描述了通过使用硝基甲烷反应性吸附的13 C CP / MAS NMR光谱从类水滑石前体获得的混合氧化物的碱度特征。在具有酸碱对的Lewis碱上,吸附物质的性质,即硝基甲烷,阴离子阴离子硝基甲烷和甲磺酸盐类似物,取决于该对上碱性和酸性部位的相对强度。使用布朗斯台德碱(如褐铁矿类型的层状双氢氧化物(LDH))无法获得这些物质。在那种情况下,建议形成甲酸盐类似物。研究了将硝基甲烷迈克尔加成到环己-2-烯-1-酮中的非均相碱催化作用。在催化剂的活性与13的活性之间建立了关系。酰基阴离子硝基甲烷的C CP / MAS NMR化学位移,是碱性强度的量度。NMR和催化结果的讨论考虑了碱度和共轭路易斯酸度的各自作用。需要碱性才能形成可与氰基硝基甲烷媲美的反应性阴离子,但路易斯酸度对阴离子型硝基甲烷的稳定性越高,活性越低。如13 C MAS NMR所示,通过降低酸碱对的Lewis酸度来提高基本强度会导致活性
Direct synthesis of carboxylic–phosphinic mixed anhydrides has been achieved by treating carbon dioxide with N‐phosphine oxide‐substituted imidazolylidenes (PoxIms) that contain both nucleophilic carbene and electrophilic phosphorus moieties. This novel mixed anhydride was efficiently derivatized into an ester, an amide, and an unsymmetrical ketone via transformation into its corresponding imidazolium
Some CC bond constructions on monosaccharides using cobaloxime-mediated radical alkyl-nitroalkylanion cross coupling reactions
作者:Bruce P. Branchaud、Gui-Xue Yu
DOI:10.1016/s0040-4039(00)79754-1
日期:1991.7
The formation of monosaccharide cobaloximes and their cross coupling reactions with nitroalkyl anions are demonstrated to be useful in CC bond constructions to produce branched-chain monosaccharides.
The c-alkylation of nitroalkame anions by l-substituted-2--butyl-4-phenyl- and -2,4-diphenyl-5,6-dihydrobenzo(ulbarh]quinolinium cations
作者:Alan R. Katritzky、M. Akram Kashmiri、Dieter K. Wittmann
DOI:10.1016/s0040-4020(01)91797-1
日期:1984.1
- The N-substituents are transferred from the title cations to the C-atom of nitroalkane anions in highyield at 25-80°C in DMSO solution. The title cations are readily available from the appropriate pyrylium cations and primary amines of types RCH2,NH2, and RR'CHNH2, allowing a general 2-step method for the preparation of higher nitro- alkanes. Spectral properties of a variety of nitroalkanes are
Mobilization of rat stomach ECL-cell histamine in response to short- or long-term treatment with omeprazole and/or YF 476 studied by gastric submucosal microdialysis in conscious rats
作者:T Konagaya、M Bernsand、P Norlén、R Håkanson
DOI:10.1038/sj.bjp.0704037
日期:2001.5
Mobilization of histamine from the ECL cells was monitored by gastric submucosal microdialysis in conscious rats. The ECL cells are known to operate under gastrin control and the purpose of the present study was to examine their in situ response to short‐term (12 h) as well as long‐term (28 days) hypergastrinaemia, induced by treatment with the proton pump inhibitor omeprazole.Hypergastrinaemia promptly raised the histamine concentration in the microdialysate. The effect was prevented by CCK2 receptor blockade (YF476). On day 7 of omeprazole treatment the microdialysate histamine concentration reached a peak, five times higher than before treatment. Subsequently (14 and 28 days), less histamine was mobilized.Gastrin infusion (4 h) raised the microdialysate histamine concentration in a dose‐dependent manner in fasted rats and freely fed rats and in rats treated with omeprazole for a week. However, while fasted and fed rats responded to low doses of gastrin, the omeprazole‐treated rats required large doses of gastrin to respond.When the amount of histamine mobilized was related to the serum gastrin concentration the following EC50 values could be calculated: fasted rats 2.3×10−10M, freely fed rats 2.5×10−10M, omeprazole‐treated rats 8.7×10−10M. The maximal histamine responses in the three groups were 18.4 pmol 4 h−1±0.8, 21.9 pmol 4 h−1±1.2 and 68.0 pmol 4 h−1±3.5, respectively.The results suggest that ECL cells, exposed to a high gastrin concentration for a week, respond with a shift in the receptor‐ligand binding affinity from high to low. Apparently, CCK2 receptors of the ECL cells are subject to dynamic changes with respect to ligand‐binding affinity.British Journal of Pharmacology (2001) 133, 37–42; doi:10.1038/sj.bjp.0704037
Experimental Evidence for the All-Up Reactive Conformation of Chiral Rhodium(II) Carboxylate Catalysts: Enantioselective Synthesis of <i>cis</i>-Cyclopropane α-Amino Acids
作者:Vincent N. G. Lindsay、Wei Lin、André B. Charette
DOI:10.1021/ja9044955
日期:2009.11.18
of chiral Rh(II)-carboxylate catalysts are described in the first catalytic asymmetric cyclopropanation of alkenes with alpha-nitro diazoacetophenones. X-ray, solution NMR, and reactivity studies made on these complexes suggest that the level of asymmetric induction strongly depends on their active symmetry, which in turn relies on the nature of the chiral ligands' substituents. The catalyst's 'All