Syntheses and characterization of novel oxoisoaporphine derivatives as dual inhibitors for cholinesterases and amyloid beta aggregation

Recent advances in the natural product analogues for the treatment of neurodegenerative diseases

Neurodegenerative diseases (NDs) represent a hallmark of numerous incapacitating and untreatable conditions, the incidence of which is escalating swiftly, exemplified by Alzheimer's disease and Parkinson's disease. There is an urgent necessity to create pharmaceuticals that exhibit high efficacy and minimal toxicity in order to address these debilitating diseases. The structural complexity and diversity of natural products confer upon them a broad spectrum of biological activities, thereby significantly contributing to the history of drug discovery. Nevertheless, natural products present challenges in drug discovery, including time-consuming separation processes, low content, low bioavailability, and other related issues. To address these challenges, numerous analogs of natural products have been synthesized. This methodology enables the rapid synthesis of analogs of natural products with the potential to serve as lead compounds for drug development, thereby paving the way for the discovery of novel pharmaceuticals. This paper provides a summary of 127 synthetic analogues featuring various natural product structures, including flavonoids, alkaloids, coumarins, phenylpropanoids, terpenoids, polyphenols, and amides. The compounds are categorized based on their efficacy in treating various diseases. Furthermore, this article delves into the structure-activity relationship (SAR) of certain analogues, offering a thorough point of reference for the systematic development of pharmaceuticals aimed at addressing neurodegenerative conditions.

Rare oxoisoaporphine alkaloids from Menispermum dauricum with potential anti-inflammatory activity

Eleven alkaloids including four previously undescribed oxoisoaporphine alkaloids, menisoxoisoaporphines A-D (1-4), four known analogues (5-8), and three aporphine alkaloids (9-11), were isolated and identified from the rhizomes of Menispermum dauricum. Their structures were elucidated by extensive spectroscopic data and single-crystal X-ray diffraction analyses. Among them, compounds 1 and 4 were the first samples of oxoisoaporphine with C-6 isopentylamino moiety, and 2 was a rare C-4 methylation product of oxoisoaporphine alkaloid. The in vitro anti-inflammatory activity of compounds 1-11 was performed by evaluating the inhibition of NO level in LPS-induced RAW264.7 macrophages. Among them, compound 4 exhibited the most potent NO inhibition activity with an IC50 value of 1.95 ± 0.33 μM. The key structure-activity relationships of those oxoisoaporphine alkaloids for anti-inflammatory effects have been summarized.

Alkaloids as drug leads in Alzheimer's treatment: Mechanistic and therapeutic insights

Alzheimer's disease (AD) has few effective treatment options and continues to be a major global health concern. AD is a neurodegenerative disease that typically affects elderly people. Alkaloids have potential sources for novel drug discovery due to their diverse chemical structures and pharmacological activities. Alkaloids, natural products with heterocyclic nitrogen-containing structures, are considered potential treatments for AD. This review explores the neuroprotective properties of alkaloids in AD, focusing on their ability to regulate pathways such as amyloid-beta aggregation, oxidative stress, synaptic dysfunction, tau hyperphosphorylation, and neuroinflammation. The FDA has approved alkaloids such as acetylcholinesterase inhibitors like galantamine and rivastigmine. This article explores AD's origins, current market medications, and clinical applications of alkaloids in AD therapy. This review explores the development of alkaloid-based drugs for AD, focusing on pharmacokinetics, blood-brain barrier penetration, and potential adverse effects. Future research should focus on the clinical evaluation of promising alkaloids, developing recently discovered alkaloids, and the ongoing search for novel alkaloids for medical treatment. A pharmaceutical option containing an alkaloid may potentially slow down the progression of AD while enhancing its symptoms. This review highlights the potential of alkaloids as valuable drug leads in treating AD, providing a comprehensive understanding of their mechanisms of action and therapeutic implications.

The Influence of Selected Antipsychotic Drugs on Biochemical Aspects of Alzheimer's Disease

The aim of this study was to assess the potency of selected antipsychotic drugs (haloperidol (HAL), bromperidol (BRMP), benperidol (BNP), penfluridol (PNF), pimozide (PIM), quetiapine (QUET) and promazine (PROM)) on the main pathological hallmarks of Alzheimer's disease (AD). Binary mixtures of donepezil and antipsychotics produce an anti-BuChE effect, which was greater than either compound alone. The combination of rivastigmine and antipsychotic drugs (apart from PNF) enhanced AChE inhibition. The tested antipsychotics (excluding HAL and PNF) significantly reduce the early stage of Aβ aggregation. BRMP, PIM, QUET and PROM were found to substantially inhibit Aβ aggregation after a longer incubation time. A test of human erythrocytes hemolysis showed that short-term incubation of red blood cells (RBCs) with QUET resulted in decreased hemolysis. The antioxidative properties of antipsychotics were also proved in human umbilical vein endothelial cells (HUVEC); all tested drugs were found to significantly increase cell viability. In the case of astrocytes, BNP, PNF, PIM and PROM showed antioxidant potential.

Development of oxoisoaporphine derivatives with topoisomerase I inhibition and reversal of multidrug resistance in breast cancer MCF-7/ADR cells

A series of oxoisoaporphine derivatives with topoisomerase I inhibition and cytotoxic activities. Among them, compound 14 showed the most potent cytotoxic activity against all cancer cell lines tested, and substantially lower cytotoxicity to LO2 cells. Molecular docking studies, dynamics simulation and a follow-up enzyme inhibition assay indicated that 14 could interfere with DNA and significantly inhibit the activity of topoisomerase I. Further mechanistic studies revealed that 14 could arrest cell cycle at the G1 phase, and finally killed MCF-7 cells via apoptosis. In addition, 14 exhibited remarkable chemoreversal ability on multidrug-resistant MCF-7/ADR breast cancer cells. Some of its mechanisms may be related to inhibition of MCF-7/ADR P-gp-mediated Rhodamine (Rh123) efflux function and expression level, as well as inhibition of ROS, increase of ADR accumulation in MCF7/ADR cells, and enhancement of ADR in inducing apoptosis of MCF7/ADR cells. As 14 has little toxic and side effects, it may have the potential for further research.

Pharmacokinetics, tissue distribution and excretion of 6-O-demethylmenisporphine, a bioactive oxoisoaporphine alkaloid from Menispermi Rhizoma, as determined by a HPLC-MS/MS method

6-O-demethylmenisporphine, a major active oxoisoaporphine alkaloid isolated from Menispermi Rhizoma, has been confirmed to possess significant bioactivities, including anti-cancer and anti-hypoxia effects. However, few researches on quantifying 6-O-demethylmenisporphine in biosamples have been performed. In this research, a sensitive HPLC-MS/MS approach for determining 6-O-demethylmenisporphine in various biological matrices (plasma, tissue, urine, bile and feces) of rat has been constructed. Carbamazepine was chosen as the internal standard (IS). All biosamples were prepared using a simple one-step acetonitrile precipitation. A Capcell Pak C18 column coupled with an isocratic mobile phase consisted of acetonitrile (0.1% formic acid)-water (90:10, v/v), was employed to separate 6-O-demethylmenisporphine from endogenous interferences. Peak responses were detected by multiple reaction monitoring (MRM) transitions with m/z 308.0 → 264.9 for 6-O-demethylmenisporphine and m/z 237.0 → 194.1 for IS in positive-ion mode. The approach exhibited perfect linearity over a range of 5-2000 ng/mL for plasma and 2-1000 ng/mL for various tissue, urine, bile and feces. The lower limit of quantification (LLOQ) for analyte among different biological samples ranged from 2 ng/mL to 5 ng/mL. The newly established method was simple, efficient and sensitive, which was successfully applied to investigate the absorption, distribution, and excretion of 6-O-demethylmenisporphine after oral dosing to rats. The results indicated that 6-O-demethylmenisporphine could be well absorbed into blood circulation and widely distributed in various tissues after oral dosing, the oral bioavailability was up to 51.52%. Meanwhile, it was widely metabolized in vivo and eliminated as the metabolites, the unconverted form was excreted mainly by feces route. The bioavailability, tissue distribution and excretion characteristics of 6-O-demethylmenisporphine were firstly revealed, which will provide references for further development of 6-O-demethylmenisporphine as an anti-tumor drug candidate.

Anticholinesterase Activity of Cinnamic Acids Derivatives: In Vitro, In Vivo Biological Evaluation, and Docking Study

Background:

Acetylcholine deficiency in the hippocampus and cortex, aggregation of amyloid-beta, and beta-secretase overactivity have been introduced as the main reasons in the formation of Alzheimer’s disease.

Objective:

A new series of cinnamic derived acids linked to 1-benzyl-1,2,3-triazole moiety were designed, synthesized, and evaluated for their acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitory activities.

Methods:

Colorimetric Ellman’s method was used for the determination of IC50% of AchE and BuChE inhibitory activity. The kinetic studies, neuroprotective activity, BACE1 inhibitory activity, evaluation of inhibitory potency on Aβ1-42 self-aggregation induced by AchE, and docking study were performed for studying the mechanism of action.

Results:

Some of the synthesized compounds, compound 7b-4 ((E)-3-(3,4-dimethoxyphenyl)-N-((1- (4-fluorobenzyl)-1H-1,2,3-triazole-4-yl) methyl) acrylamide) depicted the most potent acetylcholinesterase inhibitory activities ( IC50 = 5.27 μM ) and compound 7a-1 (N- ( (1- benzyl- 1H- 1, 2, 3- triazole - 4-yl) methyl) cinnamamide) demonstrated the most potent butyrylcholinesterase inhibitory activities (IC50 = 1.75 μM). Compound 7b-4 showed neuroprotective and β-secretase (BACE1) inhibitory activitiy. In vivo studies of compound 7b-4 in Scopolamine-induced dysfunction confirmed memory improvement.

Conculusion:

It should be noted that molecular modeling (compounds 7b-4 and 7a-1) and kinetic studies (compounds 7a-1 and 7b-4) showed that these synthesis compounds interacted simultaneously with both the catalytic site (CS) and peripheral anionic site (PAS) of AChE and BuChE.

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.

Aporphines and Alzheimer's Disease: Towards a Medical Approach Facing the Future

Alzheimer's disease (AD) is a neurodegenerative disease that reduces progressively the part cognitive inside the Central Nervous System (CNS) and that affects the memories and emotions of the patients who endure this disease. Many drugs have been assessed in patients with different evolutionary grades of the disease, having diverse results, depending on the used compound. Some of them afford dependence and many others with side effects that affect the emotional part and the economic cost of the treatment. The natural products have diversified their therapeutic uses, and have been used in the treatment of AD in accordance with its easy medical administration and bioavailability. In this review, the use of aporphines in nature for treating Alzheimer's disease, alkaloids isolated from natural and/or synthetic sources have been used principally as cholinesterase inhibitors (acetyl- and butyrylcholinesterase) as galantamine, for instance, though its use has been questioned for being slightly effective or marginal. The use of aporphines give the possibility of generating new treatments with nitrogenous chemical structures of diverse complexity and that are focused in this review comparatively and with real therapeutic scopes.

Cascade intramolecular imidoylation and C–H activation/annulation of benzimidoyl chlorides with alkynes: one-pot synthesis of 7H-dibenzo[de,h]quinoline analogues

Described herein is a cascade Lewis acid-promoted intramolecular Friedel–Crafts-type imidoylation and Rh(iii)-catalyzed C–H activation/annulation of benzimidoyl chlorides and alkynes, providing a divergent synthetic shortcut to 7H-dibenzo[de,h]quinoline analogues.

Oxoisoaporphine Alkaloids: Prospective Anti-Alzheimer's Disease, Anticancer, and Antidepressant Agents

Oxoisoaporphine alkaloids are a family of oxoisoquinoline-derived alkaloids that were first isolated from the rhizome of Menispermum dauricum DC. (Menispermaceae). It has been demonstrated that oxoisoaporphine alkaloids possess various biological properties, such as cholinesterase and β-amyloid inhibition, acting as a topoisomerase intercalator, monoamine oxidase A inhibition, and are expected to become anti-Alzheimer's disease, anticancer, and antidepressant drugs. This review provides an overview of natural sources, synthetic routes, bioactivities, structure-function relationship, and modification investigations into oxoisoaporphine alkaloids, with the aim of providing references to the structure-activity relationships for the design and development of oxoisoaporphine derivatives with higher efficacy and therapeutic potential.

Microwave-assisted extraction in combination with HPLC-UV for quantitative analysis of six bioactive oxoisoaporphine alkaloids in Menispermum dauricum DC

A novel and reliable method based on microwave-assisted extraction (MAE) followed by HPLC-UV was developed and validated for the simultaneous quantification of six pharmacologically important oxoisoaporphine alkaloids in the total plants of Menispermum dauricum DC. The optimal MAE extraction condition was performed at 60°C for 11 min with ethanol-water (70:30, v/v) as the extracting solvent, and the solvent to solid ratio was 20:1. Chromatographic separation was achieved on a reversed-phase YMC C18 column (250 × 4.6 mm, i.d., 5 µm) with a gradient mobile phase consisting of A (1% aqueous formic acid) and B (acetonitrile containing 1% formic acid) at a flow rate of 1.5 mL/min. The detection wavelength was set at 422 nm. Excellent linearity over the investigated concentration ranges was observed with values of r >0.999 for all analytes. The method developed was validated with acceptable sensitivity, intra- and inter-day precision and extraction recoveries. It was successfully applied to the determination of six alkaloids in Menispermum dauricum DC from different sources and different parts of Menispermum dauricum DC. The results obtained indicated that the method is suitable for the quality control of Menispermum dauricum DC.

(-)-Meptazinol-melatonin hybrids as novel dual inhibitors of cholinesterases and amyloid-β aggregation with high antioxidant potency for Alzheimer's therapy

The multifactorial pathogenesis of Alzheimer's disease (AD) implicates that multi-target-directed ligands (MTDLs) intervention may represent a promising therapy for AD. Amyloid-β (Aβ) aggregation and oxidative stress, two prominent neuropathological hallmarks in patients, play crucial roles in the neurotoxic cascade of this disease. In the present study, a series of novel (-)-meptazinol-melatonin hybrids were designed, synthesized and biologically characterized as potential MTDLs against AD. Among them, hybrids 7-7c displayed higher dual inhibitory potency toward cholinesterases (ChEs) and better oxygen radical absorbance capacity (ORAC) than the parental drugs. Furthermore, compound 7c could effectively inhibit Aβ self-aggregation, showed favorable safety and the blood-brain barrier (BBB) permeability. Therefore, 7c may serve as a valuable candidate that is worthy of further investigations in the treatment of AD.

Gallic acid, one of the components in many plant tissues, is a potential inhibitor for insulin amyloid fibril formation

Proteins under stressful conditions can lead to the formation of an ordered self-assembled structure, referred to as amyloid fibrils, to which many neurodegenerative diseases such as Type II diabetes, Alzheimer's, Parkinson's, Huntington's, etc., are attributed. Inhibition of amyloid fibril formation using natural products is one of the main therapeutic strategies to prevent the progression of these diseases. Polyphenols are the mostly consumed as antioxidants in a human nutrition. Herein, we have studied the effect of a simple polyphenol, gallic acid (GA), one of the main components in plant tissues, especially in tea leaves, on the insulin amyloid fibril formation. Different biophysical characterizations such as turbidity, atomic force microscopy (AFM), Thioflavin T (ThT) assays, circular dichroism, and Fourier transform-infrared spectroscopy have been used to analyze the inhibition of amyloid fibril formation. The occurrence of fibrils in an AFM image and ThT fluorescence enhancement confirms the formation of insulin amyloid fibrils when incubated under acidic pH 2 at 65 °C. In the presence of GA, absence of fibrils in AFM image and no change in the intensity of ThT fluorescence confirms the inhibition of insulin amyloid fibrils by GA. Spectroscopic results reveal that GA inhibits the conformational transition of α-helix → β-sheet, which is generally induced during the insulin fibril formation. It was found that the inhibitory effect of GA is concentration dependent and non-linear. Based on the observed results, we propose that GA interacts with native insulin, preventing nuclei formation, which is essential for fibril growth, thereby inhibiting the amyloid fibril formation. The present results thus demonstrate that GA can effectively inhibit insulin amyloid fibril formation in vitro.

Design, synthesis and biological evaluation of benzylisoquinoline derivatives as multifunctional agents against Alzheimer's disease

A novel series of benzylisoquinoline derivatives were designed, synthesized, and evaluated as multifunctional agents against Alzheimer's disease (AD). The screening results showed that most of the compounds significantly inhibited cholinesterases (ChEs), human cholinesterases (h-ChEs) and self-induced β-amyloid (Aβ) aggregation. In particular, compound 9k showed the strongest acetylcholinesterase (AChE) inhibitory activity, being 1000-fold and 3-fold more potent than its precursor benzylisoquinoline (10) and the positive control galanthamine, respectively. In addition, 9k was a moderately potent inhibitor for h-ChEs. Compared with precursor benzylisoquinoline (36.0% at 20μМ), 9k (78.4% at 20μМ) could further inhibit Aβ aggregation. Moreover, 9k showed low cell toxicity in human SH-SY5Y neuroblastoma cells. Therefore, compound 9k might be a promising lead compound for AD treatment.

Syntheses and evaluation of novel isoliquiritigenin derivatives as potential dual inhibitors for amyloid-beta aggregation and 5-lipoxygenase

A series of new isoliquiritigenin (ISL) derivatives were synthesized and evaluated as dual inhibitors for amyloid-beta (Aβ) aggregation and 5-lipoxygenase (5-LO). It was found that all these synthetic compounds inhibited Aβ (1-42) aggregation effectively with their IC₅₀ values ranged from 2.2 ± 1.5 μM to 23.8 ± 2.0 μM. These derivatives also showed inhibitory activity to 5-LO with their IC50 values ranged from 6.1 ± 0.1 μM to 35.9 ± 0.3 μM. Their structure-activity relationships (SAR) and mechanisms of inhibitions were studied. This study provided potentially important information for further development of ISL derivatives as multifunctional agents for Alzheimer's disease (AD) treatment.

Structure-based search for new inhibitors of cholinesterases

Cholinesterases are important biological targets responsible for regulation of cholinergic transmission, and their inhibitors are used for the treatment of Alzheimer’s disease. To design new cholinesterase inhibitors, of different structure-based design strategies was followed, including the modification of compounds from a previously developed library and a fragment-based design approach. This led to the selection of heterodimeric structures as potential inhibitors. Synthesis and biological evaluation of selected candidates confirmed that the designed compounds were acetylcholinesterase inhibitors with IC₅₀ values in the mid-nanomolar to low micromolar range, and some of them were also butyrylcholinesterase inhibitors.

3D-QSAR studies of azaoxoisoaporphine, oxoaporphine, and oxoisoaporphine derivatives as anti-AChE and anti-AD agents by the CoMFA method

In the present study, a series of novel azaoxoisoaporphine derivatives were reported and their inhibitory activities toward acetylcholinesterase (AChE), butyrylcholinesterase (BuChE), and Aβ aggregation were evaluated. The new compounds remained high inhibitory potency on Aβ aggregation, with inhibitory activity from 29.42% to 89.63% at a concentration of 10μM, but had no action on AChE or BuChE, which was very different from our previously reported oxoaporphine and oxoisoaporphine derivatives. By 3D-QSAR studies, we constructed a reliable CoMFA model (q(2)=0.856 and r(2)=0.986) based on the inhibitory activities toward AChE and discovered key information on structure and anti-AChE activities among the azaoxoisoaporphine, oxoaporphine, and oxoisoaporphine derivatives. The model was further confirmed by the test-set validation (q(2)=0.873, r(2)=0.937, and slope k=0.902) and Y-randomization examination. The statistically significant and physically meaningful 3D-QSAR/CoMFA model provided better insight into understanding the inhibitory behaviors of those chemicals, which may provide useful information for the rational molecular design of azaoxoisoaporphine derivatives anti-AChE and anti-AD agents.

Host-guest interaction between new nitrooxoisoaporphine and β-cyclodextrins: synthesis, electrochemical, electron spin resonance and molecular modeling studies

A new nitrooxoisoaporphine derivative was synthetized and characterized by cyclic voltammetry and electron spin resonance. Its aqueous solubility was improved by complexes formation with β-cyclodextrin, heptakis(2,6-di-O-methyl)-β-cyclodextrin and (2-hydroxypropyl)-β-cyclodextrin. In order to assess the inclusion degree reached by nitrooxoisoaporphine in cyclodextris cavity, the stability constants of formation of the complexes were determined by phase-solubility measurements obtaining in all cases a type-A(L) diagram. Moreover, electrochemical studies were carried out, where the observed change in the EPC value indicated a lower feasibility of the nitro group reduction. Additionally, a detailed spatial configuration is proposed for inclusion of derivate within the cyclodextrins cavity by 2D NMR techniques. Finally, these results are further interpreted by means of molecular modeling studies. Thus, theoretical results are in complete agreement with the experimental data.