Ester derivatives of annulated tetrahydroazocines: A new class of selective acetylcholinesterase inhibitors

Dizocilpine derivatives as neuroprotective NMDA receptor antagonists without psychomimetic side effects

We aimed to prepare novel dibenzo [a,d][7]annulen derivatives that act on N-methyl-d-aspartate (NMDA) receptors with potential neuroprotective effects. Our approach involved modifying the tropane moiety of MK-801, a potent open-channel blocker known for its psychomimetic side effects, by introducing a seven-membered ring with substituted base moieties specifically to alleviate these undesirable effects. Our in silico analyses showed that these derivatives should have high gastrointestinal absorption and cross the blood-brain barrier (BBB). Our pharmacokinetic studies in rats supported this conclusion and confirmed the ability of leading compounds 3l and 6f to penetrate the BBB. Electrophysiological experiments showed that all compounds exhibited different inhibitory activity towards the two major NMDA receptor subtypes, GluN1/GluN2A and GluN1/GluN2B. Of the selected compounds intentionally differing in the inhibitory efficacy, 6f showed high relative inhibition (∼90 % for GluN1/GluN2A), while 3l showed moderate inhibition (∼50 %). An in vivo toxicity study determined that compounds 3l and 6f were safe at 10 mg/kg doses with no adverse effects. Behavioral studies demonstrated that these compounds did not induce hyperlocomotion or impair prepulse inhibition of startle response in rats. Neuroprotective assays using a model of NMDA-induced hippocampal neurodegeneration showed that compound 3l at a concentration of 30 μM significantly reduced hippocampal damage in rats. These results suggest that these novel dibenzo [a,d][7]annulen derivatives are promising candidates for developing NMDA receptor-targeted therapies with minimal psychotomimetic side effects.

Radiosynthesis and whole-body distribution in mice of a 18 F-labeled azepino[4,3-b]indole-1-one derivative with multimodal activity for the treatment of Alzheimer's disease

Recently, the azepino[4,3-b]indole-1-one derivative 1 showed in vitro nanomolar inhibition against butyrylcholinesterase (BChE), the ChE isoform that plays a role in the progression and pathophysiology of Alzheimer's disease (AD), and protects against N-methyl- d-aspartate-induced neuronal toxicity. Three 9-R-substituted (R = F, Br, OMe) congeners were investigated. The 9-F derivative (2a) was found more potent as BChE inhibitors (half-maximal inhibitory concentration value = 21 nM) than 2b (9-Br) and 2c (9-OMe), achieving a residence time (38 s), assessed by surface plasmon resonance, threefold higher than that of 1. To progress in featuring the in vivo pharmacological characterization of 2a, herein the 18 F-labeled congener 2a was synthesized, by applying the aromatic 18 F-fluorination method, and its whole-body distribution in healthy mice, including brain penetration, was evaluated through positron emission tomography imaging. [18 F]2a exhibited a rapid and high brain uptake (3.35 ± 0.26% ID g-1 at 0.95 ± 0.15 min after injection), followed by a rapid clearance (t1/2  = 6.50 ± 0.93 min), showing good blood-brain barrier crossing. After a transient liver accumulation of [18 F]2a, the intestinal and urinary excretion was quantified. Finally, ex vivo pharmacological experiments in mice showed that the unlabeled 2a affects the transmitters' neurochemistry, which might be favorable to reverse cognition impairment in mild-to-moderate AD-related dementias.

In-vitro and in-silico studies of annelated 1,4,7,8-tetrahydroazocine ester derivatives as nanomolar selective inhibitors of human butyrylcholinesterase

Based on previous finding showing 2,3,6,11-tetrahydro-1H-azocino[4,5-b]indole as suitable scaffold of novel inhibitors of acetylcholinesterase (AChE), a main target of drugs for the treatment of Alzheimer's disease and related dementias, herein we investigated diverse newly and previously synthesized β-enamino esters (and ketones) derivatives of 1,4,7,8-tetrahydroazocines (and some azonines) fused with benzene, 1H-indole, 4H-chromen-4-one and pyrimidin-4(3H)-one. Twenty derivatives of diversely annelated eight-to-nine-membered azaheterocyclic ring, prepared through domino reaction of the respective tetrahydropyridine and azepine with activated alkynes, were assayed for the inhibitory activity against AChE and butyrylcholinesterase (BChE). As a major outcome, compound 7c, an alkylamino derivative of tetrahydropyrimido[4,5-d]azocine, was found to be a highly potent BChE-selective inhibitor, which showed a noncompetitive/mixed-type inhibition mechanism against human BChE with single digit nanomolar inhibition constant (Ki = 7.8 ± 0.2 nM). The four-order magnitude BChE-selectivity of 7c clearly reflects the effect of lipophilicity upon binding to the BChE binding cavity. The ChEs' inhibition data, interpreted by chemoinformatic tools and an in-depth in-silico study (molecular docking combined with molecular dynamics calculations), not only highlighted key structural factors enhancing inhibition potency and selectivity toward BChE, but also shed light on subtle differences distinguishing the binding sites of equine BChE from the recombinant human BChE. Compound 7c inhibited P-glycoprotein with IC50 of 0.27 μM, which may support its ability to permeate blood-brain barrier, and proved to be no cytotoxic in human liver cancer cell line (HepG2) at the BChE bioactive concentrations. Overall, the biological profile allows us to envision 7c as a promising template to improve design and development of BChE-selective ligands of pharmaceutical interest, including inhibitors and fluorogenic probes.

Toward the cholinesterase inhibition potential of TADDOL derivatives: Seminal biological and computational studies

Alzheimer's disease (AD) is a degenerative neurological disease characterized by gradual loss of cognitive skills and memory. The exact pathogenesis involved still remains unrevealed, but several studies indicate the involvement of an array of different enzymes, underlining the multifactorial character of the disease. Inhibition of these enzymes is therefore a powerful approach in the development of AD treatments, with promising candidates, including acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and monoamine oxidase. Interestingly, AChE is the target of a major pesticide family (organophosphates), with several reports indicating an intersection between the pesticide's activity and AD. In this study, various TADDOL derivatives were synthesized and their in vitro activities as AChE/BuChE inhibitors as well as their antioxidant activities were studied. Molecular modeling studies revealed the capability of TADDOL derivatives to bind to AChE and induce inhibition, especially compounds 2b and 3c furnishing IC₅₀ values of 36.78 ± 8.97 and 59.23 ± 5.31 µM, respectively. Experimental biological activities and molecular modeling studies clearly demonstrate that TADDOL derivatives with specific stereochemistry have an interesting potential for the design of potent AChE inhibitors. The encouraging results for compounds 2b and 3c indicate them as promising scaffolds for selective and potent AChE inhibitors.

Away from Flatness: Unprecedented Nitrogen-Bridged Cyclopenta[a]indene Derivatives as Novel Anti-Alzheimer Multitarget Agents

Nature-inspired, bridged polycyclic molecules share low similarity with currently available drugs, containing preferentially planar and/or achiral moieties. This "Escape from Flatland" scenario, aimed at exploring pharmacological properties of atypical molecular scaffolds, finds interest in synthetic routes leading to tridimensional-shaped molecules. Herein we report on the synthesis of N-bridged cyclopenta[a]indene derivatives, achieved through microwave-assisted thermal rearrangement of allene 3-benzazecines with high diastereoselectivity. The biological evaluation disclosed selective inhibition of human acetylcholinesterase or butyrylcholinesterase, depending on the substitution around the molecular core, which was rationalized by means of docking simulations. The most potent BChE inhibitor 31 was effective in neuroprotection from glutamatergic excitotoxicity and displayed low intrinsic cytotoxicity and good brain penetration. Overall, compound 31 and its close congeners 34 and 35 acted as multitarget agents addressing different biological events involved in neurodegeneration, particularly in the progression of Alzheimer's disease.

Interplay between Ionization and Tautomerism in Bioactive β-Enamino Ester-Containing Cyclic Compounds: Study of Annulated 1,2,3,6-Tetrahydroazocine Derivatives

Depending on the chemical scaffold, a bioactive species could reflect the interplay between ionization and tautomerism, which is often complicated by the possibility of populating different conformational states, in the case of flexible ligands. In this context, theoretical methods can be valuable to discern the role of these factors, as shown here for β-enamino esters of 1,2,3,6-tetrahydroazocino-fused ring systems, some of which had proven to be suitable scaffolds for designing novel acetylcholinesterase inhibitors. The compounds investigated herein form two clusters with distinctive experimental pK_a values (i.e., α,β-diesters and β-esters ranging within 6.1-7.3 and 8.2-9.0 pK_a intervals, respectively), which implies a drastic difference in the most populated species at physiological conditions. While chemoinformatic tools did not provide a consistent description of the actual pK_a values, the theoretical analysis performed for the protonated and neutral species of these compounds revealed a marked change in the tautomeric preference of the tetrahydroazocine moiety upon (de)protonation. Excellent agreement between the calculated and experimental pK_a values was found when the tautomeric preference of the protonated and neutral species was considered. Overall, this study highlights the potential use of high-level computational methods to disclose the mutual influence between ionization, tautomerism, and conformational preferences in multifunctional (bio)organic compounds.

Investigating 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole as scaffold of butyrylcholinesterase-selective inhibitors with additional neuroprotective activities for Alzheimer's disease

Due to the role of butyrylcholinesterase (BChE) in acetylcholine hydrolysis in the late stages of the Alzheimer's disease (AD), inhibitors of butyrylcholinesterase (BChE) have been recently envisaged, besides acetylcholinesterase (AChE) inhibitors, as candidates for treating mild-to-moderate AD. Herein, synthesis and AChE/BChE inhibition activity of some twenty derivatives of 1,2,3,4,5,6-hexahydroazepino[4,3-b]indole (HHAI) is reported. Most of the newly synthesized HHAI derivatives achieved the inhibition of both ChE isoforms with IC₅₀s in the micromolar range, with a structure-dependent selectivity toward BChE. Apparently, molecular volume and lipophilicity do increase selectivity toward BChE, and indeed the N²-(4-phenylbutyl) HHAI derivative 15d, which behaves as a mixed-type inhibitor, resulted the most potent (IC₅₀ 0.17 μM) and selective (>100-fold) inhibitor toward either horse serum and human BChE. Moreover, 15d inhibited in vitro self-induced aggregation of neurotoxic amyloid-β (Aβ) peptide and displayed neuroprotective effects in neuroblastoma SH-SY5Y cell line, significantly recovering (P < 0.001) cell viability when impaired by Aβ_1-42 and hydrogen peroxide insults. Overall, this study highlighted HHAI as useful and versatile scaffold for developing new small molecules targeting some enzymes and biochemical pathways involved in the pathogenesis of AD.

Synthesis of 1-(para-methoxyphenyl)tetrazolyl-Substituted 1,2,3,4-Tetrahydroisoquinolines and Their Transformations Involving Activated Alkynes

1-(p-Methoxyphenyl)tetrazolyl-substituted 6,7-dimethoxy(6,7-methylenedioxy)-1,2,3,4-tetrahydroisoquinolines formed tetrazolyl-substituted azocines in high yields by using activated alkynes. Unsubstituted at 6,7,8-aromatic fragment 1-tetrazolylisoquinoline interacted in several pathways forming tetrazolyl-substituted azocines, 1-tetrazolyl-1-R-vinylisoquinolines and 3-azaspiro[5.5]undeca-1,7,9-triene.

Mannich base approach to 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone: A water-soluble prodrug for a multitarget inhibition of cholinesterases, beta-amyloid fibrillization and oligomer-induced cytotoxicity

Targeting protein aggregation for the therapy of neurodegenerative diseases remains elusive for medicinal chemists, despite a number of small molecules known to interfere in amyloidogenesis, particularly of amyloid beta (Aβ) protein. Starting from previous findings in the antiaggregating activity of a class of indolin-2-ones inhibiting Aβ fibrillization, 5-methoxyisatin 3-(4-isopropylphenyl)hydrazone 1 was identified as a multitarget inhibitor of Aβ aggregation and cholinesterases with IC₅₀s in the low μM range. With the aim of increasing aqueous solubility, a Mannich-base functionalization led to the synthesis of N-methylpiperazine derivative 2. At acidic pH, an outstanding solubility increase of 2 over the parent compound 1 was proved through a turbidimetric method. HPLC analysis revealed an improved stability of the Mannich base 2 at pH2 along with a rapid release of 1 in human serum as well as an outstanding hydrolytic stability of the parent hydrazone. Coincubation of Aβ_1-42 with 2 resulted in the accumulation of low MW oligomers, as detected with PICUP assay. Cell assays on SH-SY5Y cells revealed that 2 exerts strong cytoprotective effects in both cell viability and radical quenching assays, mainly related to its active metabolite 1. These findings show that 2 drives the formation of non-toxic, off-pathway Aβ oligomers unable to trigger the amyloid cascade and toxicity.

Discovery of Potent Dual Binding Site Acetylcholinesterase Inhibitors via Homo- and Heterodimerization of Coumarin-Based Moieties

Acetylcholinesterase (AChE) inhibitors still comprise the majority of the marketed drugs for Alzheimer's disease (AD). The structural arrangement of the enzyme, which features a narrow gorge that separates the catalytic and peripheral anionic subsites (CAS and PAS, respectively), inspired the development of bivalent ligands that are able to bind and block the catalytic activity of the CAS as well as the role of the PAS in beta amyloid (Aβ) fibrillogenesis. With the aim of discovering novel AChE dual binders with improved drug-likeness, homo- and heterodimers containing 2H-chromen-2-one building blocks were developed. By exploring diverse linkages of neutral and protonatable amino moieties through aliphatic spacers of different length, a nanomolar bivalent AChE inhibitor was identified (3-[2-({4-[(dimethylamino)methyl]-2-oxo-2H-chromen-7-yl}oxy)ethoxy]-6,7-dimethoxy-2H-chromen-2-one (6 d), IC₅₀ =59 nm) from originally weakly active fragments. To assess the potential against AD, the disease-related biological properties of 6 d were investigated. It performed mixed-type AChE enzyme kinetics (inhibition constant K_i =68 nm) and inhibited Aβ self-aggregation. Moreover, it displayed an outstanding ability to protect SH-SY5Y cells from Aβ_1-42 damage.

First synthesis of heterocyclic allenes – benzazecine derivatives

Benzazecines with an allene fragment were prepared for the first time and in high yields via tandem reaction of 1-phenylethynyl-1-methyl(benzyl)-1,2,3,4-tetrahydroisoquinolines with activated alkynes in trifluoroethanol.

Lipophilicity of novel antitumour and analgesic active 8-aryl-2,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazine-3,4-dione derivatives determined by reversed-phase HPLC and computational methods

Eight novel antitumour and analgesic active 8-aryl-2,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazine-3,4-diones (1-8) have been obtained as a bioactive set of substances and their lipophilicity has been studied. The logk values of fifteen reference compounds and eight newly synthesised imidazotriazine-3,4-dione derivatives were determined by reversed-phase high performance liquid chromatography (RP-HPLC) using mixtures of methanol and water as mobile phases with different methanol concentrations. The relationships between logk values of a set of reference compounds (fifteen compounds) and investigated ones (eight compounds) and concentration of methanol was used for determination of the logkwater values by extrapolation. The partition coefficients (logP) values for reference compounds measured experimentally were taken from the literature. The calibration equation was then obtained for the standards of known lipophilicity (logPHPLC) and logkwater. In next step the partition coefficients of new synthesised solutes were calculated from the calibration equation. For the comparison purpose, additionally the partition coefficients (logPcalc.) of the examined imidazotriazine-3,4-diones were calculated by means of the Pallas 3.1.1.2. software. It was found that logkwater values as a lipophilicity measure of derivatives correlate well with partition coefficients measured experimentally (logPHPLC). Correlation between the logPHPLC and the logarithm of partition coefficient calculated by Pallas software (logPcalc.) is not so satisfactory as that for values determined experimentally. Furthermore, it has been found that the lipophilicity variation of investigated imidazotriazine-3,4-diones (1-8) correlates well with their acute toxicity expressed as log(1/LD50). The drug-likeness of all the bioactive 8-aryl-2,6,7,8-tetrahydroimidazo[2,1-c][1,2,4]triazine-3,4-diones was assessed on the basis of their structural properties by applying Lipniski's rule of five. The solutes have all four parameters important for the favourable pharmacokinetics in the human body that would make them likely orally active drugs in humans.

Molecular interactions of cholinesterases inhibitors using in silico methods: current status and future prospects

Alzheimer's disease (AD) is a neurodegenerative disorder characterized by a low amount of acetylcholine (ACh) in hippocampus and cortex. Acetylcholinesterase (AChE) is one of the most important enzymes in many living organisms including human being and other vertebrates, insects like mosquitoes, among others. Several reports have been published where it has been clearly shown that the genesis of amyloid protein plaques associated with AD is connected to modifications of both AChE and butyrylcholinesterase (BChE), since the plaque is significantly decreased in AD patients using cholinesterase inhibitors (ChEIs). This review gives some examples of these inhibitors discovered during past couple of years that have shown very prominent interactions at the active site triad of the proteins as well as different other parts of the active site like, peripheral anionic site (PAS), oxyanionic hole, anionic subsite or acyl binding pocket (ABP). Most of the inhibition and their interactions have been visualized by X-ray crystallography, but some of the other inhibitors have been studied either by molecular docking or molecular dynamic (MD) simulations or by both the in silico methods. Some of these prominent studies have been crucially observed and reported here.

Acetylcholinesterase inhibitory effect of lignans isolated fromSchizandra chinensis

The hexane extract of the fruit of Schizandra chinensis (Schisandraceae) was found to show significant inhibition of the activity of acetylcholinesterase enzyme (AChE). In further studies, fourteen lignans were isolated, and evaluated for their inhibitory effect on AChE. The compounds having both aromatic methylenedioxy and hydroxyl groups on their cyclooctadiene ring, such as gomisin C (6), gomisin G (7), gomisin D (8), schisandrol B (11) and gomisin A (13), entirely inhibited AChE in dose dependent manners, with IC50 values of 6.71 +/- 0.53, 6.55 +/- 0.31, 7.84 +/- 0.62, 12.57 +/- 1.07 and 13.28 +/- 1.68 microM, respectively. These results indicate that the lignans could potentially be a potent class of AChE inhibitors.