Coumarins as cholinesterase inhibitors: A review

Base-Promoted Chemodivergent Construction of 2H-Chromen-2-one and Chromeno[2,3-c]pyrrole Scaffolds from para-Quinone Methides and α-Alkylidene Succinimides

Herein, we evolve a base-promoted synthesis of 2H-chromen-2-one and chromeno[2,3-c]pyrrole scaffolds via (4 + 2) annulation of α-alkylidene succinimides with 2-hydroxyphenyl-substituted para-quinone methides (p-QMs). Extremely selective and switchable cyclizations were obtained by modifying the base. This metal-free protocol is highlighted by its mild reaction conditions and broad substrate scope, and the viability of the existing protocol was additionally illustrated by gram-scale synthesis and further modification. Several control experiments were performed to understand the reaction mechanism.

Copper-Catalyzed Dual Remote Asymmetric Vinylogous Alkynylallylic Substitution of Yne-Allylic Esters with Coumarins

Chiral coumarins and their derivatives are ubiquitous structural motifs found in an array of biologically and therapeutically active natural products and drugs. Herein, a highly enantioselective dual remote copper-catalyzed vinylogous alkynylallylic substitution of yne-allylic esters with coumarins has been developed. The practicality of this method is exemplified by the use of readily available starting materials; mild reaction conditions; excellent regio-, enantio-, and stereoselectivities; and the very broad substrate scope (67 examples), while the scalability and further applications of this method are illustrated by the gram-scale reaction and the series of derivations of the products.

Curcumin hybrid molecules for the treatment of Alzheimer's disease: Structure and pharmacological activities

Alzheimer's disease (AD) is the most common neurodegenerative disease among the elderly. Contemporary treatments can only relieve symptoms but fail to delay disease progression. Curcumin is a naturally derived compound that has demonstrated significant therapeutic effects in AD treatment. Recently, molecular hybridization has been utilized to combine the pharmacophoric groups present in curcumin with those of other AD drugs, resulting in a series of novel compounds that enhance the therapeutic efficacy through multiple mechanisms. In this review, we firstly provide a concise summary of various pathogenetic hypotheses of AD and the mechanism of action of curcumin in AD, as well as the concept of molecular hybridization. Subsequently, we focus on the recent development of hybrid molecules derived from curcumin, summarizing their structures and pharmacological activities, including cholinesterase inhibitory activity, Aβ aggregation inhibitory activity, antioxidant activity, and other activities. The structure-activity relationships were further discussed.

An Effective, Green Synthesis Procedure for Obtaining Coumarin-Hydroxybenzohydrazide Derivatives and Assessment of Their Antioxidant Activity and Redox Status

In this study, green synthesis of two derivatives of coumarin-hydroxybenzohydrazide, (E)-2,4-dioxo-3-(1-(2-(2,3,4-trihydroxybenzoyl)hydrazyl)ethylidene)-chroman-7-yl acetate (C-HB1), and (E)-2,4-dioxo-3-(1-(2-(3,4,5-trihydroxybenzoyl)hydrazyl)ethylidene)chroman-7-yl acetate (C-HB2) is reported. Using vinegar and ethanol as a catalyst and solvent, the reactions were carried out between 3-acetyl-4-hydroxy-coumarin acetate and corresponding trihydroxybenzoyl hydrazide. The antioxidant potential of these compounds was investigated using the DPPH and ABTS assays, as well as the FRAP test. The obtained results reveal that even at very low concentrations, these compounds show excellent radical scavenging potential. The IC50 values for C-HB1 and C-HB2 in relation to the DPPH radical are 6.4 and 2.5 μM, respectively, while they are 4.5 and 2.0 μM in relation to the ABTS radical. These compounds have antioxidant activity that is comparable to well-known antioxidants such as gallic acid, NDGA, and trolox. These results are in good correlation with theoretical parameters describing these reactions. Moreover, it was found that inhibition of DPPH● follows HAT, while inactivation of ABTS+● follows SET-PT and HAT mechanisms. Additionally, coumarin-hydroxybenzohydrazide derivatives induced moderate cytotoxic activity and show significant potential to modulate redox status in HCT-116 colorectal cancer cells. The cytotoxicity was achieved via their prooxidative activity and ability to induce oxidative stress in cancer cells by increasing O2˙- concentrations, indicated by increased MDA and GSH levels. Thus, ROS manipulation can be a potential target for cancer therapies by coumarins, as cancer cells possess an altered redox balance in comparison to normal cells. According to the ADMET analysis, the compounds investigated show good pharmacokinetic and toxicological profiles similar to vitamin C and gallic acid, which makes them good candidates for application in various fields of industry and medicine.

13C NMR-based dereplication using MixONat software to decipher potent anti-cholinesterase compounds in Mesua lepidota bark

A bio-assay guided fractionation strategy based on cholinesterase assay combined with 13C NMR-based dereplication was used to identify active metabolites from the bark of Mesua lepidota. Eight compounds were identified with the aid of the 13C NMR-based dereplication software, MixONat, i.e., sitosterol (1), stigmasterol (2), α-amyrin (3), friedelin (6), 3β-friedelinol (7), betulinic acid (9), lepidotol A (10) and lepidotol B (11). Further bio-assay guided isolation of active compounds afforded one xanthone, pyranojacareubin (12) and six coumarins; lepidotol A (10), lepidotol B (11), lepidotol E (13), lepidotin A (14), and lepidotin B (15), including a new Mammea coumarin, lepidotin C (16). All the metabolites showed strong to moderate butyrylcholinesterase (BChE) inhibition. Lepidotin B (15) exhibited the most potent inhibition towards BChE with a mix-mode inhibition profile and a Ki value of 1.03 µM. Molecular docking and molecular dynamics simulations have revealed that lepidotin B (15) forms stable interactions with key residues within five critical regions of BChE. These regions encompass residues Asp70 and Tyr332, the acyl hydrophobic pocket marked by Leu286, the catalytic triad represented by Ser198 and His438, the oxyanion hole (OH) constituted by Gly116 and Gly117, and the choline binding site featuring Trp82. To gauge the binding strength of lepidotin B (15) and to pinpoint pivotal residues at the binding interface, free energy calculations were conducted using the Molecular Mechanics Generalized Born Surface Area (MM-GBSA) approach. This analysis not only predicted a favourable binding affinity for lepidotin B (15) but also facilitated the identification of significant residues crucial for the binding interaction.

2H-chromene and 7H-furo-chromene derivatives selectively inhibit tumour associated human carbonic anhydrase IX and XII isoforms

Tumour associated carbonic anhydrases (CAs) IX and XII have been recognised as potential targets for the treatment of hypoxic tumours. Therefore, considering the high pharmacological potential of the chromene scaffold as selective ligand of the IX and XII isoforms, two libraries of compounds, namely 2H-chromene and 7H-furo-chromene derivatives, with diverse substitution patterns were designed and synthesised. The structure of the newly synthesised compounds was characterised and their inhibitory potency and selectivity towards human CA off target isoforms I, II and cancer-associated CA isoforms IX and XII were evaluated. Most of the compounds inhibit CA isoforms IX and XII with no activity against the I and II isozymes. Thus, while the potency was influenced by the substitution pattern along the chromene scaffold, the selectivity was conserved along the series, confirming the high potential of both 2H-chromene and 7H-furo-chromene scaffolds for the design of isozyme selective inhibitors.

Development of Sustainable Insecticide Candidates for Protecting Pollinators: Insight into the Bioactivities, Selective Mechanism of Action and QSAR of Natural Coumarin Derivatives against Aphids

Plants employ abundant toxic secondary metabolites to withstand insect attack, while pollinators can tolerate some natural defensive compounds. Coumarins, as promising green alternatives to chemical insecticides, possess wide application prospects in the crop protection field. Herein, the bioactivities of 30 natural coumarin derivatives against Aphis gossypii were assessed and revealed that 6-methylcoumarin exhibited potent aphicidal activity against aphids but displayed no toxicity to honeybees. Additionally, using biochemical, bioinformatic, and molecular assays, we confirmed that the action mode of 6-methylcoumarin against aphids was by inhibiting acetylcholinesterase (AChE). Meanwhile, functional assays revealed that the difference in action site, which located in Lys585 in aphid AChE (equivalent to Val548 in honeybee AChE), was the principal reason for 6-methylcoumarin being toxic to aphids but safe to pollinators. This action site was further validated by mutagenesis data, which uncovered how 6-methylcoumarin was unique selective to the aphid over honeybee or mammalian AChE. Furthermore, a 2D-QSAR model was established, revealing that the central structural feature was H3m, which offers guidance for the future design of more potent coumarin compounds. This work provides a sustainable strategy to take advantage of coumarin analogues for pest management while protecting nontarget pollinators.

Natural coumarins from Murraya paniculata as mixed-type inhibitors of cholinesterases: In vitro and in silico investigations

Currently, acetylcholinesterase (AChE) inhibiting drugs in clinical use, such as tacrine, donepezil, rivastigmine, and galanthamine, are associated with serious side effects and short half-lives. In recent years, numerous phytochemicals have been identified as inhibitors of cholinesterases with potential applications in the management of Alzheimer’s disease (AD). In this study three natural coumarins, 2′-O-ethylmurrangatin (1), murranganone (2), and paniculatin (3) isolated previously by our group from the leaves of Murraya paniculata, were tested against the two cholinesterases (ChE) enzymes, AChE and butyrylcholinesterase (BChE) using in vitro assay. Molecular docking was performed to highlight the structural properties that contribute to the molecular recognition pattern in the inhibition of ChE and the structural differences resulting in the selectivity of these compounds toward AChE. Classical enzyme inhibition kinetics data suggested that compounds 2 and 3 were potent inhibitors of AChE and BChE, while 1 was found inactive against both enzymes. The findings from molecular docking studies revealed the competitive and non-competitive inhibition mechanisms of compounds 2 and 3 against both enzymes. Molecular docking and simulations have revealed that hydrogen bonding, mediated by ketone and hydroxyl functionalities in various positions, significantly contributes to the binding of the inhibitor to the receptor. According to MD simulation studies, the stability of the ligand-AChE complex for the most active compound (3) is found to be comparable to that of the widely used drug Tacrine. In addition, to evaluate the drug-likeness of compounds, in silico ADME evaluation was performed, and the compounds presented good ADME profiles. Data suggested that the coumarin nucleus having diverse side chains at the C-8 position can serve as a potential inhibitor of cholinesterases and can act as a lead to develop a new semisynthetic drug for the treatment of AD.

Development of new Alzheimer's disease drug candidates using donepezil as a key model

Alzheimer's disease (AD) is one of the most prevalent geriatric diseases and a significant cause of high mortality. This crippling disorder is becoming more prevalent at an unprecedented rate, which has led to an increase in the financial cost of caring. It is a pathologically complicated, multifactorial disease characterized by β-amyloid precipitation, β-amyloid oligomer production, decrease in cholinergic function, and dysregulation of other neurotransmitter systems. Due to the pathogenic complexity of AD, multitarget drugs that can simultaneously alternate multiple biological targets may enhance the therapeutic efficacy. Donepezil (DNP) is the most potent approved drug for the treatment of AD. It has a remarkable effect on a number of AD-related processes, including cholinesterase activity, anti-Aβ aggregation, oxidative stress, and more. DNP resembles an excellent scaffold to be hybridized with other pharmacophoric moieties having biological activity against AD pathological factors. There have been significant attempts made to modify the structure of DNP to create new bioactive chemical entities with novel structural patterns. In this review, we highlight recent advances in the development of multiple-target DNP-hybridized models for the treatment of AD that can be used in the future in the rational design of new potential AD therapeutics. The design and development of new drug candidates for the treatment of AD using DNP as a molecular scaffold have also been reviewed and summarized.

Study on effective synthesis of 7-hydroxy-4-substituted coumarins

Many coumarin derivatives have good biological activity and application value in fluorescent probes. Therefore, synthetic routes to coumarin derivatives have also attracted the attention of many research groups. In this work, based on the Pechmann coumarin synthesis method, the influence of various Lewis acids on the reaction was discussed, and the optimal synthesis conditions of 7-hydroxy-4-substituted coumarins were explored. Based on the experimental results, a possible mechanism was proposed, which provides a reference for future industrialized production of coumarins.

Progress and Development of Carbazole Scaffold Based as Potential Anti- Alzheimer Agents Using MTDL Approach

Abstract:

Alzheimer’s is a neurodegenerative disease (NDs) found in old age people with associated most common symptom dementia. MTDLs (Multi-Target Direct Ligand strategy) is based on a combination of two or more bioactive pharmacophores into a single molecule and this phenomenon has received a great attention in the new era of modern drug discovery and emerging as a choice to treat this complex Alzheimer’s disease (AD). In last fifteen years, many research groups designed, and synthesized new carbazole integrated molecules linked with other bioactive pharmacophores like thiazoles, carvedilol, α- naphthylaminopropan-2-ol, tacrine, ferulic acid, piperazine, coumarin, chalcones, stilbene, benzyl piperidine, adamantane, quinoline, phthalocyanines, α-amino phosphonate, thiosemicarbazones, hydrazones, etc. derivatives using MTDLs approach to confront AD. The present review entails the scientific data on carbazole hybrids as potential Anti-Alzheimer activities from 2007 to 2021 that have shown potential anti-Alzheimer activities through multiple target pathways thereby promising hope for new drug development to confront AD.

Evaluation of Anti-Alzheimer Activity of Synthetic Coumarins by Combination of in Vitro and in Silico Approaches

Series of synthetic coumarin derivatives (1-16) were tested against acetylcholinesterase (AChE) and butyrylcholinesterase (BChE), two enzymes linked to the pathology of Alzheimer's disease (AD). Compound 16 was the most active AChE inhibitor with IC₅₀ 32.23±2.91 μM, while the reference (galantamine) had IC₅₀ =1.85±0.12 μM. Compounds 9 (IC₅₀ 75.14±1.82 μM), 13 (IC₅₀ =16.14±0.43 μM), were determined to be stronger BChE inhibitors than the reference galantamine (IC₅₀ =93.53±2.23 μM). The IC₅₀ value of compound 16 for BChE inhibition (IC₅₀ =126.56±11.96 μM) was slightly higher than galantamine. The atomic interactions between the ligands and the key amino acids inside the binding cavities were simulated to determine their ligand-binding positions and free energies. The three inhibitory coumarins (9, 13, 16) were next tested for their effects on the genes associated with AD using human neuroblastoma (SH-SY5Y) cell lines. Our data indicate that they could be considered for further evaluation as new anti-Alzheimer drug candidates.

Anticholinesterase Compounds from Endemic Prangos uechtritzii

In this study, the anticholinesterase effects of the extracts and isolated compounds from the roots of endemic Prangos uechtritzii Boiss & Hausskn (Apiaceae) are reported. A novel polyacetylenic compound; (+)-8-O-methyloplopantriol A along with two known polyacetylenes; (-)-panaxynol, (+)-falcarindiol and fifteen known coumarin derivatives; umbelliferone, 6-formylumbelliferone, suberosin, 7-demethylsuberosin, (+)-ulopterol, tamarin, psoralen, imperatorin, (+)-oxypeucedanin, (+)-oxypeucedanin hydrate, (+)-oxypeucedanin methanolate, (+)-marmesin, (-)-prantschimgin, (+)-decursinol, and (-)-adicardin were isolated from the hexane (Pu-HE), chloroform (Pu-CE), and methanol (Pu-ME) extracts of P. uechtritzii roots. (-)-Panaxynol, (+)-falcarindiol, 6-formylumbelliferone, (+)-decursinol, and (-)-adicardin were obtained from the genus Prangos for the first time. (+)-8-O-Methyloplopantriol A inhibited both AChE (IC50 =194.5±5.8 μM) and BChE (IC50 =51.9±2.96 μM) enzymes. (+)-Falcarindiol, 6-formylumbelliferone, 7-demethylsuberosin, tamarin, and imperatorin also exhibited BChE-specific inhibitory activities (IC50 =27.88-93.86 μM). (+)-Falcarindiol (IC50 =27.88±0.91 μM) and imperatorin (IC50 =30.89±1.40 μM) as the most active components could be led compounds to develop new BChE inhibitors with further research against Alzheimer's disease.

Polyphenols profile and enzyme inhibitory properties of Blumea lacera (Burm. f.) DC.: a potential candidate against obesity, aging, and skin disorder

Blumea lacera (Burm. f.) DC. is attracting scientific interest due to the diverse biological activities of its various parts and its use in folk medicine. The present study was undertaken to investigate the tissue-specific differential expression pattern of its total bioactive compounds. The study was further extended to whole plant phenolics profiling, in vitro enzyme inhibition activities, followed by in silico enzyme inhibition analysis to assess its potential as herbal medicine. The amount of total phenolics in different tissues was followed in decreasing order as old leaf, flower bud, root, young leaf, flower, old stem, and young stem, while that for the flavonoids was old leaf, root, young leaf, flower bud, flower, young stem, and old stem.  This study identified rosmarinic acid, quercetin, and kaempferol in this plant for the first time. The solvent extracts demonstrated strong inhibition of lipase and tyrosinase activity, along with varying degrees of inhibition of acetylcholinesterase and butyrylcholinesterase activity. Among the detected compounds, ten displayed strong in silico binding affinities with the tested enzymes. The findings provide a new insight into further investigation of the medicinal potential of this species against obesity, neurological disorders, and aberrant skin color.

Biological evaluation, molecular modeling and dynamics simulation of phenanthrenes isolated from Bletilla striata as butyrylcholinesterase inhibitors

As part of our continuous studies on natural cholinesterase inhibitors from plant kingdom, the 95% ethanol extract from tubers of Bletillastriata showed promising butyrylcholinesterase (BChE) inhibition (IC₅₀ = 8.6 μg/mL). The extracts with different polarities (petroleum ether, ethyl acetate, n-butanol, and water) were prepared and evaluated for their inhibition of cholinesterases. The most active ethyl acetate extract was subjected to a bioassay-guided isolation and afforded twenty-two bibenzyls and phenanthrenes (1–22). All isolates were further evaluated for their BChE inhibition activity, and five phenanthrenes presented promising capacity (IC₅₀ < 10 μM). Further kinetic studies indicated their modes of inhibition. Compounds 6, 8, and 14 were found to be mixed-type inhibitors, while compounds 10 and 12 could be classified as non-competitive inhibitors. The potential interaction mechanism of them with BChE was demonstrated by molecular docking and molecular dynamics simulation, showing that they could interact with catalytic active site and peripheral anionic site of BChE. These natural phenanthrenes provide new scaffold for the further design and optimization, with the aim to discover new selective BChE inhibitors for the treatment of AD.

Aminoalkoxy-substituted coumarins: Synthesis and evaluation for reactivation of inhibited human acetylcholinesterase

Reactivation of inhibited acetylcholinesterase remains an important therapeutic strategy for the treatment of poisoning by organophosphorus compounds, such as nerve agents or pesticides. Although drugs like obidoxime or pralidoxime have been used with considerable success, there is a need for new substances capable of reactivating acetylcholinesterase with a broader scope and increased efficacy. Possible screening candidates must fulfill two fundamental requirements: They must (i) show an affinity to acetylcholinesterase well balanced between sufficient binding and competitive inhibition and (ii) facilitate the nucleophilic cleavage of the phosphorylated catalytic serine residue. We attached a variety of nonaromatic primary and secondary amines to a coumarin core through selected alkoxy side linkers attached at coumarin positions 6 or 7 to obtain a small set of possible reactivators. Evaluation of their inhibition and reactivation potential in vitro showed some activity with respect to acetylcholinesterase inhibited by cyclosarin.

Recent Applications of the Multicomponent Synthesis for Bioactive Pyrazole Derivatives

Pyrazole and its derivatives are considered a privileged N-heterocycle with immense therapeutic potential. Over the last few decades, the pot, atom, and step economy (PASE) synthesis of pyrazole derivatives by multicomponent reactions (MCRs) has gained increasing popularity in pharmaceutical and medicinal chemistry. The present review summarizes the recent developments of multicomponent reactions for the synthesis of biologically active molecules containing the pyrazole moiety. Particularly, it covers the articles published from 2015 to date related to antibacterial, anticancer, antifungal, antioxidant, α-glucosidase and α-amylase inhibitory, anti-inflammatory, antimycobacterial, antimalarial, and miscellaneous activities of pyrazole derivatives obtained exclusively via an MCR. The reported analytical and activity data, plausible synthetic mechanisms, and molecular docking simulations are organized in concise tables, schemes, and figures to facilitate comparison and underscore the key points of this review. We hope that this review will be helpful in the quest for developing more biologically active molecules and marketed drugs containing the pyrazole moiety.

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.

Design, Spectroscopy, and Assessment of Cholinesterase Inhibition and Antimicrobial Activities of Novel Coumarin–Thiadiazole Hybrids

A novel series of coumarin–thiadiazole hybrids, derived from substituted coumarin-3-carboxylic acids was isolated and fully characterized with the use of a number of spectroscopic techniques and XRD crystallography. Several of the novel compounds showed intensive fluorescence in the visible region, comparable to that of known coumarin-based fluorescence standards. Moreover, the new compounds were tested as potential antineurodegenerative agents via their ability to act as acetylcholinesterase (AChE) and butyrylcholinesterase (BuChE) inhibitors. Compared to the commercial standards, only a few compounds demonstrated moderate AChE and BuChE activities. Moreover, the novel derivatives were tested for their antimicrobial activity against a panel of pathogenic bacterial and fungal species. Their lack of activity and toxicity across a broad range of biochemical assays, together with the exceptional emission of some hybrid molecules, highlights the possible use of a number of the novel hybrids as potential fluorescence standards or fluorescence imaging agents.

Effects of Linkers and Substitutions on Multitarget Directed Ligands for Alzheimer’s Diseases: Emerging Paradigms and Strategies

Alzheimer’s disease (AD) is multifactorial, progressive and the most predominant cause of cognitive impairment and dementia worldwide. The current “one-drug, one-target” approach provides only symptomatic relief to the condition but is unable to cure the disease completely. The conventional single-target therapeutic approach might not always induce the desired effect due to the multifactorial nature of AD. Hence, multitarget strategies have been proposed to simultaneously knock out multiple targets involved in the development of AD. Herein, we provide an overview of the various strategies, followed by the multitarget-directed ligand (MTDL) development, rationale designs and efficient examples. Furthermore, the effects of the linkers and substitutional functional groups on MTDLs against various targets of AD and their modes of action are also discussed.

Organocatalytic enantioselective construction of axially chiral (1H)-isochromen-1-imines

Heterocycloalkenyl atropisomers, derived from biaryl atropisomers and axially chiral styrenes, have emerged as a new class of nonbiaryl C-C atropisomers due to the benefit in improving the pharmacological activity and structural diversity. This paper proposes an intramolecular annulation strategy for constructing the heterocycloalkenyl atropisomers (1H)-isochromen-1-imines by organocatalysis. Various heterocycloalkenyl atropisomers (1H)-isochromen-1-imines were prepared in good to excellent yields with excellent enantioselectivity (up to 98% ee), and could be easily converted to atropisomeric lactones isocoumarins.

An Update on Synthesis of Coumarin Sulfonamides as Enzyme Inhibitors and Anticancer Agents

Coumarin is an important six-membered aromatic heterocyclic pharmacophore, widely distributed in natural products and synthetic molecules. The versatile and unique features of coumarin nucleus, in combination with privileged sulfonamide moiety, have enhanced the broad spectrum of biological activities. The research and development of coumarin, sulfonamide-based pharmacology, and medicinal chemistry have become active topics, and attracted the attention of medicinal chemists, pharmacists, and synthetic chemists. Coumarin sulfonamide compounds and analogs as clinical drugs have been used to cure various diseases with high therapeutic potency, which have shown their enormous development value. The diversified and wide array of biological activities such as anticancer, antibacterial, anti-fungal, antioxidant and anti-viral, etc. were displayed by diversified coumarin sulfonamides. The present systematic and comprehensive review in the current developments of synthesis and the medicinal chemistry of coumarin sulfonamide-based scaffolds give a whole range of therapeutics, especially in the field of oncology and carbonic anhydrase inhibitors. In the present review, various synthetic approaches, strategies, and methodologies involving effect of catalysts, the change of substrates, and the employment of various synthetic reaction conditions to obtain high yields is cited.

Phenolic Profile, Antioxidant and Enzyme Inhibition Properties of the Chilean Endemic Plant Ovidia pillopillo (Gay) Meissner (Thymelaeaceae)

Ovidia pillopillo (Lloime) is an endemic species of the Valdivian Forest of Chile. Little is known on the chemistry and biological activity of this plant. In this study, the phenolic profile, antioxidant capacities and enzyme inhibition capacities (against tyrosinase and cholinesterase) of the plant were investigated for the first time. The phenolic profile of the plant was obtained by UHPLC-MS fingerprinting with high resolution, which showed the presence of several flavonoids and coumarins. The antioxidant potential was measured by FRAP and ORAC (45.56 ± 1.32; 25.33 ± 1.2 μmol Trolox equivalents/g dry plant, respectively) plus ABTS and DPPH methods (IC₅₀ = 9.95 ± 0.05 and 6.65 ± 0.5 μg/mL, respectively). Moreover, the flavonoid and phenolic contents were determined (57.33 ± 0.82 and 38.42 ± 1.32, μg of Trolox and quercetin equivalents/100 g dry weight, respectively). The ethanolic extract showed cholinesterase (IC₅₀ = 1.94 ± 0.07 and 2.73 ± 0.05 μg/mL, for AChE and BuChE, respectively) and tyrosinase (4.92 ± 0.05 μg/mL) enzyme inhibition activities. Based on these in vitro studies, in silico simulations were performed, which determined that the major compounds as ligands likely docked in the receptors of the enzymes. These results suggest that Ovidia pillopillo produce interesting special coumarins and flavonoids, which are potential candidates for the exploration and preparation of new medicines.

Synthesis, Crystallographic, Quantum Chemical, Antitumor, and Molecular Docking/Dynamic Studies of 4-Hydroxycoumarin-Neurotransmitter Derivatives

In this contribution, four new compounds synthesized from 4-hydroxycoumarin and tyramine/octopamine/norepinephrine/3-methoxytyramine are characterized spectroscopically (IR and NMR), chromatographically (UHPLC-DAD), and structurally at the B3LYP/6-311++G*(d,p) level of theory. The crystal structure of the 4-hydroxycoumarin-octopamine derivative was solved and used as a starting geometry for structural optimization. Along with the previously obtained 4-hydroxycoumarin-dopamine derivative, the intramolecular interactions governing the stability of these compounds were quantified by NBO and QTAIM analyses. Condensed Fukui functions and the HOMO-LUMO gap were calculated and correlated with the number and position of OH groups in the structures. In vitro cytotoxicity experiments were performed to elucidate the possible antitumor activity of the tested substances. For this purpose, four cell lines were selected, namely human colon cancer (HCT-116), human adenocarcinoma (HeLa), human breast cancer (MDA-MB-231), and healthy human lung fibroblast (MRC-5) lines. A significant selectivity towards colorectal carcinoma cells was observed. Molecular docking and molecular dynamics studies with carbonic anhydrase, a prognostic factor in several cancers, complemented the experimental results. The calculated MD binding energies coincided well with the experimental activity, and indicated 4-hydroxycoumarin-dopamine and 4-hydroxycoumarin-3-methoxytyramine as the most active compounds. The ecotoxicology assessment proved that the obtained compounds have a low impact on the daphnia, fish, and green algae population.

First report of fatty acids in Mimosadiplotricha bee pollen with in vitro lipase inhibitory activity

Bee pollen (BP) is full of nutrients and phytochemicals, and so it is widely used as a health food and alternative medicine. Its composition and bioactivity mainly depend on the floral pollens. In this work, BP collected by Apis mellifera with different monoculture flowering crops (BP1-6) were used. The types of floral pollen in each BP were initially identified by morphology, and subsequently confirmed using molecular phylogenetic analysis. Data from both approaches were consistent and revealed each BP to be monofloral and derived from the flowers of Camellia sinensis L., Helianthus annuus L., Mimosa diplotricha, Nelumbo nucifera, Xyris complanata, and Ageratum conyzoides for BP1 to BP6, respectively. The crude extracts of all six BPs were prepared by sequential partition with methanol, dichloromethane (DCM), and hexane. The crude extracts were then tested for the in vitro (i) α-amylase inhibitory, (ii) acetylcholinesterase inhibitory (AChEI), and (iii) porcine pancreatic lipase inhibitory (PPLI) activities in terms of the percentage enzyme inhibition and half maximum inhibitory concentration (IC₅₀). The DCM partitioned extract of X. complanata BP (DCMXBP) had the highest active α-amylase inhibitory activity with an IC₅₀ value of 1,792.48 ± 50.56 µg/mL. The DCM partitioned extracts of C. sinensis L. BP (DCMCBP) and M. diplotricha BP (DCMMBP) had the highest PPLI activities with an IC₅₀ value of 458.5 ± 13.4 and 500.8 ± 24.8 µg/mL, respectively), while no crude extract showed any marked AChEI activity. Here, the in vitro PPLI activity was focused on. Unlike C. sinensis L. BP, there has been no previous report of M. diplotricha BP having PPLI activity. Hence, DCMMBP was further fractionated by silica gel 60 column chromatography, pooling fractions with the same thin layer chromatography profile. The pooled fraction of DCMMBP2-1 was found to be the most active (IC₅₀ of 52.6 ± 3.5 µg/mL), while nuclear magnetic resonance analysis revealed the presence of unsaturated free fatty acids. Gas chromatography with flame-ionization detection analysis revealed the major fatty acids included one saturated acid (palmitic acid) and two polyunsaturated acids (linoleic and linolenic acids). In contrast, the pooled fraction of DCMMBP2-2 was inactive but pure, and was identified as naringenin, which has previously been reported to be present in M. pigra L. Thus, it can be concluded that naringenin was compound marker for Mimosa BP. The fatty acids in BP are nutritional and pose potent PPLI activity.

2-Aminobenzoxazole-appended coumarins as potent and selective inhibitors of tumour-associated carbonic anhydrases

We have carried out the design, synthesis, and evaluation of a small library of 2-aminobenzoxazole-appended coumarins as novel inhibitors of tumour-related CAs IX and XII. Substituents on C-3 and/or C-4 positions of the coumarin scaffold, and on the benzoxazole moiety, together with the length of the linker connecting both units were modified to obtain useful structure-activity relationships. CA inhibition studies revealed a good selectivity towards tumour-associated CAs IX and XII (K_i within the mid-nanomolar range in most of the cases) in comparison with CAs I, II, IV, and VII (K_i > 10 µM); CA IX was found to be slightly more sensitive towards structural changes. Docking calculations suggested that the coumarin scaffold might act as a prodrug, binding to the CAs in its hydrolysed form, which is in turn obtained due to the esterase activity of CAs. An increase of the tether length and of the substituents steric hindrance was found to be detrimental to in vitro antiproliferative activities. Incorporation of a chlorine atom on C-3 of the coumarin moiety achieved the strongest antiproliferative agent, with activities within the low micromolar range for the panel of tumour cell lines tested.

Pharmacological report of recently designed multifunctional coumarin and coumarin-heterocycle derivatives

Coumarin is a naturally available molecule and has been identified as a potent pharmacophore due to its pharmacological activity. Because of this, coumarin has been exploited synthetically to prepare a wide range of derivatives. In fact, most coumarin derivatives have been found to be less toxic, which is the most essential property for a drug molecule. Such molecules are being prepared for therapeutic use as broad-spectrum pharmacological agents. Microbial diseases including viral diseases have become very common and are responsible for many deaths worldwide. In particular, microbial drug resistance is a problem that needs to be tackled in an effective manner. Also, for Alzheimer's disease, which affects most elderly persons, no efficient chemotherapy exists. In addition, although diabetes, a metabolic syndrome, can be treated with many drugs, there is no complete cure. Thus, more potent antidiabetic agents are required for the management of diabetes. Likewise, for the treatment of a wide range of ailments caused by microbes, genetic factors, or lifestyle-related factors, an efficient drug regimen is needed. In view of this, coumarin derivatives are designed and evaluated. Here, coumarin derivatives that have been reported recently are compiled, classified and evaluated critically. This study briefly takes the structure-activity relationship into consideration and suggests the next suitable step. With a focus on the most potent molecules, the pharmacological activity of the evaluated molecules is described.

Bioactivity screening of pinhão (Araucaria Angustifolia (Bertol.) Kuntze) seed extracts: the inhibition of cholinesterases and α-amylases, and cytotoxic and anti-inflammatory activities

The objective of this work was to determine the potential bioactive properties of extracts from bio-residues of pinhão (Araucaria angustifolia (Bertol.) Kuntze) seeds, namely the α-amylase and cholinesterase inhibition, cytotoxicity, and anti-inflammatory properties. The pinhão extracts evaluated were obtained from cooking water (CW) and as an ethanolic extract from residual pinhão seed shells (PS). Catechin was the major compound found in both extracts. The PS extract presented higher antioxidant levels and the better inhibition of human salivary and porcine pancreatic α-amylases when compared to the CW extract. Also, based on in vivo evaluations, the PS extract did not differ significantly from acarbose when compared to a control group. The most potent inhibitor of cholinesterases was the CW extract. No cytotoxicity toward normal cells was detected, and neither extract showed anti-inflammatory activity. The PS extract presented cytotoxic activity toward non-small-cell lung, cervical, hepatocellular and breast carcinoma cell lines. Overall, the results demonstrated the potential bioactivity of extracts obtained from pinhão bio-residues.

Non-Alkaloid Cholinesterase Inhibitory Compounds from Natural Sources

Alzheimer's disease (AD) is a severe neurodegenerative disorder of different brain regions accompanied by distresses and affecting more than 25 million people in the world. This progressive brain deterioration affects the central nervous system and has negative impacts on a patient's daily activities such as memory impairment. The most important challenge concerning AD is the development of new drugs for long-term treatment or prevention, with lesser side effects and greater efficiency as cholinesterases inhibitors and the ability to remove amyloid-beta(Aβ) deposits and other related AD neuropathologies. Natural sources provide promising alternatives to synthetic cholinesterase inhibitors and many have been reported for alkaloids while neglecting other classes with potential cholinesterase inhibition. This review summarizes information about the therapeutic potential of small natural molecules from medicinal herbs, belonging to terpenoids, coumarins, and phenolic compounds, and others, which have gained special attention due to their specific modes of action and their advantages of low toxicity and high efficiency in the treatment of AD. Some show superior drug-like features in comparison to synthetic cholinesterase inhibitors. We expect that the listed phytoconstituents in this review will serve as promising tools and chemical scaffolds for the discovery of new potent therapeutic leads for the amelioration and treatment of Alzheimer's disease.

Novel Coumarin-Thiadiazole Hybrids and Their Cu(II) and Zn(II) Complexes as Potential Antimicrobial Agents and Acetylcholinesterase Inhibitors

A series of coumarin-thiadiazole hybrids and their corresponding Cu(II) and Zn(II) complexes were synthesized and characterized with the use of spectroscopic techniques. The results obtained indicate that all the coumarin-thiadiazole hybrids act as bidentate chelators of Cu(II) and Zn(II) ions. The complexes isolated differ in their ligand:metal ratio depending on the central metal. In most cases, the Zn(II) complexes are characteristic of a 1:1 ligand:metal ratio, while in the Cu(II) complexes the ligand:metal ratio is 2:1. All compounds were tested as potential antibacterial agents against Gram-positive (Staphylococcus aureus, Staphylococcus epidermidis) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacterial strains demonstrating activities notably lower than commercially available antibiotics. The more promising results were obtained from the assessment of antineurodegenerative potency as all compounds showed moderate acetylcholinesterase (AChE) inhibition activity.

Imidazopyridazine Acetylcholinesterase Inhibitors Display Potent Anti-Proliferative Effects in the Human Neuroblastoma Cell-Line, IMR-32

Imidazo[1,2-b]pyridazine compounds are a new class of promising lead molecules to which we have incorporated polar nitro and amino moieties to increase the scope of their biological activity. Two of these substituted 3-nitro-6-amino-imidazo[1,2-b]pyridazine compounds (5c and 5h) showed potent acetylcholinesterase (AChE) inhibitory activity (IC₅₀ 40–50 nM), which we have previously reported. In this study, we wanted to test the biological efficacy of these compounds. Cytotoxicity assays showed that compound 5h mediated greater cell death with over 43% of cells dead at 100 μM and activation of caspase 3-mediated apoptosis. On the other hand, compound 5c mediated a dose-dependent decrease in cell proliferation. Both compounds showed cell cycle arrest in the G₀/G₁ phase and reduced cellular ATP levels leading to activation of adenosine monophosphate-activated protein kinase (AMPK) and enhanced mitochondrial oxidative stress. It has to be noted that all these effects were observed at doses beyond 10 μM, 200-fold above the IC₅₀ for AChE inhibition. Both compounds also inhibited bacterial lipopolysaccharide-mediated cyclooxygenase-2 and nitric oxide release in primary rat microglial cells. These results suggested that the substituted imidazo (1,2-b) pyridazine compounds, which have potent AChE inhibitory activity, were also capable of antiproliferative, anti-migratory, and anti-inflammatory effects at higher doses.

Green One-Pot Synthesis of Coumarin-Hydroxybenzohydrazide Hybrids and Their Antioxidant Potency

Compounds from the plant world that possess antioxidant abilities are of special importance for the food and pharmaceutical industry. Coumarins are a large, widely distributed group of natural compounds, usually found in plants, often with good antioxidant capacity. The coumarin-hydroxybenzohydrazide derivatives were synthesized using a green, one-pot protocol. This procedure includes the use of an environmentally benign mixture (vinegar and ethanol) as a catalyst and solvent, as well as very easy isolation of the desired products. The obtained compounds were structurally characterized by IR and NMR spectroscopy. The purity of all compounds was determined by HPLC and by elemental microanalysis. In addition, these compounds were evaluated for their in vitro antioxidant activity. Mechanisms of antioxidative activity were theoretically investigated by the density functional theory approach and the calculated values of various thermodynamic parameters, such as bond dissociation enthalpy, proton affinity, frontier molecular orbitals, and ionization potential. In silico calculations indicated that hydrogen atom transfer and sequential proton loss-electron transfer reaction mechanisms are probable, in non-polar and polar solvents respectively. Additionally, it was found that the single-electron transfer followed by proton transfer was not an operative mechanism in either solvent. The conducted tests indicate the excellent antioxidant activity, as well as the low potential toxicity, of the investigated compounds, which makes them good candidates for potential use in food chemistry.

Phytochemical profiling of Blumea laciniata (Roxb.) DC. and its phytopharmaceutical potential against diabetic, obesity, and Alzheimer's

Blumea laciniata (Roxb.) DC. is a folk medicinal annual herb of the Asteraceae family that grows in South and Southeast Asia. In order to evaluate its phytopharmaceutical potential against diabetic, obesity, and Alzheimer's, a comprehensive phytochemical profile, in vitro and in silico enzyme inhibitory activity against α-amylase, α-glucosidase, lipase, cholinesterases, and tyrosinase along with in vitro antioxidant activity were performed. Additionally, in vivo antidiabetic activity and acute toxicity were also evaluated. The total phenolic content in various organs follows the following order: old leaf > flower bud > young leaf > flower > young stem > old stem > root, while total flavonoids followed the order: flower bud > old leaf > young leaf > flower > young stem > old stem > root. The identified phenolic compounds are 3,4-dihydroxybenzoic acid, caffeic acid, vanillic acid, p-coumaric acid, syringic acid, rosmarinic acid, trans-cinnamic acid, catechin, catechol, (-) epicatechin, rutin, quercetin, myricetin, and kaempferol, which are also expressed differently in various organs. Solvent extracts demonstrated strong antioxidant activity as well as varying levels of inhibition against the enzymes tested, with strong inhibitory activity against α-amylase, α-glucosidase, and lipase. Thirteen phenolic compounds displayed strong binding affinity in silico against studied enzymes, thus documented as bioactive. Furthermore, solvent extracts significantly suppressed blood glucose levels in mice with induced diabetes and extracts were not acutely toxic. The results suggest that Blumea laciniata (Roxb.) DC. could be a potential candidate for developing new phytopharmaceuticals and bioactive ingredients.

Comprehensive chemical study on different organs of cultivated and wild Sarcandra glabra using ultra-high performance liquid chromatography time-of-flight mass spectrometry (UHPLC-TOF-MS)

To illuminate the similarities and differences between wild and cultivated Sarcandra glabra (S. glabra), we performed a comprehensively study on 26 batches of cultivated S. glabra and 2 batches of wild S. glabra. Chemical constituents and distribution characteristics of roots, stems and leaves in both wild and cultivated S. glabra were investigated through UHPLC-TOF-MS method. The result revealed that there were significant differences between roots, stems and leaves in S. glabra. And the chemical contents in the root part were less or even absence than those in leaf and stem, which suggested the root organ could be excluded as medicine. Meanwhile, the chemical contents of stems and leaves in cultivated S. glabra was sightly higher than that of wild samples. Therefore, cultivated S. glabra may have a high potential for substitution of wild S. glabra without affecting its pharmaceutical properties. In summary, our study could provide important information to the molecular basis for quality control of S. glabra.

Inhibition of Amyloid Fibrillation of HEWL by 4-Methylcoumarin and 4-Methylthiocoumarin Derivatives

BACKGROUND

Several human diseases like Parkinson's, Alzheimer's disease, and systemic amyloidosis are associated with the misfolding and aggregation of protein molecules.

OBJECTIVE

The present study demonstrated the comparison of 4-methyl coumarin and 4-methylthiocoumarin derivative for their anti-amyloidogenic and disaggregation activities. The hen egg-white lysozyme is used as a model system to study protein aggregation and disaggregation under in vitro conditions.

METHODS

Techniques used in the study were Thioflavin T fluorescence assay, intrinsic fluorescence assay, circular dichroism, transmission electron microscopy, and molecular dynamics.

RESULTS

Fifteen compounds were screened for their anti-amyloidogenic and disaggregation potential. Six compounds significantly inhibited the fibril formation, whereas ten compounds showed disaggregation property of pre-formed fibrils. Under in vitro conditions, the compound C3 and C7 showed significant inhibition of fibril formation in a concentration-dependent manner as compared to control. C3 and C7 demonstrated 93% and 76% inhibition of fibril formation, respectively. Furthermore, C3 and C7 exhibited 83% and 76% disaggregation activity, respectively, of pre-formed HEWL fibrils at their highest concentration. These anti-amyloidogenic and disaggregation potential of C3 and C7 were validated by intrinsic fluorescence, CD, molecular dynamics, and TEM study.

DISCUSSION

4-methylthiocoumarins derivatives have shown better anti-amyloidogenic activity as compared to 4-methylcoumarin derivatives for both amyloid formation as well as disaggregation of preformed amyloid fibrils. Structurally, the derivatives of 4-methylthiocoumarins (C3 and C7) contain thio group on 2nd position that might be responsible for anti-amyloidogenic activity as compared to 4- methylcoumarin derivatives (C2 and C4).

CONCLUSION

C3 and C7 are novel 4-methylthiocoumarin derivatives that can be used as a lead for alleviation and symptoms associated with protein aggregation disorders.

Antiviral Activity of Isoimperatorin Against Influenza A Virus in vitro and its Inhibition of Neuraminidase

Influenza A virus (IAV) poses a severe threat to human health and is a major public health problem worldwide. As global anti-influenza virus drug resistance has increased significantly, there is an urgent need to develop new antiviral drugs, especially drugs from natural products. Isoimperatorin, an active natural furanocoumarin, exhibits a broad range of pharmacologic activities including anticoagulant, analgesic, anti-inflammatory, antibacterial, anti-tumor, and other pharmacological effects, so it has attracted more and more attention. In this study, the antiviral and mechanistic effects of isoimperatorin on influenza A virus in vitro were studied. Isoimperatorin illustrated a broad-spectrum antiviral effect, especially against the A/FM/1/47 (H1N1), A/WSN/33 (H1N1, S31N, amantadine resistant), A/Puerto Rico/8/34 (H1N1), and A/Chicken/Guangdong/1996 (H9N2) virus strains. The experimental results of different administration modes showed that isoimperatorin had the best antiviral activity under the treatment mode. Further time-of-addition experiment results indicated that when isoimperatorin was added at the later stage of the virus replication cycle (6–8 h, 8–10 h), it exhibited an effective antiviral effect, and the virus yield was reduced by 81.4 and 84.6%, respectively. In addition, isoimperatorin had no effect on the expression of the three viral RNAs (mRNA, vRNA, and cRNA). Both the neuraminidase (NA) inhibition assay and CETSA demonstrated that isoimperatorin exerts an inhibitory effect on NA-mediated progeny virus release. The molecular docking experiment simulated the direct interaction between isoimperatorin and NA protein amino acid residues. In summary, isoimperatorin can be used as a potential agent for the prevention and treatment of influenza A virus.

Design and synthesis of novel coumarin derivatives as potential acetylcholinesterase inhibitors for Alzheimer's disease

Twenty novel 7-benzyloxycoumarin based compounds were synthesized with a variety of bioactive chemical fragments. The synthesized compounds showed remarkable acetylcholinesterase (AChE) inhibitory activity. In vitro assay revealed that compounds 7-benzyloxy-4-{[(4-phenylthiazol-2(3H)-ylidene)hydrazono]methyl}-2H-chromen-2-one (5b, IC₅₀= 0.451μM), 7-benzyloxy-4-({[4-(4-methoxyphenyl)thiazol-2(3H)-ylidene]hydrazono}methyl)-2H-chromen-2-one (5d, IC₅₀= 0.625μM), 5-amino-1-[2-(7-benzyloxy-2-oxo-2H-chromen-4-yl)acetyl]-1H-pyrazole-4-carbonitrile (13c, IC₅₀= 0.466μM), 2-(7-benzyloxy-2-oxo-2H-chromen-4-yl)-N-(2-methylimino-4-phenylthiazol-3(2H)-yl)acetamide (16a, IC₅₀= 0.500μM) and 2-(7-benzyloxy-2-oxo-2H-chromen-4-yl)-N-[4-(4-methoxyphenyl)-2-methyliminothiazol-3(2H)-yl]acetamide (16b, IC₅₀= 0.590μM) exhibited promising AChE inhibitory activity even better than donepezil (IC₅₀= 0.711μM). Kinetic study for compound 5b implied mixed type inhibitor which could bind peripheral anionic site (PAS) and catalytic active site (CAS) of AChE enzyme. In addition, in vivo evaluation of compounds 5b, 13c and 16a confirmed significant memory improvement in scopolamine-induced impairment model in tested mice. Furthermore, in silico studies were performed on the synthesized compounds which included molecular docking study at the active site of recombinant human acetylcholinesterase enzyme (rhAChE) as well as prediction of ADMET and other physicochemical parameters. A correlation between the docking results and IC₅₀ of tested compounds was routinely observed and shared similar binding pattern to the co-crystallized ligand donepezil.

Cytotoxic and apoptotic potential of some coumarin and 2-amino-3-carbonitrile selenophene derivatives in prostate cancer

3-acetyl coumarin derivatives (1a-d) are formed as a result of condensation of salicylaldehyde derivatives and ethyl acetoacetate and were converted into coumarin-selenophene hybrid compounds (2a-d) in the basic medium by modified Gewald reaction in the presence of malononitrile and selenium. Products are characterized by nuclear magnetic resonance (NMR). The prepared compounds are screened for their anticancer activity against DU-145 cell line. In addition, selected target compounds are evaluated for apoptosis and oxidative stress on DU-145 (prostate carcinoma) cell lines.

Discovery of drug-like acetylcholinesterase inhibitors by rapid virtual screening of a 6.9 million compound database

Cholinesterase inhibitors remain the mainstay of Alzheimer's disease treatment, and the search for new inhibitors with better efficacy and side effect profiles is ongoing. Virtual screening (VS) is a powerful technique for searching large compound databases for potential hits. This study used a sequential VS workflow combining ligand-based VS, molecular docking and physicochemical filtering to screen for central nervous system (CNS) drug-like acetylcholinesterase inhibitors (AChEIs) amongst the 6.9 million compounds of the CoCoCo database. Eleven in silico hits were initially selected, resulting in the discovery of an AChEI with a K_i of 3.2 µM. In vitro kinetics and in silico molecular dynamics experiments informed the selection of an additional seven analogues. This led to the discovery of two further AChEIs, with K_i values of 2.9 µM and 0.65 µM. All three compounds exhibited reversible, mixed inhibition of acetylcholinesterase. Importantly, the in silico physicochemical filter facilitated the discovery of CNS drug-like compounds, such that all three inhibitors displayed high in vitro blood-brain barrier model permeability.