一种新手性配体的合成及其锇配合物的催化作用

以1,4-二氯-2,3-二氮杂萘为原料,经两步反应合成了一种新的金鸡纳生物碱衍生物手性配体2,其结构经1H NMR,13C NMR和MS表征。OsO4-2用于催化烯烃的不对称双羟化反应,化学产率91%~94%,e.e.值93%~99%;用于催化烯烃的不对称氨羟化反应,收率45%~63%,e.e.值83%~95%。     

Synthesis of Taxol 13-C Side Chain Catalyzed by Recoverable Chiral Ligand [ QN (OH) 2 ] 2 PHAL

在可回收手性配体[ QN(OH)2]2PHAL的催化下,通过不对称氨羟化或双羟化反应合成紫杉醇13-C侧链,两种方法的产率分别为39％,97％ee和52％,99％ee,其结构经1H NMR,IR和元素分析确证.     

可回收手性配体[QN（OH）2]2PHAL催化合成紫杉醇13-C侧链

在可回收手性配体[QN(OH)2]2PHAL的催化下,通过不对称氨羟化或双羟化反应合成紫杉醇13-C侧链,两种方法的产率分别为39%,97%ee和52%,99%ee,其结构经1H NMR,IR和元素分析确证。     

手性配体[QN(OH)2]2PHAL在烯烃不对称氨羟化反应中的应用

以N-氯代氨基甲酸苄酯为氧化供氮试剂,一种可重复使用的手性配体与金属锇形成原位催化剂用于催化5种烯烃的不对称氨羟化(从)反应,表现了好的对映选择性(85％～99％)和反应活性(49％～72％).在以对氯苯乙烯为底物的从反应中,采用了两种不同的回收方法,均能有效地进行配体的回收和再利用,配体的催化活性和对映选择性基本保持...     

不对称氨羟化反应

介绍了Sharpless等人新近发现的不对称氨羟化反应,该反应可将烯烃直接转化成为手性β-氨基醇类化合物。对于有些烯烃,Sharpless不对称氨羟化反应具有高的区域选择性(20:1)和高的对映选择性(>98%e.e.)。     

一种均相催化、两相回收的手性配体的合成及其催化烯烃不对称双羟化反应

在金鸡纳生物碱衍生物配体存在下，四氧化锇催化的烯烃的不对称双羟化反应(AD)已广泛用于手性药物、精细化学品和天然产物的合成.AD反应也是合成抗癌药物紫杉醇C13-片段的实用方法之一．然而，由于配体和四氧化锇价格昂贵以及锇的毒性限制了AD反应的工业生产．近年来，在     

手性哒嗪衍生物催化烯烃的不对称双羟化和氨羟化反应

烯烃不对称双羟化反应(Asymmetric D ihydroxylation,简称AD反应)和不对称氨羟化反应(Asymmet-ric Am inohydroxylation,简称AA反应)是获得手性连二醇和手性β-氨基醇的最简便的方法[1]。这两类手性化合物在药物合成和精细化工产品合成中应用非常广泛,它们是合成紫杉醇、美托洛     

新金鸡纳生物碱衍生物配体的合成及其在烯烃的不对称双羟化反应中的应用

以简便的方法高产率地合成四种金鸡纳生物碱的对甲苯磺酸酯类配体，并将其应用于烯烃的不对称双羟化反应中，取得了较好的不对称诱导效果，双羟化反应的化学产率为82％～95％，对映体过量最高达93％ee．     

一种可回收手性配体的合成及其对烯烃不对称二羟化反应的催化性能

 用1,4-二氟蒽醌与奎宁(QN)反应可高收率地得到1,4-双-(9-O-奎宁)蒽醌((QN)2AQN),再经OsO4氧化可得到带有4个羟基的手性配体. 在不对称二羟化反应的2种不同体系中,该配体对6种烯烃的反应表现出很高的对映选择性(80%～97%)和催化活性(80%～94%). 该配体不但具有金鸡纳生物碱衍生物小分子配体优异的立体选择性,同时也能象高聚物负载的大分子配体一样能够回收和重复使用,而且用量少,活性高,后处理简单. 在以反式肉桂酸乙酯为底物的不对称二羟化反应中,在t-BuOH-H2O/K3Fe(CN)6体系中循环使用5次(配体平均回收率93%),在Me2CO-H2O/NMO(N-甲基-N-氧吗啉)体系中循环使用8次,配体的催化活性和对映选择性基本保持不变.     

一种可回收配体[QN(OH)2]2PYDZ在烯烃不对称双羟化及氨羟化反应中的应用

一种可重复使用的非负载型金鸡纳生物碱衍生物配体与金属锇形成原位催化剂用于9种烯烃的不对称双羟化(AD)反应, 表现了很好的对映选择性(85%～＞99%)和反应活性(82%～91%). 将其用于催化65种烯烃不对称氨羟化(AA)反应, 也表现了好的对映选择性(6176%～＞99%)和反应活性(50%～72%). 并采用两种不同的方法进行AD和AA反应中配体的回收和重复使用. 结果表明两种方法均可有效地进行配体的再利用.     

新手性配体(QN)2AQN的合成及其催化肉桂酸甲酯的不对称氨羟化反应研究

在AlCl₃和多聚磷酸的存在下, 以邻苯二甲酸酐和对二氟苯为原料, 通过Friedel-Crafts和环化反应, 用改进的方法以60%的产率生成1,4-二氟蒽醌. 然后通过奎宁锂与1,4-二氟蒽醌的亲核取代反应得到新型手性配体(QN)₂AQN, 产率85%. 在氧化-供氮试剂N-氯代氨基甲酸苄酯存在下, (QN)₂AQN与OsO₄原位生成的催化剂在五种肉桂酸甲酯的不对称氨羟化反应中表现出优异的对映选择性(90%～96% ee)和一般至优秀的区域选择性(75∶25～98∶2), 产率50%～70%, 高于文献报道的结果. 该手性配体易于合成, 成本低廉, 用于催化不对称氨羟化反应, 可以制备光学活性的α-氨基酸酯类化合物.     

The Sharpless asymmetric aminohydroxylation reaction: optimising ligand/substrate control of regioselectivity for the synthesis of 3- and 4-aminosugars

An investigation of the factors responsible for the sense and magnitude of regioselectivity in the Sharpless asymmetric aminohydroxylation (AA) has been conducted. Theoretical investigations of ligand-osmium binding geometry and experimental investigations of the Sharpless AA reaction on a series of functionalized pent-2-enoic acid ester substrates demonstrate that the opposite regioselectivity afforded using PHAL and AQN ligands results from a change in substrate orientation with respect to the catalyst. Two distinct ligand binding domains within the catalyst have been proposed that undergo attractive interactions with the substrates. Selective access to each of the four potential regio- and stereo-isomeric AA products could be achieved through the appropriate choice of ligand and substrate. These results have been applied toward the efficient stereoselective synthesis of naturally occurring and regioisomeric 3- and 4-aminosugar derivatives.     

The identification of ligand features essential for PXR activation by pharmacophore modeling

Drug metabolizing enzymes and transporters are often involved in clinically relevant drug-drug interactions. These functional proteins can be induced by a wide range of xenobiotics. The induction is mediated by a group of receptors known as orphan nuclear receptors. The pregnane X receptor (PXR) is a member of this receptor family and regulates the expression of multiple Cytochrome P450 enzyme families (e.g. CYP 3A and 2B), phase II enzymes (e.g. UDP glucuronosyl transferases), and transporters (e.g. multidrug resistance protein 1). The software package Catalyst was employed to derive pharmacophore models for PXR activation. A structure based pharmacophore hypothesis and several ligand based ones were compared in order to identify ligand receptor interactions essential for receptor activation. The results suggest that hydrogen bonding to Gln285 is indispensable for PXR activation. Most ligands were found to form a second hydrogen bond to His407. Hydrophobic interactions are not essential for receptor activation but contribute to ligand affinity. Highly active compounds share up to five hydrophobic features that allow the ligand to occupy large areas of the predominantly hydrophobic binding pocket.     

Reversal of regioselection in the sharpless asymmetric aminohydroxylation of aryl ester substrates

[formula: see text] The asymmetric synthesis of beta-hydroxy-alpha-amino acids is reported which relies on the use of alpha,beta-unsaturated aryl ester substrates and the dihydroquinyl alkaloid ligand system (DHQ)2-AQN to control the regio- and enantioselectivity of the asymmetric aminohydroxylation (AA) process. alpha,beta-Unsaturated ester substrates of type 1 have a significant effect on the substrate-ligand recognition event which results in a reversal of regioselectivity in the AA reaction.     

Simultaneous electroanalysis of dopamine and ascorbic acid using poly (N,N-dimethylaniline)-modified electrodes

Glassy carbon (GC) electrode is modified with an electropolymerized film of N,N-dimethylaniline (DMA). This polymer (PDMA) film-coated GC electrode is used to electrochemically detect dopamine (DA) in the presence of ascorbic acid (AA). Polymer film has the positive charge in its backbone, and in neutral solution DA exists as the positively charged species whereas AA exists as the negatively charged one. In cyclic voltammetric measurements, favorable ionic interaction (i.e., electrostatic attraction) between AA and PDMA film causes a large negative shift of the oxidation potential for AA compared to that at the bare electrode. Oxidation potential for DA is positively shifted due to the electrostatic repulsion. The PDMA film shows hydrophobicity by incorporating uncharged hydroquinone molecule within the film. DA is also incorporated into the film due to hydrophobic attraction even though DA has a positive charge. The responses of DA and AA at polymer-modified electrodes largely change with the concentration of the monomer (i.e., 0.2, 0.1 and 0.05 M DMA) used in electropolymerization and thus with the film thickness. Hydrophobicity of the polymer film shows great influence on the voltammetric responses of both DA and AA. In square wave voltammetric measurements, the PDMA film-coated electrode can separate the DA and AA oxidation potentials by about 300 mV and can detect DA at its low concentration (e.g., 0.2 microM) in the presence of 1000 times higher concentration of AA, which is close to the physiological level. AA oxidizes at more negative potential than DA. The electrode response is not affected by the oxidized product of AA. So unlike the bare electrode, the fouling effect as well as the catalytic oxidation of AA by the oxidized form of DA are eliminated at the PDMA film-coated GC electrode. The electrode exhibits the stable and sensitive response to DA.     

Zwitterionic phosphorylcholine-protected water-soluble Ag nanoparticles

The water-soluble Ag nanoparticles capped with novel zwitterionic thioalkylated phosphorylcholine were synthesized. The Ag nanoparticles showed remarkable stability in saline media with salt concentrations as high as 2.0 mol/L and plasma using UV-vis absorption spectroscopy. Similarly, compared with tiopronin and citrate-protected Ag nanoparticles, the zwitterionic phosphorylcholine Ag nanoparticles did not precipitate out of solution when charged polyelectrolytes or biopolymers were added. The zwitterionic phosphorylcholine might be a better ligand for stabilizing metal nanoparticles. Supported by the National Natural Science Foundation of China (Grant Nos. 20774082 and 50703036), National High Technology Research and Development Program of China (Grant Nos. 2006AA03Z329 and 2006AA032444) and Science and Technology Projects of Zhejiang Province (Grant No. 2007C24G2010020)     

Synthesis and reactivity of [penta(4-halogenophenyl)cyclopentadienyl][hydrotris(indazolyl)borato]ruthenium(II) complexes: rotation-induced Fosbury flop in an organometallic molecular turnstile

The preparation of ruthenium(II) complexes coordinated to a penta(4-halogeno)phenylcyclopentadienyl ligand and to the hydrotris(indazolyl)borate ligand are detailed. Our strategy involves first the coordination of the penta(4-bromo)phenylcyclopentadienyl ligand by reaction with the ruthenium-carbonyl cluster followed by the coordination of the tripodal ligand. The pentabrominated precursor was successfully converted to the pentaiodinated derivative by using the Klapars-Buchwald methodology, applied for the first time on organometallic substrates. Cross-coupling reactions were performed on both pentabromo and pentaiodo complexes to introduce in a single step the five peripheric ferrocenyl fragments required to obtain a potential molecular motor. The two ligands present in the ruthenium complexes undergo a correlated rotation that was established both experimentally by NMR experiments and an X-ray diffraction study, and theoretically by DFT calculations. The potential-energy curve obtained by DFT revealed the energy barrier of the gearing mechanism to be only 4.5 kcal mol(-1). These sterically highly constrained complexes can be regarded as organometallic molecular turnstiles.     

A trimetal chain cocooned by two heptadentate polypyridylamide ligands

Compounds of nickel in which a chain of three metal atoms is closely embraced by two interlocking heptadentate dianions derived from a chain of five pyridyl groups linked at the 2, or 2 and 6, positions by four amide nitrogen atoms are reported. This new type of extended metal atom chain (EMAC) compound differs from earlier ones in that ligand exchange at the axial positions cannot occur, because the axial ligands are part of the entire ligand. Four such compounds, all crystallographically characterized, are reported. This work is a proof-of-concept project that will be extended to other metals with these and other homologous ligands.