共查询到20条相似文献,搜索用时 31 毫秒
1.
Chun Li Wu Yan Zhang Ji Yu Guo* Xiao Tian Liang Institute of Materia Medica Chinese Academy of Medical Sciences & Peking Union Medical College Beijing 《中国化学快报》2002,13(1)
Agarofurans have been found to be active on the nervous system in our institute. 4-Butyl-a-agarofuran 1 is a promising drug candidate. In order to explore the pharmacokinetics of 1, the metabolism of 1 in vitro was studied with liver microsomes from rats. Five metabolites were isolated and structures were identified as compounds 2-6. But the absolute configuration of 2,4,5 and the position of carbonyl in 3 could not be unambiguously determined. Further determination was limited by the smal… 相似文献
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The barrier for the interconversion of the conformational atropisomers of an aryl fluorenylidene derivative was determined by variable-temperature NMR technique. In the case of a more hindered compound the two atropisomers were isolated and the structure determined by X-ray diffraction. The absolute configuration was assigned by theoretical interpretation of the Electronic Circular Dichroism spectrum (ECD). 相似文献
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The absolute configuration of sec/prim- and prim/sec-1,2-amino alcohols is determined by comparison of the (1)H NMR chemical shifts of the auxiliary OMe or CalphaH groups at the corresponding bis-( R) and bis-( S)-MPA derivatives. This is the first NMR method that allows the assignment of absolute configuration without resorting to the shifts of hydrogens at the substrate and is based on the cross anisotropic interactions between auxiliaries. 相似文献
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《Phosphorus, sulfur, and silicon and the related elements》2013,188(10):2241-2253
In the present work we describe the keto-enol equilibrium of some acylphosphonates 1 by means of 1 H, 13 C, 31 P NMR, and IR data which show that the enol form has E configuration. The keto/enol ratio is determined on the basis of 31 P NMR data. The reactivity of 1 with hydrazines derivatives and primary amines are reported. The structure of all compounds is determined by 1 H, 13 C, 31 P NMR, and IR. 相似文献
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Vidal P Pedregal C Díaz N Broughton H Aceña JL Jiménez A Espinosa JF 《Organic letters》2007,9(21):4123-4126
A novel approach for determining the absolute configuration of a chiral compound is proposed. The methodology is based on the distinct conformational effects imposed on a chiral substrate by each enantiomer of a chiral derivatizing agent. As a proof of concept, it is shown that the absolute configuration of 2-arylpyrrolidines can easily be determined by inspection of the multiplicity of the NMR signal of the methine proton of the pyrrolidine ring in the corresponding Mosher's amides. 相似文献
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The structure of rogioldiol A ((?)- 1 ), isolated from the red seaweed Laurencia microcladia, was determined. Employing the exciton-coupling technique for rogioldiol A p-bromobenzoate ( 2 ), the absolute configuration at C(9) of (?)- 1 was assigned, and, together with extensive NMR experiments, the absolute configuration at C(10) and preferred conformations of (?)- 1 were determined. The absolute configuration of the hetero-substituted cyclohexane ring was deduced in analogy from the X-ray structure of 4 , a derivative of the aldehyde 3 , which was isolated from the same seaweed and is believed to be a degradation product of (?)- 1 . 相似文献
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Based on an analysis of the ~1H NMR,FT-IR,UV-vis spectra,a chiral trimeric phenylene vinylene derivative(ChTPV) synthesized by a Wittig reaction was determined to have a trans-cis configuration, and it could be isomerized to the trans-trans isomer when treated with iodine.The melting point of ChTPV with a trans-trans configuration increased by 162.1℃compared to the trans-cis isomer,and the ChTPV with trans-trans configuration exhibited the typical liquid-crystalline texture of the smectic A in the heating process.The results indicated that the molecular configuration can influence the formation of the liquid crystalline phase of ChTPV. 相似文献
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De Qing Shi Yi Liu A. D. Feras Xiao Song Tan Jian Xin Chen 《Phosphorus, sulfur, and silicon and the related elements》2013,188(8):1937-1946
A series of novel, asymmetric-cyclic phosphoramides containing substituted pyridine were synthesized via the condensation reactions of trans 2-chloro-4-substitutedphenyl-5, 5-dimethyl-1,3,2-dioxaphosphinane 2-oxide with 2-chloro-5-aminomethylpyridine or 3-aminomethylpyridine. The reactions show good stereoselectivity. Only the cis isomer from configuration inversion was obtained, which is the thermodynamic stable product. The structures of the products were characterized by 1H NMR, 31P NMR, IR, MS, and elemental analysis. The configuration of the product was determined by X-ray diffraction analysis. The results of preliminary bioassay showed that the new compounds possess potential insecticidal and fungicidal activities. 相似文献
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The relative configuration of acyclic alpha-alkyl-beta-hydroxy carbonyl compounds can be determined by using (1)H NMR spectroscopy. The assignment can be achieved by recording the (1)H NMR spectrum of the syn-anti mixture. The upfield carbinol hydrogen signal belongs to the anti whereas the downfield to the syn stereoisomer. 相似文献
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Sibiralactone (1), a new monoterpene derivative, was isolated from the leaves of Sibiraea angustata. The structure was determined by the analysis of its NMR data and the absolute configuration was established by TDDFT ECD calculation of the solution conformers. 相似文献
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Chao JB Zhang BT 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2007,68(1):108-112
The interaction of cloxacillin sodium with beta-cyclodextrin (beta-CD) has been studied by several analytical techniques, including (1)H NMR, fluorescence spectroscopy, infrared spectroscopy. In this paper, solid inclusion complex of cloxacillin sodium with beta-CD was synthesized by the coprecipitation method. In addition, the characterization of the inclusion complex has been proved by fluorimetry, infrared spectroscopy and 1D, 2D NMR. The experimental results confirmed the existence of 1:1 inclusion complex of cloxacillin sodium with beta-CD. The formation constant of complex was determined by fluorescence method and (1)H NMR. Spacial configuration of complex has been proposed on 2D NMR technique. 相似文献
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The synthesis and the spectral properties of the hitherto unknown 9-methyl-cis-decalin-1,3-dione ( 16 ) are described. The keto-enol equilibrium of 16 in various solvents was determined by NMR. spectroscopy. The configuration and conformation of a large number of intermediates and derivatives were determined. 相似文献
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Robert W. Pow Zoё L. Sinclair Nicola L. Bell Nancy Watfa Yousef M. Abul-Haija De-Liang Long Prof. Leroy Cronin 《Chemistry (Weinheim an der Bergstrasse, Germany)》2021,27(48):12327-12334
Determining the relative configuration or enantiomeric excess of a substance may be achieved using NMR spectroscopy by employing chiral shift reagents (CSRs). Such reagents interact noncovalently with the chiral solute, resulting in each chiral form experiencing different magnetic anisotropy; this is then reflected in their NMR spectra. The Keplerate polyoxometalate (POM) is a molybdenum-based, water-soluble, discrete inorganic structure with a pore-accessible inner cavity, decorated by differentiable ligands. Through ligand exchange from the self-assembled nanostructure, a set of chiral Keplerate host molecules has been synthesised. By exploiting the interactions of analyte molecules at the surface pores, the relative configuration of chiral amino alcohol guests (phenylalaninol and 2-amino-1-phenylethanol) in aqueous solvent was establish and their enantiomeric excess was determined by 1H NMR using shifts of ΔΔδ=0.06 ppm. The use of POMs as chiral shift reagents represents an application of a class that is yet to be well established and opens avenues into aqueous host-guest chemistry with self-assembled recognition agents. 相似文献
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Xin‐Gang Xie Dr. Xun‐Wei Wu Dr. Hing‐Ken Lee Dr. Xiao‐Shui Peng Prof. Dr. Henry N. C. Wong Prof. Dr. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2010,16(23):6933-6941
Plakortone B is a naturally occurring bicyclic[3.3.0]furanolactone compound with attractive bioactivities. Although the relative configuration of plakortone B’s central core had been established by NMR spectroscopic methods, the absolute configuration of its four stereocenters remained unknown. In the present paper, all four possible isomers of plakortone B were synthesized and one of these molecules was found to be identical with the natural plakortone B on the basis of 1H, 13C NMR spectra and specific rotation comparisons. Thus, the absolute configuration of the natural plakortone B was determined to be (3S,4S,6R,10R). 相似文献
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Sun H d'Auvergne EJ Reinscheid UM Dias LC Andrade CK Rocha RO Griesinger C 《Chemistry (Weinheim an der Bergstrasse, Germany)》2011,17(6):1811-1817
The absolute configuration of small crystallizable molecules can be determined with anomalous X-ray diffraction as shown by Bijvoet in 1951. For the majority of compounds that can neither be crystallized nor easily be converted into crystallizable derivatives, stereocontrolled organic synthesis is still required to establish their absolute configuration. In this contribution, a new fundamental methodology for resolving the absolute configuration will be presented that does not require crystallization. With residual dipolar coupling enhanced NMR spectroscopy, ensembles of a limited number of structures are created reflecting the correct conformations and relative configuration. Subsequently, from these ensembles, optical rotation dispersion (ORD) spectra are predicted by DFT calculations and compared to experimental results. The combination of these two steps reveals the absolute configuration of a flexible molecule in solution, which is a big challenge to chiroptical methods and DFT in the absence of NMR spectroscopy. Here the absolute stereochemistry of the product of a new Michael addition, synthesized via a niobium(V) chiral enolate, will be elucidated by using the new methodology. 相似文献
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Toru Koizumi Reiko Yanada Hiroyasu Takagi Hajime Hirai Eiichi Yoshii 《Tetrahedron letters》1981,22(5):477-480
Diastereomerically pure bicyclic oxazaphospholes were prepared from L-prolinol and phenylphosphonic or thiophosphonic dichloride and their absolute configurations were determined based on the interpretation of NMR spectra. The base-catalyzed methanolysis of those compounds was found to proceed by exclusive PO bond cleavage with complete inversion of configuration. 相似文献