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Chemical Shift Assignments (chemical + shift_assignment)

Distribution by Scientific Domains

Chemistry	92%

Kinds of Chemical Shift Assignments

nmr chemical shift assignment

Selected Abstracts

1H,13C and 19F NMR data of N -substituted 6-(4-methoxyphenyl)-7H -pyrrolo[2,3- d]pyrimidin-4-amines in DMSO- d6

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2010
Christopher Sørum
Abstract Chemical shift assignment of seven N -substituted 6-(4-methoxyphenyl)-7H -pyrrolo[2, 3- d]pyrimidin-4-amines, six of which are fluorinated, have been performed based on 1H, 13C, 19F, and 2D COSY, HMBC and HSQC experiments. Copyright © 2009 John Wiley & Sons, Ltd. [source]

Chemical shift assignment of the transmembrane helices of DsbB, a 20-kDa integral membrane enzyme, by 3D magic-angle spinning NMR spectroscopy

PROTEIN SCIENCE, Issue 2 2008
Ying Li
Abstract The Escherichia coli inner membrane enzyme DsbB catalyzes disulfide bond formation in periplasmic proteins, by transferring electrons to ubiquinone from DsbA, which in turn directly oxidizes cysteines in substrate proteins. We have previously shown that DsbB can be prepared in a state that gives highly resolved magic-angle spinning (MAS) NMR spectra. Here we report sequential 13C and 15N chemical shift assignments for the majority of the residues in the transmembrane helices, achieved by three-dimensional (3D) correlation experiments on a uniformly 13C, 15N-labeled sample at 750-MHz 1H frequency. We also present a four-dimensional (4D) correlation spectrum, which confirms assignments in some highly congested regions of the 3D spectra. Overall, our results show the potential to assign larger membrane proteins using 3D and 4D correlation experiments and form the basis of further structural and dynamical studies of DsbB by MAS NMR. [source]

Toward direct determination of conformations of protein building units from multidimensional NMR experiments.

JOURNAL OF COMPUTATIONAL CHEMISTRY, Issue 10 2003

Abstract Knowledge of chemical shift,structure relationships could greatly facilitate the NMR chemical shift assignment and structure refinement processes that occur during peptide/protein structure determination via NMR spectroscopy. To determine whether such correlations exist for polar side chain containing amino acid residues the serine dipeptide model, For- L -Ser-NH2, was studied. Using the GIAO-RHF/6-31+G(d) and GIAO-RHF/TZ2P levels of theory the NMR chemical shifts of all hydrogen (1HN, 1H,, 1H,1, 1H,2), carbon (13C,, 13C,, 13C,) and nitrogen (15N) atoms have been computed for all 44 stable conformers of For- L -Ser-NH2. An attempt was made to establish correlation between chemical shift of each nucleus and the major conformational variables (,0, ,, ,, ,1, ,,1 and ,2). At both levels of theory a linear correlation can be observed between 1H,/,, 13C,/,, and 13C,/,. These results indicate that the backbone and side-chain structures of For- L -Ser-NH2 have a strong influence on its chemical shifts. © 2003 Wiley Periodicals, Inc. J Comput Chem 24: 1157,1171, 2003 [source]

Structure elucidation, conformational analysis and thermal effects on membrane bilayers of an antimicrobial myricetin ether derivative

JOURNAL OF HETEROCYCLIC CHEMISTRY, Issue 3 2001
C. Demetzos
The membrane perturbing 3,7,4,,5,-tetramethyl ether of myricetin 1 was isolated from Cistus monspelien-sis L. Its structure was elucidated and its conformational properties were explored using a combination of 2D NMR spectroscopy and computational chemistry. The obtained results showed that compound 1 adopts four enantiomeric pairs of low energy conformers characterized: (a) by an aromatic ring B twisted through rotation about C2-C1, bond from the rigid isoflavone ring; (b) a 4,-O-CH3 bond oriented out of the plane with equal probability upwards or downwards the phenyl ring B, while all the other O-CH3 bonds are oriented in the plane of the aryl ring. Two of these enantiomeric pairs are lowest in energy. These possible bioactive con-formers are possibly stabilized by van Der Waals interactions. The 3,,5-diacetyl derivative 2 of compound 1 was synthesized and its structure elucidation was achieved based on the chemical shift assignment of the parent compound 1. The Differential Scanning Calorimetry (DSC) results revealed that the degree of the thermal effects exerted by the flavonoids at dipalmitoylphosphatidyl choline (DPPC) bilayers followed the order 1 > 2 > myricetin. Their antimicrobial activity against Gram positive bacteria followed the same order. [source]

Application of HPLC-NMR for the Rapid Chemical Profiling of a Southern Australian Sponge, Dactylospongia sp.

JOURNAL OF SEPARATION SCIENCE, JSS, Issue 4 2009
Daniel Anthony Dias
Abstract Rapid chemical profiling of the antitumour active crude dichloromethane extract of the marine sponge, Dactylospongia sp. was undertaken. A combination of both offline (HPLC followed by NMR and MS) and on-line (on-flow and stop-flow HPLC-NMR) chemical profiling approaches was adopted to establish the exact nature of the major constituents present in the dichloromethane extract of this sponge. On-flow HPLC-NMR analysis was employed to initially identify components present in the dichloromethane extract, while stop-flow HPLC-NMR experiments were then conducted on the major component present, resulting in the partial identification of pentaprenylated p -quinol (5). Subsequent off-line RP semi-preparative HPLC isolation of 5 followed by detailed spectroscopic analysis using NMR and MS permitted the complete structure to be established. This included the first complete carbon NMR chemical shift assignment of 5 based on the heteronuclear 2-D NMR experiments, together with the first report of its antitumour activity. This study represents one of the few reports describing the application of HPLC-NMR to chemically profile secondary metabolites from a marine organism. [source]

Complete assignment of the 1H and 13C NMR spectra of garciniaphenone and keto-enol equilibrium statements for prenylated benzophenones

MAGNETIC RESONANCE IN CHEMISTRY, Issue 3 2008
Priscilla B. M. C. Derogis
Abstract This article reports the structural elucidation by IR, UV and MS spectroscopic data along with 1H and 13C NMR chemical shift assignments of two benzophenones isolated from the fruit pericarp of Garcinia brasiliensis Mart. (Clusiaceae): garciniaphenone, (1R,5S,7S)-3-benzoyl-4-hydroxy-6,6-dimethyl-5,7-di(3-methyl-2-butenyl)bicyclo[3.3.1]non-3-ene-2,9-dione, a novel triprenylated benzophenone; and 7- epi -clusianone, a tetraprenylated benzophenone that has already been extracted from another species of the same family. Furthermore, the keto-enol tautomeric equilibrium at solution-state was described for these compounds by 1D and 2D NMR spectral methods and one attempt to rationalize the different ratios between the noted tautomers was based on stereochemical features. Copyright © 2008 John Wiley & Sons, Ltd. [source]

Comparison of various density functional methods for distinguishing stereoisomers based on computed 1H or 13C NMR chemical shifts using diastereomeric penam ,-lactams as a test set

MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2007
Keith W. Wiitala
Abstract Full 1H and 13C NMR chemical shift assignments were made for two sets of penam ,-lactams: namely, the diastereomeric (2S, 5S, 6S)-, (2S, 5R, 6R)-, (2S, 5S, 6R)-, and (2S, 5R, 6S)-methyl 6-(1,3-dioxoisoindolin-2-yl)-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylates (1,4) and (2S, 5R, 6R)-, (2S, 5S, 6R)-, and (2S, 5R, 6S)-6-(1,3-dioxoisoindolin-2-yl)-3,3-dimethyl-7-oxo-4-thia-1-aza-bicyclo[3.2.0]heptane-2-carboxylic acids (6,8). Each penam was then modeled as a family of conformers obtained from Monte Carlo searches using the AMBER* force field followed by IEFPCM/B3LYP/6-31G(d) geometry optimization of each conformer using chloroform solvation. 1H and 13C chemical shifts for each conformer were computed at the WP04, WC04, B3LYP, and PBE1 density functional levels as Boltzmann averages of IEFPCM/B3LYP/6-311 + G(2d,p) energies over each family. Comparisons between experimental and theoretical chemical shift data were made using the total absolute error (|,, | T) criterion. For the 1H shift data, all methods were sufficiently accurate to identify the proper stereoisomers. Computed 13C shifts were not always successful in identifying the correct stereoisomer, regardless of which DFT method was used. The relative ability of each theoretical approach to discriminate among stereoisomers on the basis of proton shifts was also evaluated. Copyright © 2007 John Wiley & Sons, Ltd. [source]

3-Oxo-12,-hydroxyfriedelane from Maytenus gonoclada: structure elucidation by 1H and 13C chemical shift assignments and 2D-NMR spectroscopy

MAGNETIC RESONANCE IN CHEMISTRY, Issue 10 2007
Mauro Lúcio G. Oliveira
Abstract The compounds 3-oxofriedelane (1), 3,-hydroxyfriedelane (2), 3,11-dioxofriedelane (3), 3,16-dioxofrie delane (4) and 3-oxo-12,-hydroxyfriedelane (5) were isolated from the hexane extract of Maytenus gonoclada Mart. (Celastraceae) leaves. Structural formula and the stereochemistry of the new pentacyclic triterpene 3-oxo-12,-hydroxyfriedelane (5) were established through 1H and 13C NMR and DEPT 135 spectral data including 2D experiments (HMBC, HMQC, COSY, and NOESY) and mass spectrometry (GC-MS). 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]

Two isomeric epoxysitosterols from Rhododendron formosanum: 1H and 13C NMR chemical shift assignments

MAGNETIC RESONANCE IN CHEMISTRY, Issue 8 2006
Vivek Krishna
Abstract 1H and 13C NMR assignments of the two isomeric epoxysitosterols, 5,6,-epoxy-5,-stigmastan-3,-ol (1) and 5,6,-epoxy-5,-stigmastan-3,-ol (2), isolated from the leaves of Rhododendron formosanum Hemsl were achieved by 1D and 2D techniques such as DEPT, HMBC, HMQC, COSY and NOESY. Copyright © 2006 John Wiley & Sons, Ltd. [source]

1H and 13C NMR assignments of abietane diterpenes from Aegiphila lhotzkyana

MAGNETIC RESONANCE IN CHEMISTRY, Issue 9 2003
Maria Claudia Pinheiro Barros
Abstract An NMR study of one new and several known abietane diterpenes isolated from the roots of Aegiphila lhotzkyana is described. In addition to 1D NMR, several 2D shift-correlated NMR pulse sequences (1H,1H-COSY, NOESY, HMQC and HMBC) were used to establish all the structures, and unambiguously perform the 1H and 13C chemical shift assignments of the new natural diterpene and three derivatives, the NMR data for which have not been reported previously. Revision of current data assignment for teuvincenone H is also suggested. Copyright © 2003 John Wiley & Sons, Ltd. [source]

Synthesis and NMR characterization of 6-Phenyl-6-deoxy-2,3-di- O -methylcellulose,

POLYMERS FOR ADVANCED TECHNOLOGIES, Issue 6 2002
Dr Navzer (Nozar) D. Sachinvala
Abstract Cellulose (1) was converted for the first time to 6-phenyl-6-deoxy-2,3-di- O -methylcellulose (6) in 33% overall yield. Intermediates in the five-step conversion of 1 to6 were: 6- O -tritylcellulose (2), 6- O -trityl-2,3-di- O -methylcellulose (3), 2,3-di- O -methylcellulose (4); and 6-bromo-6-deoxy-2,3-di- O -methylcellulose (5). Elemental and quantitative carbon-13 analyses were concurrently used to verify and confirm the degrees of substitution in each new polymer. Gel permeation chromotography (GPC) data were generated to monitor the changes in molecular weight (DPw) as the synthesis progressed, and the compound average decrease in cellulose DPw was , 27%. Differential scanning calorimetry (DSC) and thermogravimetric analysis (TGA) were used to characterize the decomposition of all polymers. The degradation temperatures (,°C) and percent char at 500,°C of cellulose derivatives 2 to 6 were 308.6 and 6.3%, 227.6,°C and 9.7%, 273.9,°C and 30.2%, 200.4,°C and 25.6%, and 207.2,°C and 27.0%, respectively. The glass transition temperature (Tg) of6- O -tritylcellulose by dynamic mechanical analysis (DMA) occurred at 126.7,°C and the modulus (E,, Pa) dropped 8.9 fold in the transition from ,150,°C to,+,180,°C (6.6,×,109 to 7.4,×,108 Pa). Modulus at 20,°C was 3.26,×,109 Pa. Complete proton and carbon-13 chemical shift assignments of the repeating unit of the title polymer were made by a combination of the HMQC and COSY NMR methods. Ultimate non-destructive proof of carbon,carbon bond formation at C6 of the anhydroglucose moiety was established by generating correlations between resonances of CH26 (anhydroglucose) and C1,, H2,, and H6, of the attached aryl ring using the heteronuclear multiple-bond correlation (HMBC) method. In this study, we achieved three major objectives: (a) new methodologies for the chemical modification of cellulose were developed; (b) new cellulose derivatives were designed, prepared and characterized; (c) unequivocal structural proof for carbon,carbon bond formation with cellulose was derived non-destructively by use of one- and two-dimensional NMR methods. Copyright © 2002 John Wiley & Sons, Ltd. [source]