Synthesis of Some New 3-Coumaranone and Coumarin Derivatives as Dual Inhibitors of Acetyl- and Butyrylcholinesterase

TMSCF3-Mediated Conversion of Salicylates into α,α-Difluoro-3-coumaranones: Chain Kinetics, Anion-Speciation, and Mechanism

As reported by Zhao, the TBAT ([Ph3SiF2]-[Bu4N]+)-initiated reaction of ethyl salicylate with TMSCF3 in THF generates α,α-difluoro-3-coumaranones via the corresponding O-silylated ethoxy ketals. The mechanism has been investigated by in situ 19F and 29Si NMR spectroscopy, CF2-trapping, competition, titration, and comparison of the kinetics with the 3-, 4-, 5-, and 6-fluoro ethyl salicylate analogues and their O-silylated derivatives. The process evolves in five distinct stages, each arising from a discrete array of anion speciations that modulate a sequence of silyl-transfer chain reactions. The deconvolution of coupled equilibria between salicylate, [CF3]-, and siliconate [Me3Si(CF3)2]- anions allowed the development of a kinetic model that accounts for the first three stages. The model provides valuable practical insights. For example, it explains how the initial concentrations of the TMSCF3 and salicylate and the location of electron-withdrawing salicylate ring substituents profoundly impact the overall viability of the process, how stoichiometric CF3H generation can be bypassed by using the O-silylated salicylate, and how the very slow liberation of the α,α-difluoro-3-coumaranone can be rapidly accelerated by evaporative or aqueous workup.

Recent developments in the design and synthesis of benzylpyridinium salts: Mimicking donepezil hydrochloride in the treatment of Alzheimer’s disease

Background: Alzheimer’s disease (AD) is an advanced and irreversible degenerative disease of the brain, recognized as the key reason for dementia among elderly people. The disease is related to the reduced level of acetylcholine (ACh) in the brain that interferes with memory, learning, emotional, and behavior responses. Deficits in cholinergic neurotransmission are responsible for the creation and progression of numerous neurochemical and neurological illnesses such as AD.

Aim: Herein, focusing on the fact that benzylpyridinium salts mimic the structure of donepezil hydrochlorideas a FDA-approved drug in the treatment of AD, their synthetic approaches and inhibitory activity against cholinesterases (ChEs) were discussed. Also, molecular docking results and structure–activity relationship (SAR) as the most significant concept in drug design and development were considered to introduce potential lead compounds. Key scientific concepts: AChE plays a chief role in the end of nerve impulse transmission at the cholinergic synapses. In this respect, the inhibition of AChE has been recognized as a key factor in the treatment of AD, Parkinson’s disease, senile dementia, myasthenia gravis, and ataxia. A few drugs such as donepezil hydrochloride are prescribed for the improvement of cognitive dysfunction and memory loss caused by AD. Donepezil hydrochloride is a piperidine-containing compound, identified as a well-known member of the second generation of AChE inhibitors. It was established to treat AD when it was assumed that the disease is associated with a central cholinergic loss in the early 1980s. In this review, synthesis and anti-ChE activity of a library of benzylpyridinium salts were reported and discussed based on SAR studies looking for the most potent substituents and moieties, which are responsible for inducing the desired activity even more potent than donepezil. It was found that linking heterocyclic moieties to the benzylpyridinium salts leads to the potent ChE inhibitors. In this respect, this review focused on the recent reports on benzylpyridinium salts and addressed the structural features and SARs to get an in-depth understanding of the potential of this biologically improved scaffold in the drug discovery of AD.

Bioactive Aurones, Indanones, and Other Hemiindigoid Scaffolds: Medicinal Chemistry and Photopharmacology Perspectives

Hemiindigoids comprise a range of natural and synthetic scaffolds that share the same aromatic hydrocarbon backbone as well as promising biological and optical properties. The encouraging therapeutic potential of these scaffolds has been unraveled by many studies over the past years and uncovered representants with inspiring pharmacophoric features such as the acetylcholinesterase inhibitor donezepil and the tubulin polymerization inhibitor indanocine. In this review, we summarize the last advances in the medicinal potential of hemiindigoids, with a special attention to molecular design, structure-activity relationship, ligand-target interactions, and mechanistic explanations covering their effects. As their strong fluorogenic potential and photoswitch behavior recently started to be highlighted and explored in biology, giving rise to the development of novel fluorescent probes and photopharmacological agents, we also discuss these properties in a medicinal chemistry perspective.

Synthesis of 2-(2-oxo-2H-chromen-4-yl)acetamides as potent acetylcholinesterase inhibitors and molecular insights into binding interactions

Sixteen novel coumarin-based compounds are reported as potent acetylcholinesterase (AChE) inhibitors. The most active compound in this series, 5a (IC₅₀ 0.04 ± 0.01 µM), noncompetitively inhibited AChE with a higher potency than tacrine and galantamine. Compounds 5d, 5j, and 5 m showed a moderate antilipid peroxidation activity. The compounds showed cytotoxicity in the same range as the standard drugs in HEK-293 cells. Molecular docking demonstrated that 5a acted as a dual binding site inhibitor. The coumarin moiety occupied the peripheral anionic site and showed π-π interaction with Trp278. The tertiary amino group displayed significant cation-π interaction with Phe329. The aromatic group showed π-π interaction with Trp83 at the catalytic anionic site. The long chain of methylene lay along the gorge interacting with Phe330 via hydrophobic interaction. Molecular docking was applied to postulate the selectivity toward AChE of 5a in comparison with donepezil and tacrine. Structural insights into the selectivity of the coumarin derivatives toward huAChE were explored by molecular docking and 3D QSAR and molecular dynamics simulation for 20 ns. ADMET analysis suggested that the 2-(2-oxo-2H-chromen-4-yl)acetamides showed a good pharmacokinetic profile and no hepatotoxicity. These coumarin derivatives showed high potential for further development as anti-Alzheimer agents.

Synthesis and biological evaluation of 3-arylcoumarins as potential anti-Alzheimer's disease agents

Alzheimer's disease, a neurodegenerative illness, has the extremely complex pathogenesis. Accumulating evidence indicates there is a close relationship between several enzymes and Alzheimer's disease. Various substituted 3-arylcoumarin derivatives were synthesised, and their in vitro activity, including cholinesterase inhibitory activity, monoamine oxidase inhibitory activity, and antioxidant activity were investigated. Most of the compounds exhibited high activity; therefore 3-arylcoumarin compounds have the potential as drug candidates for the treatment of Alzheimer's disease.

Molecular docking studies of coumarin hybrids as potential acetylcholinesterase, butyrylcholinesterase, monoamine oxidase A/B and β-amyloid inhibitors for Alzheimer's disease

Coumarins are the phytochemicals, which belong to the family of benzopyrone, that display interesting pharmacological properties. Several natural, synthetic and semisynthetic coumarin derivatives have been discovered in decades for their applicability as lead structures as drugs. Coumarin based conjugates have been described as potential AChE, BuChE, MAO and β-amyloid inhibitors. Therefore, the objective of this review is to focus on the construction of these pharmacologically important coumarin analogues with anti-Alzheimer’s activities, highlight their docking studies and structure–activity relationships based on their substitution pattern with respect to the selected positions on the chromen ring by emphasising on the research reports conducted in between year 1968 to 2017.

Profiling donepezil template into multipotent hybrids with antioxidant properties

Alzheimer’s disease is debilitating neurodegenerative disorder in the elderly. Current therapy relies on administration of acetylcholinesterase inhibitors (AChEIs) -donepezil, rivastigmine, galantamine, and N-methyl-d-aspartate receptor antagonist memantine. However, their therapeutic effect is only short-term and stabilizes cognitive functions for up to 2 years. Given this drawback together with other pathological hallmarks of the disease taken into consideration, novel approaches have recently emerged to better cope with AD onset or its progression. One such strategy implies broadening the biological profile of AChEIs into so-called multi-target directed ligands (MTDLs). In this review article, we made comprehensive literature survey emphasising on donepezil template which was structurally converted into plethora of MTLDs preserving anti-cholinesterase effect and, at the same time, escalating the anti-oxidant potential, which was reported as a crucial role in the pathogenesis of the Alzheimer’s disease.

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.

Design, synthesis, molecular modeling and anticholinesterase activity of benzylidene-benzofuran-3-ones containing cyclic amine side chain

Aim: A series of 2-benzylidene-benzofuran-3-ones were designed from the structures of Ebselen analogs and aurone derivatives and synthesized in good yields. Materials & methods: The target compounds were prepared by the condensation reaction between appropriate benzofuranones with amino alkoxy aldehydes and evaluated as cholinesterase inhibitors by Ellman’s method. Results: The in vitro anti-acetylcholinesterase (AChE)/butyrylcholinesterase activities of the synthesized compounds revealed that 7e (IC50 = 0.045 μM) is the most active compound against AChE. Furthermore, the docking study confirmed the results obtained through in vitro experiments and predicted the possible binding conformation. Conclusion: The anticholinesterase activities of benzylidene-benzofurane-3-ones as aurone analogs revealed that the compounds bearing piperidinylethoxy residue showed better activities against AChE, introducing these compounds for further drug discovery developments.

[Formula: see text]

First total synthesis of the only known 2-isopropyliden-2H-benzofuran-3-one isolated from V. luetzelburgii

The first total synthesis of the unique isopropyliden-2H-benzofuran-3-one, isolated from Verbesina luetzelburgii, is reported in racemic and a chiral form.

Synthesis and structure-activity relationship study of benzofuran-based chalconoids bearing benzylpyridinium moiety as potent acetylcholinesterase inhibitors

A series of benzofuran-based chalconoids 6a-v were designed and synthesized as new potential AChE inhibitors. The in vitro assay of synthesized compounds 6a-v showed that most compounds had significant anti-AChE activity at micromolar or sub-micromolar levels. Among the tested compounds, 3-pyridinium derivative 6m bearing N-(2-bromobenzyl) moiety and 7-methoxy substituent on the benzofuran ring exhibited superior activity. This compound with IC₅₀ value of 0.027 μM was as potent as standard drug donepezil.

Design, synthesis and anticholinesterase activity of novel benzylidenechroman-4-ones bearing cyclic amine side chain

A series of 3-(4-(aminoalkoxy)benzylidene)-chroman-4-ones 7a-r were designed and synthesized as analogs of homoisoflavonoids which are well known natural products with diverse pharmacological properties related to Alzheimer's disease. The in vitro anti-cholinesterase activity of designed compounds 7a-r against AChE and BuChE, revealed that compounds bearing piperidinylethoxy residue showed potent activity against AChE at sub-micromolar level (IC50 values = 0.122-0.207 μM), more potent than reference drug tacrine. The structure-activity relationships study of piperidinylethoxy series demonstrated that the selectivity and physicochemical properties of compounds could be optimized by selection of a proper substituent on the C-7 position of chroman ring, while the high potency of the molecule against AChE was reserved.

Indolinone-based acetylcholinesterase inhibitors: synthesis, biological activity and molecular modeling

A series of indolinone-based compounds bearing benzylpyridinium moiety was designed as dual-binding inhibitors of acetylcholinesterase (AChE). The target compounds 3a-u were synthesized by condensation of oxindole and pyridin-4-carbalehyde, and subsequent N-benzylation. The anti-cholinesterase activity evaluation of synthesized compounds revealed that most of them had very potent inhibitory activity against AChE, superior to standard drug donepezil. Particularly, 2-chlorobenzyl derivative 3c was the most potent compound against AChE with IC50 value of 0.44 nM, being 32-fold more potent than donepezil. Also, most of compounds were more potent than standard drug donepezil against butyrylcholinesterase (BuChE). Docking study revealed that the hydrophobic aromatic part (indoline) of representative compound 3c binds to the PAS and the N-benzylpyridinium residue binds to the CAS of AChE.