香薷化学成分的研究

从香薷全草的乙醇提取物中分离出5个化合物,经对理化性质和波谱数据分析,鉴定其结构分别为:咖啡酸(1),阿魏酸正十八酯(2),β-胡萝卜苷(3),熊竹素(4)和儿茶素(5),其中化合物(2)和(5)为首次从该属植物中分离得到.     

毛细管区带电泳法测定葡萄籽中儿茶素类化合物

 采用毛细管区带电泳法测定了 10种中国产葡萄籽中的 4个主要儿茶素类化合物 :(+)儿茶素、(- )表儿茶素、(± )表没食子儿茶素、(± )表儿茶素没食子酸酯的含量。在 0 0 2mol/L硼砂和 0 0 0 5mol/L磷酸盐的混合缓冲体系 (pH 10 0 )的背景缓冲液中 ,4个化合物在 10min内取得了令人满意的分离。迁移时间的重现性(RSD)小于 2 % ,峰面积的重现性 (RSD)小于 5 %。在质量浓度为 0 0 0 5g/L～ 0 5 g/L时 ,线性相关系数大于0 995。检测限为 3mg/L～ 10mg/L。该方法简单、快速、准确 ,可作为葡萄籽分析和药用开发过程中分析儿茶素类化合物的有效方法推广使用。     

2D NMR analysis for unambiguous structural elucidation of phenolic compounds formed through reaction between (+)‐catechin and glyoxylic acid

Various phenolic compounds were synthesized in an aqueous–alcoholic solution containing (+)‐catechin and glyoxylic acid which was used as a model of fruit‐derived food browning that usually occurs during aging. After purification by semi‐preparative HPLC, the isolated compounds were subjected to homo‐ and heteronuclear proton and carbon NMR analysis including COSY, TOCSY, ROESY, HSQC and HMBC techniques. These experiments allowed the structural elucidation and complete ¹H and ¹³C NMR assignment of the isolated compounds. The strategies followed for the assignment of all proton and carbon resonances in addition to the linkage site determination are discussed. Copyright © 2002 John Wiley & Sons, Ltd.     

Identification of regioisomers of methylated kaempferol and quercetin by ultra high performance liquid chromatography quadrupole time-of-flight (UHPLC–QTOF) tandem mass spectrometry combined with diagnostic fragmentation pattern analysis

The O-methylation of active flavonoids can enhance their antiallergic, anticancerous, and cardioprotective effects depending on the methylation position. Thus, it is biologically and pharmacologically important to differentiate methylated flavonoid regioisomers. In this study, we examined the regioisomers of methylated kaempferol and quercetin using ultra high performance liquid chromatography quadrupole time-of-flight tandem mass spectrometry. The methyl groups on the flavonoids can generally be cleaved as methyl radicals in a position-independent manner. We found that methyl groups can be cleaved as methane. If there are protons adjacent the methoxy on the flavonol rings, intra-molecule proton transfer can occur via collision-induced dissociation, and one molecule of methane can then be eliminated. The remaining charged fragment ([M+H−CH₄]⁺) reflects the adjacent structure and is specific to the methoxy position. Furthermore, the retro Diels–Alder (RDA) fragmentation of methylated flavonols can generate fragments with the methoxy at the original methylated ring. Combining the position-specific [M+H−CH₄]⁺ fragment with the RDA fragments provides a diagnostic pattern for rapidly identifying methylated regioisomeric flavonols. Along with their retention behaviour, we have successfully identified ten regioisomers of methylated kaempferol and quercetin, which include six compounds previously reported in plants and shown to be biologically active. The developed approach is sensitive, rapid, reliable, and requires few standard compounds. It is highly efficient for characterising the specificity of novel flavonoid O-methyltransferases and can help direct enzymatic or chemical syntheses during the early stages of drug discovery. This method also has potential for use in identifying other methylated isomeric flavonoids.     

精确计算化学键解离能的ONIOM-G3B3方法及其在抗氧化剂研究中的应用

通过对179个有机化合物C—H,N—H,O—H键离解能的理论计算,系统评估了高精度组合从头算方法(ONIOM-G3B3)和密度泛函理论方法(B3LYP)在预测键离解能上的可靠性.研究发现ONIOM-G3B3方法可以准确预测各类有机化合物的键解离能,精度达到5.9 kJ/mol.运用ONIOM-G3B3方法成功预测了两类重要的天然抗氧化剂维生素E族和茶多酚族的键解离能,并进一步讨论了抗氧化活性、自由基清除机理及其构效关系.     

Flocculation of diatomite by methylated milk casein in seawater

A new biodegradable flocculant was prepared from a common and inexpensive protein. Milk casein was methylated in a 0.05 M HCl methyl alcohol solution at room temperature. The methylated milk casein (MeCS), having a methylation degree of 81%, was applied to the separation or flocculation of diatomite in seawater (pH 8.1+/-0.1) at room temperature (18-23 degrees C). The flocculating ability of MeCS was evaluated by a sedimentation balance method (cumulative measurement method). The diatomite suspension was effectively flocculated by the addition of a small amount of MeCS (0.25 wt% of the diatomite weight). The results of sedimentation analysis showed that the size-frequency curve had a very sharp and high peak; thus the diatomite floc formed by MeCS had a rather uniform size. The settling velocity of diatomite floc at the appropriate MeCS dosages (0.25-2 wt% of diatomite) was about 3 x 10(-3) ms(-1).     

Laccase‐catalyzed Synthesis and Antioxidant Property of Poly(catechin)

Catechin was oxidatively polymerized by laccase in a mixture of a polar organic solvent and buffer to give a new class of flavonoid polymers. Myceliophthora laccase showed high catalytic activity for the polymerization. Using a mixed solvent of acetone and pH 5 acetate buffer efficiently produced the polymer. Under the selected conditions, DMF‐soluble polymers were obtained in good yields. Effects of reaction parameters on the yield, solubility, and molecular weight of the polymer have been systematically investigated. A radical species was detected in the polymer by ESR spectroscopy. The polymers showed greatly amplified superoxide scavenging activity and xanthine oxidase inhibitory activity compared with monomeric catechin.

Superoxide scavenging activity of poly(catechin)s, n = 3. ○: catechin, □: poly(catechin).     

The Heptakis-(2,6-di-O-methyl)-β-cyclodextrin Inclusion Complex with Acetic Acid

A novel monomer-type structure of heptakis-(2,6-di-O-methyl)--cyclodextrin in a typical monoclinic herringbone scheme has been determined by single crystal X-ray diffraction. Crystal data: space group P21, Z = 2, a = 15.165(6), b = 10.613(3), c = 23.188(8) Å, = 102.02(4)°, V = 3650(3) Å3 and R = 0.094 for 2933 observed MoK reflections with I > 3(I). A unique water molecule located in the intermolecular spaces, reinforces the cohesion between the herringbone chains. The analysis of the electron density distribution suggests that an acetic acid molecule is trapped within the macrocycle cavity, alternately with a water molecule.     

绿茶儿茶素的最新合成进展

简要介绍了绿茶儿茶素的组成及活性, 重点综述了有关儿茶素及其衍生物合成研究的最新进展.     

Catechin Photolysis Suppression by Aluminum Chloride under Alkaline Conditions and Assessment with Liquid Chromatography–Mass Spectrometry

Tea is rich in catechins and aluminum. In this study, the process of catechin photolysis was applied as a model for examining the effects of aluminum chloride (AlCl₃) on the structural changes of catechin and the alteration of aluminum complexes under blue light irradiation (BLI) at pH 8 using liquid chromatography and mass spectrometry techniques. Additionally, the effects of anions on catechin upon the addition of AlCl₃ and treatment with BLI were also studied. In this study, when 1 mM catechin was treated with BLI, a superoxide anion radical (O2•−) was generated in an air-saturated aqueous solution, in addition to forming a dimeric catechin (proanthocyanidin) via a photon-induced redox reaction. The relative percentage of catechin was found to be 59.0 and 95.7 for catechin treated with BLI and catechin upon the addition of 1 mM AlCl₃ treated with BLI, respectively. It suggested that catechin treated with BLI could be suppressed by AlCl₃, while AlCl₃ did not form a complex with catechin in the photolytic system. However, under the same conditions, it was also found that the addition of AlCl₃ inhibited the photolytic formation of O2•−, and reduced the generation of proanthocyanidin, suggesting that the disconnection of proanthocyanidin was achieved by AlCl₃ acting as a catalyst under treatment with BLI. The influence of 1 mM fluoride (F−) and 1 mM oxalate (C2O42−) ions on the photolysis of 1 mM catechin upon the addition of 1 mM AlCl₃ and treatment with BLI was found to be insignificant, implying that, during the photolysis of catechin, the Al species were either neutral or negatively charged and the aluminum species did not form a complex with anions in the photolytic system. Therefore, aluminum, which is an amphoteric species, has an inherent potential to stabilize the photolysis of catechin in an alkaline conditions, while suppressing the O2•− and proanthocyanidin generation via aluminum ion catalysis in the catechin/Al system under treatment with BLI.