Combined molecular modeling and cholinesterase inhibition studies on some natural and semisynthetic O-alkylcoumarin derivatives

A Multitarget Approach against Neuroinflammation: Alkyl Substituted Coumarins as Inhibitors of Enzymes Involved in Neurodegeneration

Neurodegenerative disorders (NDs) include a large range of diseases characterized by neural dysfunction with a multifactorial etiology. The most common NDs are Alzheimer's disease and Parkinson's disease, in which cholinergic and dopaminergic systems are impaired, respectively. Despite different brain regions being affected, oxidative stress and inflammation were found to be common triggers in the pathogenesis and progression of both diseases. By taking advantage of a multi-target approach, in this work we explored alkyl substituted coumarins as neuroprotective agents, capable to reduce oxidative stress and inflammation by inhibiting enzymes involved in neurodegeneration, among which are Carbonic Anhydrases (CAs), Monoamine Oxidases (MAOs), and Cholinesterases (ChEs). The compounds were synthesized and profiled against the three targeted enzymes. The binding mode of the most promising compounds (7 and 9) within MAO-A and -B was analyzed through molecular modeling studies, providing and explanation for the different selectivities observed for the MAO isoforms. In vitro biological studies using LPS-stimulated rat astrocytes showed that some compounds were able to counteract the oxidative stress-induced neuroinflammation and hamper interleukin-6 secretion, confirming the success of this multitarget approach.

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.

Identification of first-in-class plasmodium OTU inhibitors with potent anti-malarial activity

OTU proteases antagonize the cellular defense in the host cells and involve in pathogenesis. Intriguingly, P. falciparum, P. vivax, and P. yoelii have an uncharacterized and highly conserved viral OTU-like proteins. However, their structure, function or inhibitors have not been previously reported. To this end, we have performed structural modeling, small molecule screening, deconjugation assays to characterize and develop first-in-class inhibitors of P. falciparum, P. vivax, and P. yoelii OTU-like proteins. These Plasmodium OTU-like proteins have highly conserved residues in the catalytic and inhibition pockets similar to viral OTU proteins. Plasmodium OTU proteins demonstrated Ubiquitin and ISG15 deconjugation activities as evident by intracellular ubiquitinated protein content analyzed by western blot and flow cytometry. We screened a library of small molecules to determine plasmodium OTU inhibitors with potent anti-malarial activity. Enrichment and correlation studies identified structurally similar molecules. We have identified two small molecules that inhibit P. falciparum, P. vivax, and P. yoelii OTU proteins (IC50 values as low as 30 nM) with potent anti-malarial activity (IC50 of 4.1-6.5 µM). We also established enzyme kinetics, druglikeness, ADME, and QSAR model. MD simulations allowed us to resolve how inhibitors interacted with plasmodium OTU proteins. These findings suggest that targeting malarial OTU-like proteases is a plausible strategy to develop new anti-malarial therapies.

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.

2-Oxo-2H-chromen-7-yl 4-chlorobenzoate

We describe the synthesis of 2-oxo-2H-chromen-7-yl 4-chlorobenzoate 3 in 88% yield by the O-acylation reaction of 7-hydroxy-2H-chromen-2-one 1 with 4-chlorobenzoyl chloride 2 in dichloromethane using a slight excess of triethylamine at 20 °C for 1 h. The ester 3 was completely characterized by mass spectrometry, IR, UV–Vis, 1D, and 2D NMR spectroscopy.

Studies of Coumarin Derivatives for Constitutive Androstane Receptor (CAR) Activation

Constitutive androstane receptor (CAR) activation has found to ameliorate diabetes in animal models. However, no CAR agonists are available clinically. Therefore, a safe and effective CAR activator would be an alternative option. In this study, sixty courmarin derivatives either synthesized or purified from Artemisia capillaris were screened for CAR activation activity. Chemical modifications were on position 5,6,7,8 with mono-, di-, tri-, or tetra-substitutions. Among all the compounds subjected for in vitro CAR activation screening, 6,7-diprenoxycoumarin was the most effective and was selected for further preclinical studies. Chemical modification on the 6 position and unsaturated chains were generally beneficial. Electron-withdrawn groups as well as long unsaturated chains were hazardous to the activity. Mechanism of action studies showed that CAR activation of 6,7-diprenoxycoumarin might be through the inhibition of EGFR signaling and upregulating PP2Ac methylation. To sum up, modification mimicking natural occurring coumarins shed light on CAR studies and the established screening system provides a rapid method for the discovery and development of CAR activators. In addition, one CAR activator, scoparone, did showed anti-diabetes effect in db/db mice without elevation of insulin levels.

7-Isopentenyloxycoumarin: What Is New across the Last Decade

7-Isopentenyloxycoumarin is among the most widespread naturally occurring prenyloxy umbelliferone derivatives. This secondary metabolite of mixed biosynthetic origin has been typically isolated from plants belonging to several genera of the Rutaceae and Apiaceae families, comprising widely used medicinal plants and in general plants with beneficial effects on human welfare, as well as edible fruits and vegetables. Although known for quite a long time (more than 50 years), only in the last two decades has this natural compound been revealed to exert powerful and promising pharmacological properties, such as active cancer chemopreventive, antibacterial, antiprotozoal, antifungal, anti-inflammatory, neuroprotective, and antioxidant properties, among the activities best outlined in the recent literature. The aim of this comprehensive miniature review article is to detail the novel natural sources and the effects described during the last decade for 7-isopentenyloxycoumarin and what has been reported on the mechanisms of action underlying the observed biological activities of this oxyprenylated secondary metabolite. In view of the herein described data, suggestions on how to address future research on the abovementioned natural product and structurally related derivatives in the best ways according to the authors will be also provided.

Reinvestigation of Herniaria glabra L. saponins and their biological activity

Twelve undescribed triterpenoid pentacyclic glycosides, medicagenic acid (3-O-β-D-glucuronopyranosyl-28-O-{[β-D-glucopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 2)]-[α-L-rhamnopyranosyl-(1 → 3)]-4-O-acetyl-β-D-fucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 3-O-β-D-glucuronopyranosyl-28-O-{[α-L-rhamnopyranosyl-(1 → 2)]-[β-D-apiofuranosyl-(1 → 3)]-4-O-acetyl-β-D-fucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 3-O-β-D-glucuronopyranosyl-28-O-{[α-L-rhamnopyranosyl-(1 → 2)]-3,4-O-diacetyl-β-D-fucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 28-O-{[6-O-acetyl-β-D-glucopyranosyl-(1 → 2)]-[2-O-acetyl-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 28-O-{[6-O-acetyl-β-D-glucopyranosyl-(1 → 2)]-[3-O-acetyl-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 28-O-{[6-O-acetyl-β-D-glucopyranosyl-(1 → 2)]-[4-O-acetyl-α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 28-O-{[6-O-acetyl-β-D-glucopyranosyl-(1 → 2)]-[β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid, 28-O-{[β-D-glucopyranosyl-(1 → 2)]-[β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranosyl-(1→)}-2β,3β-dihydroxyolean-12-ene-23,28-dioic acid), zanhic acid (3-O-β-D-glucuronopyranosyl-28-O-{[β-D-glucopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 2)]-[α-L-rhamnopyranosyl-(1 → 3)]-4-O-acetyl-β-D-fucopyranosyl-(1→)}2β,3β,16α-trihydroxyolean-12-ene-23,28-dioic acid, 3-O-β-D-glucuronopyranosyl-28-O-{[β-D-glucopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 2)]-β-D-fucopyranosyl-(1→)}-2β,3β,16α-trihydroxyolean-12-ene-23,28-dioic acid), 29-hydroxy-medicagenic acid (3-O-β-D-glucuronopyranosyl-28-O-{[β-D-glucopyranosyl-(1 → 3)-α-L-rhamnopyranosyl-(1 → 2)]-[α-L-rhamnopyranosyl-(1 → 3)]-4-O-acetyl-β-D-fucopyranosyl-(1→)}-2β,3β,29β-trihydroxyolean-12-ene-23,28-dioic acid) and herniaric acid (28-O-{[6-O-acetyl-β-D-glucopyranosyl-(1 → 2)]-[α-L-rhamnopyranosyl-(1 → 4)-β-D-glucopyranosyl-(1 → 6)]-β-D-glucopyranosyl-(1→)}-2β,3β-dihydroxyolean-18-ene-23,28-dioic acid) were isolated from the whole plant extract of Herniaria glabra L. (Caryophyllaceae), wild growing in the Ukraine. In addition, five known triterpenoid saponins; i.e. herniariasaponins 1, 4, 5, 6, and 7 were also isolated. Their structures were elucidated by HRESIMS, 1D and 2D NMR spectroscopy, as well as by comparison with the literature data. Twelve herniariasaponins, the purified crude extract, and the saponin fraction were evaluated in vitro for their xanthine oxidase, collagenase, elastase, and tyrosinase inhibitory activity. Moreover, herniariasaponins 4, 5, and 7 were screened for their cholinesterase inhibitory potential. As a result, no or low inhibition towards the mentioned enzymes was observed.