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1.
《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
2.
《Magnetic resonance in chemistry : MRC》2003,41(8):639-640
15N NMR spectral data for 3‐substituted (chloro, bromo, acetyl, carboxy, carboethoxy, methylsulfanyl, methylsulfinyl, N,N‐dimethylsulfamoyl, nitro) 4(1H)‐quinolinones and their 1‐methyl derivatives are presented. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
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4.
《Magnetic resonance in chemistry : MRC》2002,40(11):687-692
Continuing our systematic 15N NMR study of isoquinoline alkaloids, we report a contribution extending our previous paper. The 15N NMR chemical shifts and 15N,1H long‐range coupling pathways of tertiary and quaternary isoquinoline alkaloids of several constitutional types are presented. The selected compounds belong to the protoberberine, proaporphine, pavinane, rhoeadine and phtalideisoquinoline classes of alkaloids and were investigated by gradient‐selected inverse‐detected multiple bond correlation experiments (GHMBC and GSQMBC). In addition, x‐ray data and the principal geometric parameters of stylopine, mecambridine, norchelerythrine, isothebaine and mecambrine are reported and discussed. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
5.
《Magnetic resonance in chemistry : MRC》2003,41(7):541-544
Treatment of 2‐acetyl‐2‐methylcyclopentanone with hydrazine hydrate yielded a new condensed hexahydro‐1,3,5‐triazine (3b), which is the first example of the ketimine‐type trimers. A complete 1H, 13C and 15N NMR assignment of the compound was achieved. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
6.
In this article, we describe the characteristic 15N and 1HN NMR chemical shifts and 1J(15N–1H) coupling constants of various symmetrically and unsymmetrically substituted 1,4‐dihydropyridine derivatives. The NMR chemical shifts and coupling constants are discussed in terms of their relationship to structural features such as character and position of the substituent in heterocycle, N‐alkyl substitution, nitrogen lone pair delocalization within the conjugated system, and steric effects. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
7.
《Magnetic resonance in chemistry : MRC》2003,41(9):689-692
15N NMR chemical shifts of 2‐aryl‐1,3,4‐oxadiazoles were assigned on the basis of the 1H–15N HMBC experiment. Chemical shifts of the nitrogen and carbon atoms in the oxadiazole ring correlate with the Hammett σ‐constants of substituents in the aryl ring (r2 ≥ 0.966 for N atoms). 15N NMR data are a suitable and sensitive means for characterizing long‐range electronic substituent effects. Additionally, 13C NMR data for these compounds are presented. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
8.
《Magnetic resonance in chemistry : MRC》2002,40(7):480-482
1H, 13C and 15N NMR chemical shifts of 10 substituted pyrazolo[1,5‐a]pyrimidines were assigned based on DQF 1H, 1H COSY, PFG 1H, 13C HMQC and PFG 1H,X (X = 13C and 15N) HMBC experiments and on literature data. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
9.
Silvana Casati Ada Manzocchi Roberta Ottria Pierangela Ciuffreda 《Magnetic resonance in chemistry : MRC》2010,48(9):745-748
The complete 1H, 13C and 15N NMR signals assignments of some new isopentenyladenosine analogues were achieved using one‐ and two‐dimensional experiments (gs‐NOESY, gs‐HMQC and gs‐HMBC). Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
10.
Rubén Montalvo‐González Armando Ariza‐Castolo 《Magnetic resonance in chemistry : MRC》2012,50(1):33-39
A structural and conformational analysis of 1‐oxaspiro[2.5]octane and 1‐oxa‐2‐azaspiro[2.5]octane derivatives was performed using 1H, 13 C, and 15 N NMR spectroscopy. The relative configuration and preferred conformations were determined by analyzing the homonuclear coupling constants and chemical shifts of the protons and carbon atoms in the aliphatic rings. These parameters directly reflected the steric and electronic effects of the substituent bonded to the aliphatic six‐membered ring or to C3 or N2. The parameters also were sensitive to the anisotropic positions of these atoms in the three‐atom ring. The preferred orientation of the exocyclic substituents directed the oxidative attack. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
11.
《Magnetic resonance in chemistry : MRC》2002,40(7):467-470
In the course of saponification experiments with bis(2‐cyanoethyl) 2,6‐dimethyl‐4‐(2‐nitrophenyl)‐1,4‐dihydro‐3,5‐pyridinedicarboxylate ( 1 ), an analogue of the calcium channel blocker nifedipine, three unexpected degradation products were isolated. The compounds were identified as 3‐(2‐acetamido‐1‐carboxy‐1‐propenyl)‐1‐hydroxy‐2‐indolecarboxylic acid ( 3 ), 9‐hydroxy‐1,3‐dimethyl‐β‐carboline‐4‐carboxylic acid ( 4 ) and 6‐hydroxy‐2,4‐dimethyl‐5‐oxo‐5,6‐dihydrobenzo[c][2,7]naphthyridine‐1‐carboxylic acid ( 6 ). The structures of these compounds were deduced from one‐ and two‐dimensional 1H, 13C and natural abundance 15N NMR experiments (1H,1H‐COSY, gs‐HSQC, gs‐HMBC, 15N gs‐HMBC), and corroborated by comparison of their NMR data with the respective data for structurally similar compounds. Copyright © 2002 John Wiley & Sons, Ltd. 相似文献
12.
Roberta Ottria Silvana Casati Pierangela Ciuffreda 《Magnetic resonance in chemistry : MRC》2012,50(12):823-828
The complete 1H, 13C and 15N NMR signal assignments of some N‐ and O‐acylethanolamines, important family of naturally occurring bioactive lipid mediators, were achieved using one‐dimensional and two‐dimensional experiments (gs‐HMQC and gs‐HMBC). Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
13.
Rafael Germano Santana Derisvaldo Rosa Paiva Roberto da Silva Gomes Adriana Karla C. A. Reis 《Magnetic resonance in chemistry : MRC》2013,51(5):316-319
The complete assignment of the 1H and 13C NMR spectra of various 2‐acetamido‐3‐mercapto‐3‐methyl‐N‐aryl‐butanamides and 2‐acetamide‐3‐methyl‐3‐nitrososulfanyl‐N‐aryl‐butanamides with p‐methoxy, o‐chloro and m‐chloro substituents is reported. Copyright © 2013 John Wiley & Sons, Ltd. 相似文献
14.
Lijing Yang Jia Li Razvan Simionescu Hongbin Yan 《Magnetic resonance in chemistry : MRC》2013,51(1):60-64
N2‐Isobutyrylguanine was prepared by treatment of guanine with isobutyryl chloride. Two tautomers, 1,7‐dihydro‐2‐(isobutyroyl)amino‐6H‐purin‐6‐one and 1,9‐dihydro‐2‐(isobutyroyl)amino‐6H‐purin‐6‐one, were identified in almost 1 : 1 ratio in dichloromethane–dimethyl sulfoxide (1 : 1 v/v) by NMR spectroscopy. By using the selective‐inversion experiments, enthalpy, entropy, and free energy for activation were determined. This work represents the first report of guanine tautomers observed directly by NMR spectroscopy. Copyright © 2012 John Wiley & Sons, Ltd. 相似文献
15.
Valerie Huemer Gernot A. Eller Wolfgang Holzer 《Magnetic resonance in chemistry : MRC》2010,48(6):476-482
Various [5,6]pyrano[2,3‐c]pyrazol‐4(1H)‐thiones were synthesized in high yields by treatment of the corresponding [5,6]pyrano[2,3‐c]pyrazol‐4(1H)‐ones with Lawesson's reagent. Detailed NMR spectroscopic studies were undertaken of the title compounds. Complete and unambiguous assignment of chemical shifts (1H, 13C, 15N) and coupling constants (1H,1H; 13C,1H) was achieved by the combined application of various one‐ and two‐dimensional (1D and 2D) NMR spectroscopic techniques. Unequivocal mapping of most 13C,1H spin coupling constants is accomplished by 2D (δ, J) long‐range INEPT spectra with selective excitation. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
16.
Nelson L. C. Domingues Paulo R. Olivato Adriana K. C. A. Reis Mirta G. Mondino Filipe S. Lima Roberto Rittner 《Magnetic resonance in chemistry : MRC》2009,47(3):270-272
The complete assignment of the 1H and 13C NMR spectra of the diastereomeric pairs of some α‐arylsulfinyl‐substituted N‐methoxy‐N‐methylpropionamides with the substituents methoxy, methyl, chloro, nitro is reported. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
17.
Residual dipolar couplings (RDCs) are a rich source of structural information that goes beyond the range covered by the nuclear Overhauser effect or scalar coupling constants. They can only be measured in partially oriented samples. RDC studies of peptides in organic solvents have so far been focused on samples in chloroform or DMSO. Here, we show that stretched poly(vinyl acetate) can be used for the partial alignment of a linear β‐peptide with proteinogenic side chains in methanol. 1DCH, 1DNH, and 2DHH RDCs were collected with this sample and included as restraints in a simulated annealing calculation. Incorporation of RDCs in the structure calculation process improves the long‐range definition in the backbone of the resulting 314‐helix and uncovers side‐chain mobility. Experimental side‐chain RDCs of the central leucine and valine residues are in good agreement with predicted values from a local three‐state model. Copyright © 2016 John Wiley & Sons, Ltd. 相似文献
18.
《Magnetic resonance in chemistry : MRC》2003,41(12):1034-1037
The assignment of 1H and 13C NMR of the sesquiterpene (+)‐10β,14‐dihydroxy‐allo‐aromadendrane by means of two‐dimensional NMR is reported. Copyright © 2003 John Wiley & Sons, Ltd. 相似文献
19.
G. I. Ivanova E. R. Vão M. Temtem A. Aguiar‐Ricardo T. Casimiro E. J. Cabrita 《Magnetic resonance in chemistry : MRC》2009,47(2):133-141
Cyclodextrins are used in many drug formulations since their cavities provide microenvironments where drug molecules can enter and form inclusion complexes for controlled drug delivery. Supercritical carbon dioxide (scCO2) is an alternative to organic solvents and a very attractive medium for the preparation of these inclusion complexes. The potential ability of triacetyl‐β‐cyclodextrin (TA‐β‐CD) to form inclusion complexes in addition to its high miscibility in liquid and scCO2 could offer a chance for an economical and environmental friendly chemical processing. In this work, high‐pressure NMR studies were performed in order to obtain information on the molecular structure and dynamics of TA‐β‐CD in scCO2 at 313.15 K and 20 MPa and its ability to form inclusion complexes under these conditions was studied. The influence of scCO2 on a number of NMR spectral parameters, such as chemical shifts, spin‐spin coupling constants, nuclear Overhauser effect (NOE) and spin‐lattice relaxation (T1) has been studied. We unequivocally show for the first time structural changes of TA‐β‐CD in scCO2, like acetyl chain orientation and overall shape distortions that can affect its inclusion capability in this medium. The possibility of cavity self‐closure is discussed and the results of two inclusion studies that support cavity self‐closure, with the angiotensin‐converting enzyme inhibitor, captopril, and the nonsteroid anti‐inflammatory drug, flufenamic acid, are presented. Copyright © 2008 John Wiley & Sons, Ltd. 相似文献
20.
Guillaume Berionni Bruce Pégot Régis Goumont 《Magnetic resonance in chemistry : MRC》2010,48(2):101-110
The 15N as well as 1H and 13C chemical shifts of nine substituted tetrazolopyridines and their corresponding tetrazolopyridinium salts have been determined by using NMR spectroscopy at the natural abundance level of all nuclei in CD3CN. In this paper, we report, for the first time, the N‐alkylation reaction of electron deficient tetrazolopyridines. The treatment of tetrazolopyridines 5–13 with one equivalent of trialkyloxonium tetrafluoroborate leads to a mixture of two isomers, i.e. N3‐ and N2‐alkyl tetrazolo[1,5‐a]pyridinium salts. It has been observed that the N3‐isomer is always the major isomer, except in the case of the CF3 substituent, where the two isomers are obtained in the same amount. The quaternary tetrazolopyridinium nitrogen N3 is shielded by around 100 ppm (parts per million) with respect to the parent tetrazolopyridine. Experimental data are interpreted by means of density functional theory (DFT) calculations, including solvent‐induced effects, within the conductor‐like polarizable continuum model (CPCM). Good agreements between theoretical and experimental 1H, 13C and 15N NMR were found. The combination of multinuclear magnetic resonance spectroscopy with gauge including atomic orbital (GIAO) DFT calculations is a powerful tool in the structural elucidation for both neutral and cationic heterocycles and in the determination of the orientation of N‐alkylation of tetrazolopyridines. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献