Synthesis, antioxidant evaluation, and quantitative structure–activity relationship studies of chalcones

Lannea coromandelica (Houtt.) Merr. Induces Heme Oxygenase 1 (HO-1) Expression and Reduces Oxidative Stress via the p38/c-Jun N-Terminal Kinase-Nuclear Factor Erythroid 2-Related Factor 2 (p38/JNK-NRF2)-Mediated Antioxidant Pathway

The leaves of Lannea coromandelica (Houtt.) Merr. are used in the Garo, Pahan, and Teli tribal communities of Bangladesh as a traditional medicinal plant to treat hepatitis, diabetes, ulcers, heart disease, and dysentery. However, there have been limited phytochemical and biological studies on the bark of L. coromandelica. This study aimed to investigate the antioxidant activities of L. coromandelica bark extract (LCBE) and the underlying mechanism using RAW 264.7 cells. The LCBE was analysed by high-pressure liquid chromatography (HPLC) to detect its key polyphenolic compounds. Various in vitro antioxidant assays were performed using RAW 264.7 cells to assess the antioxidant effects of the LCBE and to understand the underlying molecular mechanism. HPLC revealed the presence of gallic acid, (−)-epigallocatechin-3-gallate, catechin, chlorogenic acid, and caffeic acid in the LCBE. The extract showed a very potent capacity to scavenge numerous free radicals through hydrogen atom transfer and/or electron donation and also quenched cellular reactive oxygen species (ROS) generation without showing any toxicity. The LCBE was found to combat the oxidative stress by enhancing the expression, at both transcriptional and translational levels, of primary antioxidant enzymes as well as phase II detoxifying enzymes, especially heme oxygenase 1, through the upregulation of the nuclear factor erythroid 2-related factor 2 (NRF2)-mediated pathway in RAW 264.7 cells via the phosphorylation of p38 kinase and c-Jun N-terminal kinase (JNK). The LCBE exhibited strong antioxidant activities and mitigated the cellular ROS production. These results provide scientific evidence of its potential as an ideal applicant for a cost-effective, readily available, and natural phytochemical, as well as a strategy for preventing diseases associated with oxidative stress and attenuating disease progress.

Synthesis, structure, and antioxidant activity of methoxy- and hydroxyl-substituted 2'-aminochalcones

ABSTRACT

Three 2'-aminochalcone derivatives (E)-1-(2-aminophenyl)-3-(4-hydroxyphenyl)prop-2-en-1-one, (E)-1-(2-aminophenyl)-3-(3,4-dihydroxyphenyl)prop-2-en-1-one, and (E)-1-(2-amino-4,5-dimethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one, have been synthesized, characterized, and tested in vitro in order to assess their antioxidant activity. All compounds were characterized on the basis of 1H NMR, 13C NMR, ESI-mass spectrometry, FT-IR, UV/Vis, and elemental analysis. The X-ray crystal structures of (E)-1-(2-aminophenyl)-3-(4-hydroxyphenyl)prop-2-en-1-one and (E)-1-(2-amino-4,5-dimethoxyphenyl)-3-(4-methoxyphenyl)prop-2-en-1-one were successfully determined showing a planar molecule geometry. Studies on the biological properties including test of free radical scavenging ability (DPPH test) and superoxide dismutase mimetic activity were performed. The results indicate that the aminochalcone carrying two hydroxyl functionalities in adjacent meta and para position exhibits a stronger antioxidant activity than the other derivatives.

GRAPHICAL ABSTRACT

In Silico Drug-Designing Studies on Flavanoids as Anticolon Cancer Agents: Pharmacophore Mapping, Molecular Docking, and Monte Carlo Method-Based QSAR Modeling

In silico molecular modeling studies were carried out on some newly synthesized flavanoid analogues. Search for potential targets for these compounds was performed using pharmacophore-mapping algorithm employing inverse screening of some representative compounds to a large set of pharmacophore models constructed from human target proteins. Further, molecular docking studies were carried out to assess binding affinity of these compounds to proteins mediating tumor growth. In vitro anticancer studies were carried out on colon cancer cell lines (HCT116) to assess validity of this approach for target identification of the new compounds. Further important structural features of compounds for anticolon cancer activity were assessed using Monte Carlo-based SMILES and hydrogen graph-Based QSAR studies. In conclusion this study have depicted successful and stepwise application of pharmacophore mapping, molecular docking, and QSAR studies in target identification and lead optimization of flavonoids.

Coumarin-Chalcone Hybrids as Peroxyl Radical Scavengers: Kinetics and Mechanisms

The primary antioxidant activity of coumarin-chalcone hybrids has been investigated using the density functional and the conventional transition state theories. Their peroxyl radical scavenging ability was studied in solvents of different polarity and taking into account different reaction mechanisms. It was found that the activity of the hybrids increases with the polarity of the environment and the number of phenolic sites. In addition, their peroxyl radical scavenging activity is larger than those of the corresponding nonhybrid coumarin and chalcone molecules. This finding is in line with previous experimental evidence. All the investigated molecules were found to react faster than Trolox with (•)OOH, regardless of the polarity of the environment. The role of deprotonation on the overall activity of the studied compounds was assessed. The rate constants and branching ratios for the reactions of all the studied compounds with (•)OOH are reported for the first time.

Synthesis and Selective Cytotoxic Activities on Rhabdomyosarcoma and Noncancerous Cells of Some Heterocyclic Chalcones

Chemically diverse heterocyclic chalcones were prepared and evaluated for cytotoxicity, aiming to push forward potency and selectivity. They were tested against rhabdomyosarcoma (RMS) and noncancerous cell line (LLC-PK1). The influence of heteroaryl patterns on rings A and B was studied. Heterocycle functionalities on both rings, such as phenothiazine, thiophene, furan and pyridine were evaluated. Notably, the introduction of three methoxy groups at positions 3, 4, 5 on ring B appears to be critical for cytotoxicity. The best compound, with potent and selective cytotoxicity (IC₅₀ = 12.51 μM in comparison with the value 10.84 μM of paclitaxel), contains a phenothiazine moiety on ring A and a thiophene heterocycle on ring B. Most of the potential compounds only show weak cytoxicity on the noncancerous cell line LLC-PK1.

Synthesis of newer 1,2,3-triazole linked chalcone and flavone hybrid compounds and evaluation of their antimicrobial and cytotoxic activities

The present study was carried out in an attempt to synthesize a new class of antimicrobial and antiplasmodial agents by copper catalyzed click chemistry to afford 25 compounds 10-14(a-e) of 1,4-disubstituted-1,2,3-triazole derivatives of chalcones and flavones. The structures of the newly synthesized compounds were established by elemental analysis, IR, (1)H NMR, (13)C NMR and Mass spectral data. The newly synthesized compounds were evaluated for their antibacterial activity against Gram positive bacteria (Staphylococcus aureus, Enterococcus faecalis), Gram negative bacteria (Escherichia coli, Pseudomonas aeruginosa, Shigella boydii, Klebsiella pneumoniae) and antifungal activity against (Candida albicans, Candida tropicalis, Candida parapsilosis, Cryptococcus neoformans, Dermatophyte) as well as molds (Aspergillus niger, Aspergillus fumigatus). The antiplasmodial and cytotoxic activities of these compounds were also evaluated against human malaria parasite Plasmodium falciparum strain 3D7 and human hepato-cellular carcinoma cells (Huh-7), respectively. Compounds 10a, 10c, 10d, 12c and 14e showed promising antibacterial activity while compounds 10e, 11d, 11e, 12c, 13a, 13b, 13e, 14a and 14d showed good antifungal activity as compared to the corresponding standard drugs. Compound 10b was found to be the most active against Plasmodium falciparum while the remaining compounds showed moderate to weak antiplasmodial activity. However, cytotoxic activities of all compounds were found ineffective against Huh-7 cells.

2-Amino-4-aryl thiazole: a promising scaffold identified as a potent 5-LOX inhibitor

Human 5-lipoxygenase (5-LOX) is a target for asthma and allergy treatment. Zileuton is the only marketed drug targeting this enzyme (IC₅₀ ∼ 1 μM). The current study identifies a promising lead molecule which could be improved to match the activity of zileuton.

Synthesis, characterization and antiamoebic activity of chalcones bearing N-substituted ethanamine tail

A series of chalcones (4-21) possessing N-substituted ethanamine were synthesized by the aldol condensation reaction of 1-(4-(2-substituted ethoxy)phenyl)ethanones with different aldehydes preceded by the reaction of 2-chloro N-substituted ethanamine hydrochloride and 4-hydroxy acetophenone. The structure of all the synthesized compounds was elucidated by various spectral and X-ray diffraction studies. The compounds were screened against HM1: IMSS strain of Entamoeba histolytica and cytotoxicity was performed on A549 (non-small cell lung cancer cell line) cells by MTT assay. Out of eighteen compounds twelve showed better activity then the standard drug metronidazole. The compound 9, 14 and 19 showed good cell viability, hence were least toxic.

Blockage of ROS and NF-κB-mediated inflammation by a new chalcone L6H9 protects cardiomyocytes from hyperglycemia-induced injuries

Increased oxidative stress and cardiac inflammation have been implicated in the pathogenesis of diabetic cardiomyopathy (DCM). We previously found that a novel chalcone derivative, L6H9, was able to reduce LPS-induced inflammatory response in macrophages. This study was designed to investigate its protective effects on DCM and the underlying mechanisms. H9C2 cells were cultured with DMEM containing 33 mmol/L of glucose in the presence or absence of L6H9. Pretreatment with L6H9 significantly reduced high glucose-induced inflammatory cytokine expression, ROS level increase, mitochondrial dysfunction, cell apoptosis, fibrosis, and hypertrophy in H9c2 cells, which may be mediated by NF-κB inhibition and Nrf2 activation. In mice with STZ-induced diabetes, oral administration of L6H9 at 20 mg/kg/day for 8 weeks significantly decreased the cardiac cytokine and ROS level, accompanied by decreasing cardiac apoptosis and hypertrophy, and, finally, improved histological abnormalities and fibrosis, without affecting the hyperglycemia. L6H9 also attenuated the diabetes-induced NF-κB activation and Nrf2 decrease in diabetic hearts. These results strongly suggest that L6H9 may have great therapeutic potential in the treatment of DCM via blockage of inflammation and oxidative stress. This study also provides a deeper understanding of the regulatory role of Nrf2 and NF-κB in DCM, indicating that they may be important therapeutic targets for diabetic complications.

Reactivity of phenolic compounds towards free radicals under in vitro conditions

The free radical scavenging activity and reducing power of 16 phenolic compounds including four hydroxycinnamic acid derivatives namely ferulic acid, caffeic acid, sinapic acid and p-coumaric acid, benzoic acid and its derivatives namely protocatechuic acid, gallic acid and vanillic acid, benzene derivatives namely vanillin, vanillyl alcohol, veratryl alcohol, veratraldehyde, pyrogallol, guaiacol and two synthetic antioxidants, butylated hydroxy anisole (BHA) and propyl gallate were evaluated using 1,1-Diphenyl-2-picrylhydrazyl radical (DPPH(•)), 2,2'-Azinobis-3- ethylbenzothiazoline-6-sulfonic acid radical (ABTS(+•)), Hydroxyl radical ((•)OH) and Superoxide radical (O2 (•-)) scavenging assays and reduction potential assay. By virtue of their hydrogen donating ability, phenolic compounds with multiple hydroxyl groups such as protocatechuic acid, pyrogallol, caffeic acid, gallic acid and propyl gallate exhibited higher free radical scavenging activity especially against DPPH(•) and O2 (•-). The hydroxylated cinnamates such as ferulic acid and caffeic acid were in general better scavengers than their benzoic acid counter parts such as vanillic acid and protocatechuic acid. All the phenolic compounds tested exhibited more than 85 % scavenging due to the high reactivity of the hydroxyl radical. Phenolic compounds with multiple hydroxyl groups also exhibited high redox potential. Exploring the radical scavenging and reducing properties of antioxidants especially those which are found naturally in plant sources are of great interest due to their protective roles in biological systems.

Synthesis and antioxidant evaluation of enantiomerically pure bis-(1,2,3-triazolylmethyl)amino esters from modified α-amino acids

The efforts for synthesis of enantiomerically pure bis-(1,2,3-triazolylmethyl)amino esters 6 are reported in good yields from an in situ generated α-azidomethyl ketone. Optimum experimental conditions were established for preparation of α-halomethyl ketones 10 and α-N,N-dipropargylamino esters 11, all derived from α-amino acids. The starting materials reacted under conventional click chemistry conditions, revealing a specific reactivity of bromomethyl ketones over chloromethyl ketones. The antioxidant activity of compounds 6 was assayed by DPPH method. The compound 6c with an IC50 of 75.57 ± 1.74 μg mL(-1) was the most active. Technically, this methodology allows the preparation of a combinatorial library of analogues with different structural characteristics depending on the nature of the modified α-amino acids employed in the synthesis.

Recent developments in biological activities of chalcones: a mini review

Chalcones represent key structural motif in the plethora of biologically active molecules including synthetic and natural products. Synthetic manipulations of chalcones or their isolation from natural sources are being investigated worldwide for the development of more potent and efficient drugs for the treatment of several dreadful diseases such as cancer, diabetes, HIV, tuberculosis, malaria etc. Over the past few years, a large volume of research papers and review articles highlighting the significance of chalcone derivatives has been compiled in the literature. The present review article focuses on the recent developments (2010-2014) on various pharmacological and medicinal aspects of chalcones and their analogues.

Heteroaryl chalcones: design, synthesis, X-ray crystal structures and biological evaluation

Chalcone derivatives have attracted increasing attention due to their numerous pharmacological activities. Changes in their structures have displayed high degree of diversity that has proven to result in a broad spectrum of biological activities. The present study highlights the synthesis of some halogen substituted chalcones 3(a–i) containing the 5-chlorothiophene moiety, their X-ray crystal structures and the evaluation of possible biological activities such as antibacterial, antifungal and reducing power abilities. The results indicate the tested compounds show a varied range of inhibition values against all the tested microbial strains. Compound 3c with a p-fluoro substituent on the phenyl ring exhibits elevated antimicrobial activity, whereas the compounds 3e and 3f displayed the least antimicrobial activities. The compounds 3d, 3e, 3f and 3i showed good ferric and cupric reducing abilities, and the compounds 3b and 3c showed the weakest reducing power in the series.

Structural correlation of some heterocyclic chalcone analogues and evaluation of their antioxidant potential

A series of six novel heterocyclic chalcone analogues 4(a–f) has been synthesized by condensing 2-acetyl-5-chlorothiophene with benzaldehyde derivatives in methanol at room temperature using a catalytic amount of sodium hydroxide. The newly synthesized compounds are characterized by IR, mass spectra, elemental analysis and melting point. Subsequently; the structures of these compounds were determined using single crystal X-ray diffraction. All the synthesized compounds were screened for their antioxidant potential by employing various in vitro models such as DPPH free radical scavenging assay, ABTS radical scavenging assay, ferric reducing antioxidant power and cupric ion reducing antioxidant capacity. Results reflect the structural impact on the antioxidant ability of the compounds. The IC₅₀ values illustrate the mild to good antioxidant activities of the reported compounds. Among them, 4f with a p-methoxy substituent was found to be more potent as antioxidant agent.

Theoretical study on the antioxidant properties of 2'-hydroxychalcones: H-atom vs. electron transfer mechanism

The free radical scavenging activity of six 2'-hydroxychalcones has been studied in gas phase and solvents using the density functional theory (DFT) method. The three main working mechanisms, hydrogen atom transfer (HAT), stepwise electron-transfer-proton-transfer (ET-PT) and sequential-proton-loss-electron-transfer (SPLET) have been considered. The O-H bond dissociation enthalpy (BDE), ionization potential (IP), proton affinity (PA) and electron transfer energy (ETE) parameters have been computed in gas phase and solvents. The theoretical results confirmed the important role of the B ring in the antioxidant properties of hydroxychalcones. In addition, the calculated results matched well with experimental values. The results suggested that HAT would be the most favorable mechanism for explaining the radical-scavenging activity of hydroxychalcone in gas phase, whereas SPLET mechanism is thermodynamically preferred pathway in aqueous solution.

Chemical reactivity and biological activity of chalcones and other α,β-unsaturated carbonyl compounds

Abstract 1. Chalcones are structural analogues of benzalacetophenone (BAP). Several derivatives have been identified in plants and anticarcinogenic and anti-inflammatory properties were attributed to the compounds, probably related to their direct antioxidant activity or stimulatory effects on the expression of endogenous defence enzymes like hemeoxygenase-1 (HO-1). HO-1 expression is triggered by the Nrf2-Keap1 signalling pathway, initiated by the addition of chalcones to thiol groups of Keap1 via Michael-type reaction. 2. The present study used a model system estimating the reactivity of different synthetic chalcones and other α,β-unsaturated carbonyl compounds with thiols and compared the chemical reactivity with the biological activity, measured by HO-1 expression in human dermal fibroblasts. 3. Chemical reactivity with the thiol group of N-acetylcysteine was determined with 5,5'-dithiobis-(2-nitrobenzoic acid) and followed chemical principles of structure-reactivity relationship. Most reactive were sulforaphane, dimethylfumarate, chalcone 3 ((2E)-1-phenyl-3-pyrimidin-2-ylprop-2-en-1-one) and chalcone 7 (1,3-diphenylprop-2-yn-1-one). This result demonstrates that α,β-unsaturated carbonyl derivatives react with thiols differently. All compounds were also biologically active; however, expression of HO-1 was not only related to the chemical reactivity but also to the lipophilicity of the molecules which likely affected transmembrane uptake. Most efficient inducers of HO-1 expression were BAP, 4-hydroxynonenal and chalcone 1 (4-[(1E)-3-oxo-3-phenylprop-1-en-1-yl]benzonitrile), chalcone 5 ((2E)-1-phenyl-3-[4-(trifluoromethyl)-phenyl]prop-2-en-1-one) and chalcone 7.

(2E)-3-(4-Methyl-phen-yl)-1-(pyridin-3-yl)prop-2-en-1-one

The title compound, C(15)H(13)NO, has two crystallographically independent mol-ecules in the asymmetric unit which differ principally in the periplanar angle formed by the benzene and pyridine rings [41.41 (3) and 17.92 (5)°]. The mol-ecules exhibit an E conformation between the keto group with respect to the olefin double bond.