NOESY Experiments (noesy + experiment)

Distribution by Scientific Domains
Distribution within Chemistry


Selected Abstracts


Low-temperature 1H and 13C NMR spectra of N -substituted 1,2,3,4-tetrahydropyrazino[1,2- a]indoles

MAGNETIC RESONANCE IN CHEMISTRY, Issue 5 2005
Alan R. Katritzky
Abstract The temperature-dependent 1H and 13C NMR spectra of 2-(2-butynyl)-10-methyl-1,2,3,4-tetrahydropyrazino[1,2- a]indole (4) (as a representative example of 1,9) in CFCl3 + CD2Cl2 solution are described and discussed. Below 183 K, the hexahydropyrazine ring inversions become slow on the NMR time-scale and 4 exists in principle as two conformational diastereomers. In fact, only one was observed with the N-2 substituent in an equatorial position as shown by a low-temperature NOESY experiment. The energy barrier for conformational interchange was calculated from NMR data to be 8.3 kcal mol,1 (1 kcal = 4.184 kJ), in agreement with quantum chemical calculations. Unambiguous assignments for all proton and carbon resonances of 1,9 were made using 1D (APT, DEPT, NOE difference) and 2D (COSY, NOESY, gHMQC, gHMBC) NMR techniques. Copyright © 2005 John Wiley & Sons, Ltd. [source]


An Efficient Synthesis of 2-Bromo-3-hydroxy Esters by Reaction of Ketones with Ethyl Dibromoacetate Promoted by Samarium Diiodide

EUROPEAN JOURNAL OF ORGANIC CHEMISTRY, Issue 9 2006
José M. Concellón
Abstract A simple and efficient samarium diiodide mediated synthesis of 2-bromo-3-hydroxy esters 1 by the reaction of a variety of ketones 2 with ethyl dibromoacetate (3) is described. The relative configuration of the major diastereoisomer obtained was established by NOESY experiments of the corresponding ,,,-epoxy esters 4 prepared from 1. Additionally, a mechanism is proposed to explain the results obtained. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2006) [source]


Purification and structure of the major product obtained by reaction of NADPH and NMNH with the myeloperoxidase/hydrogen peroxide/chloride system

FEBS JOURNAL, Issue 10 2001
Françoise Auchère
The first spectrophotometric study of the reaction of the myeloperoxidase/H2O2/Cl, system with NADPH and NMNH showed that the reaction products were not the corresponding oxidized nucleotides and that modifications would take place on the nicotinamide part of the molecule [Auchère, F. & Capeillère-Blandin, C. (1999) Biochem. J. 343, 603,613]. In this report, in order to obtain more precise information on the structural modifications and mechanism of the reaction, we focus on the purification and isolation of products derived from NADPH and NMNH by RP-HPLC. Electrospray ionization mass spectra indicated that the relative height of the peaks reflected that of the natural isotopic abundance of 35Cl and 37Cl, providing evidence that the products derived from NADPH and NMNH were monochlorinated. Moreover, calculated masses revealed the 1 : 1 addition of HOCl to the molecule. Various 1D and 2D NMR experiments provided data for the assignments of the chemical shifts of protons and carbons and the coupling constants of the protons of the chlorinated nucleotides. Further NOESY experiments allowed the characterization of the spatial structure of the chlorinated product and showed that trans HOCl addition occurred at the C5=C6 carbon double bond of the nicotinamide ring, leading to a chlorohydrin. [source]


NMR Conformational Analysis and Theoretical Calculations for 2-Aryl- 1,3-dihydroxy-4,4,5,5-tetramethylimidazolidines

HELVETICA CHIMICA ACTA, Issue 2 2004
Antônio
Conformational studies of 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-1-yl)imidazolidine (1a) and 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-3-yl)imidazolidine (1b), carried out by using 1D 1H- and 13C-NMR and 2D HMQC, HMBC, and NOESY experiments and with the aid of theoretical calculations, indicate that the OH groups are trans to the pyridinyl substituent. Because the two 1H-NMR signals of the Me groups are distinguishable and do not change between 290 and 380,K, it is proposed that 1a and 1b have each only one conformation in this temperature range. This behavior was not found with 1,3-dihydroxy-4,4,5,5-tetramethyl-2-(pyridin-2-yl)imidazolidine (1c) because its Me 1H-NMR signals cross over at 300,K. Hence, more than one conformation must be present, beyond those produced by simple inversions. Theoretical calculations including temperature and solvent effects were performed to provide further information on the conformational analysis and to help to assign the NMR data. The combination of NMR measurements and quantum-chemical calculations is shown to be a very promising strategy for conformational analysis studies in solution. [source]


Simple synthesis of 2-amino-4-(het)aryl-4,6-dihydro-1(3)(11)H -[1,3,5]triazino[2,1- b]quinazolin-6-ones,

JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 1 2008
Anton V. Dolzhenko
The 2-amino-4-(het)aryl-4,6-dihydro-1(3)(11)H -[1,3,5]triazino[2,1- b]quinazolin-6-ones were prepared readily by cyclocondensation of anthranilic acid derived 4-oxo-3,4-dihydroquinazolinyl-2-guanidine with a variety of aldehydes. The structures of the compounds were confirmed by nmr spectroscopy, including 2D NOESY experiments. [source]


Liquid chromatography coupled to nuclear magnetic resonance spectroscopy for the identification of isoflavone glucoside malonates in T. pratense L. leaves.

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 13 2004
Eva de Rijke
Abstract Previous studies revealed that the main isoflavones in extracts of leaves of T. pratense L. are biochanin A and formononetin, their 7- O -glucosides, and two glucoside malonate isomers of each of them. Since LC,MS(/MS) did not provide sufficient information to distinguish the glucoside malonate isomers, in the present paper LC,NMR as well as off-line two-dimensional NMR were used to obtain further structural information. Matrix solid-phase dispersion (MSPD) was applied to obtain sufficiently high analyte concentrations to perform LC,NMR. Stop-flow reversed-phase LC,NMR was performed using a gradient of deuterated water and deuterated acetonitrile. Off-line COSY and NOESY experiments were carried out to determine the positions of the glucose moiety on the flavonoid aglycone, and of the malonate moiety on the glucose. Based on the fragmentation patterns in MS/MS and the NMR spectra, the two formononetin glucoside malonate isomers were identified as 7- O -,-D-glucoside 6´´- O -malonate and 7- O -,-D-glucoside 4´´- O -malonate; i.e. they only differ in the substitution position of the malonate group on the glucoside ring. The biochanin A glucoside malonate isomers, however, have quite different structures. The main and later eluting isomer is biochanin A 7- O -,-D-glucoside 6´´- O -malonate, and the minor and earlier eluting isomer is 5-hydroxy-7-methoxyisoflavone 4´- O -,-D-glucoside 4´´- O -malonate: the positions of the methoxy group and the glucoside 6´´- O -malonate group on the flavonoid skeleton are interchanged. [source]


Complete multinuclear magnetic resonance characterization of a set of polyfluorinated acids and alcohols

MAGNETIC RESONANCE IN CHEMISTRY, Issue 2 2009
Alexander A. Marchione
Abstract A complete 1H, 19F, and 13C NMR assignment of a homologous series of polyfluorinated acids and alcohols is reported. These assignments were obtained chiefly through single and multiple-bond 1H,13C and 19F,13C correlation experiments (HSQC, HMBC). 19F NOESY experiments were required for assignment of two compounds with diastereotopic 19F nuclei in the CF2chain of the molecule. Copyright © 2008 John Wiley & Sons, Ltd. [source]


Unambiguous structural elucidation of base-modified purine nucleosides using NMR

MAGNETIC RESONANCE IN CHEMISTRY, Issue 1 2008
Raman Narukulla
Abstract A general and unambiguous approach has been developed for structural elucidation of modified purine nucleosides using NMR spectroscopy. Systematic assignment of proton and carbon signals of modified nucleosides was firmly established by COSY and the anomerism of the glycosidic linkage of synthetic nucleosides clearly elucidated by NOESY experiments. Characteristic properties of 15N-isotopic labelling at specific positions of nucleosides were also employed for structural studies. The reported approach is applicable to other modified nucleosides and nucleotides, as well as nucleobases. Copyright © 2007 John Wiley & Sons, Ltd. [source]


A new eremophilanolide from Senecio sinuatus Gilib

MAGNETIC RESONANCE IN CHEMISTRY, Issue 6 2007
Eleuterio Burgueño-Tapia
Abstract From the hexane extracts of Senecio sinuatus roots, the new 3,-angeloyloxy-6,-hydroxyeremophil-1(10)-en-8,,12-olide (3), along with the known compounds 3,-angeloyloxy-6,-hydroxyeremophil-1(10)-ene (1), 3,-senecioyloxy-6,-hydroxyeremophil-1(10)-ene (2), and 3,-angeloyloxy-6,,8,-dihydroxyeremophil-1(10)-en-8,,12-olide (4), were isolated. Complete 1H and 13C NMR chemical shift assignments of 1,4 were achieved using one- and two-dimensional NMR techniques, including gHMQC and gHMBC experiments. A Monte Carlo search, followed by B3LYP/6-31G*DFT calculation, provided the theoretical conformations of the eremophilane rings, which were in agreement with results derived from 1H1H NMR coupling constant analysis, and confirmed by NOESY experiments. Copyright © 2007 John Wiley & Sons, Ltd. [source]


A Conjugated Thiophene-Based Rotaxane: Synthesis, Spectroscopy, and Modeling

CHEMISTRY - A EUROPEAN JOURNAL, Issue 13 2010
Leszek Zalewski Dr.
Abstract A dithiophene rotaxane 1,,-CD and its shape-persistent corresponding dumbbell 1 were synthesized and fully characterized. 2D NOESY experiments, supported by molecular dynamics calculations, revealed a very mobile macrocycle (,-CD). Steady-state and time-resolved photoluminescence experiments in solution were employed to elucidate the excited-state dynamics for both systems and to explore the effect of cyclodextrin encapsulation. The photoluminescence (PL) spectrum of 1,,-CD was found to be blueshifted with respect to the dumbbell 1 (2.81 and 2.78,eV, respectively). Additionally, in contrast to previous observations, neither PL spectra nor the decay kinetics of both threaded and unthreaded systems showed changes upon increasing the concentration or changing the polarity of the solutions, thereby providing evidence for a lack of tendency toward aggregation of the unthreaded backbone. [source]