Tin(II)-quercetin complex: Synthesis, spectral characterisation and antioxidant activity

The complex formation between quercetin (Q) and stannous chloride (SnCl₂·2H₂O) was studied using UV-visible, IR and ¹H NMR spectroscopic techniques. Spectroscopic data suggest that Q can chelate stannous cations through both 3-hydroxy-4-carbonyl and the 3′,4′-dihydroxyl (catechol) chelation sites. The antioxidant activity of the complex was evaluated using 1,1-diphenyl-2-picrylhydrazyl (DPPH), 2,2′-azinobis 3-ethylbenzothiazoline-6-sulphonic acid (ABTS) diammonium salt and ferric reducing antioxidant power (FRAP) methods. It was shown that radical scavenging activity and ferric reducing potential of free Q was decreased after chelation of stannous cation.     

Free radical scavenging and antioxidant activity of 5,7,3′,4′-hydroxy-substituted flavonoids

The antioxidant efficiencies of 5,7,3′,4′-hydroxy-substituted flavonoids were examined. The tested compounds (quercetin, luteolin, taxifolin, (+)-catechin and eriodictyol) were selected with a view to their C-ring differentiated pattern. Each one was added in cottonseed oil at equimolar amounts and the retardation of lipid peroxidation was estimated by means of peroxide value. Furthermore, their ability to scavenge DPPH radical was studied in two solvents (methanol and ethyl acetate) and the DPPH method proved a satisfactory prediction test for the antioxidant action of flavonoids in oils when methanol was used as the reaction media. Furthermore, the comparison of the C-ring structural element contribution to the antioxidant action revealed the full substitution to be the most important followed by the 3-OH and 2,3-double bond in the presence of the 4-carbonyl. Concerning the monosubstituted flavonoids, the 4-carbonyl group induced minor activity, whereas the 3-OH increased significantly the antiradical and antioxidant action.     

黄酮对刺葡萄花色苷辅色稳定化效果的研究

研究了几种黄酮类物质对刺葡萄花色苷的辅色作用,并研究了槲皮素、黄芩素和芦丁对刺葡萄花色苷热稳定性的影响。结果表明:槲皮素对刺葡萄花色苷的辅色效果最为显著（p<0.05）,其次是黄芩素和芦丁,浓度为0.1 mmol·L-1时单位浓度辅色效果最佳;槲皮素和黄芩素辅色时,在p H2.0处,辅色效果最好,而芦丁辅色时,最佳p H为3.0。加入槲皮素、黄芩素、芦丁后,刺葡萄花色苷的降解速率常数（k）皆显著小于对照组,半衰期（t1/2）均显著高于对照组（p<0.05）。经槲皮素、黄芩素、芦丁辅色后刺葡萄花色苷的活化能（Ea）分别为88.48、91.67、83.62 k J/mol,显著（p<0.05）高于对照组的74.51 k J/mol,说明加入槲皮素、黄芩素、芦丁能提高刺葡萄花色苷的热稳定性。      

Sinensetin,rutin, 3′-hydroxy-5, 6, 7, 4′-tetramethoxyflavone and rosmarinic acid contents and antioxidative effect of the skin of apple fruit

A GC–MS method was developed for the separation and quantifiation of three flavones: sinensetin (SEN), rutin (RU) and 3′-hydroxy-5, 6, 7, 4′-tetramethoxyflavone (TMF) and rosmarinic acid (RA), a caffeic acid derivative, in the skin of apple fruit collected from different local markets of Bangladesh. The results showed significant variation in the amount of these markers in methanolic extracts of skin samples from different markets of Bangladesh, even though the values were almost identical for most of the cases. A variation in antioxidant activities, ranging from 62.82 to 92.34%, and variations in total phenolics, ranging from 6.69 to 10.20 mg caffeic acid/g dry weight of the methanol extracts, were observed. Antioxidative potency of the methanolic extracts was comparable to that of pure quercetin and the synthetic antioxidant butylated hydroxylanisole (BHA).     

Flavonol glucosides in Allium species: A comparative study by means of HPLC–DAD–ESI-MS–MS

Cultivars and consumption typologies of some Allium species can significantly vary from a chemical point of view and even small differences can be important for their characterization and differentiation. Bulbs of three varieties and four consumption typologies of onion (Allium cepa L.) and two varieties of shallot (Allium ascalonicum Hort.) were subjected to HPLC–DAD–ESI-MS–MS analysis. Seven flavonol glucosides were identified in all the samples, two of which, quercetin 3,4′-diglucoside and quercetin 4′-glucoside, represent about the 90% of the overall contents. Cultivars and consumption typologies of the Allium species under study show significant differences in flavonol contents, from the very low quantity of antioxidant compounds in white onion, about 7 mg/kg against 600–700 mg/kg that were found in red and gold varieties, to the enormous content of flavonols that are present in onions of prompt consumption, where quercetin 4′-glucoside exceeds 1 g/kg and quercetin 3-glucoside is present in a ratio higher then 10:1 with respect to its value in the other onion typologies. Shallots are very rich in the two major flavonols.     

Antioxidant flavonol glycosides in mulberry (Morus alba L.) leaves isolated based on LDL antioxidant activity

Oxidation of low-density lipoprotein (LDL) has been implicated in atherogenesis. Antioxidants that prevent LDL from oxidation may reduce atherosclerosis. We investigated LDL antioxidant activity and extracted compounds of mulberry (Morus alba L.) leaves. The LDL antioxidant activity of 60% ethanol extracted of mulberry leaves, which inhibits human LDL oxidation induced by copper ion, was determined on the basis of oxidation lag time and calculated as epigallocatechin 3-gallate equivalents (58.3 μmol of EGCG equivalent/g of dry weight). Three flavonol glycosides [quercetin 3-(6-malonylglucoside), rutin (quercetin 3-rutinoside) and isoquercitrin (quercetin 3-glucoside)] were identified as the major LDL antioxidant compounds by LC-MS and NMR. The amounts of these flavonol glycosides in mulberry leaves and mulberry-leaf tea were determined by HPLC. Our results showed that quercetin 3-(6-malonylglucoside) and rutin were the predominant flavonol glycosides in the mulberry leaves.     

Structure-dependent membrane interaction of flavonoids associated with their bioactivity

Plant foods contain various flavonoids with nutraceutical and health benefits. Structurally different flavonoids were compared by the potency to interact with liposomal membranes in the context of their mode of action. A series of fluorescence polarisation measurements showed that flavonoids (1–10 μM) structure-dependently acted on the deeper regions of lipid bilayers to decrease membrane fluidity. Their comparative effects on cell-mimetic membranes, consisting of unsaturated phospholipids and cholesterol, characterised the structure–membrane interactivity relationship: 3-hydroxylation of the C ring, non-modification of the B ring and 5,7-dihydroxylation of the A ring led to the greatest membrane interactivity, followed by 3′,4′-dihydroxylation of the B ring. Galangin and quercetin, meeting such a structural requirement, inhibited the proliferation of tumour cells at 10–100 μM, together with rigidifying cell membranes, but not membrane-inactive flavonoids. The structure-dependent membrane interaction, which modifies the fluidity, is mechanistically associated with flavonoid bioactivity in a membranous lipid phase.     

New diarylheptanoids from the rhizome of Alpinia officinarum Hance

Three diarylheptanoids, officinaruminane A (1), officinaruminane B (2), 5(S)-acetoxy-7-(4-dihydroxyphenyl)-1-phenyl-3-heptanone (3), together with six known ones , (5R)-5-hydroxy-1-(4-hydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-3-heptanone (4),(5R)-5-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-7-(4,5-dihydroxy-3-methoxyphenyl)-3-heptanone (5), 1-phenyl-7-(4-hydroxy-3-methoxyphenyl)-4E-en-3-heptanone (6), 1-(4-hydroxyphenyl)-7-(4-hydroxy-3-methoxyphenyl)-4E-en-3-heptanone (7), 1-phenyl-7-(4-hydroxyphenyl)- 4E- en-3-heptanone (8), and 3,6-furan-7-(4′′-hydroxy-3′′-methoxyphenyl)-1-phenylheptane (9), were isolated from the rhizomes of Alpinia officinarum Hance by column chromatography on silica gel, MPLC and preparative thin-layer chromatography (TLC). The structures of these compounds were elucidated on the basis of mass spectrometry, ¹H NMR, ¹³C NMR, HMQC and HMBC data. Among them, 1 is a diarylheptanoid with a pyridine ring, and 2 is a diarylheptane monoterpene.     

Combining the observation of cell morphology with the evaluation of key inflammatory mediators to assess the anti-inflammatory effects of geranyl flavonoid derivatives in breadfruit

Ligation of the receptor for advanced glycation end products (RAGE) is critical for monocyte activation involved in diabetic inflammation. In this study, the effects of the geranyl flavonoid derivatives (6-geranyl-7,4′-dihydroxyflavanone, AC-1; 4,2′,4′-trihydroxy-3′-[6-hydroxy-3,7-dimethyl-2(E),7-octadienyl]chalcone, AC-2; 3,4,2′,4′-tetrahydroxy-3′-geranyldihydrochalcone, AC-3; 4,2′,4′-trihydroxy-5′-geranyldihydrochalcone, AC-4) isolated from the fruit of Artocarpus communis (breadfruit) on the human THP-1 monocyte (THP-1) activation stimulated by S100B, a ligand of RAGE, were evaluated. The morphology of S100B-induced THP-1, which may be essential for the elucidation of the functional role of S100B in monocyte activation was investigated. We also directly demonstrated that S100B-induced THP-1 exhibited the morphological characteristics of inflammation, which were inhibited by the addition of AC-2, AC-3 or AC-4. Moreover, AC-2, AC-3 or AC-4 inhibited S100B-induced ROS generation, mRNA expression of inflammatory mediators (COX-2, TNF-α, IL-6 and RAGE) and IL-6 secretion. Thus, geranyl flavonoid derivatives of breadfruit may have potent implications to prevent diabetic inflammation.     

Isolation and structure elucidation of novel phenolic constituents from Sorbus domestica fruits

In the framework of the detailed phytochemical analysis of Sorbus domestica fruits at several maturity stages and additively to the phenolic compounds elucidated by LC-DAD-MS (ESI+), ten more, novel phenolic compounds were isolated after preparative work and their structure elucidation was achieved with UV–vis, NMR (¹H, ¹³C, COSY, HSQC, HMBC, NOESY, TOCSY, ROESY), LC-DAD-MS (ESI+) and HR-NanoESI-QqTOF-MS/MS. The novel compounds belong to the categories of hydroxybenzoic acid derivatives (Compounds 1, 2, 3), polyphenolic phenylpropanoid derivative (Compound 4), quercetin glycosides (Compounds 5, 6), flavanol glycoside (Compound 7), quercetin dimmer (Compound 8) and biphenyls (Compounds 9, 10). Their structures were established as: Vannilic acid 4-O-α-L-rhamnoside (1), protocatechuic acid anhydrite (2), trivanilloyl-(1,3,4-trihydroxybenzol) ester (3), 3-{4-(bis[4-hydroxy-3-(5-hydroxypentanoyloxy) phenyl) methoxy]-3,5-dihydroxy phenyl} propanoic acid (4), quercetin 3-O-β-D-glucopyranosyl(1′′′→2′′)-α-L-rhamnosyl(1′′′′→3′′′)-α-L-rhamnosyl(1′′′′′→3′′′′)-α-L-arabinofuranoside, quercetin 3-O-α-L-rhamnosyl(1′′′→3′′)-β-D-glucopyranoside (6), 5,7,3′,6′-tetrahydroxyflavanol 7-O-β-D-glucopyranoside (7), (7-O-4′′′, 4′O-7′′) quercetin dimmer (8), [2,2′-dihydroxy, 4-(propionic acid hexyl ester), 4′-(propionic acid heptyl ester)] biphenyl (9) and [2,6,2′,6′-tetrahydroxy, 4,4′-bis-(propionic acid hexyl ester)] biphenyl (10).     

6种黄酮协同抗氧化作用及构效关系研究

以ABTS~+·清除能力为指标,采用Chou-Talalay中效原理设计试验,研究6种结构不同的小分子黄酮协同抗氧化作用及构效关系。结果表明:6种黄酮化合物对ABTS~+·清除能力依次为:5,6,7-三羟基黄酮6-羟基黄酮3,7-二羟基黄酮5-羟基黄酮3-羟基黄酮7-羟基黄酮抗坏血酸,其中5,6,7-三羟基黄酮、6-羟基黄酮和3,7-二羟基黄酮氧化作用效果显著;在不同浓度下,两种黄酮复配物对ABTS+·清除能力的联合作用指数CI值有较大差异;3,7-二羟基黄酮和其它5种黄酮都有明显的协同作用。充分说明6种黄酮化合物之间的协同抗氧化作用与化合物的羟基位置和数量有关,具有C_(3,7)-二羟基是协同抗氧化作用的主要结构特点。     

Antioxidant activity of stem and root extracts of Rhubarb (Rheum ribes): An edible medicinal plant

The antioxidant activity of chloroform and methanol extract of roots and stems of Rhubarb (Rheum ribes L.), which are used for medicinal purposes and also its fresh stems and petioles are consumed as vegetable, was studied. The antioxidant potential of both extracts of roots and stems were evaluated using different antioxidant tests, namely total antioxidant (lipid peroxidation inhibition activity), DPPH (1,1-diphenyl-2-picrylhydrazyl) radical scavenging, superoxide anion radical scavenging, ferric reducing power, and cupric reducing power (CUPRAC), and metal chelating activities. Total antioxidant activity was also measured according to the β-carotene bleaching method, and all four extracts exhibited stronger activity than known standards, namely butylated hydroxytoluene (BHT) and α-tocopherol. Particularly, higher activity was exhibited by roots with 93.1% and 84.1% inhibitions of chloroform and methanol extracts, while 82.2% and 82.0% inhibitions by stem extracts, respectively. However, both methanol extracts exhibited higher DPPH radical scavenging activity than the corresponding chloroform extracts, moreover, methanol extract of the stems showed better activity than BHT. In addition, both root extracts showed more potent superoxide anion radical scavenging activity than BHT, and comparable with well known radical scavenger l-ascorbic acid. Except chloroform extract of the roots, the other three extracts exhibited better metal chelating activity than quercetin. Also, total phenolic and flavonoid contents in both extracts of the roots and stems of R. ribes were determined as pyrocatechol and quercetin equivalents, respectively.     

Preparation,characterisation and activity of the inclusion complex of paeonol with β-cyclodextrin

The inclusion complex of β-cyclodextrin (β-CD) and paeonol (2′-hydroxy-4′-methoxyacetophenone, PAE) was synthesised and characterised by thermal gravimetric analysis (TGA) and two-dimensional rotating frame spectroscopy (2D ROESY). The antioxidant activity and tyrosinase inhibition activity were also studied. The TGA results indicated that the thermal stability of PAE was improved when it was included with β-CD. Based on the 2D ROESY analysis, an inclusion structure of the PAE–β-CD complex was proposed, in which PAE penetrated β-CD in a tilted manner due to the interaction of intermolecular hydrogen bonds between PAE and β-CD. The complex of PAE with β-CD increased the antioxidant activity and tyrosinase-inhibiting activity of PAE.     

Tyrosinase inhibitors from paper mulberry (Broussonetia papyrifera)

Fractionation of a chloroform-soluble extract from twigs of Broussonetia papyrifera, led to the isolation of one new compound, 3,5,7,4′-tetrahydroxy-3′-(2-hydroxy-3-methylbut-3-enyl)flavone (1), and 10 known compounds, uralenol (2), quercetin (3), isolicoflavonol (4), papyriflavonol A (5), broussoflavonol F (6), 5,7,3′,5′-tetrahydroxyflavanone (7), luteolin (8), isoliquiritigenin (9), broussochalcone A (10) and 5,7,3′,4′-tetrahydroxy-3-methoxyflavone (11). Their structures were identified by interpretation of MS, ¹H NMR, ¹³C NMR, HMQC and HMBC data. Their inhibitory activities on mushroom tyrosinase using l-tyrosine as substrate were investigated and the IC₅₀ values of 3,5,7,4′-tetrahydroxy-3′-(2-hydroxy-3-methylbut-3-enyl)flavone, uralenol, quercetin and broussoflavonol F were found to be 96.6, 49.5, 57.8, and 82.3 μM, respectively, better than arbutin, a well-known tyrosinase inhibitor.     

马兰提取物抗氧化性研究

目的：考查马兰中水提取物和乙醇提取物抗氧化活性。方法：分别以水和乙醇为提取液,探讨马兰中水提取物和乙醇提取物的抗氧化活性,包括还原能力以及清除DPPH自由基、羟自由基、超氧阴离子自由基和H2O2的能力。 结果：提取物主要成分为黄酮类化合物。马兰水提取物的抗氧化活性为：超氧阴离子自由基(IC50 2.2μg/mL)＞H2O2(IC50 2.8μg/mL)＞羟自由基(IC50 5.6μg/mL)＞DPPH自由基(IC50 8.5μg/mL) ＞金属螯合性(IC50 28.0μg/mL)。而马兰乙醇提取物的抗氧化活性为：H2O2(IC50 2.0μg/mL) ＞超氧阴离子自由基(IC50 2.1μg/mL)>羟自由基(IC50 2.5μg/mL)> DPPH自由基(IC50 5.6μg/mL) ＞金属螯合性(IC50 51.2μg/mL)。结论：马兰提取物具有较强的抗氧化活性。     

Effects of quercetin metabolites on the enhancing effect of β-carotene on DNA damage and cytochrome P1A1/2 expression in benzo[a]pyrene-exposed A549 cells

A549 cells were pre-incubated with β-carotene (BC) alone or in combination with quercetin or three major quercetin metabolites in human plasma, quercetin 3-glucuronide (Q3G), quercetin 3′-sulphate (Q3′S) and isorhamnetin, followed by incubation with benzo[a]pyrene (BaP), to investigate the effects of these compounds on the BaP-induced harmful effects of BC. All the quercetin metabolites at 10 μM inhibited BaP + BC-induced cell death. Q3′S, Q3G and isorhamnetin also significantly decreased BaP ± BC-induced DNA damage by 64%, 60% and 24%, respectively. In a similar order, these compounds suppressed BaP + BC-induced cytochrome P450 (CYP)1A1/1A2 expression by 10–50%. Q3G and Q3′S significantly decreased the intracellular reactive oxygen species formation induced by BaP + BC; however, Q3G had the best effect on decreasing the loss of BC induced by Fe/NTA. The combined effects of quercetin metabolites were additive. This study indicates that quercetin metabolites decrease the BaP-induced harmful effect of β-carotene in A549 cells by downregulating the expression of CYP1A1/1A2, at least in part.     

Antioxidant/pro-oxidant properties of model phenolic compounds. Part II: Studies on mixtures of polyphenols at different molar ratios by chemiluminescence and LC–MS

The behaviour of four known antioxidants (quercetin, ascorbic acid, catechin and caffeic acid) and their mixtures at different molar ratios was studied in view of elaborating predictions over an eventual pro-oxidant or synergistic antioxidant activity. The Co(II)–EDTA luminol chemiluminescence showed that the mixture of quercetin and ascorbic acid at ratio 2:1 had the most pronounced antioxidant activity, while that of quercetin and caffeic acid at ratio 1:2 showed the least antioxidant activity, which may be interpreted as a strong propensity for pro-oxidant behaviour. The LC–MS analysis for the two mixtures revealed a significant amount of unoxidised quercetin in the case of quercetin with ascorbic acid, whereas in the case of quercetin with caffeic acid this amount was negligible. This observation supports the fact that the first combination was more antioxidant than the second, through efficient quercetin recycling (reduction of the quinone by ascorbic acid; redox cycling of quinones).     

A new flavone from antioxidant extracts of Pistacia terebinthus

Acetone and methanol extracts of the fruits of Pistacia terebinthus L. subsp. terebinthus L. were studied for their antioxidant activity by investigating their total phenolic and flavonoid contents, β-carotene bleaching potential, DPPH radical scavenging effect, scavenging activity on superoxide anion radical, reducing power, and metal chelating effect on ferrous ion. Both extracts showed very similar chemical profile by checking on TLC plates, and exhibited high scavenging activity on superoxide anion radical and DPPH radical. Due to these similarities they were combined and fractionated on a silica gel column for their constituents, and the most active three fractions in DPPH assay were purified to afford a new flavone 6′-hydroxyhypolaetin 3′-methyl ether (1) besides a group of known flavonoids apigenin, luteolin, luteolin 7-O-glucoside, quercetin, quercetagetin 3-methyl ether 7-O-glucoside, isoscutellarein 8-O-glucoside. Their structures were established by UV, UV shift reagents, and ¹H NMR spectroscopic techniques. Antioxidant activity of the new flavone was investigated by β-carotene bleaching and DPPH radical scavenging activity methods, and it showed a high activity in the first system, but not so good in the latter.     

Profiling and quantifying quercetin glucosides in onion (Allium cepa L.) varieties using capillary zone electrophoresis and high performance liquid chromatography

There is increasing evidence that flavonols demonstrate beneficial properties for human health. Quercetin is the major flavonol present in onion (Allium cepa cv) and is present predominantly as quercetin 3,4′-diglucoside and quercetin 4′-monoglucoside. These compounds are known to be potent free radical scavengers and antioxidants, and are considered to be protective against cardiovascular disease. Analysis for the presence of these compounds has therefore become more important. Robust capillary zone electrophoresis and high performance liquid chromatography procedures were developed for profiling and quantifying the levels of quercetin 3,4′-diglucoside and quercetin 4′-monoglucoside in 70% methanol/water extracts of six different onion varieties available in Victoria, Australia. Quercetin 3,4′-diglucoside, which is not commercially available as a reference standard, was isolated from freeze-dried onion powder by preparative high performance liquid chromatography and used to quantify the levels in the onion extracts. Significant differences in the levels and ratios of the two compounds were seen between red, brown and white onion varieties (e.g. ‘Redwing’; quercetin 3,4′-diglucoside 191 mg/100 g DW, quercetin 4′-monoglucoside 85 mg/100 g DW; ‘Cream Gold’, quercetin 3,4′-diglucoside 153 mg/100 g DW, quercetin 4′-monoglucoside 58 mg/100 g DW, ‘Spanish white’; quercetin 3,4′-diglucoside <1 mg/100 g DW, quercetin 4′-monoglucoside <1 mg/100 g DW).     

Isolation and characterisation of the isoflavones from sprouted chickpea seeds

Seven isoflavones were isolated from sprouted chickpea seeds by chromatography on silica gel column, polyamide column, sephadex LH-20 column and preparing thin-layer chromatography (TLC), respectively. The structures were characterised with one- and two-dimensional NMR in combination with mass and IR spectrometry. The obtained isoflavones were biochanin A (5,7-dihydroxyflavone-4′-methoxyflavone, (1); calycosin (7,3′-dihydroxy-4′-methoxyisoflavone, (2); formononetin (7-hydroxy-4′-methoxyisoflavone, (3); genistein (5,7,4′-trihydroxyisoflavone, (4); trifolirhizin (maackiain-3-O-β-d-glucopyranoside, (5); ononin (7-O-β-d-glucosyl-7-hydroxy-4′-methoxyisoflavone, (6); sissotrin (7-O-β-d-glucosyl-5,7-dihydroxy-4′-methoxyisoflavone, (7).