Synthesis and In Vitro Antioxidant Activity of New 3-Substituted-2-Oxindole Derivatives

A series of new 1,3-dihydro-3-hydroxy-3-(2-phenyl-2-oxoethyl)-2H-indol-2-ones (1a-g) and 1,3-dihydro-3-(2-phenyl-2-oxoethylidene)-2H-indol-2-ones (2a-g) were synthesised by Knoevenagel condensation of substituted indole-2,3-diones (isatins) with various acetophenones. The synthesised compounds were characterised by their physical data, elemental, IR, ¹H NMR, ¹³C NMR and mass spectral analyses and their in vitro antioxidant activity was determined by 2,2-diphenyl-1-picrylhydrazyl free radical scavenging assay. These compounds showed moderate to good antioxidant activities as compared with the standard, ascorbic acid. The antioxidant potential of 3-hydroxy-3-substituted oxindoles (1a-g) increased in a concentration-dependent manner from 10 to 500 μg/ml with 5-fluoro and 5-methyl analogues showing maximum activity. Of 3-aroyl methylene indol-2-ones (2a-g), majority of compounds with halogen substitution at position 5 of isatin ring exhibited good antioxidant activity within a concentration range of 5-100 μg/ml and the maximum activity was observed at 20 and 25 μg/ml concentrations. Thus, our study provides evidence that some newly synthesised isatin derivatives exhibit substantial antioxidant activity at low concentrations.     

磺化槲皮素金属配合物的合成、表征及抗氧化、抗菌活性研究

目的 研究磺化槲皮素金属配合物的合成方法及抗氧化、抗菌活性。方法 通过磺化、金属配位等步骤合成4种槲皮素磺酸金属配合物,以DPPH清除率、抑菌环的大小检测配合物的抗氧化、抗菌活性。结果 槲皮素磺酸锌配合物对金黄色葡萄球菌的抑制作用随浓度的增大而提高,在浓度为7.5 mg·mL^-1时其抑菌环为3.60 mm,对大肠杆菌没有抑制作用,其他磺酸金属配合物的抑菌效果并不明显。槲皮素磺酸金属配合物对DPPH的清除率随浓度的升高而增强,当槲皮素磺酸配合物的浓度达到40 mg·mL^-1时槲皮素磺酸锌配合物、槲皮素磺酸铜配合物、槲皮素磺酸钴配合物和槲皮素磺酸锰配合物清除率分别达到47.55%,91.40%,46.74%,68.22%。结论 通过磺化合成的槲皮素磺酸金属配合物具有抗菌和抗氧化的活性。     

Synthesis and antioxidant properties of (3,4-dihydroxyphenyl)(2,3,4-trihydroxyphenyl)methanone and its derivatives

(3,4-Dihydroxyphenyl)(2,3,4-trihydroxyphenyl)methanone (5) and its two derivatives with bromine were synthesized from reactions such as bromination and demethylation of (3,4-dimethoxyphenyl)(2,3,4-trimethoxyphenyl)methanone (6). The Wolf-Kishner reduction product (9) of 6 and its three derivatives with bromine were obtained. 4-(3,4-Dihydroxybenzyl)benzene-1,2,3-triol and its dibromide derivative (16) were also synthesized from 9 and the corresponding dibromide derivative. The in vitro antioxidant activities of nine new compounds synthesized in these reactions were determined by analyzing the radical scavenging activities of bromophenols for 2,2'-azino-bis(3-ethylbenzthiazoline-6-sulfonic acid) (ABTS), 1,1-diphenyl-2-picryl-hydrazyl (DPPH), N,N-dimethyl-p-phenylenediamine (DMPD), and the superoxide anion radical (O(2)(·-)) and examining the total reducing power through Fe(3+)-Fe(2+) transformation, FRAP and CUPRAC assays and the ferrous ions (Fe(2+)) chelating activities. Moreover, the results of these activities were compared to those of standard antioxidant compounds such as butylated hydroxyanisole (BHA), butylated hydroxytoluene (BHT), α-tocopherol, and trolox. The results showed that the synthesized bromophenols had effective antioxidant power. The phenol 5 with two phenolic rings and five phenolic hydroxyl groups was the most potent antioxidant and radical scavenger. In conclusion, the new compounds are promising molecules to be used owing to their potential antioxidant properties.     

Antioxidant evaluation of O-methylated metabolites of catechin, epicatechin and quercetin

Catechins and quercetin are major polyphenols in many plant foods that have been related to health promotion. In the human organism they are largely metabolized to different metabolites, which are further found in plasma and should contribute to the biological effects associated to the intake of the parent compounds. An important step in quercetin and catechins metabolism is the O-methylation of the catechol group, which can be expected to have an effect on their antioxidant and scavenging properties. In the present work, the 3′- and 4′-methylethers of catechin and epicatechin have been prepared and characterised and their antioxidant activity evaluated and compared to that of the corresponding quercetin derivatives. The antioxidant activity was assessed using the ferric reducing power (FRAP) assay and two methods based on the ability to scavenge the ABTS⁺ radical cation at different pH values. In these assays the three flavonoids behave as better radical scavengers and reducing compounds than usually recognised antioxidants like α-tocopherol. The O-methylation of the hydroxyls of the catechol B-ring resulted in a decrease of the antioxidant activity with regard to the parent compounds. However, the methylated metabolites still retain significant radical scavenging activity at pH 7.4, suggesting that they could act as potential antioxidants in physiological conditions. Quercetin and its methylated metabolites showed, in general, greater activity than (epi)catechin and their O-methyl derivatives, although a relatively high antioxidant activity was found in the case of 3′-O-methyl catechin at pH 7.4, comparable to those of its parent compound and the quercetin metabolites. It was confirmed that the antioxidant activity of the flavonoids assayed was strongly dependent on the pH of the medium, showing higher activity at greater pH values. The results obtained are expected to contribute to the understanding of the mechanisms involved in the biological effects attributed to the intake of flavonoid-rich diets.     

Synthesis and Antioxidant Activity of New Pyridines Containing Gallate Moieties

Pyridines containing the galloyl moiety have been prepared utilizing 4‐acetyl pyrogallol. In addition, fused pyridines were synthesized from the obtained pyridines via further chemical transformations. The results indicated that compound 4a showed stronger DPPH scavenging activity than the other compounds, and the scavenging effect decreased in the following order 4a > t‐BHQ > 2a > 2b > 3a > 3b > 4b . Accordingly, other antioxidant assays were conducted for 4a . The results suggested that compound 4a could be a good antioxidant candidate. The absence of mortality of rats receiving 5000 mg/kg body weight of 4a as single oral dose may indicate that it could be a safe antioxidant and may be used for further studies.

     

Antioxidant activity of selected plant species; potential new sources of natural antioxidants

The aim of this study was to examine six plants from Serbia for their potential antioxidant activity. Therefore, six antioxidant activity assays were carried out, including: total antioxidant capacity, DPPH free-radical scavenging, the inhibitory activity toward lipid peroxidation, Fe³⁺- reducing power, Fe²⁺- chelating ability and hydroxyl radical scavenging activity. Total phenolic and flavonoid contents were also determined for each alcoholic extract. Cotinus coggygria extract contained the highest amount of total phenols (413 mg GAE /g dry extract), while the highest proportion of flavonoids was found in the Echium vulgare methanol extract (105 mg RU/g). Cotinus coggygria and Halacsya sendtneri alcoholic extracts showed the highest total antioxidant capacity (313 and 231 mg AA/g dry extract), as well as DPPH free-radical scavenging (IC₅₀ = 9 and 99 μg/ml), inhibitory activity toward lipid peroxidation (IC₅₀ = 3 and 17 μg/ml) and reducing power. Whereas, the greatest hydroxyl radical scavenging activity, as well as ferrous ion chelating ability showed Echium vulgare, Echium rubrum and Halacsya sendtneri.     

Antioxidant,free radical scavenging activities of Salvia brachyantha and its protective effect against oxidative cardiac cell injury

In this study, antioxidant and free radical scavenging activities of an endemic Salvia species (Salvia brachyantha (Bordz) probed. was assessed in vitro using 1,1-diphenyl-2-picryhydrazyl (DPPH) radical, β-carotene linoleic acid, superoxide anion radical, hydroxyl radical, and reducing power assays. Regarding our data, the plant extract exhibited antioxidant and radical scavenging activities at different magnitudes of potency. In addition, this study was undertaken to assess whether methanol extract of S. brachyantha could increase the endogenous antioxidant enzymes in cells, and where such increased cellular defences could provide protection against oxidative cell injury. Pre treatment of rat heart cell lines with 100 μg/ml of plant extract for 24 h significantly prevented cell damage and enhanced activity of antioxidant enzymes induced by a treatment with xanthine/xanthine oxidase. Increased reactive oxygen species and cell apoptosis induced by xanthine/xanthine oxidase was dose-dependently prevented when cells were pre treated for 24 h with plant extract. These results indicated that S. brachyantha could protect against cell injury via induction of the antioxidant enzyme defences. The extract of this plant might be valuable antioxidant natural sources and seemed to be applicable in both healthy medicine and food industry.     

Regioselective Synthesis,Characterization, and Antimicrobial Activities of Some New Monosaccharide Derivatives

A regioselective acylation series of methyl α-D-glucopyranoside (1), methyl 3-O-benzoyl-4,6-O-benzylidene-α-D-mannopyranoside (1A), and methyl 4,6-O-benzylidene-2-O-(3,5-dinitrobenzoyl)-α-D-mannopyranoside (1B) has been carried out by the direct acylation method and afforded the 2,6-di-O-glucopyranoside and 2 or 3-O-mannopyranoside derivatives in an excellent yield. In order to obtain newer products, the 2,6-di-O-glucopyranoside derivative was further transformed to a series of 3,4-di-O-acyl derivatives containing a wide variety of functionalities in a single molecular framework. The structures of the newly synthesized compounds were elucidated on the basis of IR, ¹H-NMR, ¹³C-NMR, ¹³C-DEPT spectral data, and elemental analysis. These synthesized derivatives were screened for in vitro antimicrobial activities against ten human pathogenic and five phytopathogenic microorganisms. A number of test compounds showed remarkable antimicrobial activity comparable to, and in some cases even higher than, the standard antibiotics employed. It was observed that methyl 3,4-di-O-(3-chlorobenzoyl)-2,6-di-O-hexanoyl-α-D-glucopyranoside (8) exhibited a varied range of MIC from 12.5 μg/disc to 25 μg/disc by the disk diffusion method and 1000 μg/mL to 1250 μg/mL by the broth macrodilution method.     

镰形棘豆黄酮类成分提取工艺与体外抗氧化活性研究

摘要 目的用正交实验法对镰形棘豆提取工艺进行优化,体外实验评价镰形棘豆总黄酮提取物的抗氧化活性。方法以镰形棘豆总黄酮的提取率和出膏率为评价指标,采用L9（34）正交实验设计法,优化镰形棘豆水提取工艺。选择清除羟自由基的Fenton法、清除1,1 二苯基 2 三硝基苯肼（DPPH）自由基法及还原能力,检测镰形棘豆总黄酮的体外抗氧化能力。结果镰形棘豆最佳水提取工艺为用药材10倍量体积的水,80 ℃热回流提取3次,每次1.0 h。该水提物中总黄酮含量达到（72.92±5.04） mg·g－1。镰形棘豆总黄酮提取物对羟自由基、DPPH自由基具有良好的清除能力,达到50%清除率所需药物的浓度（EC50）分别为1.10 mg·mL－1和262.57 μg·mL－1。结论该工艺可以显著提高提取物中黄酮类成分的含量,方法可靠,简便易行。富集后的镰形棘豆总黄酮具有良好的抗氧化活性,且活性与剂量呈正相关。     

Synthesis,In Vitro Antimicrobial and Antioxidant Activities of Some New 4,5‐Dihydro‐1H‐1,2,4‐triazol‐5‐one Derivatives

A series of compounds derived from 4,5‐dihydro‐1H‐1,2,4‐triazol‐5‐one were synthesized and characterized by spectral data. The 12 new compounds were analyzed for their potential in vitro antioxidant activities by three different methods. Compound 4f showed the best activity for the iron binding. In addition, the compounds 4 were titrated potentiometrically with tetrabutylammonium hydroxide in non‐aqueous solvents. The RP‐HPLC capacity factors (k′) of the series were also determined on a C18 column, with methanol/water as the mobile phase. The correlation between log k′ with the percentage of methanol in the mobile phase was used for the determination of the log k_w values for these compounds. The antimicrobial activities of these compounds were also screened against bacteria and yeast.     

Synthesis,Antiplatelet and Vasorelaxing Activities of Xanthone Derivatives

A series of ω‐aminoalkoxylxanthones was synthesized and tested in vitro for their ability to inhibit platelet aggregation and cause vasorelaxing action. Compounds 4 , 5 , 12 , 17 , and 18 showed significant antiplatelet effects on thrombin‐, arachidonic acid (AA)‐, collagen‐, and platelet activating factor (PAF)‐induced washed rabbit platelet aggregation and exhibited inhibition of primary and secondary aggregation induced by adenosine‐5'‐diphosphate (ADP) in human platelet‐rich‐plasma (PRP). Compounds 4 , 17 , and 18 revealed vasorelaxing activities in rat thoracic aorta. We concluded that these compounds may be developed as new antithrombotic agents.     

Antioxidant properties, total phenols and pollen analysis of propolis samples from Portugal

Pollen analysis, total phenols content and antioxidant activity were studied for the first time in Portuguese propolis samples from Bornes and Fundão regions. Total phenols content was determined by colorimetric assay and their amount was of 329 mg/g of GAE in Bornes sample and 151 mg/g of GAE in Fundão propolis. The antioxidant capacity of propolis extracts was assessed through the scavenging effects on DPPH (2,2-diphenyl-1-picrylhydrazyl) and reducing power of iron (III)/ ferricyanide complex assays. A concentration-dependent antioxidative capacity was verified in DPPH and reducing power assays. Low values of EC₅₀ on DPPH scavenging assay were obtained for Bornes and Fundão propolis (of 6.22 μg/mL and 52.00 μg/mL, respectively). For reducing power the values were 9.00 μg/mL, for Bornes propolis, and 55.00 μg/mL, for Fundão propolis. The high activity of propolis from Bornes could be related with their different pollen composition. The results obtained indicate that Portuguese propolis is an important source of total phenols showing antioxidant properties that could be beneficial for human health.     

Antioxidant Activities of Plants Used in Traditional Medicine in Turkey

Ethanol extracts from 6 species representing six different families, used in traditional medicine in Turkey were evaluated for their antioxidant activities. The inhibition of superoxide anion formation and lipid peroxidation levels of Ononis spinosa, Centranthus longiflorus, Lythrum salicaria, Plantago major, Juglans regia and Teucrium polium extracts were tested using in vitro standard procedures and IC₅₀ values were determined. In vitro tests included superoxide anion radical scavenging activity and lipid peroxidation. All ethanol extracts of plants showed concentration-dependent superoxide anion radical scavenging activity. The results of the superoxide anion formation assay showed that the ethanol extract of Centranthus longiflorus was found to be most potent inhibitor (IC₅₀ 0.77?mg/ml) and followed by Plantago major (IC₅₀ 1.21?mg/ml), Juglans regia (IC₅₀ 1.39?mg/ml), Ononis spinosa (IC₅₀ 1.35?mg/ml), Teucrium polium (IC₅₀ 3.10?mg/ml) and Lythrum salicaria (IC₅₀ 5.00?mg/ml). All the extracts, excluding Ononis spinosa and Teucrium polium, showed concentration-dependent inhibitory effect on lipid peroxidation. IC₅₀ values of the effective ethanol extracts of plants on lipid peroxidation were as follows: Juglans regia (IC₅₀ 3.3?mg/ml), Plantago major (IC₅₀ 3.4?mg/ml), Centranthus longiflorus (IC₅₀ 3.9?mg/ml) and Lythrum salicaria (IC50 5.3?mg/ml). The results showed that Centranthus longiflorus, Plantago major and Juglans regia extracts had the highest antioxidant capacities among the six species examined.