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排序方式: 共有602条查询结果,搜索用时 31 毫秒
181.
Dr. Ben Bradshaw Carlos Luque‐Corredera Gisela Saborit Prof. Dr. Carlos Cativiela Ruth Dorel Dr. Carles Bo Prof. Dr. Josep Bonjoch 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(41):13881-13892
A diastereoselective synthesis of cis‐5‐oxodecahydroquinolines is described in which three stereocenters are generated in a one‐pot reaction. The reaction involves a lithium hydroxide‐promoted Robinson annulation/intramolecular aza‐Michael domino process from an achiral acyclic tosylamine‐tethered β‐keto ester. The development and scope of this reaction was facilitated through the use of DFT‐based mechanistic studies, which enabled the observed diastereodivergent course of the azacyclization to be rationalized. The varying stereochemistry and stability of the resulting decahydroquinolines was found to depend on whether a β‐keto ester or ketone were embedded in the substrates undergoing aminocyclization. This synthetic approach gave access not only to both diastereomeric cis‐decahydroquinolines from the same precursor, but also to the corresponding trans isomers, through an epimerization processes of the corresponding N‐unsubstituted cis‐5‐oxodecahydroquinolines. The described methodology provides advanced building‐blocks with the three relative stereochemistries required for the total synthesis of phlegmarine alkaloids. 相似文献
182.
Eva Jambor Agnes Bona Janos Schmidt Laszlo Mark Robert Ohmacht 《Journal of separation science》2013,36(5):827-831
The preparation of the so‐called bonded phase liquid chromatographic packings is usually carried out by heating the silica, the silane, a catalyst, or a scavenger in an appropriate solvent (often toluene.) Due to the longtime of boiling, the procedure is time and energy consuming, and solvent intensive. The goal of this work is to present a simple, environment‐friendly preparation method with reduced solvent consumption to synthetize RP liquid chromatographic stationary phases. The effects of reaction conditions (amount of reagents, composition of the reagent, microwave energy, reaction time, reproducibility of the synthesis) are discussed. Pore structure, surface coverage, the change of the pore structure and surface coverage upon reaction are demonstrated, the efficiency of the column (van Deemter plot for different solutes) is presented. A variety of applications (aromatic hydrocarbons, halobenzenes, bioactive peptides, resveratrol from red wine) demonstrates the separation power of the new phase. 相似文献
183.
Lykke L Rodríguez-Escrich C Jørgensen KA 《Journal of the American Chemical Society》2011,133(38):14932-14935
The first catalytic enantioselective synthesis of oxaziridines is presented. The oxidation of aryl and alkyl aldimines with m-CPBA under organocatalytic conditions using cinchona alkaloid-derived catalysts furnished optically active oxaziridines in good yields and high enantioselectivities (up to 94% ee). Mechanistic investigations indicate a stepwise enantioselective oxidation process. 相似文献
184.
Alba Espargar Salom Llabrs Sven J. Saupe Carles Curutchet F. Javier Luque Raimon Sabat 《Angewandte Chemie (International ed. in English)》2020,59(21):8104-8107
Amyloids are characterized by their capacity to bind Congo red (CR), one of the most used amyloid‐specific dyes. The structural features of CR binding were unknown for years, mainly because of the lack of amyloid structures solved at high resolution. In the last few years, solid‐state NMR spectroscopy enabled the determination of the structural features of amyloids, such as the HET‐s prion forming domain (HET‐s PFD), which also has recently been used to determine the amyloid–CR interface at atomic resolution. Herein, we combine spectroscopic data with molecular docking, molecular dynamics, and excitonic quantum/molecular mechanics calculations to examine and rationalize CR binding to amyloids. In contrast to a previous assumption on the binding mode, our results suggest that CR binding to the HET‐s PFD involves a cooperative process entailing the formation of a complex with 1:1 stoichiometry. This provides a molecular basis to explain the bathochromic shift in the maximal absorbance wavelength when CR is bound to amyloids. 相似文献
185.
186.
Dr. Miguel A. Huertos Dr. Israel Cano Dr. Nuno A. G. Bandeira Dr. Jordi Benet‐Buchholz Prof. Dr. Carles Bo Prof. Dr. Piet W. N. M. van Leeuwen 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(49):16121-16127
The reaction of [CuI(HSC6H4PPh2)]2 with NaBH4 in CH2Cl2/EtOH led to air‐ and moisture‐stable copper hydride nanoparticles (CuNPs) containing phosphinothiolates as new ligands, one of which was isolated by crystallization. The X‐ray crystal structure of [Cu18H7L10I] (L=?S(C6H4)PPh2) shows unprecedented features in its 28‐atom framework (18 Cu and 10 S atoms). Seven hydrogen atoms, in hydride form, are needed for charge balance and were located by density functional theory methods. H2 was released from the copper hydride nanoparticles by thermolysis and visible light irradiation. 相似文献
187.
IMTL logic was introduced in [12] as a generalization of the infinitely-valued logic of Lukasiewicz, and in [11] it was proved
to be the logic of left-continuous t-norms with an involutive negation and their residua. The structure of such t-norms is
still not known. Nevertheless, Jenei introduced in [20] a new way to obtain rotation-invariant semigroups and, in particular,
IMTL-algebras and left-continuous t-norm with an involutive negation, by means of the disconnected rotation method. In order
to give an algebraic interpretation to this construction, we generalize the concepts of perfect, bipartite and local algebra
used in the classification of MV-algebras to the wider variety of IMTL-algebras and we prove that perfect algebras are exactly
those algebras obtained from a prelinear semihoop by Jenei's disconnected rotation. We also prove that the variety generated
by all perfect IMTL-algebras is the variety of the IMTL-algebras that are bipartite by every maximal filter and we give equational
axiomatizations for it. 相似文献
188.
We study the structure of classifying spaces of Kač-Moody groups from a homotopy theoretic point of view. They behave in
many respects as in the compact Lie group case. The mod p cohomology algebra is noetherian and Lannes'T functor computes the mod p cohomology of classifying spaces of centralizers of elementary abelian p-subgroups. Also, spaces of maps from classifying spaces of finite p-groups to classifying spaces of Kač-Moody groups are described in terms of classifying spaces of centralizers while the classifying
space of a Kač-Moody group itself can be described as a homotopy colimit of classifying spaces of centralizers of elementary
abelian p-subgroups, up to p-completion. We show that these properties are common to a larger class of groups, also including parabolic subgroups of Kač-Moody
groups, and centralizers of finite p-subgroups.
Received: 15 June 2000 / in final form: 20 September 2001 / Published online: 29 April 2002 相似文献
189.
In this paper conditions are given guaranteeing that the Core equals the D-core (the set of unDominated imputations). Under these conditions, we prove the non-emptiness of the intersection of the Weber set with the imputation set. This intersection has a special stability property: it is externally stable. As a consequence we can give a new characterization (th. 3.2) for the convexity of a cooperative game in terms of its stability (von Neumann-Morgenstern solutions) using the Weber set. 相似文献
190.