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961.
The Bakkenolide group 1 3 of sesquiterpenes present two interesting synthetic problems. The cisdimethyl cis-hydrindane portion 2, because of its structural and stereochemical relationship with the eremophilane sesqui terpenes,4 has synthetic solutions available.5 The spiro-β-methylene-γ-butyrolactone unit 3,6 which is presently unique to this class of natural products, has been synthesised by four different routes.7–10 相似文献
962.
Aquation of the 1:2 complex between CrIII and nitrilotriacetic acid (NTA) was monitored using a combination of capillary electrophoresis (CE), ultraviolet–visible (UV–vis) spectrophotometry, and attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopy. To our knowledge, this is the first published report of the use of either CE or ATR-FTIR to monitor the kinetics of ligand exchange reactions of CrIII–aminocarboxylate complexes. The aquation products were identified as the 1:1 CrIII complex with NTA and “free” NTA. The 1:1 complex dimerized to form a 2:2 complex in a slower subsequent reaction step. Rates of disappearance of the 1:2 complex were first-order under all experimental conditions. First-order rate constants for aquation, kobs (h−1), measured using all three techniques were similar at equivalent pH conditions, and with values reported previously in the literature. Measured kobs values exhibited a complicated pH dependence with three distinct regions: (i) at pH < 6.5, kobs values increased with decreasing pH, (ii) between pH 6.5 and 8.0, kobs values were relatively constant, and (iii) at 8.0 < pH < 10.0, kobs increased with increasing pH and then leveled off. A kinetic model incorporating five distinct aquation pathways was successfully employed to model the pH dependence of kobs from 0.0 < pH < 10.0. These results show that CE and ATR-FTIR can be used as tools for better understanding ligand exchange processes occurring in aqueous solution. 相似文献
963.
Ludovic Drouin Dr. E. Cristina Stanca‐Kaposta Dr. Priptal Saundh Antony J. Fairbanks Dr. Sebastian Kemper Timothy D. W. Claridge Dr. John P. Simons Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(16):4057-4069
The effect of carbon is subtle but sweet : The flexible C‐linkage in the newly synthesised C‐glycosyl mimetic, Manα(1,6)‐C‐ManαOPh allows OH? π bonding, both in the gas phase and in aqueous solution. This interaction is absent in the O‐linked disaccharide (see figure).
964.
Elias Vervecken Michel Van Overschelde Timothy Noël Yaşar Gök Susana Alvárez Rodríguez Simon Cogen Johan Van der Eycken 《Tetrahedron: Asymmetry》2010,21(19):2321-2328
Various chiral ligands bearing phosphorus or nitrogen donor atoms were obtained in a straightforward manner starting from trans-(2R,3R)-diphenylcyclopropane-1,1-dimethanol as a key structure. These chiral ligands were tested and compared in palladium(0)-catalyzed asymmetric allylic alkylation reactions (up to 71% ee) and rhodium(I)-catalyzed asymmetric hydrogenations (up to 88% ee). Moreover, in the asymmetric allylic alkylation, we observed excellent activity with a diphosphinite ligand (TOF = 600 mol 17 × [mol Pd × h)?1]. 相似文献
965.
The synthesis of a novel C2-symmetric bisphosphane ligand was accomplished starting from trans-(2R,3R)-bis(3′,5′-diphenylphenyl)cyclopropane-1,1-dimethanol as a key intermediate. This ligand was tested in the asymmetric rhodium(I)-catalyzed 1,4-addition to cyclic enones. We also compared the new ligand with a similar phosphane ligand with a less bulky cyclopropane backbone. Good yields (up to 99%) and enantioselectivities (up to 89% ee) were observed. We demonstrated that the presence of a more bulky cyclopropane backbone resulted in a less effective ligand. 相似文献
966.
Isoxazole‐Derived Amino Acids are Bromodomain‐Binding Acetyl‐Lysine Mimics: Incorporation into Histone H4 Peptides and Histone H3 下载免费PDF全文
Angelina R. Sekirnik David S. Hewings Natalie H. Theodoulou Lukass Jursins Katie R. Lewendon Laura E. Jennings Timothy P. C. Rooney Tom D. Heightman Stuart J. Conway 《Angewandte Chemie (International ed. in English)》2016,55(29):8353-8357
A range of isoxazole‐containing amino acids was synthesized that displaced acetyl‐lysine‐containing peptides from the BAZ2A, BRD4(1), and BRD9 bromodomains. Three of these amino acids were incorporated into a histone H4‐mimicking peptide and their affinity for BRD4(1) was assessed. Affinities of the isoxazole‐containing peptides are comparable to those of a hyperacetylated histone H4‐mimicking cognate peptide, and demonstrated a dependence on the position at which the unnatural residue was incorporated. An isoxazole‐based alkylating agent was developed to selectively alkylate cysteine residues in situ. Selective monoalkylation of a histone H4‐mimicking peptide, containing a lysine to cysteine residue substitution (K12C), resulted in acetyl‐lysine mimic incorporation, with high affinity for the BRD4 bromodomain. The same technology was used to alkylate a K18C mutant of histone H3. 相似文献
967.
Herein, a rapid and simple gold nanoparticle based colorimetric and dynamic light scattering (DLS) assay for the sensitive detection of cholera toxin has been developed. The developed assay is based on the distance dependent properties of gold nanoparticles which cause aggregation of antibody-conjugated gold nanoparticles in the presence of cholera toxin resulting discernible color change. This aggregation induced color change caused a red shift in the plasmon band of nanoparticles which was measured by UV–Vis spectroscopy. In addition, we employed DLS assay to monitor the extent of aggregation in the presence of different concentration of cholera toxin. Our assay can visually detect as low as 10 nM of cholera toxin which is lower than the previously reported colorimetric methods. The reported assay is very fast and showed an excellent specificity against other diarrhetic toxins. Moreover, we have demonstrated the feasibility of our method for cholera toxin detection in local lake water. 相似文献
968.
Timothy A. Brown Hao Chen Richard N. Zare 《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2015,127(38):11335-11337
The N,N‐dimethylaniline (DMA) radical cation DMA.+, a long‐sought transient intermediate, was detected by mass spectrometry (MS) during the electrochemical oxidation of DMA. This was accomplished by coupling desorption electrospray ionization (DESI) MS with a waterwheel working electrode setup to sample the surface of the working electrode during electrochemical analysis. This study clearly shows that DESI‐based electrochemical MS is capable of capturing electrochemically generated intermediates with half‐lives on the order of microseconds, which is 4–5 orders of magnitude faster than previously reported electrochemical mass spectrometry techniques. 相似文献
969.
Emily Kerr Egan H. Doeven Gregory J. Barbante Conor F. Hogan David J. Bower Paul S. Donnelly Timothy U. Connell Paul S. Francis 《Chemical science》2015,6(1):472-479
We demonstrate the mixed annihilation electrogenerated chemiluminescence of tris(2,2′-bipyridine)ruthenium(ii) with various cyclometalated iridium(iii) chelates. Compared to mixed ECL systems comprising organic luminophores, the absence of T-route pathways enables effective predictions of the observed ECL based on simple estimations of the exergonicity of the reactions leading to excited state production. Moreover, the multiple, closely spaced reductions and oxidations of the metal chelates provide the ability to finely tune the energetics and therefore the observed emission colour. Distinct emissions from multiple luminophores in the same solution are observed in numerous systems. The relative intensity of these emissions and the overall emission colour are dependent on the particular oxidized and reduced species selected by the applied electrochemical potentials. Finally, these studies offer insights into the importance of electronic factors in the question of whether the reduced or oxidized partner becomes excited in annihilation ECL. 相似文献
970.
Frampton MJ Claridge TD Latini G Brovelli S Cacialli F Anderson HL 《Chemical communications (Cambridge, England)》2008,(24):2797-2799
Highly luminescent inclusion complexes consisting of poly(para-phenylene) (PPP) or poly(4,4'-diphenylene-vinylene) (PDV) in the helical cavity of amylose have been synthesised, structurally characterised by nuclear Overhauser spectroscopy and used to fabricate electroluminescent light-emitting diodes. 相似文献