Interest of novel N-alkylpyridinium-indolizine hybrids in the field of Alzheimer's disease: Synthesis, characterization and evaluation of antioxidant activity, cholinesterase inhibition, and amyloid fibrillation interference

Involvement of the serotonergic system in the antidepressant-like effect of 1-(phenylselanyl)-2-(p-tolyl)indolizine in mice

RATIONALE

Depression is a mental disorder that affects approximately 280 million people worldwide. In the search for new treatments for mood disorders, compounds containing selenium and indolizine derivatives show promising results.

OBJECTIVES AND METHODS

To evaluate the antidepressant-like effect of 1-(phenylselanyl)-2-(p-tolyl)indolizine (MeSeI) (0.5-50 mg/kg, intragastric-i.g.) on the tail suspension test (TST) and the forced swim test (FST) in adult male Swiss mice and to elucidate the role of the serotonergic system in this effect through pharmacological and in silico approaches, as well to evaluate acute oral toxicity at a high dose (300 mg/kg).

RESULTS

MeSeI administered 30 min before the FST and the TST reduced immobility time at doses from 1 mg/kg and at 50 mg/kg and increased the latency time for the first episode of immobility, demonstrating an antidepressant-like effect. In the open field test (OFT), MeSeI did not change the locomotor activity. The antidepressant-like effect of MeSeI (50 mg/kg, i.g.) was prevented by the pre-treatment with p-chlorophenylalanine (p-CPA), a selective tryptophan hydroxylase inhibitor (100 mg/kg, intraperitoneally-i.p. for 4 days), with ketanserin, a 5-HT_2A/2C receptor antagonist (1 mg/kg, i.p.), and with GR113808, a 5-HT₄ receptor antagonist (0.1 mg/kg, i.p.), but not with WAY100635, a selective 5-HT_1A receptor antagonist (0.1 mg/kg, subcutaneous-s.c.) and ondansetron, a 5-HT₃ receptor antagonist (1 mg/kg, i.p.). MeSeI showed a binding affinity with 5-HT_2A, 5 -HT_2C, and 5-HT₄ receptors by molecular docking. MeSeI (300 mg/kg, i.g.) demonstrated low potential to cause acute toxicity in adult female Swiss mice.

CONCLUSION

In summary, MeSeI exhibits an antidepressant-like effect mediated by the serotonergic system and could be considered for the development of new treatment strategies for depression.

Integrated in silico and experimental discovery of trimeric peptide ligands targeting Butyrylcholinesterase

Butyrylcholinesterase (BChE) is recognized as a high value biotherapeutic in the treatment of Alzheimer's disease and drug addiction. This study presents the rational design and screening of an in-silico library of trimeric peptides against BChE and the experimental characterization of peptide ligands for purification. The selected peptides consistently afforded high BChE recovery (> 90 %) and purity, yielding up to a 1000-fold purification factor. This study revealed a marked anti-correlated conformational movement governed by the ionic strength and pH of the aqueous environment, which ultimately controls BChE binding and release during chromatographic purification; and highlighted the role of residues within and allosteric to the catalytic triad of BChE in determining biorecognition, thus providing useful guidance for ligand design and affinity maturation.

The Eschenmoser's Salt as a Formylation Agent for the Synthesis of Indolizinecarbaldehydes and Their Use for Colorimetric Nitrite Detection

C-H bond formylation is the most immediate way to incorporate the versatile formyl group into (hetero)aromatics. However, the type of reagents and severe conditions involved in the classical formylation methods often curtail their application, especially in the presence of other functional groups. Herein, we present the Eschenmoser's salt, a commercially available (dimethylamino)methylating chemical, as a useful reagent for the C-H formylation of indolizines and other compounds. The method is straightforward and mild, furnishing indolizinecarbaldehydes in modest-to-good yields with exclusive and remote regioselectivity. Furthermore, these compounds can be easily transformed into push-pull dyes and are highly selective in the colorimetric detection of nitrite, a substance extensively employed as preservative in the food industry, the concentration of which is crucial to control to prevent harmful effects in living organisms. The assay is simple, allowing the naked-eye detection of nitrite in solution or on a cotton swab for a wide range of concentrations.

Effect of mono- and diketone group in curcumin analogues on amyloid fibrillation of hen egg white lysozyme

Curcumin has attracted more attention because of its inhibition efficacy on protein amyloid fibrillation. However, the inhibition mechanism was still ambiguous and the clinical application of curcumin was greatly limited because of its poor stability at physiological conditions for the presence of β-diketone moiety. In this paper, a new mono-ketone-containing curcumin analogue (MDHC) was designed and synthesized to realize the possible inhibition mechanism and unveil the important role of β-diketone moiety of curcumin in the inhibition process of amyloid fibrillation using hen egg white lysozyme (HEWL) as model protein. Although all experiment results (ThT, CR, ANS and TEM) showed that the inhibitory capacity of curcumin was better than MDHC, MDHC still could show obvious inhibition effect. Molecular docking showed that both curcumin and MDHC could bind with HEWL by hydrogen bond of phenloic hydroxyl and the binding energy of MDHC was higher than that of curcumin. All the findings inferred that β-diketone group was one of great important groups in the inhibition process of HEWL amyloid fibrillation, which provided more room to construct novel inhibition reagents.

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.

Recent advance on pleiotropic cholinesterase inhibitors bearing amyloid modulation efficacy

Due to the hugely important roles of neurotransmitter acetylcholine (ACh) and amyloid-β (Aβ) in the pathogenesis of Alzheimer's disease (AD), the development of multi-target directed ligands (MTDLs) focused on cholinesterase (ChE) and Aβ becomes one of the most attractive strategies for combating AD. To date, numerous preclinical studies toward multifunctional conjugates bearing ChE inhibition and anti-Aβ aggregation have been reported. Noteworthily, most of the reported multifunctional cholinesterase inhibitors are carbamate-based compounds due to the initial properties of carbamate moiety. However, because their easy hydrolysis in vivo and the instability of the compound-enzyme conjugate, the mechanism of action of these compounds is rare. Thus, non-carbamate compounds are of great need for developing novel cholinesterase inhibitors. Besides, given that Aβ accumulation begins to occur 10-15 years before AD onset, modulating Aβ is ineffective only in inhibiting its aggregation but not eliminate the already accumulated Aβ if treatment is started when the patient has been diagnosed as AD. Considering the limitation of current Aβ accumulation modulators in ameliorating cognitive deficits and ineffectiveness of ChE inhibitors in blocking disease progression, the development of a practically valuable strategy with multiple pharmaceutical properties including ChE inhibition and Aβ modulation for treating AD is indispensable. In this review, we focus on summarizing the scaffold characteristics of reported non-carbamate cholinesterase inhibitors with Aβ modulation since 2020, and understanding the ingenious multifunctional drug design ideas to accelerate the pace of obtaining more efficient anti-AD drugs in the future.