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1.
2.
A method for the preparation of methyl 4-O-methyl-alpha-D-glucopyranuronate and its single crystal X-ray structure determination are reported. The molecule adopts an almost ideal (4)C1 ((degree)C3) conformation. 相似文献
3.
On the Reaction of Some 2H-Pyran-2-one Derivatives with Primary Amines The versatile reactivity of 6-unsubstituted 2H-pyran-2-ones towards aliphatic and aromatic amines has been studied. It was found that the result of the reaction depends not only on the substitution of 2H-pyran-2-ones and on the structure of amines, but also on the stoichiometric ratio of reacting compounds. 相似文献
4.
Vratislav Langer Dalma Gyepesov Jozef Lusto Juraj Kronek Eva Scholtzov Miroslav Ko 《Acta Crystallographica. Section C, Structural Chemistry》2006,62(7):o416-o418
In the crystal structure of the title compound, C11H13NO2, there are strong intermolecular O—H⋯N hydrogen bonds which, together with weak intramolecular C—H⋯O hydrogen bonds, lead to the formation of infinite chains of molecules, held together by weak intermolecular C—H⋯O hydrogen bonds. A theoretical investigation of the hydrogen bonding, based on density functional theory (DFT) employing periodic boundary conditions, is in agreement with the experimental data. The cluster approach shows that the influence of the crystal field and of hydrogen‐bond formation are responsible for the deformation of the 2‐oxazoline ring, which is not planar and adopts a 4T3 (C3TC2) conformation. 相似文献
5.
The nucleophilic attack of substituted anilines at position 6 of methyl coumalate (1) opens the α-pyrone ring to form 4-arylamino-3-(methoxycarbonyl)butadien-1-carboxylic acid 2 (Scheme 1). The latter are easily decarboxylated at room temperature in polar aprotic solvents to 1-arylamino-2-(methoxycarbonyl)butadiene 4 which smoothly undergo regio- and stereospecific Diels-Alder reactions with different dienophiles. 相似文献
6.
Roland Hellinger Jeannie Horak Wolfgang Lindner 《Analytical and bioanalytical chemistry》2013,405(25):8105-8120
The fluorescent tag 6-aminoquinolyl-N-hydroxysuccinimidyl carbamate (AQC; AccQ Fluor reagent kit from Waters) is a commercial N-terminal label for proteinogenic amino acids (AAs), designed for reversed-phase separation and quantification of the AA racemates. The applicability of AQC-tagged AAs and AA-type zwitterionic compounds was tested for enantiomer separation on the tert-butyl carbamate modified quinine and quinidine based chiral stationary phases, QN-AX and QD-AX employing polar-organic elution conditions. The investigated test analytes included the enantiomers of the positional isomers of isoleucine (Ile), threonine, homoserine, and 4-hydroxyproline. Furthermore, β-AAs, cyclic, and heterocyclic AAs including trans-2-amino-cyclohexane carboxylic acid and trans-2-aminocyclohexyl sulfonic acid, phenylalanine derivatives substituted with halides with increasing electronegativity and 3,4-dihydroxyphenylalanine, cysteine-related derivatives including homocysteic acid, methionine sulfone, cysteine-S-acetic acid, and cysteine-S-acetamide as well as a small range of aminophosphonic acids were enantioseparated. A mechanistic interaction study of AQC-AAs in comparison with fluoresceine isothiocyanate-labeled AAs was performed. The chiral and chemoselective recognition processes involved in enantiomer separation and retention was systematically discussed. Special emphasis was set on the influential factors exhibited by the chemistry, branching position, and spatial properties of the investigated zwitterionic analytes. The general interest to separate and distinguish between different types of branched-chained AAs and metabolic side products thereof lies in the toxicity of some of these compounds, which makes for instance allo–Ile an attractive candidate in disease-related biomarker research. Figure
Separation of the four AQC-tagged isomers of 4-hydroxyproline (trans-D, cis-D, trans-L and cis-L) on the chiral stationary phase QD-AX 相似文献
7.
Dalma Gyepesov Vratislav Langer 《Acta Crystallographica. Section C, Structural Chemistry》2013,69(2):111-113
The structure analysis of so‐called 9CaO·4CrO3·Cr2O3 proved it to be the title compound, decacalcium hexakis[chromate(V)] chromate(VI), with the simultaneous presence of unusual chromium oxidation states. The structure determination was carried out on a crystal that had inversion twinning. The CrVIO4 tetrahedron is situated on a threefold axis and is disordered over two possible orientations that share three O atoms, while the CrVO4 tetrahedra are in general positions and are ordered. The charge is balanced by Ca2+ cations, one of which is located on a threefold axis. The Ca2+ ions are coordinated by six, seven or eight O atoms. The compound is a significant phase in the CaO–CrOx system and its formation reduces the refractoriness of calcium‐rich compositions in an oxidizing atmosphere. 相似文献
8.
Prof. Dr. Andrei V. Malkov Dr. Sigitas Stončius Dr. Mark Bell Dr. Fabiomassimo Castelluzzo Dr. Pedro Ramírez‐López Dr. Lada Biedermannová Prof. Dr. Vratislav Langer Dr. Lubomír Rulíšek Prof. Dr. Pavel Kočovský 《Chemistry (Weinheim an der Bergstrasse, Germany)》2013,19(28):9167-9185
Detailed kinetic and computational investigation of the enantio‐ and diastereoselective allylation of aldehydes 1 with allyltrichlorosilanes 5 , employing the pyridine N‐oxides METHOX ( 9 ) and QUINOX ( 10 ) as chiral organocatalysts, indicate that the reaction can proceed through a dissociative (cationic) or associative (neutral) mechanism: METHOX apparently favors a pentacoordinate cationic transition state, while the less sterically demanding QUINOX is likely to operate via a hexacoordinate neutral complex. In both pathways, only one molecule of the catalyst is involved in the rate‐ and selectivity‐determining step, which is supported by both experimental and computational data. 相似文献
9.
10.
A new variant of SQ–SQ pulse sequence (SQSQh) for relative sign determination and detection of small silicon–carbon couplings over more than one bond is presented. In the SQSQh sequence, proton detection replaces carbon detection used in the original SQ–SQ pulse sequence (SQSQc). The theoretical gain in sensitivity was experimentally tested on two samples (trimethylsiloxyethane, 1, and 1,2,4‐tris(trimethylsiloxy)benzene, 2), the experimentally found gain provided by the SQSQh over the SQSQc method varied between 6 and 8. The method can be applied to linear spin systems, i.e. to systems where the silicon is coupled to the carbon in question and to any hydrogen not necessarily bonded to the carbon. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献