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991.
Deng J Wang F Yan W Zhu J Jiang H Wang W Li J 《Chemical communications (Cambridge, England)》2012,48(1):148-150
A highly enantioselective organocatalytic protocol for conjugate addition of new nucleophilic carbonylmethyl 2-pyridinylsulfone to enals has been developed in good yields and with high enantioselectivities. The resulting Michael adducts are versatile building blocks for a variety of organic transformations. 相似文献
992.
Four novel lanthanide coordination polymers [Pr(mal)(OH)(bipy) · 2H2O]n (1), {[Dy1(SBA)3(H2O)2][Dy2(SBA)3(H2O)2] · 4H2O}n (2), {[Tb(OHnic)(Onic)(H2O)5 · (OHnicH)] · H2O}n (3) and {[Sm(OHnic)(Onic)(H2O)5 · (OHnicH)] · H2O}n (4) (Hmal = maleic acid, HSBA = 4-sulfobenzoic acid, OHnicH = 6-hydroxynicotinic acid and bipy = 2,2′-bipyridine) have been synthesized and determined by single crystal X-ray diffraction. Complex 1 is a 1-D helical chain with seven-coordinated praseodymium centers. Complex 2 forms 1-D chain-like molecular structure containing two crystallographically unique dysprosium centers, the Dy1 center is seven-coordinated while Dy2 is eight-coordinated. The isomorphous complexes 3 and 4 exhibit an unprecedented 1-D chain-like polymeric structure through hydroxyl oxygen atoms of bridging Onic2− anions linking up the neighboring central ions, and there exist three types of 6-OHnicH ligands in the structural unit which is rare for lanthanide carboxylate complexes. The photophysical properties of these complexes were studied using ultraviolet absorption spectra, fluorescence excitation and emission spectra. 相似文献
993.
Hong-yu Li Yan Wang Arindam Chatterjee Sreenivasa R. Mundla Matthew Voss J. Scott Sawyer 《Tetrahedron》2007,63(47):11763-11770
A simple and efficient synthesis of dihydropyrrolopyrazole boronic acid intermediate (5) has been developed. Utilization of a three-component Suzuki-Miyaura/etherification with microwave heating led to advanced compound 11 in high yield and with easy purification. Reaction of compound 11 with methanesulfonyl chloride at room temperature furnished the 1,3 O-N rearranged product (12), which is postulated to proceed via an intramolecular mechanism. The outlined synthesis provides a highly efficient and high-yielding route that is amenable to rapid analog synthesis. 相似文献
994.
Wang J Chen Y Lin M Fan G Zhao W Wu Y Yan C Wang J 《Journal of separation science》2007,30(3):381-390
A pressurized CEC (pCEC) method with postcolumn detection cell had been developed for quantifying the lignans from Fructus schisandrae extracts. The effects of different experimental conditions, such as the ACN content of the mobile phase, the concentration and pH of the buffer, the applied voltage, and the supplementary pressure were studied. Five lignans (schisandrin, gomisin A, schisantherin C, deoxyschizandrin, schisandrin B) were baseline separated using a mobile phase of ACN-phosphate buffer (pH 5.4; 5 mM) (40:60 v/v) under -4 kV applied voltage. The method showed the satisfactory retention time and peak area repeatability. The calibration curves were linear in the range 50.0-1000.0 microg/mL for schisandrin, 20.0-500.0 microg/mL for gomisin A, 10.0-200.0 microg/mL for schisantherin C, 20.0-500.0 microg/mL for deoxyschizandrin, and 20.0-500.0 microg/mL for schisandrin B. The correlation coefficients were between 0.9978 and 0.9989. With this pCEC system, fingerprints of F. schisandrae were preliminarily established to distinguish two members S. chinensis (Turcz.) Baill. and S. sphenanthera Rehd. Et Wils. of F. schisandrae by characteristic peaks, and evaluate the quality of various sources of raw materials by determining the contents of the five lignans. 相似文献
995.
996.
Dai Y Mu X Tan Y Lin K Yang Z Zheng N Fu G 《Journal of the American Chemical Society》2012,134(16):7073-7080
Carbon monoxide can adsorb specifically on Pd(111) to induce the formation of unique Pd nanostructures. In the copresence of CO and H(2), single-crystalline Pd tetrapod nanocrystals have now been successfully prepared. The Pd tetrapods are enclosed by (111) surfaces and are yielded through hydride formation. Density functional theory calculations revealed that the formation of PdH(x) in the presence of H(2) reduces the binding energy of CO on Pd and thus helps to decrease the CO coverage during the synthesis, which is essential to the formation of the PdH(x) tetrapod nanocrystals. In addition to tetrapod nanocrystals, tetrahedral nanocrystals were also produced in the copresence of CO and H(2) when the reaction temperature was ramped to further lower the CO coverage. Upon aging in air, the as-prepared PdH(x) nanocrystals exhibited a shape-dependent hydrogen releasing behavior. The conversion rate of PdH(x) tetrapod nanocrystals into metallic Pd was faster than that of tetrahedral nanocrystals. 相似文献
997.
998.
We herein report comparative analysis of two versions of the biosynthetic gene clusters of antimycins, a natural product family possessing up to 44 distinct entities. The biosynthetic pathway of antimycins is amenable to the high structural variation of the substrates, supported by successes in heterologous expression of the ant cluster and in fluorine incorporation. The latter facilitated the investigation of the structure-activity relationship into the usually invariable 3-formamidosalicylic acid moiety of the molecules. 相似文献
999.
In this paper, a novel method has been established to determine levodopa with the detection system of potassium ferricyanide‐Fe(III). In the presence of potassium ferricyanide, it has been demonstrated that Fe(III) is reduced to Fe(II) by levodopa at pH 4.0. In addition, the in situ formed Fe(II) reacts with potassium ferricyanide to form soluble prussian blue (KFeIII[FeII(CN)6]). Beer's law is obeyed in the range of levodopa concentrations of 0.01–4.00 μg mL?1 at the maximal absorption wavelength of 735 nm. The linear regression equation is A = 0.0082 + 0.61365 C (μg mL?1) with a correlation coefficient of 0.9996. The detection limit (3σ/k) is 9 ng mL?1, and R.S.D. is 0.73% (n = 11). Moreover, the apparent molar absorption coefficient of indirect determination of levodopa is 1.2 × 105 Lmol?1cm?1. The parameters with regard to determination are optimized, and the reaction mechanism is discussed. This method has been successfully applied to determine levodopa in pharmaceutical, serum and urine samples. Analytical results obtained with this novel assay are satisfactory. 相似文献
1000.
Xin XL Deng S Zhang BJ Huang SS Tian Y Ma XC An L Shu XH Yao JH Cui X 《Natural product communications》2011,6(6):781-784
Biotransformation of deoxyandrographolide (1) by Alternaria alternata AS 3.4578 gave five derivatives identified by spectral methods including 2D NMR as the known dehydroandrographolide (2) and 9beta-hydroxy-dehydroandrographolide (3) and the new compounds 9beta-hydroxy-deoxyandrographolide (4), 3alpha,17,19-trihydroxy-8,13-ent-labdadien-15,16-olide (5) and 3-oxo-9beta-hydroxy-deoxyandrographolide (6). 相似文献