共查询到20条相似文献,搜索用时 31 毫秒
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The structurally complex antifungal agent posaconazole has been well characterized by conventional 1H‐ and 13C‐NMR studies. In contrast, 15N resonance assignments have never been reported. We now wish to report the assignment of the eight 15N resonances of posaconazole using two‐dimensional long‐range 1H‐15N GHMBCAD NMR data. The 15N resonance assignments were undertaken to facilitate the evaluation of the impact of 1H‐15N heteronuclear shift correlation data in the Computer‐Assisted Structure Elucidation (CASE) of complex molecular structures. J. Heterocyclic Chem., (2011). 相似文献
3.
1H, 13C, and 15N NMR chemical shifts have been measured for 2-aminopyridine N-oxide (1), its eleven derivatives (2–10, 13, 14), and 3-Cl and 3-Br substituted 4-nitropyridine N-oxides (11, 12). δ(15N) of pyridine ring nitrogen in 2-acetylaminopyridine N-oxides are 5.9–11.5 ppm deshielded from those in 2-aminopyridine N-oxides. When amino and acetylamino substituents are in 4-position, δ(15N) of ring nitrogen is 21.3 ppm deshielded in the acetylated derivative. The strong resonance interaction between 2-amino and 5-nitro groups reflects in the decrease of amino nitrogen shielding about 5.3–17.9 ppm. Also, 1H and 13C NMR spectral data are in agreement with 15N NMR results reflected as deshielded amino protons and carbons C-2 and C-5. The pyridine nitrogen chemical shift in all amino- and acetylamino derivatives vary between ?101.2 and ?126.7 ppm, which has been connected with the tautomeric balance in our earlier studies. 相似文献
4.
Rosalinda Contreras Jean Michel Grevy Zureima García‐Hernndez Marisol Gizado‐Rodriguez Bernd Wrackmeyer 《Heteroatom Chemistry》2001,12(6):542-550
A series of aminodiphenylphosphanes 1 [Ph2P‐N(H)tBu ( a ), ‐NEt2 ( b ), ‐NiPr2 ( c )], 2 [Ph2P‐NHPh ( a ), ‐NH‐2‐pyridine ( b ), ‐NH‐3‐pyridine ( c ), ‐NH‐4‐pyridine ( d ), NH‐pyrimidine ( e ), NH‐2,6‐Me2‐C6H3 ( f ), NH‐3‐Me‐2‐pyridine ( g )], 3 [Ph2P‐N(Me)Ph ( a ), ‐NPh2 ( b )], and N‐pyrrolyldiphenylphosphane 4 (Ph2P‐NC4H4) was prepared and studied by NMR (1H, 13C, 31P, 15N NMR) spectroscopy. The isotope‐induced chemical shifts 1Δ14/15N(31P) were determined at natural abundance of 15N by using HEED INEPT experiments. A dependence of 1Δ14/15N(31P) on the substituents at nitrogen was found (alkyl < H < aryl; increasingly negative values). The magnitude and sign of the coupling constants 1J(31P,15N) (positive sign) are dominated by the presence of the lone pair of electrons at the phosphorus atom. The X‐ray structural analysis of 2b is reported, showing the presence of dimers owing to intermolecular hydrogen bridges in the solid state. © 2001 John Wiley & Sons, Inc. Heteroatom Chem 12:542–550, 2001 相似文献
5.
L. Stefaniak John D. Roberts M. Witanowski B. T. Hamdi G. A. Webb 《Magnetic resonance in chemistry : MRC》1984,22(4):209-214
15N NMR chemical shift data are presented for 14 azolopyridines, together with the results of INDO/S-SOS calculations of nitrogen shieldings. Previous 14N NMR results for some of these compounds are reinterpreted. The 14N data and their assignments are shown to be reliable for the indolizine nitrogen atom from arguments based on relative line widths. The pyridine-type nitrogens are more reliably assigned from the 15N spectra combined with the results of the INDO/S-SOS calculations for individual molecules. A combination of 14N and 15N NMR spectra, together with the shielding calculations, provides a basis for unambiguous assignments of all the various nitrogen environments considered. 相似文献
6.
《Angewandte Chemie (Weinheim an der Bergstrasse, Germany)》2017,129(35):10569-10573
The hyperpolarization of heteronuclei via signal amplification by reversible exchange (SABRE) was investigated under conditions of heterogeneous catalysis and microtesla magnetic fields. Immobilization of [IrCl(COD)(IMes)], [IMes=1,3‐bis(2,4,6‐trimethylphenyl), imidazole‐2‐ylidene; COD=cyclooctadiene] catalyst onto silica particles modified with amine linkers engenders an effective heterogeneous SABRE (HET‐SABRE) catalyst that was used to demonstrate a circa 100‐fold enhancement of 15N NMR signals in 15N‐pyridine at 9.4 T following parahydrogen bubbling within a magnetic shield. No 15N NMR enhancement was observed from the supernatant liquid following catalyst separation, which along with XPS characterization supports the fact that the effects result from SABRE under heterogeneous catalytic conditions. The technique can be developed further for producing catalyst‐free agents via SABRE with hyperpolarized heteronuclear spins, and thus is promising for biomedical NMR and MRI applications. 相似文献
7.
The 15N NMR spectra of the O-inside cis-fused conformer of perhydropyrido[1,2-c][1,3]thiazine shows a shielding of the nitrogen of 23.0 ppm relative to the trans-fused conformer. In contrast, 15N shifts for the cis-and trans-fused conformers of perhydro-oxazolo[3,4-a]pyridine and perhydrothiazolo[3,4-a]pyridine show corresponding shieldings of only 0.6 and 2.5 ppm, respectively. 相似文献
8.
Valentin Joubert Virginie Silvestre Maxime Lelièvre Virginie Ladroue Fabrice Besacier Serge Akoka Gérald S. Remaud 《Magnetic resonance in chemistry : MRC》2019,57(12):1136-1142
The position-specific 15N isotope content in organic molecules, at natural abundance, is for the first time determined by using a quantitative methodology based on 15N Nuclear Magnetic Resonance (NMR) spectrometry. 15N NMR spectra are obtained by using an adiabatic “Full-Spectrum” INEPT sequence in order to make possible 15N NMR experiments with a high signal-to-noise ratio (>500), to reach a precision with a standard deviation below 1‰ (0.1%). This level of precision is required for observing small changes in 15N content associated to 15N isotope effects. As an illustration, the measurement of an isotopic enrichment factor ε for each 15N isotopomer is presented for 1-methylimidazole induced during a separation process on a silica column. The precision expressed as the long-term repeatability of the methodology is good enough to evaluate small changes in the 15N isotope contents for a given isotopomer. As observed for 13C, inverse and normal 15N isotope effects occur concomitantly, giving access to new information on the origin of the 15N isotope effects, not detectable by other techniques such as isotope ratio measured by Mass Spectrometry for which bulk (average) values are obtained. 相似文献
9.
S. Braun 《Magnetic resonance in chemistry : MRC》1976,8(5):273-274
The 13C,15N coupling constants in three 1,2,4-triazine-4-15N derivatives and in a substituted pyrimidine-1-15N have been determined and are compared with those in pyridine and quinoline. Of special interest are the data of the 5-(2-dimethylamino-1-propenyl)-3,6-dimethyl-1,2,4-triazine-4-15N, since one observes a characteristic alternation of the absolute value of J(13C,15N) along the sidechain and a hitherto unobserved very large 13C,15N coupling constant through four bonds of 3·9 Hz, the origin of which is attributed to the influence of the lone pair orbital on the 15N at position 4. 相似文献
10.
Natural abundance 15N NMR spectra have been obtained for bilirubin IX-α using polarization transfer via the INEPT and SINEPT-2 techniques. The resonances for all four nitrogens are clearly resolved. 15N chemical shifts and 15N? 1H coupling constants over one and three bonds are reported. Heteronuclear chemical shift correlation between 15N and 1H for the four NH groups has been established by means of the SINEPT-2 pulse sequence. 相似文献
11.
《Magnetic resonance in chemistry : MRC》2002,40(5):353-360
The 15N NMR chemical shifts of N7‐ and N9‐substituted purine derivatives were investigated systematically at the natural abundance level of the 15N isotope. The NMR chemical shifts were determined and assigned using GSQMBC, GHMBC, GHMQC and GHSQC experiments in solution. 15N cross‐polarization magic angle spinning data were recorded for selected compounds in order to study the principal values of the 15N chemical shifts. Geometric parameters obtained by using RHF/6–31G** and single‐crystal x‐ray structural analysis were used to calculate the chemical‐shielding constants (GIAO and IGLO) which were then used to assign the nitrogen resonances observed in the solid‐state NMR spectra and to determine the orientation of the principal components of the shift tensors. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
12.
Line intensities in 15N NMR spectra are strongly influenced by spin-lattice and spin–spin relaxation times, relaxation mechanisms and experimental conditions. Special care has to be taken in using 15N spectra for quantitative purposes. Quantitative aspects are discussed for the 15N NMR of molecules with different nitrogen functional groups and also mixtures of nitrogen-containing compounds. It is shown that, in general, quantitative data are obtainable from integration of 15N lines in proton decoupled 15N NMR spectra using NOE suppression. Addition of paramagnetic relaxation reagents (PARR) under controlled conditions is frequently needed to accomplish the experiment within reasonable time limits. 相似文献
13.
L. Stefaniak John D. Roberts M. Witanowski G. A. Webb 《Magnetic resonance in chemistry : MRC》1984,22(4):215-220
15N NMR data are reported for 42 azoles, taken mostly at a standard concentration and in a common solvent (0.5 M dimethyl sulfoxide with a 0.01 M increment of Cr(acac)3 for each nitrogen atom present). Signal assignments were assisted by comparison with 14N line widths, the use of 2J(15N1H) couplings, and shielding calculations obtained by the INDO/S–SOS approach. The generally large differences in nitrogen-shielding changes permitted rather facile shift assignments. 相似文献
14.
Dr. Nikita V. Chukanov Dr. Oleg G. Salnikov Ivan A. Trofimov Mohammad S. H. Kabir Dr. Kirill V. Kovtunov Prof. Igor V. Koptyug Prof. Eduard Y. Chekmenev 《Chemphyschem》2021,22(10):960-967
Signal Amplification by Reversible Exchange (SABRE) technique enables nuclear spin hyperpolarization of wide range of compounds using parahydrogen. Here we present the synthetic approach to prepare 15N-labeled [15N]dalfampridine (4-amino[15N]pyridine) utilized as a drug to reduce the symptoms of multiple sclerosis. The synthesized compound was hyperpolarized using SABRE at microtesla magnetic fields (SABRE-SHEATH technique) with up to 2.0 % 15N polarization. The 7-hour-long activation of SABRE pre-catalyst [Ir(IMes)(COD)Cl] in the presence of [15N]dalfampridine can be remedied by the use of pyridine co-ligand for catalyst activation while retaining the 15N polarization levels of [15N]dalfampridine. The effects of experimental conditions such as polarization transfer magnetic field, temperature, concentration, parahydrogen flow rate and pressure on 15N polarization levels of free and equatorial catalyst-bound [15N]dalfampridine were investigated. Moreover, we studied 15N polarization build-up and decay at magnetic field of less than 0.04 μT as well as 15N polarization decay at the Earth's magnetic field and at 1.4 T. 相似文献
15.
Hans R. Kricheldorf 《Magnetic resonance in chemistry : MRC》1980,13(1):52-58
Various cyclodipeptides containing glycine, alanine, leucine, valine, phenylalanine, phenylglycine and sarcosine units were synthesized by cyclization of dipeptide pentachlorophenyl esters. The 13C and natural abundance 15N NMR spectra of these heterocycles were measured in trifluoroacetic acid and compared with the spectra of the corresponding amino acids and polypeptides. The 13C NMR carbonyl signals of all cyclodipeptides show a 1.5–4.0 ppm upfield shift relative to the corresponding polypeptides. The 15N NMR signals show no such consistent relationship. The substituent effects and the neighbouring residue effects observed in the 15N NMR spectra of the cyclodipeptides are different from those of polypeptides, while the one bond N? H coupling constant of cis and trans amide groups was almost identical. The nitrogen and the carbonyl signal of the Gly units in cyclo-Gly-Phe show an extraordinary downfield shift, reflecting the interaction of the phenyl group with the 2,5-dioxopiperazine ring. 相似文献
16.
E. Rosenberg Kenneth L. Williamson John D. Roberts 《Magnetic resonance in chemistry : MRC》1976,8(3):117-119
15N chemical shifts of twenty-four substituted indoles have been determined in natural abundance (in organic solvents) using Fourier transform NMR. The overall chemical shift range is 27 ppm, with groups in the 2-, 3- and 5-ring positions showing the largest substituent effects. Substituents capable of resonance interaction with the indole nitrogen give shifts in the expected directions but they cannot be correlated with known substituent parameters. Compounds measured in DMSO give 0·2 to 10·2 ppm downfield shifts with respect to the same compound measured in CDCl3. 13C NMR data for previously unreported compounds are also reported. 相似文献
17.
《Magnetic resonance in chemistry : MRC》2002,40(3):202-206
15N NMR data for a series of 12 para‐substituted benzamidoximes and benzamidinium salts were determined in dimethyl sulfoxide. For the amino group of benzamidoximes 1J(N,H) coupling constants were determined using polarization transfer techniques; the other 15N atoms were not detectable owing to fast exchange processes and, thus, standard proton noise decoupled spectra had to be measured. The 15N NMR chemical shifts of the oxime‐type nitrogen atom and the benzamidinium amino group (with two exceptions) correlate with Hammett σ° values (r2>0.95). 15N NMR shift data are a suitable and sensitive means for characterizing far‐ranging electronic substituent effects in these functional groups. Additionally, 13C NMR data in dimethyl sulfoxide solution are given. All spectroscopic data will be used for investigations into the mechanisms of the enzymes involved in the metabolic cycle of oxidation and reduction of benzamidines and benzamidoximes. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
18.
H. Kalchhauser M. Kriech H. Ahorn W. Sommergruber 《Monatshefte für Chemie / Chemical Monthly》1993,124(3):333-337
Summary Proton-detected H-relayed N,H correlation NMR spectroscopy at natural abundance of15N has been used to demonstrate the enormous value of heteronuclear NMR spectroscopy for the proton assignment of medium-sized oligopeptides.
Zweidimensionalerelayed 15N,1H-korrelierte NMR-Spektroskopie an einem Pentadecapeptid bei natürlicher Häufigkeit von15N
Zusammenfassung Anhand1H-detektierterrelayed-N,H-korrelierter NMR-Spektroskopie bei natürlicher Häufigkeit von15N wird die große Bedeutung der heteronuklearen Kernresonanzspektroskopie für die Protonenzuordnung mittlerer Oligopeptide demonstriert.相似文献
19.
A. V. Afonin V. K. Voronov E. I. Enikeeva M. A. Andrayankov 《Russian Chemical Bulletin》1987,36(4):697-700
Conclusions
15N (14N) and17O NMR spectra have been obtained on vinyl ethers of pyridine and quinoline, with unenriched samples. The principal factor determining the chemical shifts is p- conjugation of the unshared pairs of the heteroatom with the unsaturated fragments of the molecule; an additional contribution in the case of the15N signals comes from interaction of the nitrogen atom with a proton through space.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 4, pp. 769–773, April, 1987. 相似文献
20.
Gary E. Martin Bruce D. Hilton Patrick A. Irish Kirill A. Blinov Antony J. Williams 《Journal of heterocyclic chemistry》2007,44(5):1219-1222