Synthesis, Anticholinesterase, Antioxidant, and Anti-Aflatoxigenic Activity of Novel Coumarin Carbamate Derivatives

Recent Developments in Coumarin Derivatives as Neuroprotective Agents

BACKGROUND

Neurodegenerative diseases are among the diseases that cause the foremost burden on the health system of the world. The diseases are multifaceted and difficult to treat because of their complex pathophysiology, which includes protein aggregation, neurotransmitter breakdown, metal dysregulation, oxidative stress, neuroinflammation, excitotoxicity, etc. None of the currently available therapies has been found to be significant in producing desired responses without any major side effects; besides, they only give symptomatic relief otherwise indicated off-episode relief. Targeting various pathways, namely choline esterase, monoamine oxidase B, cannabinoid system, metal chelation, β-secretase, oxidative stress, etc., may lead to neurodegeneration. By substituting various functional moieties over the coumarin nucleus, researchers are trying to produce safer and more effective neuroprotective agents.

OBJECTIVES

This study aimed to review the current literature to produce compounds with lower side effects using coumarin as a pharmacophore.

METHODS

In this review, we have attempted to compile various synthetic strategies that have been used to produce coumarin and various substitutional strategies used to produce neuroprotective agents from the coumarin pharmacophore. Moreover, structure-activity relationships of substituting coumarin scaffold at various positions, which could be instrumental in designing new compounds, were also discussed.

RESULTS

The literature review suggested that coumarins and their derivatives can act as neuroprotective agents following various mechanisms.

CONCLUSION

Various studies have demonstrated the neuroprotective activity of coumarin due to an oxaheterocyclic loop, which allows binding with a broad array of proteins, thus motivating researchers to explore its potential as a lead against various neurodegenerative diseases.

Umbelliferone and Its Synthetic Derivatives as Suitable Molecules for the Development of Agents with Biological Activities: A Review of Their Pharmacological and Therapeutic Potential

Umbelliferone (UMB), known as 7-hydroxycoumarin, hydrangine, or skimmetine, is a naturally occurring coumarin in the plant kingdom, mainly from the Umbelliferae family that possesses a wide variety of pharmacological properties. In addition, the use of nanoparticles containing umbelliferone may improve anti-inflammatory or anticancer therapy. Also, its derivatives are endowed with great potential for therapeutic applications due to their broad spectrum of biological activities such as anti-inflammatory, antioxidant, neuroprotective, antipsychotic, antiepileptic, antidiabetic, antimicrobial, antiviral, and antiproliferative effects. Moreover, 7-hydroxycoumarin ligands have been implemented to develop 7-hydroxycoumarin-based metal complexes with improved pharmacological activity. Besides therapeutic applications, umbelliferone analogues have been designed as fluorescent probes for the detection of biologically important species, such as enzymes, lysosomes, and endosomes, or for monitoring cell processes and protein functions as well various diseases caused by an excess of hydrogen peroxide. Furthermore, 7-hydroxy-based chemosensors may serve as a highly selective tool for Al3+ and Hg2+ detection in biological systems. This review is devoted to a summary of the research on umbelliferone and its synthetic derivatives in terms of biological and pharmaceutical properties, especially those reported in the literature during the period of 2017-2023. Future potential applications of umbelliferone and its synthetic derivatives are presented.

Antioxidant Activity of Coumarins and Their Metal Complexes

Ubiquitously present in plant life, coumarins, as a class of phenolic compounds, have multiple applications-in everyday life, in organic synthesis, in medicine and many others. Coumarins are well known for their broad spectrum of physiological effects. The specific structure of the coumarin scaffold involves a conjugated system with excellent charge and electron transport properties. The antioxidant activity of natural coumarins has been a subject of intense study for at least two decades. Significant research into the antioxidant behavior of natural/semi-synthetic coumarins and their complexes has been carried out and published in scientific literature. The authors of this review have noted that, during the past five years, research efforts seem to have been focused on the synthesis and examination of synthetic coumarin derivatives with the aim to produce potential drugs with enhanced, modified or entirely novel effects. As many pathologies are associated with oxidative stress, coumarin-based compounds could be excellent candidates for novel medicinal molecules. The present review aims to inform the reader on some prominent results from investigations into the antioxidant properties of novel coumarin compounds over the past five years.

Synthesis, DFT investigations, antioxidant, antibacterial activity and SAR-study of novel thiophene-2-carboxamide derivatives

Synthetic strategy for the synthesis of thiophene 2-carboxamide derivatives substituted with hydroxyl, methyl and amino groups at position-3 was proposed. The strategy includes the cyclization of the precursor ethyl 2-arylazo-3-mercapto-3-(phenylamino)acrylate derivatives, 2-acetyl-2-arylazo-thioacetanilide derivatives and N-aryl-2-cyano-3-mercapto-3-(phenylamino)acrylamide derivatives with N-(4-acetylphenyl)-2-chloroacetamide in alcoholic sodium ethoxide. IR, ¹H NMR, and mass spectroscopic analyses were used to characterize the synthesized derivatives. In addition, molecular, electronic properties of the synthesized products were studied by the density functional theory (DFT) where they exhibited close HOMO-LUMO energy gap (ΔE_H-L) in which the amino derivatives 7a-c have the highest while the methyl derivatives 5a-c were the lowest. Using the ABTS method, the antioxidant properties of the produced compounds were evaluated, where amino thiophene-2-carboxamide 7a exhibit significant inhibition activity 62.0% compared to ascorbic acid The antibacterial activity against two pathogenic Gram-positive bacteria (Staphylococcus aureus and Bacillus subtilis) and two of pathogenic Gram-negative bacteria (Escherichia coli and Pseudomonas aeruginosa) revealed that 7b records the highest activity index compared to ampicillin 83.3, 82.6, 64.0, 86.9%, respectively. Furthermore, the thiophene-2-carboxamide derivatives were docked with five different proteins with the use molecular docking tools and the results explained interactions between amino acid residue of enzyme and compounds. Compounds 3b and 3c showed the highest binding score with 2AS1 protein.

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.

Structure and therapeutic uses of butyrylcholinesterase: Application in detoxification, Alzheimer's disease, and fat metabolism

Structural information of butyrylcholinesterase (BChE) and its variants associated with several diseases are discussed here. Pure human BChE has been proved safe and effective in treating organophosphorus (OPs) poisoning and has completed Phase 1 and 2 pharmacokinetic (PK) and safety studies. The introduction of specific mutations into native BChE to endow it a self-reactivating property has gained much progress in producing effective OPs hydrolases. The hydrolysis ability of native BChE on cocaine has been confirmed but was blocked to clinical application due to poor PK properties. Several BChE mutants with elevated cocaine hydrolysis activity were published, some of which have shown safety and efficiency in treating cocaine addiction of human. The increased level of BChE in progressed Alzheimer's disease patients made it a promising target to elevate acetylcholine level and attenuate cognitive status. A variety of selective BChE inhibitors with high inhibitory activity published in recent years are reviewed here. BChE could influence the weight and insulin secretion and resistance of BChE knockout (KO) mice through hydrolyzing ghrelin. The BChE-ghrelin pathway could also regulate aggressive behaviors of BChE-KO mice.

Synthesis and Biological Evaluation of Novel Coumarins with tert-Butyl and Terpene Substituents

Coumarins with terpene and tert-butyl substituents were synthesized via Pechmann condensation reaction. New derivatives were investigated in different model system for the exhibition of antioxidant, radical scavenging and membrane-protective activities. It has been found that 4-methylcoumarin derivatives with monoterpene moieties exhibit high antioxidant activities. The most active and promising for further investigations is 5-hydroxy-6,8-diisobornyl-4-methylcoumarin, containing two isobornyl substituents on the benzopyran ring.