bluuebunny/crossref_metadata_2025_split huggingface dataset:
31P13C shift correlated 2D NMR spectra of the AA'X spin system: Determination of PP coupling constants and their relative signs in symmetrical diphosphonates
Authors: Beckmann H. , Grossmann G. , Ohms G. 
Published: May 2005

AbstractThe indirect determination of PP coupling constants and their relative signs in some symmetrical diphosphonates by 31P13C 2D NMR is introduced. Advantages and disadvantages of this method and others for the determination of the coupling constants of chemically equivalent nuclei are discussed. Strong coupling effects are analysed by means of simulated 2D spectra and the product operator formalism.
Structural and conformational characterization of (Z)‐17‐[2‐(triphenylstannyl)vinyl]‐4‐estren‐17β‐ol using 2D proton detected 1H13C relay and 2D NOESY spectroscopy
Authors: Kayser François , Biesemans Monique , Pan Huade , Gielen Marcel , Willem Rudolph 
Published: May 2005

AbstractTwo‐dimensional proton detected heteronuclear 1H13C relayed coherence transfer, combined with 2D NOESY spectroscopy at 500 MHz, allowed the complete assignment of the 13C and 1H spectra of (Z)‐17‐[2‐(triphenylstannyl)vinyl]‐4‐estren‐17β‐ol. The conformation of this compound in solution was established from a 2D NOESY build‐up experiment and compared with the solid‐state structure obtained from previous x‐ray diffraction analysis. Proton–proton coupling constants were obtained from phase‐sensitive 1H double quantum filtered COSY spectroscopy.
Long‐range 13C1H coupling constants in 3‐carene and α‐pinene
Authors: Denisov Aleksej Y. U. , Tyshchishin Evgenij A. , Tkachev Aleksej V. , Mamatyuk Viktor I. 
Published: May 2005

AbstractLong‐range 13C1H coupling constants exceeding 0.3 Hz were measured for the hydrocarbons 3‐carene and α‐pinene by a heteronuclear 2D J‐resolved proton‐flip experiment with selective proton excitation. The dependences of the vicinal 3J(C, H) coupling constants on the dihedral angles were studied, and the peculiarities of the couplings through the double bond and cyclopropane framework were demonstrated. The dependences of the 4J(C, H) coupling constants in the allylic fragments of the molecular framework are discussed, and the long‐range nJ(C, H) coupling constants with the olefinic protons in camphene were investigated for the same purpose.
Application of DEFT and SEFT for signal‐to‐noise ratio enhancement and T2‐selective spectra in 29Si MAS NMR of zeolites
Authors: Anderson Michael W. 
Published: May 2005

AbstractDriven equilibrium and spin–echo Fourier transform spectroscopy (DEFT and SEFT) were used to observe 29Si high‐resolution solid‐state nuclear magnetic resonance with magic‐angle spinning (MAS NMR) spectra of zeolites. The sequences allow the measurement of T2 relaxation times, dramatic improvements in signal‐to‐noise ratios and selective observation of signals with long T2 relaxation times. This last criterion permits the simplification of 29Si spectra of highly aluminous zeolites, yielding important crystallographic information.
Proton and carbon chemical shift assignment and dynamic investigation of the macrolide antibiotic tylosin
Authors: Rossi Claudio , Donati Alessandro , Picchi Maria Pia , Sansoni Maria Rosaria , Corbini Gianfranco , Corti Piero 
Published: May 2005

AbstractThe NMR spectral properties of the antibiotic tylosin were investigated. DQ‐COSY and HETCOR two‐dimensional spectra were used for the assignment of both the proton and protonated carbon signals. Selective (H)C‐NOE, were proposed for the controversial quaternary carbon assignments. The analysis of molecular motion in solution based on carbon spin–lattice relaxation rates shows that tylosin exhibits dynamics that are typical of each molecular moiety. A higher degree of free motion is observed with increasing distance from the macrolide nucleus.
Fluorine substituent effects for tryptophan in 13C nuclear magnetic resonance
Authors: Lee Minsu , Phillips Robert S. 
Published: May 2005

AbstractThe 13C and 1H NMR spectra of monofluorotryptophans and difluorotryptophans in methanol‐d4 were assigned based on 1D and 2D NMR techniques. Fluorine substituent effects on the chemical shifts (SCSs) of tryptophan were calculated and compared with those for indole. The fluorine SCSs for the indole ring of tryptophan are 38 ∼ 39 for the α‐carbon − 11 ∼ − 15 for the β‐carbon, O ∼ 4 for the γ‐carbon and − 3 ∼ − 4 ppm for the δ‐carbon. The fluorine SCSs were also applied to 4,7‐ and 5,7‐difluorotryptophans and the effects were found to be additive.
Conformational equilibria in the solid state: Conformational equilibrium in bicyclo[3.3.1]nonane derivatives studied by solid‐state spectroscopy
Authors: Riddell Frank G. , Rogerson Martin 
Published: May 2005

AbstractSeveral derivatives of bicyclo [3.3.1]nonan‐9‐one were examined by CP/MAS NMR spectroscopy in the solid state. Contrary to an earlier report based on X‐ray crystallography, no conclusive evidence was found for the existence of a chair/chair‐chair/boat equilibrium in the temperature range −100 to +20 °C. It is concluded that if such solidstate equilibria exist they have free energies of activation for ring inversion in the solid of less than 31 kJ mol−1.
Spectral assignment of 2″‐O‐β‐D‐glucopyranosylsaikosaponin b2 by two‐dimensional NMR techniques
Authors: Lin Long‐Ze , Lin Lee‐Juian , Cordell Geoffrey A. , Luo Si‐Qi , Jiang Hui‐Fang 
Published: May 2005

AbstractA new derivative of saikosaponin was isolated from the roots of Bupleurum longicaule and identified as 2″‐O‐β″‐D‐glucopyranosylsaikosaponin b2. Its 1H and 13C NMR data and the connectivities of the sugar moiety were assigned by use of a combination of two‐dimensional NMR techniques (DQF‐COSY, HOHAHA, ROESY, HETCOR and HMBC).
Critical evaluation of an empirically modified Karplus equation
Authors: Ōsawa Eiji , Ouchi Tatsuro , Saito Nobuhisa , Yamato Masaru , Lee Oh Seuk , Seo Mi‐Kyo 
Published: May 2005

AbstractA recently reported modified Karplus equation often produces large errors exceeding 1 Hz in the calculated vicinal H/H coupling constants [3J(H, H)], in spite of the high claimed accuracy of 0.33 Hz in the standard deviation. Critical examination of the equation against a large body of experimental 3J(H,H) values identified the following sources of errors: inaccurate proton positions in three‐ and four‐membered rings, effects of polar solvents, especially on vicinal polyhalogenated compounds, conformer distributions obtained by inadequate computational methods and varying conditions for NMR measurements. When these are taken in to account the accuracy of the equation can be considered to have a standared deviation of 0.69 Hz. A small set of 3J(H,H) data calculated by the re‐parameterized extended Hückel theory could be fitted well to a shortened form of the modified Karplus equation. This result suggests that a set of coupling constants derived by theoretical calculations may offer a better standard set for the study of the modification of the Karplus equation.
Relative and absolute configurations of the quinolizidine alkaloids anagyrine and thermopsine and assignment of the 1H and 13C NMR spectra of anagyrine
Authors: Robins David J. , Rycroft David S. 
Published: May 2005

AbstractA recent proposal to revise the relative configurations of the quinolizidine alkaloids anagyrine and thermopsine is refuted. 1H and 13C NMR chemical shift assignments of anagyrine which were published at the same time are erroneous, and assignments published slightly earlier by the present authors should be retained.
E, Z isomerization studies of ethyl 2‐oxo‐3‐indolinylidenecyanoacetates by 1H NMR spectroscopy
Authors: Morales‐Rios Martha S. , Mora‐Pérez Yolanda , Joseph‐Nathan Pedro 
Published: May 2005

AbstractThe kinetics of base‐catalysed E/Z isomerization for a series of ethyl 2‐oxo‐3‐indolinylidenecyanoacetates in CDCl3 solutions were studied by 1H NMR spectroscopy. Both polarizable double bond considerations and steric requirements of the base must be considered in explaining the results. The E/Z equilibrium of ethyl 1‐carbethoxy‐2‐oxo‐3‐indolinylidenecyanoacetate was reached faster than those of ethyl 2‐oxo‐3‐indolinylidenecyanoacetate and the 1‐methyl derivative by a factor of ca. 10 in the presence of triethylamine, and the isomerizations were faster when quinuclidine was used. In pure DMSO‐d6 solutions, the equilibria were established upon dissolution, but addition of small amounts of acid slowed the isomerization process in these systems.
Algal carotenoids 47–NMR study of all‐trans‐peridinin, including complete 1H and 13C NMR assignments
Authors: Krane Jostein , Aakermann Torunn , Liaaen‐Jensen Synnøve 
Published: May 2005

AbstractThe allenic C37 skeletal carotenoid all‐trans‐(3S, 5R, 6R, 3′S, 5′R, 6′S)‐peridinin, isolated from Amphidinium carterae by an improved isolation procedure, was subjected to a detailed 1H and 13C NMR spectroscopic analysis. Complete assignments of the 500.13 MHz 1H and 125.76 MHz 13C spectra, including determination of coupling constants and relative stereochemistry, were obtained by ID and 2D techniques. These included 1H1H chemical shift correlated spectroscopy (2D COSY), phase‐sensitive double‐quantum COSY, difference 1D NOE experiments, 1D and 2D total correlation spectroscopy (HOHAHA, TOCSY) and 1D and 2D rotating frame nuclear Overhauser spectroscopy (ROESY, CAMELSPIN). The 13C NMR assignments were obtained through editing sequences (DEPT) and heterocorrelated 2D experiments. In particular, the 1H detected multiple bond 1H13C correlated 2D experiment proved valuable for assignments of all 13 quatenary carbons together with 13 methine carbons in peridinin [C37H47O6(COCH3)]. Detailed analysis of the proton coupling constants supported the conformations and relative stereochemistry of the two end‐groups. Spectral simulation of protons in the conjugated chain was necessary in order to ascertain more accurate chemical shifts for some protons in the strongly overlapping olefinic region. Variation in the trans double bond 3J(H, H) coupling was noted along the conjugated chain.
Stereochemistry–activity relationships of ACE inhibitors. Conformational studies by 1H and 13C NMR of perindopril and selected stereoisomers
Authors: Bouchet J. P. , Volland J. P. , Laubie M. , Vincent M. , Marchand B. , Platzer N. 
Published: May 2005

AbstractPerindopril, the tert‐butylamine salt of 1‐{(2S)‐2‐[(1S)‐(1‐carbethoxybutyl)amino]‐1‐oxopropyl}‐(2S,3aS,7aS)‐perhydroindole‐2‐carboxylic acid, is an inhibitor of angiotensin‐converting enzyme (ACE) and a new drug for the treatment of hypertension. The interaction between the inhibitor and the enzyme was investigated by studying the active diacid metabolite of perindopril, its stereoisomers and a desmethyl analogue. The pharmacological study allowed the measurement of the in vitro activities of the different compounds. The 1H and 13C NMR studies have shown that the cis‐trans equilibrium about the amide bond is strongly dependent on the configuration of the chiral centres and on the pH of the solution. The pKa of the different acid‐base species were measured. The results show that perhydroindole derivatives are potent inhibitors of ACE as long as they fulfil the following basic requirements: (1) an S configuration of the carbon bearing the terminal carboxy group; (2) an S methyl substituent in the alanine residue; however, the inhibitor potency is not modified on the replacement of the alanine residue of the perindopril by a glycine residue; and (3) less stringently, an S configuration of the C‐1 butyl carbon. Under these conditions the Zn binding ligand (chain carboxylate group) is devoid of steric hindrance in the trans conformers. No direct relationship appeared between the relative amount of the trans form and the activity. The cyclic skeleton of the perhydroindole derivatives provided a strong hydrophobic interaction with the active enzymatic site, whatever the configurations at C‐3a and C‐7a. Lipophilic interactions involving the different parts of the inhibitor are not independent of each other.
Revised assignment of the 1H NMR spectrum of the quinolizidine alkaloid lupinine
Authors: Rycroft David S. , Robins David J. , Sadler Ian H. 
Published: May 2005

AbstractThe 1H NMR spectrum of the quinolizidine alkaloid lupinine was studied at 200 and 600 MHz. A full assignment of the 1H signals was achieved by application of a variety of NMR techniques, including homonuclear 1H NOE difference, 2D δH/δH COSY and direct δC/δH correlation experiments. This results in some changes to the current literature assignments; particularly important is the conclusion that the chemical shift difference between the equatorial (β) and axial (α) protons at C‐9 is negative (−0.47 ppm) rather than positive. The currently accepted assignment of the 13C NMR spectrum has been confirmed by independent, and more direct, means.
Further improvements in the flock sequence
Authors: Carpenter Katharine A. , Reynolds William F. , Yang Ji‐Ping , Enriquez Raul G. 
Published: May 2005

AbstractThe phase cycle for the FLOCK experiment was modified to provide improved suppression of artifacts and improved signal‐to‐noise ratios. An alternative version of FLOCK in which the initial BIRD pulse during t1 is replaced by a one‐step J filter is shown to give comparable performance, while a phase‐sensitive version of FLOCK shows the expected \documentclass{article}\pagestyle{empty}\begin{document}$ \sqrt 2 $\end{document} increase in sensitivity. Finally, while it is shown that phase‐sensitive FLOCK without decoupling during acquisition can be used to measure nJ(C,H) (n ≤ 2), there are serious limitations to this approach.
Identification and ab initio carbon‐13 NMR assignment of a proanthocyanidin from Prunus jacquemontii
Authors: Pant Geeta , Nautiyal Anil K. , Rawat Mohan S. M. , Sutherland James K. , Morris Gareth A. 
Published: May 2005

AbstractThe concerted use of 1D and 2D multiple pulse NMR methods allowed the identification and assignment of a proanthocyanidin, ent‐epiafzelechin(4α → 8; 2α → O → 7)‐epicatechin, extracted from the bark of Prunus jacquemontii. Reference deconvolution with the FIDDLE algorithm was successfully used for line shape correction of a 13C spectrum with poor signal‐to‐noise ratio. Over 70 long‐range proton– 13C correlations were determined with the HMBC experiment, following modifications to improve instrument signal reproducibility, illustrating the value of this experiment when applied to systems with relatively few protons.
NMR study of inversion isomerism in some isoxazolidines
Authors: Wazeer Mohammed I. M. , Ali Sk. Asrof 
Published: May 2005

AbstractCarbon‐13 NMR spectra were recorded for two series of isoxazolidines, 3 (a 5/5 fused system) and 4 (a 6/5 fused system), over the temperature range − 100 to +60°C. Whereas all the compounds in series 3 existed solely as one isomer throughout this temperature range, some compounds in series 4 showed the presence of two isomers of unequal population at low temperatures. The major isomer was shown to be the trans conformer, which is in equilibrium with the minor isomer (cis conformer) through a relatively slow nitrogen inversion. The monosubstituted isoxazolidines 4 having endo substituents at either C‐2 or C‐3 and 2,3‐di‐ and 2,2,3‐trisubstituted compounds showed the presence of only one isomer throughout the temperature range. The barriers to nitrogen inversion were determined by band shape analysis and were in the range 65.2–‐69.0 kj mol−1.
37Cl/35Cl isotope effects in 13C NMR spectroscopy of chlorohydrocarbons
Authors: Aliev Abil E. , Harris Kenneth D. M. 
Published: May 2005

AbstractIsotope effects on the chemical shift of 13C directly bonded to the isotopes 35Cl and 37Cl are reported for a wide range of chlorohydrocarbons. By recording 13C NMR spectra under conditions of composite pulse 1H decoupling, 13C resonances can be obtained that are sufficiently narrow to allow the very small splittings of the order of a few ppb due to the 35Cl/37Cl isotope effect to be resolved at ambient temperature. Observation of this phenomenon allows the routine identification of 13C resonances due to carbon atoms directly bonded to chlorine, since, for natural abundance samples, the isotope effect splits the 13C signal into a set of lines with a characteristic intensity distribution. Various structural features influencing the magnitude of the isotope effect have been elucidated, and the temperature dependence of the isotope effect is also discussed. From low‐temperature 13C NMR spectra for chlorocyclohexane, isotope shifts for the carbon atom directly bonded to chlorine were measured separately for the axial and equatorial conformations. The measured values indicate that the isotope shift is larger for the axial conformation.
13C NMR of some aryl‐methylated trans‐β‐methyl‐β‐nitrostyrenes
Authors: Dawson Brian A. , By Arnold W. , Avdovich Hajro W. 
Published: May 2005

AbstractThe 13C NMR chemical shifts of ten arylmethylated trans‐β‐methyl‐β‐nitrostyrenes and the parent compound were measured and the spectra interpreted. Chemical shift assignments for the aryl‐methylated compounds have not, to our knowledge, been reported previously. The data are based on 1 D and 2D experiments performed at 9.4 T.
NMR assignments and conformational analysis of yuanhuacin
Authors: Zhou Bing‐Nan , Xue Liang , Lin Long‐Ze , Lin Lee‐Juian , Johnson Michael E. , Cordell Geoffrey A. 
Published: May 2005

AbstractStereochemical assignments of yuanhuacin were performed through two‐dimensional COSY, ROESY, 1H and 13C shift correlation spectroscopy (HETCOR and FLOCK), and ambiguous assignments were resolved through molecular modeling comparisons. This combination of techniques is applicable for the assignment of 1H and 13C chemical shifts of polycyclic compounds containing high percentages of quaternary carbons.
13C and 15N NMR study of 2,3‐diphenyl‐1,2,3,4‐tetrazolium‐5‐aminides
Authors: Koźwińnski Wiktor , Jaźzwiński Jaroslaw , Stefaniak Lech 
Published: May 2005

Abstract13C, 14N and 15N NMR data are reported for some mesoionic 2,3‐diphenyltetrazoles with nitrogen‐containing exocyclic groups, and the data confirm their cyclic structures. The protonated forms of these mesoionic structures contain hydrogen atoms at the exocyclic groups.
Carbon‐13 and phosphorus‐31 NMR study of some crown ethers containing phosphorus atoms
Authors: Vincent E. J. , Bibout M. El Malouli , Peiffer G. , Siv C. , Pannell K. 
Published: May 2005

AbstractEight mono‐ and diphosphacrown ethers (from an 11–22‐membered ring) were studied by 13C and 31P NMR spectroscopy and their chemical shifts are reported.
Nitrogen‐15 NMR studies of 5‐substituted indoles and 4‐substituted acetanilides. Evidence for cross‐conjugation effects
Authors: Morales‐Rios Martha S. , Joseph‐Nathan Pedro , Wrackmeyer Bernd , Kupče Ēeriks 
Published: May 2005

AbstractThe 15N chemical shifts and 1J(15N, 1H) coupling constants were measured for a series of 5‐substituted indoles and 4‐substituted acetanilides. The cross‐conjugation effect in both series was demonstrated by linear correlations between the 15N SCS values versus an empirical balance of the deuterium‐induced isotope shifts of the carbons directly bonded to the NH(D) residue. In the case of indoles this empirical balance involves the average of 2Δ(C‐2) and 2Δ(C‐7a), whereas for acetanilides values obtained by subtraction of 2Δ(CO) from 2Δ(C‐1) are implicated.
Structural and conformational analysis of (E)‐erythromycin A oxime
Authors: McGill John M. , Johnson Ross 
Published: May 2005

AbstractA complete and unambiguous assignment of the 1H and 13C NMR spectra of (E)‐erythromycin A oxime in acetone‐d6 was accomplished by two‐dimensional chemical shift correlation methods. The 1H NMR NOE data, in conjunction with molecular modeling techniques, were used to predict the predominant solution conformation of erythromycin A oxime in acetone‐d6. This conformational analysis was used to explain the lack of facial selectivity observed in the reduction of the oxime.
Complete 1H and 13C assignments of ractopamine hydrochloride using 2D and selective 1D NMR methods
Authors: Huwe J. K. , Castellino S. , Smith D. J. 
Published: May 2005

AbstractThe 1H and 13C NMR resonances for ractopamine hydrochloride have been assigned. H,H‐COSY and H,C‐COSY were used to assign the aliphatic moiety of the molecule and to correlate protons and carbons on the same ring system. Long‐range selective proton decoupling (LSPD) experiments were used to assign quaternary carbons and to distinguish the two ring systems.
Assignment of the 13C NMR spectrum of anisomycin and the 1H and 13C NMR spectra of deacetylanisomycin
Authors: LeFevre J. W. , Maier S. E. , Deng W. 
Published: May 2005

AbstractThe 13C NMR spectrum of anisomycin and the 1H and 13C NMR spectra of deacetylanisomycin were assigned using one‐ and two‐dimensional NMR analysis. The techniques included INEPT, 1H13C HETCORR and 1H‐1H COSY spectroscopy.
Complete proton and 13C NMR spectral assignments of pentalongin
Authors: De Kimpe Norbert , Van Puyvelde Luc , Schripsema Jan , Erkelens Cees , Verpoorte Robert 
Published: May 2005

AbstractThe 1H and 13C NMR spectra of pentalongin, a physiologically active natural product, were completely assigned. Some previous assignments were revised. All 13C1H coupling constants, both one‐bond and long‐range, were also measured.
NMR and molecular mechanics studies on the solution‐state conformation of (−)‐scopolamine free base
Authors: Glaser Robert 
Published: May 2005

AbstractThe NMR parameters of (−)‐scopolamine free base in CDCl3 determined by Sarazin et al. were used to reevaluate some of the stereochemical conclusions recently reported by the authors. Similarly to the case with the protonated salt, the major contributor to the fast exchange limit time‐averaged structure of the free base tropate ester moiety appears to be the rotamer in which the phenyl and hydroxyl groups are antiperiplanar. Long‐range heteronuclear coupling constants for the carboxyl carbon and also for the aromatic ipso carbon have been reassigned. Vicinal homonuclear coupling constants involving the methine proton and the two internally diastereotopic protons in the (S)‐CHCH2OH moiety have also been reassigned. Four conformational archetypes were calculated by molecular mechanics for the (−)‐(Ns,Cα‐S)‐scopolamine free base equatorial N‐methyl diastereomer based on x‐ray crystallographically determined scopolamine structural analogues. The degree of anisochronicity (and their relative shifts) exhibited by the internally diastereotopic oxiranyl protons and carbons and the observation of NOE intensity enhancement of oxiranyl protons upon {H‐aromatic} can be interpreted as arising from an interconverting profile of conformations at the fast exchange limit. While a conformation similar to that of the solid‐state hydrobromide sesquihydrate salt appears to be a major contributor to the time‐averaged structure, other conformations can also play minor roles.
Determination of chemical‐shift tensor orientations in methylene groups by separated‐local‐field NMR
Authors: Schmidt‐Rohr K. , Wilhelm M. , Johansson A. , Spiess H. W. 
Published: May 2005

AbstractThe 13C chemical‐shift tensor orientations in the OCH2CH2O moieties of poly(ethylene oxide) (PEO) and poly(ethylene terephthalate) (PET) were determined by means of 1H13C separated‐local‐field NMR spectroscopy, and the literature values for the shift tensors in polyethylene (PE) and polyoxymethylene (POM) were improved. An angular resolution of ± 4° was attained on standard equipment with 90° pulse lengths exceeding 4 μs. Relatively high uniformity of the methylene tensor orientations, complying with local molecular symmetry, was found.