Photoswitchable Pseudoirreversible Butyrylcholinesterase Inhibitors Allow Optical Control of Inhibition in Vitro and Enable Restoration of Cognition in an Alzheimer's Disease Mouse Model upon Irradiation

A Bright Future for Photopharmaceuticals Addressing Central Nervous System Disorders: State of the Art and Challenges Toward Clinical Translation

Photopharmacology is an innovative approach that uses light to activate drugs. This method offers the potential for highly localized and precise drug activation, making it particularly promising for the treatment of neurological disorders. Despite the enticing prospects of photopharmacology, its application to treat human central nervous system (CNS) diseases remains to be demonstrated. In this review, we provide an overview of prominent strategies for the design and activation of photopharmaceutical agents in the field of neuroscience. Photocaged and photoswitchable drugs and bioactive molecules are discussed, and an instructive list of examples is provided to highlight compound design strategies. Special emphasis is placed on photoactivatable compounds for the modulation of glutamatergic, GABAergic, dopaminergic, and serotonergic neurotransmission for the treatment of neurological conditions, as well as various photoresponsive molecules with potential for improved pain management. Compounds holding promise for clinical translation are discussed in-depth and their potential for future applications is assessed. Neurophotopharmaceuticals have yet to achieve breakthrough in the clinic, as both light delivery and drug design have not reached full maturity. However, by describing the current state of the art and providing illustrative case studies, we offer a perspective on future opportunities in the field of neurophotopharmacology focused on addressing CNS disorders.

Small-Molecule Fluorescent Probes for Butyrylcholinesterase

Butyrylcholinesterase plays an indispensable role in organisms, and its abnormal expression poses a significant threat to human health and safety, covering various aspects including liver-related diseases, diabetes, obesity, cardiovascular and cerebrovascular diseases, and neurodegenerative diseases. In addition, toxic substances such as organophosphorus and carbamate pesticides markedly inhibit BChE activity. BChE activity serves as a critical parameter for the clinical diagnosis of acute organophosphorus pesticide poisoning and the evaluation of organophosphorus and carbamate pesticide residues. Therefore, the accurate and reliable detection of butyrylcholinesterase activity is particularly urgent and important for in-depth analysis of its biological function, diagnosis and therapy of related diseases, drug screening and sensitive detection of pesticide residues. Fluorescent probes have become a promising tool for sensing and imaging of butyrylcholinesterase, due to its advantages of high spatio-temporal resolution, high selectivity, non-invasive, high sensitivity, and tailored molecule structures. Here, this paper provides a comprehensive overview of the research progress in the sensing, imaging and therapy of butyrylcholinesterase utilizing fluorescent probes. This paper might be a useful guideline for researchers to design new high-performance fluorescence probes for BChE, and making further contributions to this intriguing field.

Light-Activated Pharmacological Tools for Exploring the Cholinergic System

Cholinergic transmission plays a critical role in both the central and peripheral nervous systems, affecting processes such as learning, memory, and inflammation. Conventional cholinergic drugs generally suffer from poor selectivity and temporal precision, leading to undesired effects and limited therapeutic efficacy. Photopharmacology aims to overcome the limitations of traditional drugs using photocleavable or photoswitchable ligands and spatiotemporal patterns of illumination. Spanning from muscarinic and nicotinic modulators to cholinesterase inhibitors, this review explores the development and application of light-activated compounds as tools for unraveling the role of cholinergic signaling in both physiological and pathological contexts, while also paving the way for innovative phototherapeutic approaches.

Time-Resolved Levodopa Cascade Polymerization Tuned by Bimetallic MOF Fluorescent Nanozyme and Boric Acid for Butyrylcholinesterase Activity Dual-Mode Assay

A ratiometric fluorescence-photothermal dual-mode assay method is constructed for the detection of butyrylcholinesterase (BChE) activity based on time-resolved levodopa (L-DOPA) cascade polymerization. First, a newly designed bimetallic metal-organic framework (MOF), Eu/Co-DPA (DPA: pyridine-2,6-dicarboxylic acid), is screened out as a fluorescent nanozyme with high catalytic activity and superior luminescence properties. In the presence of boric acid (BA), L-DOPA forms BA-esterified L-DOPA, which is catalyzed by Eu/Co-DPA to form the oligomers with strong blue fluorescence. Meanwhile, the red fluorescence of Eu/Co-DPA is quenched by the oligomers, generating a sensitive turn-on/off ratiometric fluorescence response. As polymerization time increases, Eu/Co-DPA cleaves the borate ester bonds to expose the catechol structures of the oligomers, which facilitates the further oxidation and polymerization of the oligomers, promoting the formation of poly(L-DOPA) nanoparticles with a high photothermal conversion efficiency (30.33%). Then, by using thiocholine (butyrylthiocholine enzymolysis product) to inhibit the catalytic activity of Eu/Co-DPA, BChE activity is detected through the change in fluorescence and photothermal dual signals. Both assay modes have low detection limits (0.021 and 0.024 U L-1) and high accuracy (93.3-105.3% recovery). The detection results of real human serum indicate that both assay modes show 100.0% agreement with the standard method. To our knowledge, this work first combines bimetallic MOFs and a BA regulator to tune the structure of L-DOPA polymers, providing a pathbreaking paradigm for preparing catecholamine-based fluorescence-photothermal organic polymers.

Optical control of butyrylcholinesterase (BChE) activity via photoswitchable azobenzene for potential treatment of Alzheimer's disease

Photopharmacology is an emerging method in medicinal chemistry to achieve light-controlled drug activity. Azobenzene-based photoswitchable ligands have found widespread application as chemical tools in photopharmacological studies. This study pioneers the design and synthesis of a novel series of photoswitchabled butyrylcholinesterase (BChE) inhibitors, achieved by strategically integrating an azo moiety into an N-benzyl benzamide scaffold. Through a meticulous investigation of the structure-activity relationship (SAR), we discovered that the lead compound, Azo-9, exhibits dynamic cis/trans conformational shifts, dynamically modulating its BChE-binding efficacy. This unique property translates into potential therapeutic benefits, including neuroprotection and cognitive enhancement. Complementary molecular docking simulations underscored the preferential binding of the cis-isomer of Azo-9 to BChE, which was subsequently validated in a glutamate-mediated neuronal injury model. Collectively, Azo-9 emerges as a promising precision tool for Alzheimer's disease (AD) therapy, while also facilitating deeper insights into the disease's underlying mechanisms.

Synthesis of tricarbonylated propargylamine and conversion to 2,5-disubstituted oxazole-4-carboxylates

The N,O-acetal derived from diethyl mesoxalate (DEMO) undergoes elimination of acetic acid upon treatment with a base, leading to the formation of N-acylimine in situ. Lithium acetylide readily attacks the imino group to afford N,1,1-tricarbonylated propargylamines. When the resulting propargylamine reacts with butyllithium, ring closure occurs between the ethynyl and carbamoyl groups, yielding 2,5-disubstituted oxazole-4-carboxylates. This cyclization also occurs when the propargylamine is heated with ammonium acetate, resulting in double activation.

Recent Progress in Regulating the Activity of Enzymes with Photoswitchable Inhibitors

Photoregulation of biomolecules has become crucial tools in chemical biology, because light enables access under mild conditions and with delicate spatiotemporal control. The control of enzyme activity in a reversible way is a challenge. To achieve it, a facile approach is to use photoswitchable inhibitors. This review highlights recent progress in photoswitchable inhibitors based on azobenzenes units. The progress suggests that the incorporation of an azobenzene unit to a known inhibitor is an effective method for preparing a photoswitchable inhibitor, and with these photoswitchable inhibitors, the activity of enzymes can be regulated by optical control, which is valuable in both basic science and therapeutic applications.

New insights into butyrylcholinesterase: Pharmaceutical applications, selective inhibitors and multitarget-directed ligands

Butyrylcholinesterase (BChE), also known as pseudocholinesterase and serum cholinesterase, is an isoenzyme of acetylcholinesterase (AChE). It mediates the degradation of acetylcholine, especially under pathological conditions. Proverbial pharmacological applications of BChE, its mutants and modulators consist of combating Alzheimer's disease (AD), influencing multiple sclerosis (MS), addressing cocaine addiction, detoxifying organophosphorus poisoning and reflecting the progression or prognosis of some diseases. Of interest, recent reports have shed light on the relationship between BChE and lipid metabolism. It has also been proved that BChE is going to increase abnormally as a compensator for AChE in the middle and late stages of AD, and BChE inhibitors can alleviate cognitive disorders and positively influence some pathological features in AD model animals, foreboding favorable prospects and potential applications. Herein, the selective BChE inhibitors and BChE-related multitarget-directed ligands published in the last three years were briefly summarized, along with the currently known pharmacological applications of BChE, aiming to grasp the latest research directions. Thereinto, some emerging strategies for designing BChE inhibitors are intriguing, and the modulators based on target combination of histone deacetylase and BChE against AD is unprecedented. Furthermore, the involvement of BChE in the hydrolysis of ghrelin, the inhibition of low-density lipoprotein (LDL) uptake, and the down-regulation of LDL receptor (LDLR) expression suggests its potential to influence lipid metabolism disorders. This compelling prospect likely stimulates further exploration in this promising research direction.

Smart photopharmacological agents: LaVO4:Eu3+@vinyl phosphonate combining luminescence imaging and photoswitchable butyrylcholinesterase inhibition

The combination of photoswitchability and bioactivity in one compound provides interesting opportunities for photopharmacology. Here, we report a hybrid compound that in addition allows for its visual localization. It is the first demonstration of its kind and it even shows high photoswitchability. The multifunctional nanomaterial hybrid, which we present, is composed of luminescent LaVO4:Eu3+ nanoparticles and vinyl phosphonate, the latter of which inhibits butyrylcholinesterase (BChE). This inhibition increases 7 times when irradiated with a 266 nm laser. We found that it is increased even further when vinyl phosphonate molecules are conjugated with LaVO4:Eu3+ nanoparticles, leading in total to a 20-fold increase in BChE inhibition upon laser irradiation. The specific luminescence spectrum of LaVO4:Eu3+ allows its spatial localization in various biological samples (chicken breast, Daphnia and Paramecium). Furthermore, laser irradiation of the LaVO4:Eu3+@vinyl phosphonate hybrid leads to a drop in luminescence intensity and in lifetime of the Eu3+ ion that can implicitly indicate photoswitching of vinyl phosphonate in the bioactive state. Thus, combining enhanced photoswitchability, bioactivity and luminescence induced localizability in a unique way, hybrid LaVO4:Eu3+@vinyl phosphonate can be considered as a promising tool for photopharmacology.

Direct detection of acetylcholinesterase by Fe(HCOO)2.6(OH)0.3. H2O nanosheets with oxidase-like activity on a smartphone platform

Monitoring acetylcholinesterase (AChE) is crucial in clinical diagnosis and drug screening. Traditional methods for detecting AChE usually require the addition of intermediates like acetylthiocholine, which complicates the detection process and introduces interference risks. Herein, we develop a direct colorimetric assay based on alkaline iron formate nanosheets (Fe(HCOO)2.6(OH)0.3·H2O NSs, Fef NSs) for the detection of AChE without any intermediates. The as-prepared Fef NSs exhibit oxidase-like activity, catalyzing the generation of O2·-, 1O2 and ·OH, which leads to a color change from colorless to blue when exposed to 3,3',5,5'-tetramethylbenzidine. AChE directly inhibits the oxidase-like activity of Fef NSs, resulting in a hindered color reaction, enabling the detection of AChE. The biosensor has a linear detection range of 0.1-30 mU/mL, with a minimum detection limit of 0.0083 mU/mL (S/N = 3), representing a 100-fold improvement in detection sensitivity over the traditional Ellman's method. Satisfactory results were obtained when analyzing real AChE samples. Attractively, a method for the quantitative detection of AChE by a smartphone is established based on the Fef NSs. This method enables instant acquisition of AChE concentrations, achieving real-time visualized detection.

Photoinduced dual bond rotation of a nitrogen-containing system realized by chalcogen substitution

Photoinduced concerted multiple-bond rotation has been proposed in some biological systems. However, the observation of such phenomena in synthetic systems, in other words, the synthesis of molecules that undergo photoinduced multiple-bond rotation upon photoirradiation, has been a challenge in the photochemistry field. Here we describe a chalcogen-substituted benzamide system that exhibits photoinduced dual bond rotation in heteroatom-containing bonds. Introduction of the chalcogen substituent into a sterically hindered benzamide system provides sufficient kinetic stability and photosensitivity to enable the photoinduced concerted rotation. The presence of two different substituents on the phenyl ring in the thioamide derivative enables the generation of a pair of enantiomers and E/Z isomers. Using these four stereoisomers as indicators of which bonds are rotated, we monitor the photoinduced C-N/C-C concerted bond rotation in the thioamide derivative depending on external stimuli such as temperature and photoirradiation. Theoretical calculations provide insight on the mechanism of this selective photoinduced C-N/C-C concerted rotation.

Dual-Mode Ratiometric Electrochemical and Turn-On Fluorescent Detection of Butyrylcholinesterase Utilizing a Single Probe for the Diagnosis of Alzheimer's Disease

Biomarkers detection in blood with high accuracy is crucial for the diagnosis and treatment of many diseases. In this study, the proof-of-concept fabrication of a dual-mode sensor based on a single probe (Re-BChE) using a dual-signaling electrochemical ratiometric strategy and a "turn-on" fluorescent method is presented. The probe Re-BChE was synthesized in a single step and demonstrated dual mode response toward butyrylcholinesterase (BChE), a promising biomarker of Alzheimer's disease (AD). Due to the specific hydrolysis reaction, the probe Re-BChE demonstrated a turn-on current response for BChE at -0.28 V, followed by a turn-off current response at -0.18 V, while the fluorescence spectrum demonstrated a turn-on response with an emission wavelength of 600 nm. The developed ratiometric electrochemical sensor and fluorescence detection demonstrated high sensitivity with BChE concentrations with a low detection limit of 0.08 μg mL^-1 and 0.05 μg mL^-1, respectively. Importantly, the dual-mode sensor presents the following advantages: (1) dual-mode readout can correct the impact of systematic or background error, thereby achieving more accurate results; (2) the responses of dual-mode readout originate from two distinct mechanisms and relatively independent signal transduction, in which there is no interference between two signaling routes. Additionally, compared with the reported single-signal electrochemical assays for BChE, both redox potential signals were detected in the absence of biological interference within a negative potential window. Furthermore, it was discovered that the outcomes of direct dual-mode electrochemical and fluorescence quantifications of the level of BChE in serum were in agreement with those obtained from the use of commercially available assay kits for BChE sensing. This method has the potential to serve as a useful point-of-care tool for the early detection of AD.

Dual-Acting Small Molecules: Subtype-Selective Cannabinoid Receptor 2 Agonist/Butyrylcholinesterase Inhibitor Hybrids Show Neuroprotection in an Alzheimer's Disease Mouse Model

We present the synthesis and characterization of merged human butyrylcholinesterase (hBChE) inhibitor/cannabinoid receptor 2 (hCB₂R) ligands for the treatment of neurodegeneration. In total, 15 benzimidazole carbamates were synthesized and tested for their inhibition of human cholinesterases, also with regard to their pseudoirreversible binding mode and affinity toward both cannabinoid receptors in radioligand binding studies. After evaluation in a calcium mobilization assay as well as a β-arrestin 2 (βarr2) recruitment assay, two compounds with balanced activities on both targets were tested for their immunomodulatory effect on microglia activation and regarding their pharmacokinetic properties and blood-brain barrier penetration. Compound 15d, containing a dimethyl carbamate motif, was further evaluated in vivo, showing prevention of Aβ_25-35-induced learning impairments in a pharmacological mouse model of Alzheimer's disease for both short- and long-term memory responses. Additional combination studies proved a synergic effect of BChE inhibition and CB₂R activation in vivo.

Amber Light Control of Peptide Secondary Structure by a Perfluoroaromatic Azobenzene Photoswitch

The incorporation of photoswitches into the molecular structure of peptides and proteins enables their dynamic photocontrol in complex biological systems. Here, a perfluorinated azobenzene derivative triggered by amber light was site-specifically conjugated to cysteines in a helical peptide by perfluoroarylation chemistry. In response to the photoisomerization (trans→cis) of the conjugated azobenzene with amber light, the secondary structure of the peptide was modulated from a disorganized into an amphiphilic helical structure.

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.

Clinical Biomarkers and Novel Drug Targets to Cut Gordian Knots of Alzheimer's Disease

BACKGROUND

Alzheimer's disease (AD), the primary cause of dementia, escalating worldwide, has no proper diagnosis or effective treatment. Neuronal cell death and impairment of cognitive abilities, possibly triggered by several brain mechanisms, are the most significant characteristic of this disorder.

METHODS

A multitude of pharmacological targets have been identified for potential drug design against AD. Although many advances in treatment strategies have been made to correct various abnormalities, these often exhibit limited clinical significance because this disease aggressively progresses into different regions of the brain, causing severe deterioration.

RESULTS

These biomarkers can be game-changers for early detection and timely monitoring of such disorders.

CONCLUSION

This review covers clinically significant biomarkers of AD for precise and early monitoring of risk factors and stages of this disease, the potential site of action and novel targets for drugs, and pharmacological approaches to clinical management.

From tryptamine to the discovery of efficient multi-target directed ligands against cholinesterase-associated neurodegenerative disorders

A novel class of benzyl-free and benzyl-substituted carbamylated tryptamine derivatives (CDTs) was designed and synthesized to serve as effective building blocks for the development of novel multi-target directed ligands (MTDLs) for the treatment of neurological disorders linked to cholinesterase (ChE) activity. The majority of them endowed butyrylcholinesterase (BuChE) with more substantial inhibition potency than acetylcholinesterase (AChE), according to the full study of ChE inhibition. Particularly, hybrids with dibenzyl groups (2b-2f, 2j, 2o, and 2q) showed weak or no neuronal toxicity and hepatotoxicity and single-digit nanomolar inhibitory effects against BuChE. Through molecular docking and kinetic analyses, the potential mechanism of action on BuChE was first investigated. In vitro H2O2-induced HT-22 cells assay demonstrated the favorable neuroprotective potency of 2g, 2h, 2j, 2m, 2o, and 2p. Besides, 2g, 2h, 2j, 2m, 2o, and 2p endowed good antioxidant activities and COX-2 inhibitory effects. This study suggested that this series of hybrids can be applied to treat various ChE-associated neurodegenerative disorders such as Alzheimer's disease (AD) and Parkinson's disease (PD), as well as promising building blocks for further structure modification to develop efficient MTDLs.

Novel benzimidazole-based pseudo-irreversible butyrylcholinesterase inhibitors with neuroprotective activity in an Alzheimer's disease mouse model

As levels of acetylcholinesterase (AChE) decrease while levels of butyrylcholinesterase (BChE) increase in later stages of Alzheimer's disease (AD), BChE stands out as a promising target for treatment of AD. Therefore, several benzimidazole-carbamates were designed based on docking studies to inhibit BChE selectively over AChE, while retaining a reasonable solubility. Synthesized molecules exhibit IC50 values from 2.4 μM down to 3.7 nM with an overall highly hBChE-selective profile of the designed compound class. After evaluation of potential neurotoxicity, the most promising compound was further investigated in vivo. Compound 11d attenuates Aβ25-35-induced learning impairments in both spontaneous alternation and passive avoidance responses at a very low dosage of 0.03 mg kg-1, proving selective BChE inhibition to lead to effective neuroprotectivity in AD.

Development of an Indole-Amide-Based Photoswitchable Cannabinoid Receptor Subtype 1 (CB1R) "Cis-On" Agonist

Activation of the human cannabinoid receptor type 1 (hCB₁R) with high spatiotemporal control is useful to study processes involved in different pathologies related to nociception, metabolic alterations, and neurological disorders. To synthesize new agonist ligands for hCB₁R, we have designed different classes of photoswitchable molecules based on an indole core. The modifications made to the central core have allowed us to understand the molecular characteristics necessary to design an agonist with optimal pharmacological properties. Compound 27a shows high affinity for CB₁R (K_i (cis-form) = 0.18 μM), with a marked difference in affinity with respect to its inactive "trans-off" form (CB₁R K_i trans/cis ratio = 5.4). The novel compounds were evaluated by radioligand binding studies, receptor internalization, sensor receptor activation (GRABeCB2.0), Western blots for analysis of ERK1/2 activation, NanoBiT βarr2 recruitment, and calcium mobilization assays, respectively. The data show that the novel agonist 27a is a candidate for studying the optical modulation of cannabinoid receptors (CBRs), serving as a new molecular tool for investigating the involvement of hCB₁R in disorders associated with the endocannabinoid system.

Design, synthesis and biological evaluation of light-driven on-off multitarget AChE and MAO-B inhibitors

Neurodegenerative diseases are multifactorial disorders characterized by protein misfolding, oxidative stress, and neuroinflammation, finally resulting in neuronal loss and cognitive dysfunctions. Nowadays, an attractive strategy to improve the classical treatments is the development of multitarget-directed molecules able to synergistically interact with different enzymes and/or receptors. In addition, an interesting tool to refine personalized therapies may arise from the use of bioactive species able to modify their activity as a result of light irradiation. To this aim, we designed and synthesized a small library of cinnamic acid-inspired isomeric compounds with light modulated activity able to inhibit acetylcholinesterase (AChE) and monoamine oxidase B (MAO-B), with remarkable selectivity over butyrylcholinesterase (BChE) and MAO-A, which have been investigated as the enzyme targets related to Alzheimer's disease (AD). The inhibitory activities were evaluated for the pure E-diastereomers and the E/Z-diastereomer mixtures, obtained upon UV irradiation. Molecular docking studies were carried out to rationalize the differences in the inhibition potency of the E and Z diastereomers of the best performing analogue 1c. Our preliminary findings may open-up the way for developing innovative multitarget photo-switch drugs against neurodegenerative diseases.

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.

Synthesis and Biological Evaluation of Flavonoid‐Cinnamic Acid Amide Hybrids with Distinct Activity against Neurodegeneration in Vitro and in Vivo

Flavonoids are polyphenolic natural products and have shown significant potential as disease‐modifying agents against neurodegenerative disorders like Alzheimer's disease (AD), with activities even in vivo. Hybridization of the natural products taxifolin and silibinin with cinnamic acid led to an overadditive effect of these compounds in several phenotypic screening assays related to neurodegeneration and AD. Therefore, we have exchanged the flavonoid part of the hybrids with different flavonoids, which show higher efficacy than taxifolin or silibinin, to improve the activity of the respective hybrids. Chemical connection between the flavonoid and cinnamic acid was realized by an amide instead of a labile ester bond to improve stability towards hydrolysis. To investigate the influence of a double bond at the C‐ring of the flavonoid, the dehydro analogues of the respective hybrids were also synthesized. All compounds obtained show neuroprotection against oxytosis, ferroptosis and ATP‐depletion, respectively, in the murine hippocampal cell line HT22. Interestingly, the taxifolin and the quercetin derivatives are the most active compounds, whereby the quercetin derivate shows even more pronounced activity than the taxifolin one in all assays applied. As aimed for, no hydrolysis product was found in cellular uptake experiments after 4 h whereas different metabolites were detected. Furthermore, the quercetin‐cinnamic acid amide showed pronounced activity in an in vivo AD mouse model at a remarkably low dose of 0.3 mg/kg.

Discovery of carbamate-based N-salicyloyl tryptamine derivatives as novel pleiotropic agents for the treatment of Alzheimer's disease

In this work, based on the potential anti-AD molecule previously studied by our group, we continue to introduce different substituents at different positions to improve both drug-like properties and on target activities. 33 N-salicyloyl tryptamine-carbamate hybrids were designed, synthesized and evaluated as cholinesterase inhibitors. H327 was the most potent BChE inhibitor (eqBChE IC₅₀ = 0.057 ± 0.005 μM), and showed threefold improved inhibitory potency than the positive drug rivastigmine (eqBChE IC₅₀ = 0.19 ± 0.001 μM). In addition, H327 as a pseudo-irreversible BChE inhibitor was endowed with neuroprotective, antioxidative and anti-neuroinflammatory properties. Cytotoxicity and acute toxicity tests confirmed the safety of compound H327. The pharmacokinetics study showed that compound H327 had a longer T_1/2 time and higher bioavailability than the lead compound 1 g. Compound H327 was able to cross the blood-brain barrier (BBB) in vivo. Moreover, the behavioral tests showed that compound H327 could significantly improve scopolamine-induced cognitive impairment in vivo. Overall, these results demonstrated that compound H327 is a promising multi-target agent for the treatment of AD.