Comparing the Affinities of Flavonoid Isomers with Protein by Fluorescence Spectroscopy

Abstract

Dietary flavonoids can be detected in plasma as protein‐bound conjugates. Flavonoids–protein interaction is expected to modulate the bioavailability of flavonoids. In this work, the binding flavonoid isomers (galangin, baicalein, apigenin, and genistein; MW=270.25) and B‐ring hydroxylation flavonols (galangin, kaempferol, quercetin, and myricetin, which share the same structure on the A and C rings but have 0, 1, 2, and 3 moieties of ‐OH on the B‐ring, respectively) to protein were investigated by fluorescence quenching method. The apparent binding constants (K _a ) of were flavonoid isomers determined as: flavones (10⁶–10⁷ L mol^?1)>isoflavone≈flavonol (10⁵ L mol^?1). For B‐ring hydroxylation flavonols, the binding affinity increased with increasing number of hydroxyl groups on the B‐ring. The binding constants (K _a ) were determined as follows: myricetin>quercetin>kaempferol>galangin.     

Forced Degradation of Flavonol Glycosides Extraced from Ginkgo biloba

The degradation of flavonol glycosides extracted from Ginkgo biloba was performed under different conditions and the degraded products were determined by reversed-phase high performance liquid chromatography (RP-HPLC) method. Four stress conditions including acid(0.1 mol/L HCl), base(0.1 mol/L NaOH), temperature (70 ℃) and oxidation(0.03% H₂O₂, volume fraction) were used for the forced degradation studies. The pH stabilities of the flavonol glycosides were determined in phosphate buffers of varying pH values from 4.5 to 7.4. The degradation rate constants and half-life of three Ginkgo flavonol aglycones(quercetin, kaempferol and isorhamnetin) which represent Ginkgo flavonol glycosides were calculated in forced degradation and pH-stability studies of them. The results indicate that the three substances were more stable when incubated under acid condition and showed pH-dependent stability. The degradation was observed to follow first-order kinetics in all degradation studies. The stability results could provide important bases on development, preparation and storage of products of Ginkgo biloba extract and should be significantly considered during the further formulation development.     

大黄柳叶中新黄酮苷的结构鉴定

利用聚酰胺柱色谱法和制备型高效液相色谱法从柳属植物大黄柳叶中分离得到了一种新黄酮苷和两个已知黄酮化合物。利用核磁共振谱、质谱、紫外光谱、红外光谱对化合物结构进行了分析和表征。结果表明,新化合物为地奥亭7-O-β-D-吡喃木糖（1→6）β-D吡喃葡萄糖苷,为从自然界中首次发现的新黄酮苷类化合物。2种已知黄酮化合物为槲皮素3-O-芸香糖苷和槲皮素3-O-β-D-吡喃半乳糖苷。     

高效液相色谱-串联质谱法同时测定银杏保健茶中的16种黄酮类功效成分

建立了银杏保健茶中16种黄酮类物质的液相色谱-串联质谱(LC-MS/MS)测定方法。16种黄酮成分分别为儿茶素、牡荆素、葛根素、大豆苷元、水飞蓟宾、槲皮素、木犀草素、芹菜素、柚皮素、橙皮素二氢查尔酮、山柰酚、橙皮素、异鼠李素、黄芩素、川陈皮素、桔皮素。实验优化了液相色谱条件和质谱参数。采用C₁₈柱分离,流动相为乙腈-水(含0.1%甲酸)梯度洗脱,流速0.25 mL/min,以电喷雾离子源正离子多反应监测(MRM)模式进行MS/MS检测。16种黄酮类物质在各自的线性范围内具有良好的线性关系,相关系数大于0.996,低、中、高3个添加水平的平均回收率在70.9%~100.0%之间,相对标准偏差小于10%。通过检测发现实际样品中9种黄酮物质含量较高,分别是:山柰酚、槲皮素、橙皮素、牡荆素、木犀草素、儿茶素、芹菜素、柚皮素、异鼠李素,占总量的99.6%,此9种物质可作为银杏保健茶的质量控制指标。本法简便、快速、准确可靠,可用于控制银杏保健茶的质量。     

Discovery of a Prenylated Flavonol Derivative as a Pin1 Inhibitor to Suppress Hepatocellular Carcinoma by Modulating MicroRNA Biogenesis

Peptidyl‐prolyl cis‐trans isomerase Pin1 plays a crucial role in the development of human cancers. Recently, we have disclosed that Pin1 regulates the biogenesis of miRNA, which is aberrantly expressed in HCC and promotes HCC progression, indicating the therapeutic role of Pin1 in HCC therapy. Here, 7‐(benzyloxy)‐3,5‐dihydroxy‐2‐(4‐methoxyphenyl)‐8‐(3‐methylbut‐2‐en‐1‐yl)‐4H‐chromen‐4‐one ( AF‐39 ) was identified as a novel Pin1 inhibitor. Biochemical tests indicate that AF‐39 potently inhibits Pin1 activity with an IC₅₀ values of 1.008 μm , and also displays high selectivity for Pin1 among peptidyl prolyl isomerases. Furthermore, AF‐39 significantly suppresses cell proliferation of HCC cells in a dose‐ and time‐dependent manner. Mechanistically, AF‐39 regulates the subcellular distribution of XPO5 and increases miRNAs biogenesis in HCC cells. This work provides a promising lead compound for HCC treatment, highlighting the therapeutic potential of miRNA‐based therapy against human cancer.     

Elucidation of the Structure of Lignin–Carbohydrate Complexes in Ginkgo CW-DHP by 13C-2H Dual Isotope Tracer

To elucidate the chemical linkages between lignin and carbohydrates in ginkgo cell walls, ¹³C-²H-enriched cell wall-dehydrogenation polymers (CW-DHP) were selectively prepared with cambial tissue from Ginkgo biloba L. by feeding D-glucose-[6-²H₂], coniferin-[α-¹³C], and phenylalanine ammonia-lyase (PAL) inhibitor. The abundant detection of ¹³C and ²H confirmed that D-glucose-[6-²H₂] and coniferin-[α-¹³C] were involved in the normal metabolism of ginkgo cambial cells that had been effectively labelled with dual isotopes. In the ginkgo CW-DHP, ketal and ether linkages were formed between the C-α of lignin side chains and carbohydrates, as revealed by solid state CP/MAS ¹³C-NMR differential spectroscopy. Furthermore, the DMSO/TBAH ionic liquids system was used to fractionate the ball-milled CW-DHP into three lignin-carbohydrate complex (LCC) fractions: glucan–lignin complex (GL), glucomannan–lignin complex (GML), and xylan–lignin complex (XL). The XRD determination indicated that the cellulose type I of the GL was converted into cellulose type II during the separation process. The molecular weight was in the order of Ac-GL > Ac-GML > XL. The ¹³C-NMR and ¹H-NMR differential spectroscopy of ¹³C-²H-enriched GL fraction indicated that lignin was linked with cellulose C-6 by benzyl ether linkages. It was also found that there were benzyl ether linkages between the lignin side chain C-α and glucomannan C-6 in the ¹³C-²H-enriched GML fraction. The formation of ketal linkages between the C-α of lignin and xylan was confirmed in the ¹³C-²H-enriched XL fraction.     

胶束电动毛细管色谱法用于中成药原料银杏浸膏中黄酮的质量控制

研究建立了胶束电动毛细管色谱法测定中药银杏浸膏(GBE)中黄酮的方法。以SDS作表面活性剂，在 25kV电压下，考察了不同缓冲体系的pH值及浓度对黄酮的3个水解产物槲皮素、山奈酚、异鼠李素分离度的影响。结果表明，选择25mmol/L硼砂-25mmol/L磷酸二氢钾—1％(V／V)甲醇电解液，15min之内槲皮素、山奈酚、异鼠李素可得到很好分离。把MECC定量分析的结果与反相高效液相色谱进行了对比，表明所建立的MECC法用于中药中的黄酮测定是可靠的。     

Flavonoid glycosides from Astragalus galegiformis leaves

New flavonoid oligosides, the structures of which were established by chemical transformations and UV, IR, PMR, and ¹³C NMR spectra, were isolated from Astragalus galegiformis leaves. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 6, pp. 555–558, November–December, 2006.     

荧光分析法测定银杏酚酸

根据银杏酚酸在紫外光激发下能产生荧光的性质，建立了检测银杏酚酸的荧光分光光度法。以80％乙醇80℃回流8h提取银杏外种皮，提取液经硅胶柱层析后得酚酸样品。以白果酸为标样，激发波长345nm、发射波长420nm测定银杏酚酸。线性回归方程为，y=2．5024x＋0．4152；线性范围为0．50～100mg／L，相关系数r=0．9922，相对标准偏差2．6％；检出限0．11mg／L。     

A New Flavonol Oligosaccharide from the Seeds of Aesculus chinensis

Aesculus chinensis is a traditional chinese medicinal plant widely distributed in China, which has been used to treat stomach disease. From recent research its seeds contain many flavonoids and proanthocyanidin A2, which have potential venotonic and vasoprotective action and powerful antioxidant activity. In this paper, we report the isolation and the structure elucidation of a new flavonol oligosacchride. Bioassay results showed that the compound exhibited an antivirus activity. …