormal proteins distort the neurons. Despite the high potencies of the synthesized molecules; they could not get on the clinical tests up to human usage. In this review article, the recent research carried out with respect to inhibition of AChE, BuChE, NO, BACE1, MAOs, Aβ, H3R, DAPK, CSF1R, 5-HT4R, PDE, σ₁R and GSK-3β is compiled and organized. The summary is focused mainly on cholinesterases, Aβ, BACE1 and MAOs classes of potential inhibitors. The review also covers structure activity relationship of most potent compounds of each class of inhibitors alongside redesign and remodeling of the most significant inhibitors in order to expect cutting edge inhibitory properties towards AD. Alongside the molecular docking studies of the some final compounds are discussed.

New classes of carbazoles as potential multi-functional anti-Alzheimer's agents

Multi-Target approach is particularly promising way to drug discovery against Alzheimer's disease. In the present study, we synthesized a series of compounds comprising the carbazole backbone linked to the benzyl piperazine, benzyl piperidine, pyridine, quinoline, or isoquinoline moiety through an aliphatic linker and evaluated as cholinesterase inhibitors. The synthesized compounds showed IC₅₀ values of 0.11-36.5 µM and 0.02-98.6 µM against acetyl- and butyrylcholinesterase (AChE and BuChE), respectively. The ligand-protein docking simulations and kinetic studies revealed that compound 3s could bind effectively to the peripheral anionic binding site (PAS) and anionic site of the enzyme with mixed-type inhibition. Compound 3s was the most potent compound against AChE and BuChE and showed acceptable inhibition potency for self- and AChE-induced Aβ_1-42 aggregation. Moreover, compound 3s could significantly protect PC12 cells against H₂O₂-induced toxicity. The results suggested that the compounds 3s could be considered as a promising multi-functional agent for further drug discovery development against Alzheimer's disease.

Nature and Hierarchy of Hydrogen-Bonding Interactions in Binary Complexes of Azoles with Water and Hydrogen Peroxide

In the present study, the hydrogen-bonded complexes of azole with water and hydrogen peroxide are systematically investigated by second-order Møller-Plesset perturbation theory and density functional theory with dispersion function calculations. This study suggests that the ability of pyrrolic nitrogen (NH) atom to function as hydrogen-bond donor increases with the introduction of nitrogen atoms in the ring, whereas the ability of pyridinic nitrogen (N) atom to act as hydrogen-bond acceptor reduces with successive aza substitution in the ring. With introduction of nitrogen atoms in the ring, the vibrational frequency, stabilization energy, and electron density in the σ antibonding orbitals of the X-H (X = N, C of azole) bond of the complexes all increase or decrease systematically. Decomposition analysis of total stabilization energy showed that the electrostatic energy term is a dominant attractive contribution in comparison to induction and dispersion terms in all of the complexes under study.

Novel tetrahydrocarbazole benzyl pyridine hybrids as potent and selective butryl cholinesterase inhibitors with neuroprotective and β-secretase inhibition activities

Butyrylcholinesterase (BuChE) inhibitors have become interesting target for treatment of Alzheimer's disease (AD). A series of dual binding site BuChE inhibitors were designed and synthesized based on 2,3,4,9-tetrahydro-1H-carbazole attached benzyl pyridine moieties. In-vitro assay revealed that all of the designed compounds were selective and potent BuChE inhibitors. The most potent BuChE inhibitor was compound 6i (IC₅₀ = 0.088 ± 0.0009 μM) with the mixed-type inhibition. Docking study revealed that 6i is a dual binding site BuChE inhibitor. Also, Pharmacokinetic properties for 6i were accurate to Lipinski's rule. In addition, compound 6i demonstrated neuroprotective and β-secretase (BACE1) inhibition activities. This compound could also inhibit AChE-induced and self-induced Aβ peptide aggregation at concentration of 100 μM and 10 μM respectively. Generally, the results are presented as new potent selective BuChE inhibitors with a therapeutic potential for the treatment of AD.

Synthesis and biological evaluation of chalcone-triazole hybrid derivatives as 15-LOX inhibitors

An efficient aldol condensation/click reaction sequence is employed for the synthesis of chalcone-triazole-based derivatives in moderate to good yields. The ability of target compounds to inhibit 15-lipoxygenase enzyme was investigated and moderate to low inhibitory activities were observed for the synthesized compounds.

Acetamide Derivatives of Chromen-2-ones as Potent Cholinesterase Inhibitors

Alzheimer's disease (AD), a neurodegenerative disorder, is a serious medical issue worldwide with drastic social consequences. Inhibition of cholinesterase is one of the rational and effective approaches to retard the symptoms of AD and, hence, consistent efforts are being made to develop efficient anti-cholinesterase agents. In pursuit of this, a series of 19 acetamide derivatives of chromen-2-ones were synthesized and evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) inhibitory potential. All the synthesized compounds exhibited significant anti-AChE and anti-BChE activity, with IC₅₀ values in the range of 0.24-10.19 μM and 0.64-30.08 μM, respectively, using donepezil hydrochloride as the standard. Out of 19 compounds screened, 3 compounds, viz. 22, 40, and 43, caused 50% inhibition of AChE at 0.24, 0.25, and 0.25 μM, respectively. A kinetic study revealed them to be mixed-type inhibitors, binding with both the CAS and PAS sites of AChE. The above-selected compounds were found to be effective inhibitors of AChE-induced and self-mediated Aβ_1-42 aggregation. ADMET predictions demonstrated that these compounds may possess suitable blood-brain barrier (BBB) permeability. Hemolytic assay results revealed that these compounds did not lyse human RBCs up to a thousand times of their IC₅₀ value. MTT assays performed for the shortlisted compounds showed them to be negligibly toxic after 24 h of treatment with the SH-SY5Y neuroblastoma cells. These results provide insights for further optimization of the scaffolds for designing the next generation of compounds as lead cholinesterase inhibitors.

The Hypnotic, Anxiolytic, and Antinociceptive Profile of a Novel µ-Opioid Agonist

5'-4-Alkyl/aryl-1H-1,2,3-triazole derivatives PILAB 1-12 were synthesized and a pharmacological screening of these derivatives was performed to identify a possible effect on the Central Nervous System (CNS) and to explore the associated mechanisms of action. The mice received a peritoneal injection (100 µmol/kg) of each of the 12 PILAB derivatives 10 min prior to the injection of pentobarbital and the mean hypnosis times were recorded. The mean hypnosis time increased for the mice treated with PILAB 8, which was prevented when mice were administered CTOP, a µ-opioid antagonist. Locomotor and motor activities were not affected by PILAB 8. The anxiolytic effect of PILAB 8 was evaluated next in an elevated-plus maze apparatus. PILAB 8 and midazolam increased a percentage of entries and spent time in the open arms of the apparatus compared with the control group. Conversely, a decrease in the percentages of entries and time spent in the closed arms were observed. Pretreatment with naloxone, a non-specific opioid antagonist, prior to administration of PILAB 8 exhibited a reverted anxiolytic effect. PILAB 8 exhibited antinociceptive activity in the hot plate test, and reduced reactivity to formalin in the neurogenic and the inflammatory phases. These data suggest that PILAB 8 can activate µ-opioid receptors to provoke antinociceptive and anti-inflammatory effects in mice.

Synthesis of Novel Benzimidazole and Benzothiazole Derivatives Bearing a 1,2,3-triazole Ring System and their Acetylcholinesterase Inhibitory Activity

A series of 20 novel benzimidazole and benzothiazole derivatives linked to a 1,2,3-triazole ring system was synthesised, characterised and evaluated for in vitro acetylcholinesterase (AChE) inhibitory activity. Several copper catalysts and solvents were screened to establish the optimal conditions for the preparation of the target compounds. Three different linkers were used to optimise the enzyme inhibitory effect. Out of the 20 compounds, 13 showed some AChE inhibition. The most potent compound, which showed 84% inhibition at 100 μM, contained a 1-(2-fluorobenzyl)-1,2,3-triazole linked to a benzimidazole group. A docking simulation study showed that the most active compound bound preferentially to the catalytic anionic subsite of the AChE enzyme.

Design, synthesis, crystal structure, biological evaluation and molecular docking studies of carbazole-arylpiperazine derivatives

Subtype-selective α₁-adrenoceptor (AR) antagonists display optimum therapeutic efficacies for the treatment of benign prostatic hyperplasia (BPH). In this study, we designed and synthesized novel carbazole-arylpiperazines derivatives (1 and 2) on the basis of the proposed pharmacophore model for α₁-AR antagonists. Structural properties were investigated using single-crystal X-ray diffraction analysis. Comparison of crystal structures with ligand-based pharmacophore models revealed that the two agents may possess antagonistic effects on α_1D subtype. Tissue functional assay in vitro showed that compound 2 exerted strong antagonistic activity on α_1B-AR (pA₂ 7.13) with a poor selectivity for α_1A and α_1D subtypes. Compound 1 exhibited enhanced antagonistic effect on α_1D subtype (pA₂ 7.06) and excellent selectivity for α_1D over α_1B (α_1D/α_1B ratio=79.4). To illustrate the relationship between antagonistic activity and chemical structure, molecular docking studies were performed using the homology models of α₁ receptors. Binding mechanism indicated that small hydrophobic substituents attached to the arylpiperazine moiety were essential for rational design of α_1D-selective antagonists.

The importance of triazole scaffold in the development of anticonvulsant agents

Epilepsy is one of the most important neurological disorders with high prevalence worldwide. Many epileptic patients are not completely treated with available drugs and need multiple therapies. Also, many antiepileptic drugs have shown unwanted side effects and drug interactions. Therefore there are continuing interests to find new anticonvulsant drugs. Triazole ring has been found in the structure of many compounds with diverse biological effects. Due to the success of several triazole-containing drugs that entered the pharmaceutical market as CNS-active drugs, this class of heterocyclic compounds has great importance for discovery and development of new anticonvulsant drugs. In this article, we have tried to summarize the latest efforts which have been made in the design and development of triazole-derived anticonvulsant agents.