Synthesis of novel phenserine-based-selective inhibitors of butyrylcholinesterase for Alzheimer's disease

Cholinesterase Inhibitory Activity of Paeoniflorin: Molecular Dynamics Simulation, and In Vitro Mechanistic Investigation

Alzheimer's disease (AD), a neurological disorder, is one of the major reasons for memory loss in the world. AD is characterized by a sequela of cognitive and functional decline caused by brain cell degeneration. Paeoniflorin is a monoterpenoid glycoside found in plants of the Paeoniaceae family, which are known for their medicinal properties including dementia. In this project, we report actions of paeoniflorin on the two related cholinesterases (ChE): acetylChE (AChE) and butyrylChE (BuChE). Paeoniflorin, in a dose-dependent (maximum inhibition at 1 mg/mL) manner, inhibited both AChE (0.06-1 mg/mL) and BuChE (0.007-1 mg/mL) enzymes with maximum inhibition of AChE enzyme at 90.3 ± 1.4%, while 99.4 ± 0.3% for BuChE enzyme. The EC50 value for the inhibitory effect of the compound against AChE was 0.52 mg/mL (0.18-1.52), while against BuChE was 0.13 mg/mL (0.08-0.21). The observed ani-ChE action was like an effect also mediated by the known ChE blocker physostigmine. Molecular interactions between paeoniflorin and both ChE enzymes were additionally sought via molecular docking and molecular dynamics simulations for 100 ns, that showed paeoniflorin interacted with the active-site gorge of AChE and BuChE via hydrogen bonds and water bridging with the many amino acids of the AChE and BuChE enzymes. This study presents the ChE inhibitory potential of paeoniflorin against both AChE and BuChE enzymes. With this kind of inhibitory activity, the chemical can potentially increase ACh levels and may have use in the treatment of dementia of AD.

Comprehensive Review on the Genus Haloxylon: Pharmacological and Phytochemical Properties

AIMS

This review aimed to review the biological, pharmacological, and phytochemical aspects of the genus Haloxylon.

BACKGROUND

Plants of the genus Haloxylon have been used for a long time in traditional medicine, and they are distributed in the western Mediterranean region to the Middle East, Iran, Mongolia, Burma, and southwest China. The studied parts of Haloxylon species include aerial parts, leaves, branches, seeds, roots, rhizosphere, soil, and whole plants, used to treat several diseases, including sexual disorders, hepatobiliary disorders, eye disorders, skin diseases and hemorrhoids, diarrhea, and effective in the treatment of various ailments such as snake bite, stomach ache, diabetes, wounds, earache and sciatica pain, windbreak dune fixation, feeding of livestock and firewood.

OBJECTIVES

Till now, no review on the genus Haloxylon has been conducted. This review aimed to provide updated information on the genus Haloxylon, including traditional medicinal uses, valorization and exploitation of medicinal plants, phytochemistry, botanical characterization, pharmacological and toxicological research focusing on the medicinal properties of several Haloxylon species, especially their antioxidant, antibacterial, anti-inflammatory, cytotoxic and antifungal activities, as well as the effect of each bioactive molecule isolated from these species and their pharmacological use, including the preclinical evaluation of new drugs.

MATERIALS AND METHODS

The present work was conducted using various scientific databases, including Science Direct, Scopus, PubMed, Google Scholar, etc. Correct plant names were verified from plantlist.org. The results of this search were interpreted, analyzed, and documented based on the obtained bibliographic information.

RESULTS

Among all species of the Chenopodiaceae family, 6 species of the Haloxylon genus have approved antioxidant activity, 5 species have antibacterial activity, 3 species have anti-inflammatory activity, 2 species have cytotoxic activity, and 3 species have antifungal activity. The majority of the chemical constituents of this plant include flavonoids, alkaloids, phenols, saponins, glycosides, and tannins. Among them, the main bioactive constituents would be present in the alkaloid fraction. The study of more than 9 Haloxylon plants has identified more than 46 compounds. Pharmacological research proved that crude extracts and some pure compounds obtained from Haloxylon had activities for the treatment of different diseases. The objective of the present study was focused on antioxidant, antibacterial, anti-inflammatory, cytotoxic and antifungal diseases. From the study of the phytochemistry of the Haloxylon family, it was concluded that all studied plants had active compounds. Among them, 11 isolated molecules have medicinal activities with antioxidant properties, 10 molecules showed antibacterial effects, more than 6 molecules have anti-inflammatory properties, more than 9 isolated molecules have medicinal activities against cytotoxic diseases, and more than 28 molecules have antifungal effects. Therefore, the safety of Haloxylon herbal medicine should be considered a top priority in the early stages of development and clinical trials.

CONCLUSION

Several previously conducted studies have validated multiple traditional uses of Haloxylon species. Further research is needed on Haloxylon plants before they can be fully utilized in the clinic as a potent drug candidate, as researchers are mainly focusing on alkaloids, diterpenoids, and triterpenoids, whereas there are many other types of compounds that may possess novel biological activities.

Discovery of new, highly potent and selective inhibitors of BuChE - design, synthesis, in vitro and in vivo evaluation and crystallography studies

The symptomatic and disease-modifying effects of butyrylcholinesterase (BuChE) inhibitors provide an encouraging premise for researching effective treatments for Alzheimer's disease. Here, we examined a series of compounds with a new chemical scaffold based on 3-(cyclohexylmethyl)amino-2-hydroxypropyl, and we identified a highly selective hBuChE inhibitor (29). Based on extensive in vitro and in vivo evaluations of the compound and its enantiomers, (R)-29 was identified as a promising candidate for further development. Compound (R)-29 is a potent hBuChE inhibitor (IC₅₀ = 40 nM) with selectivity over AChE and relevant off-targets, including H₁, M₁, α_1A and β₁ receptors. The compound displays high metabolic stability on human liver microsomes (90% of the parent compound after 2 h of incubation), and its safety was confirmed through examining the cytotoxicity on the HepG2 cell line (LC₅₀ = 2.85 μM) and hERG inhibition (less than 50% at 10 μM). While (rac)-29 lacked an effect in vivo and showed limited penetration to the CNS in pharmacokinetics studies, compound (R)-29 exhibited a procognitive effect at 15 mg/kg in the passive avoidance task in scopolamine-treated mice.

Pseudo-irreversible butyrylcholinesterase inhibitors: Structure-activity relationships, computational and crystallographic study of the N-dialkyl O-arylcarbamate warhead

Alongside reversible butyrylcholinesterase inhibitors, a plethora of covalent butyrylcholinesterase inhibitors have been reported in the literature, typically pseudo-irreversible carbamates. For these latter, however, most cases lack full confirmation of their covalent mode of action. Additionally, the available reports regarding the structure-activity relationships of the O-arylcarbamate warhead are incomplete. Therefore, a follow-up on a series of pseudo-irreversible covalent carbamate human butyrylcholinesterase inhibitors and the structure-activity relationships of the N-dialkyl O-arylcarbamate warhead are presented in this study. The covalent mechanism of binding was tested by IC₅₀ time-dependency profiles, and sequentially and increasingly confirmed by kinetic analysis, whole protein LC-MS, and crystallographic analysis. Computational studies provided valuable insights into steric constraints and identified problematic, bulky carbamate warheads that cannot reach and carbamoylate the catalytic Ser198. Quantum mechanical calculations provided further evidence that steric effects appear to be a key factor in determining the covalent binding behaviour of these carbamate cholinesterase inhibitors and their duration of action. Additionally, the introduction of a clickable terminal alkyne moiety into one of the carbamate N-substituents and in situ derivatisation with azide-containing fluorophore enabled fluorescent labelling of plasma human butyrylcholinesterase. This proof-of-concept study highlights the potential of this novel approach and for these compounds to be further developed as clickable molecular probes for investigating tissue localisation and activity of cholinesterases.

Development of homology model, docking protocol and Machine-Learning based scoring functions for identification of Equus caballus's butyrylcholinesterase inhibitors

Machine learning (ML), an emerging field in drug design, has the potential to predict in silico toxicity, shape-based analysis of inhibitors, scoring function (SF) etc. In the present study, a homology model, docking protocol, and a dedicated SF have been developed to identify the inhibitors of horse butyrylcholinesterase (BChE) enzyme. Horse BChE enzyme has homology with human BChE and is a substitute for the screening of in vitro inhibitors. The developed homology model was validated and the active site residues were identified from Cavityplus to generate grid box for docking. The validation of docking involved comparison of interactions of ligands co-crystallised with human BChE and the docked poses of the corresponding ligands with horse BChE. A high degree of similarity in the interaction profiles of generated poses validated the docking protocol. Scoring of ligands was further validated by docking with known BChE inhibitors. The binding energies obtained from SF was correlated with IC₅₀ values of inhibitors through classification and regression-based methods, which indicated poor predictivity of native SF. Therefore, protein-ligand binding energy, interaction profile, and ligand descriptors were used to develop and validate the classification and regression-based models. The validated extra tree binary classifier, random forest and extra tree regression-based models were compiled as a protein-ligand SF and were made available to the users through web application and python library. ML models exhibited improved area under the curve for ROC and good correlation between the predicted and observed IC₅₀ values, than the Autodock SF. Communicated by Ramaswamy H. Sarma.

Grid-Type Quaternary Metallosupramolecular Compounds Inhibit Human Cholinesterases through Dynamic Multivalent Interactions

We report the implementation of coordination complexes containing two types of cationic moieties, i. e. pyridinium and ammonium quaternary salt, as potential inhibitors of human cholinesterase enzymes. Utilization of ligands containing NNO-coordination site and binding zinc metal ion allowed mono- and tetra-nuclear complexes to be obtained with corner and grid structural type, respectively, thus affecting the overall charge of the compounds (from +1 to +8). We were able to examine for the first time the multivalency effect of metallosupramolecular species on their inhibitory abilities towards acetylcholinesterase (AChE) and butyrylcholinesterase (BChE). Importantly, resolution of the crystal structures of the obtained enzyme-substrate complexes provided a better understanding of the inhibition process at the molecular level.

Role of Shankhpushpi (Convolvulus pluricaulis) in neurological disorders: An umbrella review covering evidence from ethnopharmacology to clinical studies

C. pluricaulis Choisy (C. pluricaulis), a perennial herb aka C. microphyllus Sieb. and C. Prostratus Forsk. is being used as a traditional folk medicine for a variety of ailments. In this article, we collected information about C. pluricaulis through electronic search using PubMed, SciFinder, Google Scholar, and Web of Science as well as network pharmacology is done. This comprehensive review sheds light on the plant profile, phytochemistry, neuropharmacological, and toxicological data of C. pluricaulis. The crude herb and its metabolites have exhibited a wide range of in vitro and in vivo neuropharmacological effects, including memory enhancement, anxiolytic, tranquilizing, anti-depressant, anti-stress, neurodegenerative, anti-inflammatory, anti-oxidant, analgesic, sedative, anti-convulsant, and Alzheimer's disease-reversing effects. Network pharmacology results indicate that compounds from C. pluricaulis interact with various proteins, neuro synapses, signaling pathways, and serotonergic synapse which plays a crucial role in neurotransmission, Alzheimer's disease, long-term depression, addictions to alcohol, cognitive disorders, psychological conditions, and increasing serotonin concentration in synapses.

Recent advance on carbamate-based cholinesterase inhibitors as potential multifunctional agents against Alzheimer's disease

Alzheimer's disease (AD), as the fourth leading cause of death among the elderly worldwide, has brought enormous challenge to the society. Due to its extremely complex pathogeneses, the development of multi-target directed ligands (MTDLs) becomes the major strategy for combating AD. Carbamate moiety, as an essential building block in the development of MTDLs, exhibits structural similarity to neurotransmitter acetylcholine (ACh) and has piqued extensive attention in discovering multifunctional cholinesterase inhibitors. To date, numerous preclinical studies demonstrate that carbamate-based cholinesterase inhibitors can prominently increase the level of ACh and improve cognition impairments and behavioral deficits, providing a privileged strategy for the treatment of AD. Based on the recent research focus on the novel cholinesterase inhibitors with multiple biofunctions, this review aims at summarizing and discussing the most recent studies excavating the potential carbamate-based MTDLs with cholinesterase inhibition efficacy, to accelerate the pace of pleiotropic cholinesterase inhibitors for coping AD.

Sarcorucinine-D Inhibits Cholinesterases and Calcium Channels: Molecular Dynamics Simulation and In Vitro Mechanistic Investigations

Acetylcholinesterase (AChE) inhibitors and calcium channel blockers are considered effective therapies for Alzheimer’s disease. AChE plays an essential role in the nervous system by catalyzing the hydrolysis of the neurotransmitter acetylcholine. In this study, the inhibition of the enzyme AChE by Sarcorucinine-D, a pregnane type steroidal alkaloid, was investigated with experimental enzyme kinetics and molecular dynamics (MD) simulation techniques. Kinetics studies showed that Sarcorucinine-D inhibits two cholinesterases—AChE and butyrylcholinesterase (BChE)—noncompetitively, with K_i values of 103.3 and 4.66 µM, respectively. In silico ligand-protein docking and MD simulation studies conducted on AChE predicted that Sarcorucinine-D interacted via hydrophobic interactions and hydrogen bonds with the residues of the active-site gorge of AChE. Sarcorucinine-D was able to relax contractility concentration-dependently in the intestinal smooth muscles of jejunum obtained from rabbits. Not only was the spontaneous spasmogenicity inhibited, but it also suppressed K⁺-mediated spasmogenicity, indicating an effect via the inhibition of voltage-dependent Ca²⁺ channels. Sarcorucinine-D could be considered a potential lead molecule based on its properties as a noncompetitive AChE inhibitor and a Ca²⁺ channel blocker.

Neuroprotective Effect of Otostegia limbata Against PTZ-Induced Mice Model of Epilepsy by Attenuated Expression of p-NFκB and TNF-α

Epilepsy is a chronic neurological disorder characterized by recurrent unprovoked seizures. Currently available antiepileptic drugs have severe side effects and do not offer complete cure. Herbal remedies have been used for centuries to treat many neurodegenerative disorders. Otostegia limbata L. belongs to the largest and medicinally important family Lamiaceae and is distributed in hilly areas of Pakistan. This study was designed to assess the antioxidant, anti-inflammatory, and anticonvulsant potential of O. limbata. The methanolic extract showed significant antioxidant activity assessed by (1,1-diphenyl 2-picrylhydrazyl) free-radical scavenging assay, nitric oxide scavenging, and iron chelation antioxidant assays. The methanolic extract was evaluated for its anticonvulsant effect, employing the pentylenetetrazole (PTZ)-induced mice model of epilepsy. Three different doses of O. limbata (100, 200, and 300 mg/kg) were administered orally 30 min before PTZ [50 mg/kg, intraperitoneal (i.p.)] injection, while diazepam was used as a positive control. The extract at 300 mg/kg significantly decreased the duration and increased the latency of the PTZ-induced seizures. The expression of inflammatory cytokines tumor necrosis factor α (p-TNF-α) and phosphorylated transcription factor nuclear factor kappa B (p-NF-κB), in the cortex and hippocampus of the brains of treated mice were analyzed through enzyme-linked immunosorbent assay and western blot analysis. The morphological changes and number of surviving neurons were recorded through hematoxylin and eosin staining. The seizure score and survival rate of the treated group showed considerable differences as compared to the PTZ group. TNF-α and p-NF-K b expression were downregulated as compared to the PTZ group. The anticonvulsant effect may be the outcome of the antioxidant potential and high levels of phenols and flavonoids detected in the methanolic plant extract through Fourier transform infrared spectrophotometer and gas chromatography–mass spectrometry analysis.

Formation of Pyrroloindolines via the Alkylation of Tryptamines with Trichloroacetimidates

Pyrroloindolines and related systems are present in a large number of complex natural products. These core structures have generated considerable synthetic interest, as many of the compounds possess challenging, elaborate structures and interesting biological properties. Recently we have focused on using trichloroacetimidates for the synthesis of these fascinating molecules. Trichloroacetimidates can be used as an electrophilic source of an alkyl group to form the pyrroloindoline directly from tryptamine derivatives. In this manner trichloroacetimidates provide a flexible solution to forming highly functionalized pyrroloindoline core structures, needing only a catalytic amount of a Lewis acid to effect the requisite transformations.

Carbamate group as structural motif in drugs: a review of carbamate derivatives used as therapeutic agents

Due to their very good chemical and proteolytic stability, ability to penetrate cell membranes, and resemblance to a peptide bond, carbamate derivatives have received much attention in recent years and got an important role in modern drug discovery and medicinal chemistry. Today, carbamates make structural and/or functional part of many drugs and prodrugs approved and marketed for the treatment of various diseases such as cancer, epilepsy, hepatitis C, HIV infection, and Alzheimer's disease. In drugs they can play a role in drug-target interaction or improve the biological activity of parent molecules. In prodrugs they are mainly used to delay first-pass metabolism and enhance the bioavailability and effectiveness of compounds. This brief review takes a look at the properties and use of carbamates in various fields of medicine and provides quick insights into the mechanisms of action for some of them.

Synthesis and in vitro evaluation of vanillin derivatives as multi-target therapeutics for the treatment of Alzheimer's disease

A number of novel naphthalimido and phthalimido vanillin derivatives were synthesised, and evaluated as antioxidants and cholinesterase inhibitors in vitro. Antioxidant activity was assessed using DPPH, FRAP, and ORAC assays. All compounds demonstrated enhanced activity compared to the parent compound, vanillin. They also exhibited BuChE selectivity in Ellman's assay. A lead compound, 2a (2-(3-(bis(4-hydroxy-3-methoxybenzyl)amino)propyl)-1H-benzo[de]isoquinoline-1,3(2H)-dione), was identified and displayed strong antioxidant activity (IC₅₀ of 16.67 µM in the DPPH assay, a 25-fold increase in activity compared to vanillin in the FRAP assay, and 9.43 TE in the ORAC assay). Furthermore, 2a exhibited potent BuChE selectivity, with an IC₅₀ of 0.27 µM which was around 53-fold greater than the corresponding AChE inhibitory activity. Molecular modelling studies showed that molecules with bulkier groups, as in 2a, exhibited better BuChE selectivity. This work provides a promising basis for the development of multi-target hybrid compounds based on vanillin as potential AD therapeutics.

Studies on the cholinesterases inhibiting compounds from the Cassiopea andromeda venom

Cholinesterase inhibitors find application in the combat and care of several diseases, especially AD. Jellyfish venoms are the most promising sources of potent cholinesterase inhibitors. Therefore, it is of interest to study cholinesterases inhibiting compounds from the Cassiopea andromeda venom. We report bioactive compounds using the GC-MC method followed by molecular modeling and docking data analysis. The GC-MS analysis of the crude venom led to the identification of seven bioactive compounds (C1-C7), comprising the steroidal alkaloids, phenolic and carotenoid derivatives. The venom exhibited inhibitory activities against the cholinesterase enzymes. The compound C2, a Dioxolane steroid, displayed the strongest inhibition on both AChE and BChE activities for further consideration.

A Multi-layered Variable Selection Strategy for QSAR Modeling of Butyrylcholinesterase Inhibitors

Background:

Alzheimer’s disease (AD), a neurological disorder, is the most common cause of senile dementia. Butyrylcholinesterase (BuChE) enzyme plays a vital role in regulating the brain acetylcholine (ACh) neurotransmitter, but in the case of Alzheimer’s disease (AD), BuChE activity gradually increases in patients with a decrease in the acetylcholine (ACh) concentration via hydrolysis. ACh plays an essential role in regulating learning and memory as the cortex originates from the basal forebrain, and thus, is involved in memory consolidation in these sites.

Methods:

In this work, we have developed a partial least squares (PLS)-regression based two dimensional quantitative structure-activity relationship (2D-QSAR) model using 1130 diverse chemical classes of compounds with defined activity against the BuChE enzyme. Keeping in mind the strict Organization for Economic Co-operation and Development (OECD) guidelines, we have tried to select significant descriptors from the large initial pool of descriptors using multi-layered variable selection strategy using stepwise regression followed by genetic algorithm (GA) followed by again stepwise regression technique and at the end best subset selection prior to development of final model thus reducing noise in the input. Partial least squares (PLS) regression technique was employed for the development of the final model while model validation was performed using various stringent validation criteria.

Results:

The results obtained from the QSAR model suggested that the quality of the model is acceptable in terms of both internal (R2= 0.664, Q2= 0.650) and external (R2 Pred= 0.657) validation parameters. The QSAR studies were analyzed, and the structural features (hydrophobic, ring aromatic and hydrogen bond acceptor/donor) responsible for enhancement of the activity were identified. The developed model further suggests that the presence of hydrophobic features like long carbon chain would increase the BuChE inhibitory activity and presence of amino group and hydrazine fragment promoting the hydrogen bond interactions would be important for increasing the inhibitory activity against BuChE enzyme.

Conclusion:

Furthermore, molecular docking studies have been carried out to understand the molecular interactions between the ligand and receptor, and the results are then correlated with the structural features obtained from the QSAR models. The information obtained from the QSAR models are well corroborated with the results of the docking study.

Carbodiimide-based synthesis of N-heterocycles: moving from two classical reactive sites to chemical bond breaking/forming reaction

Carbodiimides are a unique class of heterocumulene compounds that display distinctive chemical properties. The rich chemistry of carbodiimides has drawn increasing attention from chemists in recent years and has made them exceedingly useful compounds in modern organic chemistry, especially in the synthesis of N-heterocycles. This review has outlined the extensive application of carbodiimides in the synthesis of N-heterocycles from the 1980s to today. A wide range of reactions for the synthesis of various types of N-heterocyclic systems (three-, four-, five-, six-, seven-, larger-membered and fused heterocycles) have been developed on the basis of carbodiimides and their derivatives.

N-alkylpiperidine carbamates as potential anti-Alzheimer's agents

Compounds capable of interacting with single or multiple targets involved in Alzheimer's disease (AD) pathogenesis are potential anti-Alzheimer's agents. In our aim to develop new anti-Alzheimer's agents, a series of 36 new N-alkylpiperidine carbamates was designed, synthesized and evaluated for the inhibition of cholinesterases [acetylcholinesterase (AChE) and butyrylcholinesterase (BChE)] and monoamine oxidases [monoamine oxidase A (MAO-A and monoamine oxidase B (MAO-B)]. Four compounds are very promising: multiple AChE (IC₅₀ = 7.31 μM), BChE (IC₅₀ = 0.56 μM) and MAO-B (IC₅₀ = 26.1 μM) inhibitor 10, dual AChE (IC₅₀ = 2.25 μM) and BChE (IC₅₀ = 0.81 μM) inhibitor 22, selective BChE (IC₅₀ = 0.06 μM) inhibitor 13, and selective MAO-B (IC₅₀ = 0.18 μM) inhibitor 16. Results of enzyme kinetics experiments showed that despite the carbamate group in the structure, compounds 10, 13, and 22 are reversible and non-time-dependent inhibitors of AChE and/or BChE. The resolved crystal structure of the complex of BChE with compound 13 confirmed the non-covalent mechanism of inhibition. Additionally, N-propargylpiperidine 16 is an irreversible and time-dependent inhibitor of MAO-B, while N-benzylpiperidine 10 is reversible. Additionally, compounds 10, 13, 16, and 22 should be able to cross the blood-brain barrier and are not cytotoxic to human neuronal-like SH-SY5Y and liver HepG2 cells. Finally, compounds 10 and 16 also prevent amyloid β_1-42 (Aβ_1-42)-induced neuronal cell death. The neuroprotective effects of compound 16 could be the result of its Aβ_1-42 anti-aggregation effects.

Recent applications of the Wittig reaction in alkaloid synthesis

The Wittig reaction is the chemical reaction of an aldehyde or ketone with a triphenyl phosphonium ylide (the Wittig reagent) to afford an alkene and triphenylphosphine oxide. Noteworthy, this reaction results in the synthesis of alkenes in a selective and predictable fashion. Thus, it became as one of the keystone of synthetic organic chemistry, especially in the total synthesis of natural products, where the selectivity of a reaction is paramount of importance. A literature survey disclosed the existence of vast numbers of related reports and comprehensive reviews on the applications of this important name reaction in the total synthesis of natural products. However, the aim of this chapter is to underscore, the applications of the Wittig reaction in the total synthesis of one the most important and prevalent classes of natural products, the alkaloids, especially those showing important and diverse biological activities.

Alzheimer's Disease Pharmacotherapy in Relation to Cholinergic System Involvement

Alzheimer’s disease, a major and increasing global health challenge, is an irreversible, progressive form of dementia, associated with an ongoing decline of brain functioning. The etiology of this disease is not completely understood, and no safe and effective anti-Alzheimer’s disease drug to prevent, stop, or reverse its evolution is currently available. Current pharmacotherapy concentrated on drugs that aimed to improve the cerebral acetylcholine levels by facilitating cholinergic neurotransmission through inhibiting cholinesterase. These compounds, recognized as cholinesterase inhibitors, offer a viable target across key sign domains of Alzheimer’s disease, but have a modest influence on improving the progression of this condition. In this paper, we sought to highlight the current understanding of the cholinergic system involvement in Alzheimer’s disease progression in relation to the recent status of the available cholinesterase inhibitors as effective therapeutics.

A fluorescent probe for butyrylcholinesterase activity in human serum based on a fluorophore with specific binding affinity for human serum albumin

Non-specific binding of a fluorescent probe to human serum albumin is problematic because it induces signal interference when the probe detects the target biomarker in human serum. To eliminate this problem, we used intrinsically problematic non-specific fluorescence in designing a fluorescent probe for butyrylcholinesterase activity in serum. The probe containing a fluorophore with specific binding affinity for albumin could sensitively detect butyrylcholinesterase activity in serum with high selectivity to acetylcholinesterase and screen the efficiency of butyrylcholinesterase inhibitors.

Highly Selective Butyrylcholinesterase Inhibitors with Tunable Duration of Action by Chemical Modification of Transferable Carbamate Units Exhibit Pronounced Neuroprotective Effect in an Alzheimer's Disease Mouse Model

In this study, the carbamate structure of pseudo-irreversible butyrylcholinesterase (BChE) inhibitors was optimized with regard to a longer binding to the enzyme. A set of compounds bearing different heterocycles (e.g., morpholine, tetrahydroisoquinoline, benzimidazole, piperidine) and alkylene spacers (2 to 10 methylene groups between carbamate and heterocycle) in the carbamate residue was synthesized and characterized in vitro for their binding affinity, binding kinetics, and carbamate hydrolysis. These novel BChE inhibitors are highly selective for hBChE over human acetycholinesterase (hAChE), yielding short-, medium-, and long-acting nanomolar hBChE inhibitors (with a half-life of the carbamoylated enzyme ranging from 1 to 28 h). The inhibitors show neuroprotective properties in a murine hippocampal cell line and a pharmacological mouse model of Alzheimer's disease (AD), suggesting a significant benefit of BChE inhibition for a disease-modifying treatment of AD.

Discovery of New Selective Butyrylcholinesterase (BChE) Inhibitors with Anti-Aβ Aggregation Activity: Structure-Based Virtual Screening, Hit Optimization and Biological Evaluation

In this study, a series of selective butyrylcholinesterase (BChE) inhibitors was designed and synthesized from the structural optimization of hit 1, a 4-((3,4-dihydroisoquinolin-2(1H)-yl)methyl)benzoic acid derivative identified by virtual screening our compound library. The in vitro enzyme assay results showed that compounds 9 ((4-((3,4-dihydroisoquinolin-2(1H)-yl)methyl)phenyl)(pyrrolidin-1-yl)methanone) and 23 (N-(2-bromophenyl)-4-((3,4-dihydroisoquinolin-2(1H)-yl)methyl)benzamide) displayed improved BChE inhibitory activity and good selectivity towards BChE versus AChE. Their binding modes were probed by molecular docking and further validated by molecular dynamics simulation. Kinetic analysis together with molecular modeling studies suggested that these derivatives could target both the catalytic active site (CAS) and peripheral anionic site (PAS) of BChE. In addition, the selected compounds 9 and 23 displayed anti-Aβ_1–42 aggregation activity in a dose-dependent manner, and they did not show obvious cytotoxicity towards SH-SY5Y neuroblastoma cells. Also, both compounds showed significantly protective activity against Aβ_1-42-induced toxicity in a SH-SY5Y cell model. The present results provided a new valuable chemical template for the development of selective BChE inhibitors.

Ni-Catalyzed enantioselective reductive aryl-alkenylation of alkenes: application to the synthesis of (+)-physovenine and (+)-physostigmine

A Ni-catalyzed enantioselective reductive aryl-alkenylation of alkenes for the synthesis of functionalized oxindoles is developed. With this method, a concise formal synthesis of (+)-physovenine and (+)-physostigmine has been completed.

Comprehensive review of mechanisms of pathogenesis involved in Alzheimer's disease and potential therapeutic strategies

AD is a progressive neurodegenerative disorder and a leading cause of dementia in an aging population worldwide. The enormous challenge which AD possesses to global healthcare makes it as urgent as ever for the researchers to develop innovative treatment strategies to fight this disease. An in-depth analysis of the extensive available data associated with the AD is needed for a more comprehensive understanding of underlying molecular mechanisms and pathophysiological pathways associated with the onset and progression of the AD. The currently understood pathological and biochemical manifestations include cholinergic, Aβ, tau, excitotoxicity, oxidative stress, ApoE, CREB signaling pathways, insulin resistance, etc. However, these hypotheses have been criticized with several conflicting reports for their involvement in the disease progression. Several issues need to be addressed such as benefits to cost ratio with cholinesterase therapy, the dilemma of AChE selectivity over BChE, BBB permeability of peptidic BACE-1 inhibitors, hurdles related to the implementation of vaccination and immunization therapy, and clinical failure of candidates related to newly available targets. The present review provides an insight to the different molecular mechanisms involved in the development and progression of the AD and potential therapeutic strategies, enlightening perceptions into structural information of conventional and novel targets along with the successful applications of computational approaches for the design of target-specific inhibitors.

Synthesis and Evaluation of the 4-Substituted 2-Hydroxy-5-Iodochalcones and Their 7-Substituted 6-Iodoflavonol Derivatives for Inhibitory Effect on Cholinesterases and β-Secretase

A series of 2-aryl-3-hydroxy-6-iodo-4H-chromen-4-ones substituted at the 7-position with a halogen atom (X = F, Cl and Br) or methoxy group and their corresponding 4-substituted 2-hydroxy-5-iodochalcone precursors were evaluated in vitro for inhibitory effect against acetylcholinesterase (AChE), butyrylcholinesterase (BChE) and β-secretase (BACE1) activities. Although moderate inhibitory effect was observed for the chalcones against AChE, derivatives 2h, 2j and 2n exhibited significant inhibitory effect against BChE and BACE-1. The 2-aryl-7-fluoro-8-iodoflavonols 3b and 3c, on the other hand, exhibited increased activity and selectivity against AChE and reduced effect on BACE-1. The flavonols 3h, 3i, 3k, 3l and 3p exhibited moderate inhibitory effect against AChE, but significant inhibition against BChE. Compounds 2j and 3l exhibited non-competitive mode of inhibition against BACE-1. Molecular docking predicted strong interactions with the protein residues in the active site of BACE-1 implying these compounds bind with the substrate. Similarly docking studies predicted interaction of the most active compounds with both CAS and PAS of either AChE or BChE with mixed type of enzyme inhibition confirmed by kinetic studies.

A patent review of butyrylcholinesterase inhibitors and reactivators 2010-2017

INTRODUCTION

Butyrylcholinesterase (BuChE) has obtained a renewed interest as therapeutic target in Alzheimer's disease (AD), when changes in BuChE activity and expression along disease progression were highlighted as well as correlation between BuChE levels and cognitive function.

AREAS COVERED

During the last eight years, fourteen patents on BuChE inhibitors (BuChEI) have been submitted. Only three of them relate to BuChE selective inhibitors, while four of them focus on multitarget inhibitors which address different key pathological factors other than BuChE. Two patents report on non-selective acetylcholinesterase (AChE)/BuChE inhibitors, while four patents deal with natural compounds and their derivatives. One patent relates to antitoxic agents to treat exposure to ChEI pesticides and nerve agents.

EXPERT OPINION

Increasing evidence supports BuChE as a more beneficial target in moderate-to-severe forms of AD in comparison to the well-known AChE. However, hitting a single pathological target is likely not sufficient to halt the disease progression. Therefore, patented BuChE inhibitors with a multifunctional profile may open new therapeutic avenues, since the additional activities could reinforce the therapeutic effects. Unfortunately, in vivo studies are limited and key parameters, such as ADMET data, are missing. This lack of information makes difficult to forecast the development of patented BuChEIs into effective drug candidates.

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 characterization of new inhibitors of cholinesterases based on N-phenylcarbamates: In vitro study of inhibitory effect, type of inhibition, lipophilicity and molecular docking

Based on current treatment of Alzheimer's disease, where the carbamate inhibitor Rivastigmine is used, two series of carbamate derivatives were prepared: (i) N-phenylcarbamates with additional carbamate group (1-12) and (ii) N-phenylcarbamates with monosaccharide moiety (13-24). All compounds were tested for the inhibitory effect on both of the cholinesterases, electric eel acetylcholinesterase (eeAChE) and butyrylcholinesterase from equine serum (eqBChE) and the inhibitory activity (expressed as IC₅₀ values) was compared with that of the established drugs Galanthamine and Rivastigmine. The compounds with two carbamate groups 1-12 revealed higher inhibitory efficiency on both cholinesterases in compared with monosaccharide derived carbamates 13-24 and with Rivastigmine. The significant decrease of inhibitory efficiency on eqBChE (also for eeAChE but in less manner) was observed after deacetalization of monosaccharide. Moreover, the type of inhibitory mechanism of five chosen compounds was studied. It was found, that compounds with two carbamate groups act presumably via a mixed inhibitory mechanism and the compounds with monosaccharide moiety act as non-competitive inhibitors. The lipophilicity of tested compounds was determined using partition coefficient. Specific positions of the inhibitors in the binding sites of cholinesterases were determined using molecular modeling and the results indicate the importance of phenylcarbamate orientation in the catalytic gorges of both enzymes.

Selective dual cholinesterase inhibitors from Aconitum laeve

New lycoctonine-type dual cholinesterase inhibitor, swatinine-C (1), along with three known norditerpenoid alkaloids, hohenackerine (2), aconorine (5) and lappaconitine (6) and two synthetically known but phytochemically new benzene derivatives, methyl 2-acetamidobenzoate (3) and methyl 4-[2-(methoxycarbonyl)anilino]-4-oxobutanoate (4), was isolated from the roots of A. laeve. Structures of new and known compounds (1-6) were established on the basis of latest spectroscopic techniques and by close comparison with the data available in literature. In vitro, compounds (1-6) were tested against AChE and BChE inhibitory activities. Compounds 1 and 2 showed competitive inhibition against AChE (IC₅₀= 3.7 μM, 4.53 μM) and BChE (IC₅₀= 12.23 μM, 9.94 μM), respectively. Compounds 5 and 6 showed promising noncompetitive type of inhibitory profile against AChE (IC₅₀= 2.51 and 6.13 μM) only. Compounds 3 and 4 showed weak inhibitory profile against both AChE and BChE.

Isolation, crystal structure determination and cholinesterase inhibitory potential of isotalatizidine hydrate from Delphinium denudatum

CONTEXT

Delphinium denudatum Wall (Ranunculaceae) is a rich source of diterpenoid alkaloids and is widely used for the treatment of various neurological disorders such as epilepsy, sciatica and Alzheimer's disease.

OBJECTIVE

The present study describes crystal structure determination and cholinesterase inhibitory potential of isotalatazidine hydrate isolated from the aerial part of Delphinium denudatum.

MATERIALS AND METHODS

Phytochemical investigation of Delphinium denudatum resulted in the isolation of isotalatazidine hydrate in crystalline form. The molecular structure of the isolated compound was established by X-ray diffraction. The structural data (bond length and angles) of the compound were calculated by Density Functional Theory (DFT) using B3LYP/6-31 + G (p) basis set. The cholinesterase inhibitory potential of the isolated natural product was determined at various concentrations (62.5, 125, 250, 500 and 1000 μg/mL) followed by molecular docking to investigate the possible inhibitory mechanism of isotalatazidine hydrate.

RESULTS

The compound crystallized in hexagonal unit cell with space group P65. Some other electronic properties such as energies associated with HOMO-LUMO, band gaps, global hardness, global electrophilicity, electron affinity and ionization potential were also calculated by means of B3LYP/6-31 + G (p) basis set. The compound showed competitive type inhibition of both acetylcholinesterase (AChE) and butyrylcholinesterase (BChE) with IC50 values of 12.13 μM and 21.41 μM, respectively.

DISCUSSION AND CONCLUSION

These results suggest that isotalatazidine hydrate is a potent dual cholinesterase inhibitor and can be used as a target drug in Alzheimer diseases. This is first report indicating isotalatazidine hydrate with anticholinesterase potential.

Isosteroidal alkaloids as potent dual-binding site inhibitors of both acetylcholinesterase and butyrylcholinesterase from the bulbs of Fritillaria walujewii

Five new isosteroidal alkaloids, walujewine A (1), walujewine B (4), walujewine C (5), walujewine D (6), walujewine E (10) were isolated from the bulbs of Fritillaria walujewii together with seven known isosteroidal alkaloids (2, 3, 7-9, 11, 12). Their structures were elucidated on the basis of IR, ESI-MS, HR-ESI-MS, 1D and 2D NMR spectroscopic data analyses and single-crystal X-ray diffraction. All the isolates were tested for ChE inhibiting activity by the Ellman's method. Compounds 3-5 and 8-10 were potent dual AChE-BChE inhibitors, and compound 1 showed highly selective AChE inhibition. The structure-activity relationship of compounds 1-12 was discussed in details. And kinetic analysis showed that compounds 1, 3-5, and 8-10 were mixed-type reversible inhibitors of AChE, simultaneously binding to the catalytic and peripheral anionic sites, which was verified by in silico docking studies. The docking simulation also showed that active compound 3 and 8 created many interactions with the CAS and PAS gorges of BChE, revealing their mixed-type inhibition. ADMET analysis further confirmed the therapeutic potential of some isosteroidal alkaloids based on their high BBB-penetration.

Amino derivatives of platanic acid act as selective and potent inhibitors of butyrylcholinesterase

A set of thirtyfive 30-norlupan derivatives (2-36) was prepared from the natural triterpenoid platanic acid (PA), and the hydroxyl group at C-3, the carboxyl group at C-17 and the carbonyl group at C-20 were modified. These derivatives were tested for their inhibitory activity for the enzymes acetylcholinesterase (AChE, from electric eel) and butyrylcholinesterase (BChE, from equine serum) using Ellman's assay. Extra enzyme kinetic studies were performed. The most active compound was (3β, 20R)-3-acetyloxy-20-amino-30-norlupan-28-oate (32) showing a K_i value of 0.01 ± 0.003 μM for BChE. This compound proved to be a selective (F_B = 851), mixed-type inhibitor for BChE.