Isocoumarines: Structural Study by NMR and by AM1 Semi-Empirical Method

Study of a serie of isocoumarins by ¹³C and ¹⁷O NMR spectrometry and AM1 method is reported. These methods gave valuable informations on electronic effect and the structure of isocoumarins.     

Complete Analysis of the 1H and 13C NMR Spectra of 5-Isopropylsulfonyl-2-Norbornenes Through the Application of Two-Dimensional NMR Techniques

Total assignment of ¹³C and ¹H NMR spectra of the 5-isopropylsulfonyl-2-norbornenes 2 was achieved using the concerted application of two-dimensional homonuclear and heteronuclear chemical shift correlations. The stereochemistry of both the diastereoisomers endo 2a and exo 2b have been established using the magnitude of the proton coupling constants.     

Convenient Synthesis 1H, 13C NMR Study and X-Ray Crystal Structure Determination of Some New Disubstituted Thiophenes

2,5-, 3,4- and 2,3-Thienylenediacrylic (1, 4 and 7 respectively) were synthesized in one step reaction by catalytic vinylation of the corresponding dibromothiophenes in the presence of cyclohexylamine salt of acrylic acid. 2,4-Thienylenediacrylic acid 10 was prepared by catalytic vinylation of 3-(4-bromo-2-thienyl)acryilic acid.     

Two-Dimensional NMR Spectroscopy in Complete Analysis of the 1H and 13C NMR Spectra of the Ionophore A 23187 and its Calcium Salt

The complete assignment of the proton carbon spectra of the A 23187 Ionophore and its calcium salt is presented.     

1H and 13C NMR Spectral Study of Some 2r-Aryl-6c-phenylthian-4-ones,Their 1-Oxides and 1,1-Dioxides

ABSTRACT

Four 2r-aryl-6c-phenylthian-4-ones 1b?1e and their 1-oxides 2b?2e and 1,1-dioxides 3b?3e have been newly synthesized. ¹H and ¹³C NMR spectra have been recorded for all these compounds and 2r,6c-diphenylthian-4-one 1-oxide 2a. ¹³C NMR spectrum has been recorded for the sulfone 3a of 1a. For selected compounds ¹H-¹H COSY, HSQC, HMBC, and NOESY spectra have been recorded. The vicinal proton–proton coupling constants suggest that in all these compounds, the heterocyclic ring adopts chair conformation with equatorial orientations of the aryl and phenyl groups. Proton and carbon chemical shifts suggest that in the sulfoxides, the S=O bond is axial and enhances the J _aa value by some special effect. The S = O bond causes a significant upfield shift even on carbons without hydrogens. Significant solvent shifts also were observed.     

Assignments of 1H and 13C NMR Spectral Data for Benzoylecgonine,a Cocaine Metabolite

The complete assignment of the ¹H and ¹³C NMR spectra of benzoylecgonine, a cocaine metabolite, was performed, with the aid of some 2D experiments such as gCOSY and gHSQC.     

1H AND 13C NMR Assignments of Artheethers

The ¹H and ¹³C nmr assignments for all hydrogen and carbon atoms were made for β and α arteethers (5 and 6) based on chemical shift theory and 2D-nmr techniques (COSY and HETCOR).     

1H NMR Study of Hydrogen Bonding and Hydrogen to Deuterium Isotope Exchange in Ureido Sugars

Abstract

The acidic properties of ureido NH protons in two new derivatives of methyl 3,4,6-triacetyl-2-deoxy-β-D-glucopyranoside and i-butylamine (1) and L-leucine (2) were studied by ¹H NMR. Stronger influence of polar aprotic solvents, more effective interaction with nitroxyl radical and faster H/D exchange indicate that N1'-H proton which is proximate to the glucopyranose ring is more acidic than N3'-H one in both ureido sugars, this conclusion was supported by semi-empirical AM1 calculation. Hydrogen to deuterium exchange rates are 1.2 x 10^?2 to 5.5x 10^?3 M^?1 min^?l. Significantly slower exchange of N3'-H proton standing by Leu residue in 2 can be explained by the existence of internal H-bonds.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-Phenyl)-3a, 4-dihydro (1,2,4) oxadiazolo(4,5-a), 1, 5-benzodiazepines Using 2D NMR Spectroscopy

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic environment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

Assignment of the 1H and 13C Spectra of 5-Methylthio-4H-1-(p-R1-phenyl)-3a-(p-R2-phenyl)-3a,4-dihydro (1,2,4) oxadiazolo(4,5-a), 1,5-benzodiazepines using 2D NMR Spectroscopy.

The ¹H NMR spectra of the title benzodiazepines derivatives is highly congested because all the protons are in aromatic enviroment so many proton signals remain overlap even 300 MHz or higher fields. With this in mind, the assignment of the ¹H and ¹³C spectra of these compounds obtained using COSY, NOESY, HMQC and HMBC experiments is reported.     

NMR Study of Pentafluoroaniline - Hydrogen Bonding and Proton Exchange

The temperature and concentration dependence of ¹H NMR chemical shifts of pentafluoroaniline and aniline in acetone (Ac), dimethylsulphoxide (DMSO) and hexamethylphosphortriamide (HMPA) indicate that the effect of hydrogen bond formation, δ = δ_obs - δ_A' is similar for both anilines. The analysis of ¹H NMR spectra showed, that proton exchange of t-butyl alcohol (tBA) and 2,6-di-t-butylphenol (DTBPh) with pentafluoroaniline is slower than that with aniline.     

17O and 13C NMR Studies of Isobenzopyrylium Salts

¹³C and ¹⁷O NMR chemical shifts for a series of isobenzopyrylium salts are reported. The oxygen signal range from 300 to 270 ppm as a double bonded carboxylic oxygen, From the ¹⁷O and ¹³C data valuable informations on the conjugative and substituent effects of isobenzopyrylium salts were obtained.     

1H NMR Studies of 1-Ethylimidazole Binding to Cytochrome C

Abstract

Kinetic and equilibrium data for 1-EtIm binding to cyt c at temperature range of 303–319K have been determined at pH 7.0 by using ¹HNMR method. Thermodynamic values (ΔH°=39.5 kJ mol^?1, ΔS° = 154 J mol^?1K^?1 and Ea = 142 kJ mol^?1) are obtained from Van't Hoff and Arrhenius's relations. Some hyperfine shifted resonances of l-EtIm cyt c have been assigned for the first time using 1D saturation transfer experiments. The origin of the asymmetric spin density distribution in heme groups of 1-EtIm cyt c and the reason of low affinity of cytochrome c for 1-EtIm are also discussed move toward upfield from original position. However, Te-2, 4 substituents in cyt c are more electron withdrawing than the propionic acid side chains, which lead to the 5-methyl group going toward downfield.     

取代基对多取代氮苄叉苯胺化合物分子桥键（CH=N）的13C NMR和1H NMR的影响

Fifty-three samples of multi-substituted benzylideneanilines XArCH=NArYs (abbreviated XBAYs) were synthesized and their NMR spectra were determined. An extensional study of substituent effects on the ¹H NMR chemical shifts (^δH(CH=N)) and ¹³C NMR chemical shifts (^δC(CH=N)) of the CH=N bridging group from di-substituted to multi-substituted XBAYs was made based on a total of 182 samples of XBAYs, together with the NMR data of other 129 samples of di-substituted XBAYs quoted from literatures. The results show that the substituent specific cross-interaction effect parameter (Δ(Σσ)²)plays an important role in quantifying the ^δC(CH=N) values of XBAYs, but it is negligible for quantifying the ^δH(CH=N) values; the other substituent parameters also present different influences on the ^δC(CH=N) and ^δH(CH=N). On the whole, the contributions of X and Y to the ^δC(CH=N) of XBAYs are balanced, but the ^δH(CH=N) values of XBAYs mainly rely on the contributions of X.     

13C NMR Study of the Natural Glycosides Vicine and Convicine

¹³C NMR parameters have been obtained for vicine and convicine in DMSO, D₂O/DMSO and D₂O. Complete assignment of the spectra has been achieved. Interpretation of spin-lattice relaxation rates and heteronu-clear NOES has yielded evidence of intramolecular structuring in the case of vicine and not in that of ronvirine and also of a complex network of solute-solvent interactions.     

C-13 and H-1 NMR Assignments of the Chamigrenes Prepacifenol and Dehydroxyprepacifenol Epoxioes

A complete assignment of the signals in the ¹H and ¹³C NMR spectra and the stereostructural analysis of the compounds prepacifenol epoxide and the new dehydroxyprepacifenol epoxide are presented. These compounds were extracted from the marine mollusc Aplysia dactylomela and represent the first occurrence of chamigrenes found in Brazilian waters. The NMR analyses are supported by NOE difference and COSY experiments and also by gradient selected HMBC, HSQC-TOCSY and HSQC-DE. ¹H spectra simulations were done for the final fitting of the chemical shifts and coupling constants.     

Quantitative Evaluation of the Lactate Signal Loss and Its Spatial Dependence in PRESS Localized H NMR Spectroscopy

Localized ¹H NMR spectroscopy using the 90°−t₁−180°−t₁+t₂−180°−t₂−Acq. PRESS sequence can lead to a signal loss for the lactate doublet compared with signals from uncoupled nuclei which is dependent on the choice of t₁ and t₂. The most striking signal loss of up to 78% of the total signal occurs with the symmetrical PRESS sequence (t₁=t₂) at an echo time of 2/J (290 ms). Calculations have shown that this signal loss is related to the pulse angle distributions produced by the two refocusing pulses which leads to the creation of single quantum polarization transfer (PT) as well as to not directly observable states (NDOS) of the lactate AX₃ spin system: zero- and multiple-quantum coherences, and longitudinal spin orders. In addition, the chemical shift dependent voxel displacement (VOD) leads to further signal loss. By calculating the density operator for various of the echo times TE=n/J, n=1, 2, 3, …, we calculated quantitatively the contributions of these effects to the signal loss as well as their spatial distribution. A maximum signal loss of 75% can be expected from theory for the symmetrical PRESS sequence and TE=2/J for Hamming filtered sinc pulses, whereby 47% are due to the creation of NDOS and up to 28% arise from PT. Taking also the VOD effect into account (2 mT/m slice selection gradients, 20-mm slices) leads to 54% signal loss from NDOS and up to 24% from PT, leading to a maximum signal loss of 78%. Using RE-BURP pulses with their more rectangular pulse angle distributions reduces the maximum signal loss to 44%. Experiments at 1.5 T using a lactate solution demonstrated a maximum lactate signal loss for sinc pulses of 82% (52% NDOS, 30% PT) at TE=290 ms using the symmetrical PRESS sequence. The great signal loss and its spatial distribution is of importance for investigations using a symmetrical PRESS sequence at TE=2/J.     

Evidence for a dipolar-coupled AM system in carnosine in human calf muscle from in vivo 1H NMR spectroscopy

Spin systems with residual dipolar couplings such as creatine, taurine, and lactate in skeletal muscle tissue exhibit first-order spectra in in vivo 1H NMR spectroscopy at 1.5 T because the coupled protons are represented by (nearly) symmetrized eigenfunctions. The imidazole ring protons (H2, H4) of carnosine are suspected to form also a coupled system. The ring's stiffness could enable a connectivity between these anisochronous protons with the consequence of second-order spectra at low field strength. Our purpose was to study whether this deviation from the Paschen-Back condition can be used to detect the H2-H4 coupling in localized 1D 1H NMR spectra obtained at 1.5 T (64 MHz) from the human calf in a conventional whole-body scanner. As for the hydrogen hyperfine interaction, a Breit-Rabi equation was derived to describe the transition from Zeeman to Paschen-Back regime for two dipolar-coupled protons. The ratio of the measurable coupling strength (Sk) and the difference in resonance frequencies of the coupled spins (Deltaomega) induces quantum-state mixing of various degree upon definition of an appropriate eigenbase of the coupled spin system. The corresponding Clebsch-Gordan coefficients manifest in characteristic energy corrections in the Breit-Rabi formula. These additional terms were used to define an asymmetry parameter of the line positions as a function of Sk and Deltaomega. The observed frequency shifts of the resonances were found to be consistent with this parameter within the accuracy achievable in in vivo NMR spectroscopy. Thus it was possible to identify the origin of satellite peaks of H2, H4 and to describe this so far not investigated type of residual dipolar coupling in vivo.     

TOTAL ASSIGNMENT OF 1H AND 13C NMR SPECTRA OF A BRIDGED TRIRUTHENIUM CLUSTER-POLYPYRIDINE DIMER BASED ON 2D (COSY,HMQC, AND HMBC) TECHNIQUES

The bridged ruthenium cluster-polypyridine dimer [Ru₃O(CH₃COO)₆(py)₂(tmbpy)Ru(bpy)₂(Cl)](PF₆)₂ (py = pyridine, = 2, 2′-bipyridine and tmbpy = 4, 4′-trimethylenedipyridine) has been synthesized and structurally characterized based on ¹H and ¹³C NMR spectroscopy. This species exhibits a complex pattern of NMR signals due to the presence of a paramagnetic [Ru₃O] core and seven non-equivalent aromatic rings. 2D NMR (COSY, HMQC and HMBC) correlation techniques have been required for the total assignment of the ¹H and ¹³C NMR spectra.