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91.
Asymmetric Synthesis of Spirocyclic β‐Lactams through Copper‐Catalyzed Kinugasa/Michael Domino Reactions 下载免费PDF全文
Tao Shu Long Zhao Sun Li Dr. Xiang‐Yu Chen Dr. Carolina von Essen Prof. Dr. Kari Rissanen Prof. Dr. Dieter Enders 《Angewandte Chemie (International ed. in English)》2018,57(34):10985-10988
The first copper‐catalyzed highly chemo‐, regio‐, diastereo‐, and enantioselective Kinugasa/Michael domino reaction for the desymmetrization of prochiral cyclohexadienones is described. In the presence of a chiral copper catalyst, alkyne‐tethered cyclohexadienones couple with nitrones to generate the chiral spirocyclic lactams with excellent stereoselectivity (up to 97 % ee, >20:1 dr). The new method provides direct access to versatile highly functionalized spirocyclic β‐lactams possessing four contiguous stereocenters, including one quaternary and one tetra‐substituted stereocenter. 相似文献
92.
Sara Busi Manu Lahtinen Reijo Sillanp Kari Rissanen 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(10):m458-m460
The title compound, (C16H20N)2[Fe2Br6O], crystallizes with one dibenzyldimethylammonium cation and one half of a μ‐oxo‐bis[tribromoferrate(III)] anion in the asymmetric unit. The bridging oxo group is situated on an inversion centre, resulting in a linear conformation for the Fe—O—Fe unit. The iron(III) cations have tetrahedral geometry, with bond angles in the range 106.8 (1)–112.2 (1)°. The ion pairs are held together by Coulombic forces and C—H⋯Br hydrogen bonds. Each Br− anion forms one hydrogen bond. No C—H⋯O hydrogen bonds are found between the O atom in the Fe—O—Fe unit and surrounding counter‐cations, consistent with the linear configuration of the Fe—O—Fe unit. 相似文献
93.
Kari Dahl Astrid Hald Poul J?rgensen Ivar Martinsen Yngvar Thomassen 《Fresenius' Journal of Analytical Chemistry》1990,338(4):526-529
Summary Studies have been made of both short and long term stability of trace elements in lyophilized human body fluid reference materials, as well as the stability of mercury in reconstituted urine solutions. No detectable concentration changes for mercury, lead and aluminium occurred during the 5-year period. There are large differences in the amounts of mercury loss among different reconstituted materials. Addition of traces of gold to the solutions minimized the mercury loss and increased the useable time of the reconstituted material from hours to 8 days. A certification process based on direct determinations by reference laboratories and by comparison against master lots of the same material and against similar certified reference materials is presented. Values for calcium, copper and mercury obtained from reference laboratories and using the data transfer principle have been assigned in new batches of urine and serum. 相似文献
94.
Using an STO -3G basis set, energy localized molecular orbitals (LMO ) were determined for the ten electron series HF, H2O, NH3, and CH4 as well as for CH3OH and C2H2F2. The method of conjugate gradients is shown to be a viable alternative to other non-eigenvalue methods. The characterization of the LMO in terms of first and second moment measures indicates that the STO -3G basis set LMO may be accurately correlated to larger sp basis set LMO . Also, it is shown that the first and second moment measures display a good linear correlation with the classical concept of electronegativity. 相似文献
95.
Raymond A. Poirier Raymond Daudel Roy E. Kari Imre G. Csizmadia 《International journal of quantum chemistry》1984,25(2):411-421
Closed-shell RHF one-electron properties are calculated for H2S using a total of 41 different s, p basis sets and two polarized basis sets (6–31G* and 6–31G**). Total energies and geometries alone are not a comprehensive criteria for selecting the best basis sets. It is shown here that the comparison of a number of one-electron properties can serve as an excellent criteria for testing basis sets. The quality or reliability of a basis set is taken as being its agreement with a large uncontracted s, p basis set (s, p limit). 相似文献
96.
Rainey MA Callaway K Barnes R Wilson B Dalby KN 《Journal of the American Chemical Society》2005,127(30):10494-10495
Five hundred protein kinases phosphorylate 10 000 proteins in human cells. Frequently, more than one site in a protein is phosphorylated, and often by more than one protein kinase. The mechanistic basis underlying the overlapping specificity of the phospho-proteome is not well understood. We are interested in understanding why ERK2, a proline-directed protein kinase, phosphorylates only a fraction of the (S/T-P) sites found in the surface loops of proteins, at an appreciable rate. To address this fundamental question, we utilized a well-established protein substrate EtsDelta138, which comprises a globular ERK2-recognition domain (pnt domain) and an unstructured peptide-like N-terminal tail. This tail contains T38, the sole ERK2 phosphorylation site. We mutated the TP motif, which is recognized by the active site and found that mutagenesis of the T-38/P-39 motif to TD, TR, TA, TG, and TV has no effect on the stability of the ternary complex but does decrease kcat. We also investigated the effect of perturbing the binding between ERK2 and the pnt domain, which occurs outside the active site, to find that mutation of the pnt domain (F120A) leads to a 10-fold decrease in binding but the kcat remains the same. The data support a mechanism of proximity-mediated catalysis, where the docking of the pnt domain, outside the active site, increases the effective concentration of the TP motif near the active site. The data are consistent with the notion that the interaction between ERK2 and the pnt domain provides uniform binding energy and stabilizes each enzyme intermediate and transition state to an equal extent. While other steps on the reaction pathway contribute towards the specificity of the ERK2 reaction, a docking interaction provides the initial basis for substrate recognition. Those residues within the docked complex, which have the ability to access the active site with an appropriate geometry, can be phosphorylated at an efficient rate if followed by a proline or small hydrophobic amino acid. 相似文献
97.
p-(1H-phenanthro[9,10-d]imidazol-2-yl)- substituted calix[4]arene, a deep cavity for guest inclusion
The reaction of tetra-p-formyltetra-O-propylcalix[4]arene with phenanthrenequinone in the presence of NH(4)OAc affords compound 2, a new class of calixarene with an expanded aromatic cavity, that could be stabilized by hydrogen-bonded bridges and/or ion pairing, thus preventing collapse into fully stacked pinched cone conformations as depicted. Two partially protonated calixarenes interdigitate in the solid state to give rise to a self-assembled face-to-face dimer, stabilized by pi-pi stacking interactions. 相似文献
98.
Solution and Solid‐State Studies on the Halide Binding Affinity of Perfluorophenyl‐Armed Uranyl–Salophen Receptors Enhanced by Anion–π Interactions 下载免费PDF全文
Luca Leoni Dr. Rakesh Puttreddy Dr. Ondřej Jurček Andrea Mele Dr. Ilaria Giannicchi Dr. Francesco Yafteh Mihan Prof. Kari Rissanen Prof. Antonella Dalla Cort 《Chemistry (Weinheim an der Bergstrasse, Germany)》2016,22(52):18714-18717
The enhancement of the binding between halide anions and a Lewis acidic uranyl–salophen receptor has been achieved by the introduction of pendant electron‐deficient arene units into the receptor skeleton. The association and the occurrence of the elusive anion–π interaction with halide anions (as tetrabutylammonium salts) have been demonstrated in solution and in the solid state, providing unambiguous evidence on the interplay of the concerted interactions responsible for the anion binding. 相似文献
99.
100.