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941.
The first total synthesis of (-)-calicoferol B (III) is described. The cyclozirconation product I, prepared in enantiomerically pure form, was converted into the CD ring chiron II. This was coupled with the aromatic A-ring, and then the side chain was constructed with control of relative and absolute configuration to complete the total synthesis of III. The first total synthesis of (-)-calicoferol B (1) is described. The cyclozirconation product 8, prepared in enantiomerically pure form, was converted into the CD ring chiron 6. This was coupled with the aromatic A-ring, and then the side chain was constructed with control of relative and absolute configuration to complete the total synthesis of 1. 相似文献
942.
This paper describes the results of the evaluation of retention dependence on the physicochemical properties of solutes in linear gradient elution by reversed-phase liquid chromatography (RPLC) based on linear solvation energy relationships (LSERs). Retention time data on Inertsil ODS(3) column by linear gradient elution were collected for both acetonitrile-water and methanol-water binary mobile phases under various gradient steepness. Based on the LSERs, the retention times were linearly correlated with the physicochemical properties (size, dipolarity, and hydrogen bond donor-acceptor acidity and basicity) of solutes. As predicted by LSERs, very acceptable linear relationships are observed for both mobile phases. While the magnitudes of the coefficients are modified by the gradient steepness, their signs are consistent with those obtained by isocratic elution. As obtained for isocratic elution, the dominant factors to retention in linear gradient elution of RPLC are the solutes' size and hydrogen bond acceptor basicity. The conclusions of the study allow us to predict retention in chromatographic method development by gradient elution. 相似文献
943.
944.
945.
Eight ionic organotin compounds [R2SnCl2(2-quin)]−(HNEt3)+ have been synthesized by reactions of 2-quinH with R2SnCl2 (R = PhCH21, 2-Cl-C6H4CH22, 4-Cl-C6H4CH23, 2-F-C6H4CH24, 4-F-C6H4CH25, 4-CN-C6H4CH26, Ph 7, 2,4-Cl2-C6H3CH28) in the presence of organic base NEt3, and their structures have been characterized by elemental analysis, IR and multinuclear NMR (1H, 13C, 119Sn) spectroscopies. The structure of [(2,4-Cl2-C6H3CH2)2SnCl2(2-quin)]−(NEt3)+ (8) has been determined by X-ray diffraction study. Studies show that compound 8 has a monomeric structure with the central tin atom six-coordinate in a distorted octahedral configuration and the nitrogen atoms of the 2-quin ligands are coordinating to the tin atom in all the eight compounds. 相似文献
946.
In recent years, many optically active β-amino alcohols, mostly derived from naturally occurring α-amino acids, have been incorporated into the asymmetric synthesis as chiral auxiliaries or ligands.1 An effective asymmetric catalysts, the oxazaborolidine-borane reagents, which were originally pioneered by Itsuno and Corey,2 were generally prepared from chiral β-amino alcohols by the reaction with boric acid or formed in situ in the presence of borane. These reagents provide excellent enanti… 相似文献
947.
Electroosmotic flow controllable coating on a capillary surface by a sol-gel process for capillary electrophoresis 总被引:1,自引:0,他引:1
A simple coating procedure employing a sol-gel process to modify the inner surface of a bare fused-silica capillary with a positively charged quaternary ammonium group is established. Scanning electron microscopic studies reveal that a smooth coating with 1 to approximately 2 microm thickness can be obtained at optimized coating conditions. With 40 mM citrate as a running electrolyte, the plot of electroosmotic flow (EOF) versus pH shows a unique three-stage EOF pattern from negative to zero and then to positive over a pH range of 2.5 to 7.0. At pH above 5.5, the direction of the EOF is from the anode to the cathode, as is the case in a bare fused-silica capillary, and the electroosmotic mobility increases as the pH increases. However, the direction of the EOF is reversed at pH below 4.0. Over the pH range of 4.0 to 5.5, zero electroosmotic mobility is obtained. Such a three-stage EOF pattern has been used to separate six aromatic acids under suppressed EOF and to separate nitrate and nitrite with the anions migrating in the same direction as the EOF. The positively charged quaternary ammonium group on the coating was also utilized to minimize the adsorption problem during the separation of five basic drugs under suppressed EOF and during the separation of four basic proteins with the cations migrate in the opposite direction as the EOF. Also, the stability and reproducibility of this column are good. 相似文献
948.
[C6N2H18]2[Mo5O15(HPO4)2]·H2O的水热合成与结构表征 总被引:6,自引:0,他引:6
通过水热法合成了一个新化合物[C6N2H18]2[Mo5O15(HPO4)2]·H2O,并通过IR光谱、ICP、元素分析、差热与热重分析和X射线单晶衍射分析等手段进行了表征.结果表明,晶体属三方晶系,P3(2)21空间群,a=1.1231(1)nm,c=2.2802(5)nm,V=2.4911(7)nm3,Dx=2.835Mg/m3,Z=6,最后的一致性因子R=0.0227,wR=0.0675.阴离子中Mo5O15构成一环状结构,2个HPO4一个连在环的下方,一个连在环的上方,形成类似于“飞碟”状的结构,阳离子为2个质子化的四甲基乙二胺. 相似文献
949.
950.
Xiao Wen Hu Zhi Min Zheng Cai Hong Xu 《中国化学快报》2007,18(11):1351-1352
Three new 1,3-bis(phenylethynyl)disilazanes were synthesized from the reaction of 1,3-dichlorodisilazanes with (phenylethy- nyl)lithium,and characterized by infrared (IR) spectra,nuclear magnetic resonance (NMR) and mass spectrometry (MS). 相似文献