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701.
We present here the stereoselective synthesis of a series of 2/3-N-pyrrolidine derivatives of glycosides produced by diastereoselective double reductive amination ring closure of 1,4-dicarbonyl compounds. These precursors were produced by tandem ozonolysis-reduction or Wacker oxidation of known alkenes. The potential of these new compounds as glycosidase inhibitors is illustrated for compound 16, showing selective inhibition of β-d-galactosidase. 相似文献
702.
Ligand effects for intramolecular Pd-catalysed aryl amidation reaction were examined for the synthesis of seven-membered benzolactam rings. In an attempt to produce an eight-membered ring, tandem C-N/C-O bond forming reactions occurred to give a novel spiro-benzofuran-lactam structure. 相似文献
703.
The potential of ion mobility (IM) spectrometry in combination with mass spectrometry (MS) for real-time reaction monitoring is reported. The combined IM-MS approach using electrospray ionization affords gas-phase analyte characterization based on both mass-to-charge (m/z) ratio and gas-phase ion mobility (drift time). The use of IM-MS analysis is demonstrated for the monitoring of the reaction products formed when 7-fluoro-6-hydroxy-2-methylindole is deprotonated by aqueous sodium hydroxide. Real-time reaction monitoring was carried out over a period of several hours, with the reaction mixture sampled and analysed at intervals of several minutes. Product ion relative intensity is enhanced selectively in the ion mobility-selected mass spectrum, compared to mass spectrometry alone. The combined IM-MS approach has potential as a rapid and selective technique to aid pharmaceutical process control and for the elucidation of reaction mechanism. 相似文献
704.
Clark IP George MW Greetham GM Harvey EC Long C Manton JC McArdle H Pryce MT 《The journal of physical chemistry. A》2012,116(3):962-969
The photochemistry of (η(6)-anisole)Cr(CO)(3) and (η(6)-thioanisole)Cr(CO)(3) was investigated by picosecond time-resolved infrared spectroscopy in n-heptane solution at 298 K. Two independent excited states are populated following 400 nm excitation of each of these complexes. An excited state with some metal-to-CO charge-transfer character is responsible for the CO-loss process, which is slow compared to CO-loss from Cr(CO)(6). Observed first order rate constants of 1.8 × 10(10) s(-1) and 2.5 × 10(10) s(-1) were obtained for the anisole and thioanisole complexes, respectively. The second excited state has metal-to-arene charge transfer character and results in a haptotropic shift of the thioanisole ligand. DFT calculations characterized the excited states involved and the nature of the haptotropic shift intermediate observed for the thioanisole species. 相似文献
705.
Davies SG Foster EM Frost AB Lee JA Roberts PM Thomson JE 《Organic & biomolecular chemistry》2012,10(30):6186-6200
"Matching" and "mismatching" effects in the doubly diastereoselective conjugate additions of the antipodes of lithium N-benzyl-(N-α-methylbenzyl)amide to enantiopure cis- and trans-dioxolane containing α,β-unsaturated esters have been investigated. High levels of substrate control were established first upon conjugate addition of achiral lithium N-benzyl-N-isopropylamide to both tert-butyl (S,S,E)-4,5-O-isopropylidene-4,5-dihydroxyhex-2-enoate and tert-butyl (4R,5S,E)-4,5-O-isopropylidene-4,5-dihydroxyhex-2-enoate. However, upon conjugate addition of lithium (R)-N-benzyl-(N-α-methylbenzyl)amide and lithium (S)-N-benzyl-(N-α-methylbenzyl)amide to these substrates, neither reaction pairing reinforced the apparent sense of substrate control. These reactions do not, therefore, conform to the classical doubly diastereoselective "matching" or "mismatching" pattern usually exhibited by this class of reaction. A comparison of these reactions with the previously reported doubly diastereoselective conjugate addition reactions of lithium amide reagents to analogous substrates is also discussed. 相似文献
706.
Ilia Rodushkin Emma Engström Douglas C. Baxter 《Analytical and bioanalytical chemistry》2010,396(1):365-377
In theory, state of the art inductively coupled plasma mass spectrometry (ICP–MS) instrumentation has the prerequisite sensitivity
to carry out multi-elemental trace analyses at sub-ng L−1 to sub-pg L−1 levels in solution. In practice, constraints mainly imposed by various sources of contamination in the laboratory and the
instrument itself, and the need to dilute sample solutions prior to analysis ultimately limit detection capabilities. Here
we review these sources of contamination and, wherever possible, propose remedial strategies that we have found efficacious
for ameliorating their impact on the results of multi-elemental trace analyses by ICP–MS. We conclude by providing a list
of key points to consider when developing methods and preparing the laboratory to routinely meet the demands of multi-elemental
analyses at trace analytical levels by ICP–MS. 相似文献
707.
Kim DH Jarvis RM Allwood JW Batman G Moore RE Marsden-Edwards E Hampson L Hampson IN Goodacre R 《Analytical and bioanalytical chemistry》2010,398(7-8):3051-3061
It has been shown that the HIV protease inhibitors indinavir and lopinavir may have activity against the human papilloma virus (HPV) type 16 inhibiting HPV E6-mediated proteasomal degradation of p53 in cultured cervical carcinoma cells. However, their mode and site of action is unknown. HPV-negative C33A cervical carcinoma cells and the same cells stably transfected with E6 (C33AE6) were exposed to indinavir and lopinavir at concentrations of 1 mM and 30 μM, respectively. The intracellular distribution of metabolites and metabolic changes induced by these treatments were investigated by Raman microspectroscopic imaging combined with the analysis of cell fractionation products by liquid chromatography-mass spectrometry (LC-MS). A uniform cellular distribution of proteins was found in drug-treated cells irrespective of cell type. Indinavir was observed to co-localise with nucleic acid in the nucleus, but only in E6 expressing cells. Principal components analysis (PCA) score maps generated on the full Raman hypercube and the corresponding PCA loadings plots revealed that the majority of metabolic variations influenced by the drug exposure within the cells were associated with changes in nucleic acids. Analysis of cell fractionation products by LC-MS confirmed that the level of indinavir in nuclear extracts was approximately eight-fold greater than in the cytoplasm. These data demonstrate that indinavir undergoes enhanced nuclear accumulation in E6-expressing cells, which suggests that this is the most likely site of action for this compound against HPV. 相似文献
708.
Francesco Rosalbino Daniele Macciò Adriana Saccone Emma Angelini Stefano Delfino 《Journal of Solid State Electrochemistry》2010,14(8):1451-1455
The characteristics of oxide films on Zr and Zr–Nb alloys (with Nb content of 2.5, 5, and 10 at.%) galvanostatically formed (at a current density of 100 μA cm?2) in 0.5 M H2SO4 solution were investigated by means of electrochemical impedance spectroscopy. Electrochemical impedance spectroscopy spectra were interpreted in terms of an “equivalent circuit” with the circuit elements representing the electrochemical properties of a single layer oxide. The resistance of the oxide films was found to increase with increased Nb content in the alloy while the capacitance showed an opposite trend. The stability of the anodic oxide films grown in the sulfuric acid solution on Zr and Zr–Nb alloys was investigated by simultaneously measuring the electrode capacitance and resistance at a working frequency of 1 kHz as a function of exposure time to naturally aerated 3 M NaOH solution. Analyses of the electrode capacitance and resistance values indicated a decrease in chemical dissolution rate of the oxide films with the increase of Nb content in the alloy. 相似文献
709.
The use of tetrafluoropyrimidine as a scaffold for the synthesis of 2,4,6-trisubstituted pyrimidine derivatives by three sequential nucleophilic aromatic substitution processes is assessed. Reactions of tetrafluoropyrimidine with various amine nucleophiles followed by a series of nitrogen and oxygen centred nucleophilic species gave a range of 4,6-disubstituted-2,5-difluoropyrimidine systems regioselectively and in good yield. Displacement of a further fluorine atom from representative difluoropyrimidine derivatives proceeded to give trisubstituted pyrimidine derivatives although mixtures of products could be obtained depending upon the substrate. 相似文献
710.
Adam N. Swinburne Martin J. Paterson Kathrin H. Fischer Sara Jane Dickson Emma V. B. Wallace Warwick J. Belcher Andrew Beeby Dr. Jonathan W. Steed Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(5):1480-1492
A series of tri‐ and tetrapodal viologen‐based anion receptors showing a colourimetric response to carboxylates, such as acetate, have been synthesised. Alteration of the anion binding sites allows for binding site competition within a receptor. This results in a delayed colourimetric response for urea derivatives compared with pyridinium systems because the anions are initially bound to the periphery of the receptor, away from the viologen unit. DFT calculations and experimental measurements allow the colour change to be assigned to an anion–receptor charge‐transfer process, facilitated by the exceptionally low reduction potential of the cationic host compounds. Evidence for electron transfer to give the viologen radical cation is also seen in some cases. 相似文献