Novel tacrine–ebselen hybrids with improved cholinesterase inhibitory, hydrogen peroxide and peroxynitrite scavenging activity

Regioselective 1,4-/1,3-Difunctionalization of 1,3-Enynes with Selenosulfonates in Water

1,4-/1,3-Regioselective bifunctionalization of 1,3-enynes with selenosulfonates in water under catalyst-free conditions for the construction of sulfonyl allene and 1,3-disulfonyl-conjugated dienes respectively have been developed. The reactions feature mild reaction conditions in aqueous solution and remarkable regioselectivity controlled by substrates.

Selenium-containing compounds: a new hope for innovative treatments in Alzheimer's disease and Parkinson's disease

Neurodegenerative diseases are challenging to cure. To date, no cure has been found for Alzheimer's disease or Parkinson's disease, and current treatments are able only to slow the progression of the diseases and manage their symptoms. After an introduction to the complex biology of these diseases, we discuss the beneficial effect of selenium-containing agents, which show neuroprotective effects in vitro or in vivo. Indeed, selenium is an essential trace element that is being incorporated into innovative organoselenium compounds, which can improve outcomes in rodent or even primate models with neurological deficits. Herein, we critically discuss recent findings in the field of selenium-based applications in neurological disorders.

Ru-Catalyzed and Selenium-Directed Selective Formation of ortho- and Dialkenylated Selanes, Mixed Organoselenoethers, and Isoselenochromenes

Herein, the Ru-catalyzed chemo- and regioselective formation of four novel organoselenium compounds is established. Mono- and dialkenylated selanes were formed by the Se-directed o-C-H activation of benzyl(phenyl)selanes with alkynes. Unprecedented debenzylative/dearylative hydroselenations of alkynes were performed by slightly varying the amount of catalyst and temperature. Catalyst-driven direct formation of novel isoselenochromenes is also recorded. Altogether, 45 new organoseleno compounds were synthesized in good amounts with varieties of alkynes and selanes. This is the first report of its kind to deal with the synthesis of novel, challenging, and unusual organoseleno compounds in one reaction.

Tacrine-Based Hybrids: Past, Present, and Future

Alzheimer's disease (AD) is a neurodegenerative disorder which is characterized by β-amyloid (Aβ) aggregation, τ-hyperphosphorylation, and loss of cholinergic neurons. The other important hallmarks of AD are oxidative stress, metal dyshomeostasis, inflammation, and cell cycle dysregulation. Multiple therapeutic targets may be proposed for the development of anti-AD drugs, and the "one drug-multiple targets" strategy is of current interest. Tacrine (THA) was the first clinically approved cholinesterase (ChE) inhibitor, which was withdrawn due to high hepatotoxicity. However, its high potency in ChE inhibition, low molecular weight, and simple structure make THA a promising scaffold for developing multi-target agents. In this review, we summarized THA-based hybrids published from 2006 to 2022, thus providing an overview of strategies that have been used in drug design and approaches that have resulted in significant cognitive improvements and reduced hepatotoxicity.

An overview on the synthesis of carbohydrate-based molecules with biological activity related to neurodegenerative diseases

In the context of the search for multitarget drugs with improved efficacy against neurodegenerative disorders, carbohydrate derivatives have emerged as promising candidates for Alzheimer's therapy. Herein we describe the synthesis and biological evaluation of several classes of sugar-based compounds, where most of them contain heterocyclic aromatic moieties that bear known biological properties and high affinity for the cholinesterase active site. This general idea led to the synthesis of compounds with high inhibitory potency against acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE), enzymatic selectivity and combined properties such as antioxidant and neuroprotection, in addition to the absence of toxicity.

Design, Synthesis, biological investigations and molecular interactions of triazole linked tacrine glycoconjugates as Acetylcholinesterase inhibitors with reduced hepatotoxicity

Tacrine is a known Acetylcholinesterase (AChE) inhibitors having hepatotoxicity as main liability associated with it. The present study aims to reduce its hepatotoxicity by synthesizing tacrine linked triazole glycoconjugates via Huisgen's [3 + 2] cycloaddition of anomeric azides and terminal acetylenes derived from tacrine. A series of triazole based glycoconjugates containing both acetylated (A-1 to A-7) and free sugar hydroxyl groups (A-8 to A-14) at the amino position of tacrine were synthesized in good yield taking aid from molecular docking studies and evaluated for their in vitro AChE inhibition activity as well as hepatotoxicity. All the hybrids were found to be non-toxic on HePG2 cell line at 200 μM (100 % cell viability) as compared to tacrine (35 % cell viability) after 24 h of incubation period. Enzyme kinetic studies carried out for one of the potent hybrids in the series A-1 (IC₅₀ 0.4 μM) revealed its mixed inhibition approach. Thus, compound A-1 can be used as principle template to further explore the mechanism of action of different targets involved in Alzheimer's disease (AD) which stands as an adequate chemical probe to be launched in an AD drug discovery program.

Nickel(II)-meclofenamate complexes: Structure, in vitro and in silico DNA- and albumin-binding studies, antioxidant and anticholinergic activity

Five novel nickel(II) complexes with the non-steroidal anti-inflammatory drug sodium meclofenamate (Na-mclf) have been synthesized and characterized in the absence or co-existence of the nitrogen-donors imidazole (Himi), 2,2'-bipyridylamine (bipyam), 2,2'-bipyridylketoxime (Hpko) and 2,9-dimethyl-1,10-phenanthroline (neoc); namely [Ni(mclf-O)₂(Himi)₂(MeOH)₂], [Ni(mclf-O)₂(MeOH)₄], [Ni(mclf-O)(mclf-O,O')(bipyam)(MeOH)]·0.25MeOH, [Ni(mclf-O,O')₂(neoc)] and [Ni(mclf-O)₂(Hpko-N,N')₂]·MeOH·0.5H₂O. The affinity of the complexes for calf-thymus (CT) DNA was investigated by various techniques and intercalation is suggested as the most possible interaction mode. The interaction of the complexes for bovine and human serum albumins was also investigated in order to determine the binding constants, concluding that the complexes bind reversibly to albumins for the transportation towards their target cells or tissues and their release upon arrival at biotargets. The antioxidant activity of the compounds was evaluated via their ability to scavenge 1,1-diphenyl-picrylhydrazyl and 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) free radicals and to reduce H₂O₂. For the determination of the anticholinergic ability of the complexes the in vitro inhibitory activity against the enzymes acetylcholinesterase and butyrylcholinesterase was evaluated and presented promising results. The in silico molecular modeling calculations employed provide useful insights for the understanding of the mechanism of action of the studied complexes at a molecular level. This applies on both the impairment of DNA by its binding with the studied complexes and transportation through serum albumins, as well as the ability of these compounds to act as anticholinergic agents.

Toxicology and pharmacology of synthetic organoselenium compounds: an update

Here, we addressed the pharmacology and toxicology of synthetic organoselenium compounds and some naturally occurring organoselenium amino acids. The use of selenium as a tool in organic synthesis and as a pharmacological agent goes back to the middle of the nineteenth and the beginning of the twentieth centuries. The rediscovery of ebselen and its investigation in clinical trials have motivated the search for new organoselenium molecules with pharmacological properties. Although ebselen and diselenides have some overlapping pharmacological properties, their molecular targets are not identical. However, they have similar anti-inflammatory and antioxidant activities, possibly, via activation of transcription factors, regulating the expression of antioxidant genes. In short, our knowledge about the pharmacological properties of simple organoselenium compounds is still elusive. However, contrary to our early expectations that they could imitate selenoproteins, organoselenium compounds seem to have non-specific modulatory activation of antioxidant pathways and specific inhibitory effects in some thiol-containing proteins. The thiol-oxidizing properties of organoselenium compounds are considered the molecular basis of their chronic toxicity; however, the acute use of organoselenium compounds as inhibitors of specific thiol-containing enzymes can be of therapeutic significance. In summary, the outcomes of the clinical trials of ebselen as a mimetic of lithium or as an inhibitor of SARS-CoV-2 proteases will be important to the field of organoselenium synthesis. The development of computational techniques that could predict rational modifications in the structure of organoselenium compounds to increase their specificity is required to construct a library of thiol-modifying agents with selectivity toward specific target proteins.

Copper(II) complexes with meclofenamate ligands: Structure, interaction with DNA and albumins, antioxidant and anticholinergic activity

The interaction of copper(II) with the non-steroidal anti-inflammatory drug sodium meclofenamate (Na-mclf) in the presence or absence of the nitrogen-donor co-ligands pyridine (py) or 2,2'-bipyridylamine (bipyam), yielded the novel Cu(II) complexes [Cu₂(mclf-O,O')₄(MeOH)₂]·2MeOH (1·2MeOH), [Cu(mclf-O)₂(py)₃]·H₂O·0.5MeOH (2·H₂O·0.5MeOH) and [Cu(mclf-O,O')₂(bipyam)] (3). The characterization of the complexes was achieved by various techniques, including single-crystal X-ray crystallography. In order to study the binding mode and strength of the complexes to calf-thymus (CT) DNA, various techniques were employed which suggested intercalation between the DNA-bases as the most possible interaction mode. Competitive studies with ethidium bromide (EB) revealed the ability of the complexes to displace the EB from the EB-DNA adduct, verifying the intercalative binding mode. The affinity of the complexes to bovine and human serum albumin proteins (SAs) was investigated by fluorescence emission spectroscopy and the corresponding binding constants bear relatively high values, showing that the complexes bind tightly and possibly reversibly to SAs. The antioxidant activity of the complexes against 1,1-diphenyl-picrylhydrazyl (DPPH), 2,2'-azinobis(3-ethylbenzothiazoline-6-sulfonic acid) (ABTS) radicals and the ability to reduce H₂O₂ proved to be of significant magnitude. The in vitro inhibitory activity against the enzymes acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) was evaluated, in order to assess the anticholinergic ability of the complexes, which appeared promising.

Model Amphipathic Peptide Coupled with Tacrine to Improve Its Antiproliferative Activity

Drug repurposing and drug combination are two strategies that have been widely used to overcome the traditional development of new anticancer drugs. Several FDA-approved drugs for other indications have been tested and have demonstrated beneficial anticancer effects. In this connection, our research group recently reported that Tacrine, used to treat Alzheimer's Disease, inhibits the growth of breast cancer MCF-7 cells both alone and in combination with a reference drug. In this view, we have now coupled Tacrine with the model amphipathic cell-penetrating peptide (CPP) MAP, to ascertain whether coupling of the CPP might enhance the drug's antiproliferative properties. To this end, we synthesized MAP through solid-phase peptide synthesis, coupled it with Tacrine, and made a comparative evaluation of the parent drug, peptide, and the conjugate regarding their permeability across the blood-brain barrier (BBB), ability to inhibit acetylcholinesterase (AChE) in vitro, and antiproliferative activity on cancer cells. Both MAP and its Tacrine conjugate were highly toxic to MCF-7 and SH-SY5Y cells. In turn, BBB-permeability studies were inconclusive, and conjugation to the CPP led to a considerable loss of Tacrine function as an AChE inhibitor. Nonetheless, this work reinforces the potential of repurposing Tacrine for cancer and enhances the antiproliferative activity of this drug through its conjugation to a CPP.

Multi-Target Drug Candidates for Multifactorial Alzheimer's Disease: AChE and NMDAR as Molecular Targets

Alzheimer's disease (AD) is one of the most common forms of dementia among elder people, which is a progressive neurodegenerative disease that results from a chronic loss of cognitive activities. It has been observed that AD is multifactorial, hence diverse pharmacological targets that could be followed for the treatment of AD. The Food and Drug Administration has approved two types of medications for AD treatment such as cholinesterase inhibitors (ChEIs) and N-methyl-D-aspartic acid receptor (NMDAR) antagonists. Rivastigmine, donepezil, and galantamine are the ChEIs that have been approved to treat AD. On the other hand, memantine is the only non-competitive NMDAR antagonist approved in AD treatment. As compared with placebo, it has been revealed through clinical studies that many single-target therapies are unsuccessful to treat multifactorial Alzheimer's symptoms or disease progression. Therefore, due to the complex nature of AD pathophysiology, diverse pharmacological targets can be hunted. In this article, based on the entwined link of acetylcholinesterase (AChE) and NMDAR, we represent several multifunctional compounds in the rational design of new potential AD medications. This review focus on the significance of privileged scaffolds in the generation of the multi-target lead compound for treating AD, investigating the idea and challenges of multi-target drug design. Furthermore, the most auspicious elementary units for designing as well as synthesizing hybrid drugs are demonstrated as pharmacological probes in the rational design of new potential AD therapeutics.

Base-Promoted Multicomponent Reactions: A Synthesis of 2-Amino-1,3-selenazole Derivatives

New practical synthesis of 2-amino-1,3-selenazole with transition metal-free multicomponent reaction is reported here. A series of 2-amino-1,3-selenazole derivatives were afforded by the nucleophilic addition of amines to isoselenocyanate formed in situ, followed by Michael addition reaction and aromatization. The products were isolated from moderate to excellent yields.

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.

Development and Therapeutic Potential of Selenazo Compounds

Incorporation of selenium (Se) atom into small molecules can substantially enhance their antioxidant, anti-inflammatory, antimutagenic, antitumoral or chemopreventive, antiviral, antibacterial, antifungal, antiparasitic, and neuroprotective effects. Specifically, selenazo compounds have received great attention owing to their chemical properties, pharmaceutical applications, and low toxicity. In this Perspective, we compile extensive literature evidence with the description and discussion of the most recent advances in different selenazo and selenadiazo motifs as potential pharmacological candidates. We also provide some perspectives on the challenges and future directions in the advancement of these selenazo compounds, each of which could generate drug candidates for various diseases.

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.

Synthesis and activity towards Alzheimer's disease in vitro: Tacrine, phenolic acid and ligustrazine hybrids

A series of novel tacrine-phenolic acid dihybrids and tacrine-phenolic acid-ligustrazine trihybrids were synthesized, characterized and screened as novel potential anti-Alzheimer drug candidates. These compounds showed potent inhibition activity towards cholinesterases (ChEs), among of them, 9i was the most potent one towards acetylcholinesterase (eeAChE, IC₅₀ = 3.9 nM; hAChE, IC₅₀ = 65.2 nM). 9i could also effectively block β-amyloid (Aβ) self-aggregation with an inhibition ratio of 47% at 20 μM. In addition, its strong anti-oxidation activity could protect PC12 cells from CoCl₂-damage in the experimental condition while no neurotoxicity. Furthermore, its hepatotoxicity was lower than tacrine in vitro and in vivo. Kinetic and molecular modeling studies revealed that 9i worked in a mixed-type way, could interact simultaneously with catalytic active site (CAS) and peripheral anionic site (PAS) of AChE. Therefore, 9i was a promising multifunctional candidate for the treatment of AD.

Novel multitarget-directed tacrine derivatives as potential candidates for the treatment of Alzheimer's disease

Alzheimer’s disease (AD) is a neurodegenerative disorder, which is complex and progressive; it has not only threatened the health of elderly people, but also burdened the whole social medical and health system. The available therapy for AD is limited and the efficacy remains unsatisfactory. In view of the prevalence and expected increase in the incidence of AD, the design and development of efficacious and safe anti-AD agents has become a hotspot in the field of pharmaceutical research. Due to the multifactorial etiology of AD, the multitarget-directed ligands (MTDLs) approach is promising in search for new drugs for AD. Tacrine, which is the first acetylcholinesterase (AChE) inhibitor, has been selected as the ideal active fragment because of its simple structure, clear activity, and its superiority in the structural modification, thus it could be introduced into the overall molecular skeletons of the multi-target-directed anti-AD agents. In this review, we have summarized the recent advances (2012 to the present) in the chemical modification of tacrine, which could provide the reference for the further study of novel multi-target-directed tacrine derivatives to treat AD.

Recent progress in repositioning Alzheimer's disease drugs based on a multitarget strategy

Alzheimer's disease (AD) is a serious progressive neurological disorder, characterized by impaired cognition and profound irreversible memory loss. The multifactorial nature of AD and the absence of a cure so far have stimulated medicinal chemists worldwide to follow multitarget drug-design strategies based on repositioning approved drugs. This review describes a summary of recently published works focused on tailoring new derivatives of US FDA-approved acetylcholinesterase inhibitors, in addition to huperzine (a drug approved in China), either by hybridization with other pharmacophore elements (to hit more AD targets), or by combination of two FDA-approved drugs. Besides the capacity for improving the cholinergic activity, these polyfunctional derivatives are also able to tackle other important neuroprotective properties, such as anti-β-amyloid aggregation, scavenging of radical oxygen species, modulation of redox-active metals or inhibition of monoamine oxidase, thereby resulting in potentially novel and more effective therapeutics for the treatment of AD.

Convergent Synthesis of Two Fluorescent Ebselen-Coumarin Heterodimers

The organo-seleniumdrug ebselen exhibits a wide range of pharmacological effects that are predominantly due to its interference with redox systems catalyzed by seleno enzymes, e.g., glutathione peroxidase and thioredoxin reductase. Moreover, ebselen can covalently interact with thiol groups of several enzymes. According to its pleiotropic mode of action, ebselen has been investigated in clinical trials for the prevention and treatment of different ailments. Fluorescence-labeled probes containing ebselen are expected to be suitable for further biological and medicinal studies. We therefore designed and synthesized two coumarin-tagged activity-based probes bearing the ebselen warhead. The heterodimers differ by the nature of the spacer structure, for which—in the second compound—a PEG/two-amide spacer was introduced. The interaction of this probe and of ebselen with two cysteine proteases was investigated.

Synthesis and pharmacological evaluation of donepezil-based agents as new cholinesterase/monoamine oxidase inhibitors for the potential application against Alzheimer's disease

In a continuing effort to develop multitargeted compounds as potential treatment agents against Alzheimer's disease (AD), a series of donepezil-like compounds were designed, synthesized and evaluated. In vitro studies showed that most of the designed compounds displayed potent inhibitory activities toward AChE, BuChE, MAO-B and MAO-A. Among them, w18 was a promising agent with balanced activities, which exhibited a moderate cholinesterase inhibition (IC₅₀, 0.220 μM for eeAChE; 1.23 μM for eqBuChE; 0.454 μM for hAChE) and an acceptable inhibitory activity against monoamine oxidases (IC₅₀, 3.14 μM for MAO-B; 13.4 μM for MAO-A). Moreover, w18 could also be a metal-chelator, and able to cross the blood-brain barrier with low cell toxicity on PC12 cells. Taken together, these results suggested that w18 might be a promising multitargeted compound for AD treatment.

Design, synthesis and evaluation of novel ferulic acid-memoquin hybrids as potential multifunctional agents for the treatment of Alzheimer's disease

A novel series of ferulic acid-memoquin hybrids were designed, synthesized and evaluated as multifunctional agents for the treatment of Alzheimer's disease (AD). The in vitro studies showed that most of the compounds exhibited a significant ability to inhibit acetylcholinesterase (AChE) (IC50 of 3.2-34.7μM) and self-induced β-amyloid (Aβ1-42) aggregation (30.8-39.1%, 25μM), to act as potential antioxidants (ORAC-FL value of 0.9-1.3). In particular, compound 17d had the greatest ability to inhibit AChE (IC50=3.2μM), and Aβ1-42 aggregation (30.8%) was also an excellent antioxidant and neuroprotectant. Moreover, it is capable of disaggregating self-induced Aβ aggregation. Furthermore, 17d could cross the blood-brain barrier (BBB) in vitro. The results showed that compound 17d is a potential multifunctional agent for the treatment of AD.

Tacrine-propargylamine derivatives with improved acetylcholinesterase inhibitory activity and lower hepatotoxicity as a potential lead compound for the treatment of Alzheimer's disease

A series of tacrine-propargylamine derivatives were synthesised and evaluated as possible anti-Alzheimer's disease (AD) agents. Among these derivatives, compounds 3a and 3b exhibited superior activities and a favourable balance of AChE and BuChE activities (3a: IC50 values of 51.3 and 77.6 nM; 3b: IC50 values of 11.2 and 83.5 nM). Compounds 3a and 3b also exhibited increased hAChE inhibitory activity compared with tacrine by approximately 5- and 28-fold, respectively, and low neurotoxicity. Importantly, these compounds also had lower hepatotoxicity than tacrine. Based on these results, compounds 3a and 3b could be considered as potential lead compounds for the treatment of AD and other AChE related diseases, such as schizophrenia, glaucoma and myasthenia gravis.

Design, synthesis and evaluation of novel 5,6,7-trimethoxyflavone-6-chlorotacrine hybrids as potential multifunctional agents for the treatment of Alzheimer's disease

A series of 5,6,7-trimethoxyflavone-6-chlorotacrine hybrids were designed, synthesized and evaluated as multifunctional agents for the treatment of Alzheimer's disease (AD). The results showed that the target compounds exhibited good acetylcholinesterase (AChE) inhibitory potencies, high selectivity toward AChE over butyrylcholinesterase (BuChE), potential antioxidant activities and significant inhibitory potencies of self-induced beta-amyloid peptide (Aβ) aggregation. In particular, compound 14c had the strongest AChE inhibitory activity with IC50 value of 12.8 nM, potent inhibition of self-induced Aβ1-42 aggregation with inhibition ratio of 33.8% at 25 μM. Moreover, compound 14c acted as an antioxidant, as well as a neuroprotectant. Furthermore, 14c could cross the blood-brain barrier (BBB) in vitro. The results showed that compound 14c might be a potential multifunctional candidate for the treatment of AD.

Synthesis and bioevaluation of 2-phenyl-4-methyl-1,3-selenazole-5-carboxylic acids as potent xanthine oxidase inhibitors

A series of 2-phenyl-4-methyl-1,3-selenazole-5-carboxylic acid derivatives (8a-f, 9a-m) were synthesized and evaluated for inhibitory activity against xanthine oxidase in vitro. Structure-activity relationship analyses have also been presented. Most of the target compounds exhibited potency levels in the nanomolar range. Compound 9e emerged as the most potent xanthine oxidase inhibitor (IC50 = 5.5 nM) in comparison to febuxostat (IC50 = 18.6 nM). Steady-state kinetics measurements with the bovine milk enzyme indicated a mixed type inhibition with Ki and Ki' values of 0.9 and 2.3 nM, respectively. A molecular modeling study on compounds 9e was performed to gain an insight into its binding mode with xanthine oxidase, and to provide the basis for further structure-guided design of new non-purine xanthine oxidase inhibitors related with 2-phenyl-4-methyl-1,3-selenazole-5-carboxylic acid scaffold.