bluuebunny/crossref_metadata_2025 huggingface dataset:
Water signal suppression by T2‐relaxation enhancement promoted by Dy(III) complexes
Authors: Aime Silvio , Botta Mauro , Barbero Luca , Uggeri Fulvio , Fedeli Franco
Published: May 2005

A novel method for water signal suppression in 1H NMR spectra is proposed for biological systems. It is based on the acquisition of a spin–echo spectrum in the presence of Dy(III) complexes, which cause a marked decrease of the water proton T2 through the modulation of ΔωM (chemical shift difference between the bulk and coordinated water resonance) by τM (time associated with the exchange between the two sites).
1H NMR T1(min) data and structure in a series of rhenium polyhydride complexes and the contribution of M‐H dipole–dipole relaxation
Authors: Luo Xiao‐Liang , Howard Judith A. K. , Crabtree Robert H.
Published: May 2005

The unusual species [ReH5(H2){P(p‐tolyl)3}2], for which a neutron diffraction study shows an intermediate HH bond distance of 1.357 Å, is studied by variable‐temperature 1H NMR spin‐lattice (T1) relaxation time measurements. The T1 relaxation rate goes through a maximum at low temperature and the resulting T1 (min) value is 66 ms. This is within the range of T1(min) values found for classical ReH7L2 complexes, so H2 complexes with such long HH bond distances are undetectable by the T1 method. The observed T1(min) value is compared with that calculated from the neutron diffraction data. We consider not only the usual proton–proton dipole–dipole (HHDD) contributions to the relaxation but also the metal‐hydride dipole–dipole (MHDD) contributions. The latter are shown to be negligible for most transition metals, but not for Nb, V, Re, Mn, Co and Ta. Inclusion of the MHDD contributions leads to better agreement between the calculated and observed T1(min) values for a series of rhenium polyhydride complexes. The MHDD relaxation also accounts for most of the disparity previously noted between the calculated and observed T1(min) values for Re2H8(PEt2Ph)4.
Interactions of aminoglycosides with phosphatidylinositol: A 15N nuclear magnetic resonance study
Authors: Schanck André , Brasseur Robert , Mingeot‐Leclercq Marie‐Paule , Tulkens Paul M.
Published: May 2005

The 15N NMR spectra of eight aminoglycosides were interpreted. The effect of mixing 20 mol.% of various aminoglycosides with phosphatidylinositol in aqueous dispersion was studied by 15N NMR, and correlations were found between the degree of interaction of the aminoglycoside for phosphatidylinositol and the calculated energy of interaction of the antibiotic with the negatively charged phospholipid and the inhibitory potency of the drug towards lysosomal phospholipase A1, a critical parameter in the nephrotoxic potential of aminoglycosides.
13C NMR substituent effects in aliphatic systems: Principal component analysis and correlations with electronegativities
Authors: Zalewski Romuald I. , Schneider Hans‐Jörg , Buchheit Ulrich
Published: May 2005

Principal component (PC) or factor analysis was applied to 13C substituent effects (literature SCS values) in α to δ positions of 47 aliphatic frameworks with 4–13 different substituents X. Two PC terms for each substituent X are sufficient to describe 99.3% of all C‐α shifts within < ± 0.6 ppm, even in the largest data matrix containing 13 × 47 = 611 shifts; shifts in β. γ and δ positions require a third PC term for a similar percentage SCS accuracy. Scaling problems with the different order of magnitudes between α to δ SCS variations are avoided by analysing the corresponding data sets separately; this approach, together with the large data base, leads to a dominating first PC term for C‐α which unambiguously correlates with substituent electronegativities (EN), in contrast to an earlier factor analysis. The same result is obtained by direct comparison of α‐SCS with different EN scales, including for the first time group electronegativities. PCs for β to γ SCS indicate only less consistent trends, which again agree partially with results from direct correlations, but not with EN values. The present PC analysis did not include stereochemical descriptors, but furnishes clear distinctions between clusters of (pseudo‐) equatorially or axially substituted compounds. The PC loadings for C‐α also lead to the unambiguous distinction of primary, secondary, tertiary and quaternary carbon atoms.
Determination of the conformation in solution of three 1,2‐3,4‐Di‐O‐methylenepyranoses: NMR and molecular mechanics studies
Authors: Giraud Bouchra , Nouguier Robert , Jaime Carlos , Virgili Albert
Published: May 2005

The conformational analysis of three 1,2‐3,4‐di‐O‐Methylenepyranoses was carried out using NMR (coupling constants and homonuclear Overhauser effect) and theoretical (MM2 calculations) methods. A preferred twist–boat conformation was found.
Measurement of inter‐proton distances from cross‐relaxation rates determined by a selective null inversion–recovery NMR method
Authors: Liu Maili , Farrant R. Duncan , Lindon John C.
Published: May 2005

An efficient method of measuring proton spin–lattice cross‐relaxation rates in small molecules is proposed. The method involves measuring the difference in relaxation rates in a non‐selective experiment and in one with all resonances except one of interest inverted. This procedure yields cross‐relaxation rates between this nucleus and all other nuclei. These rates are independent of the effects of non‐excited heteronuclei and of non‐dipolar contributions and can be used to determine relative inter‐proton distances. The method was tested using 7‐azaindole and compared favourably with the standard NOE method for estimating proton proximities requiring less data acquisition time.
Structural elucidation of two major metabolites of crisnatol in the rat by NMR and mass spectrometry
Authors: Shockcor John P. , Patel Dipak K. , Johnson Robert L. , Taylor Lester C. E. , Chandrasurin Pisal
Published: May 2005

NMR and mass spectral data are presented in support of the structures of two metabolites of crisnatol, 2‐[(6‐chrysenylmethyl)amino]‐2‐methylpropane‐1,3‐diol, a novel DNA intercalator currently undergoing Phase II clinical trials as an anticancer agent. Elucidation of the structures of the major rat urinary metabolite as trans‐1,2‐dihydro‐1,2‐dihydroxycrisnatol, and the major rat fecal metabolite as 1‐hydroxycrisnatol, using 2D NMR techniques are described.
Comparison of the Woessner and the ‘model‐free’ approaches for the analysis of carbon‐13 spin–lattice relaxation data for methyl groups
Authors: Gillies Duncan G. , Matthews Stephen J. , Sutcliffe Leslie H.
Published: May 2005

Carbon‐13 NMR relaxation data obtained for methyl groups in two dicyclohexane compounds were used to compare the Woessner and ‘model‐free’ approaches. It is shown that the extra flexibility offered by the latter leads to a more successful analysis of the data.
1H NMR model studies of amphotericin B: Comparison of x‐ray and NMR stereochemical data
Authors: Sowiński Pawel , Pawlak Jan , Borowski Edward , Gariboldi Pierluigi
Published: May 2005

1H NMR data for amphotericin B methoxycarbonylmethylamide extracted from DQF‐COSY, ROESY and 1D spectra were compared with x‐ray data for amphotericin B. The conformation of amphotericin B in solution was identical with that found by x‐ray analysis in the solid state. Most of the relay artifacts observed in the ROESY spectrum were recognized, and their pathways of formation were assigned.
Lanthanide‐induced shifts in the 17O NMR spectra of 1,6‐anhydro‐β‐D‐hexopyranoses. Evidence for tridentate complexing
Authors: Schulte J. , Lauterwein J.
Published: May 2005

The complexation of four 1,6‐anhydro‐β‐D‐hexopyranoses with europium(III) was studied in aqueous solution by natural abundance 17O NMR. The paramagnetic ion induced contact shifts of individual hydroxy and ether resonances to low frequency. A clear indication of tridentate complexes was obtained, proving the involvement of the oxygen atom of the anhydro ring in talosan and mannosan and that of the pyranose ring in glucosan.
Conformation of adenosine 5′‐phosphate in solution, deduced from experimental and simulated proton T1 values
Authors: Shibata Susumu
Published: May 2005

A computer program developed for the simulation of proton spin‐lattice relaxation times (T1) was applied to the conformational analysis of adenosine 5′‐phosphate (5′‐AMP) in neutral D2O solution. The T1 values of all the non‐exchangeable protons of 5′‐AMP were calculated from the atomic coordinates of the hydrogens and the rotational correlation times by numerically solving a simultaneous differential equation for all the proton magnetizations of the molecule. However, no single conformation gave a good enough agreement between the calculated and observed T1 values. 5′‐AMP in solution must therefore be in conformational equilibrium.

The equilibrium around the C‐4′–C‐5′ bond was fixed as gauche‐trans (16%), gauche‐gauche (68%) and trans‐gauche (16%) from the spin coupling constant. A correlation was found to exist between two conformational equilibria, anti ⇌ syn and 2′‐endo ⇌ 3′‐endo. The best agreement between the calculated and observed T1 values was obtained for an equilibrium between three conformers, 2′‐endo‐anti (Z = 60°) 40–53%, 3′‐endo‐anti (Z = 30°) 18–28% and 2′‐endo‐syn (Z = 220–260°) 27–30%. This equilibrium was consistent with all the currently available information about the conformation of 5′‐AMP in solution. 5′‐AMP exists only in the anti conformation in the crystal. This is similar to our results that the anti is the major conformation at 58–81%, but the syn conformer also exists as 19–42% in solution.
13C chemical shifts and 1H‐13C coupling constants of N‐phenyl‐, N‐p‐fluorophenyl‐ and N‐o‐nitrophenylpyrazoles
Authors: Begtrup Mikael , Vedsø Per , Cabildo Pilar , Claramunt Rosa Maria , Elguero Jose , Meutermans Wim
Published: May 2005

The 13C chemical shifts and some 1H13C coupling constants of twelve N‐arylpyrazoles are reported. The assignments were made by using the effects of a fluorine substituent and two‐dimensional techniques.
Determination of absolute values of dipolar cross‐relaxation rates for ligands bound to macromolecules using double‐selective T1
Authors: Gaggelli Elena , Valensin Gianni , Kushnir Tamir , Navon Gil
Published: May 2005

Measuring double‐selective and single‐selective proton relaxation rates has been shown to provide directly the dipolar cross‐relaxation rate of any pair of protons in a ligand molecule. The same measurements for a ligand exchanging between a free and a macromolecule‐bound state yield the cross‐relaxation rate of the bound ligand provided that the rate of exchange is relatively fast, thus allowing one to obtain dynamic and conformational features of the bound ligand. As an example, rigid binding of sulphisomidine to bovine serum albumin has been demonstrated.
Multinuclear magnetic resonance and x‐ray diffraction studies of aminonitropyridines
Authors: Kolehmainen Erkki , Laihia Katri , Rissanen Kari , Rasala Danuta , Gawinecki Ryszard
Published: May 2005

The 15N NMR spectra for 21 aminonitropyridines were measured and their chemical shifts assigned. The 1H and 13C NMR chemical shifts and spin–spin coupling constants were also determined for 16 compounds of this series. In order to relate the structural properties of nitramino groups and their 15N NMR chemical shifts in 2‐ and 4‐nitramino‐3‐nitropyridines, which differ remarkably from all other amino groups studied, low‐temperature 1H NMR, 17O NMR, comparative INEPT and IR spectroscopic studies were carried out. In addition, the x‐ray crystal structure of 2‐nitramino‐3‐nitropyridine was determined. Comparative spectroscopic studies showed that the nitramino derivatives exhibit different characteristics to the other compounds studied. Based on the x‐ray structural data, the nitramino group differs markedly from separate aryl‐bound amino and nitro groups. The nitramino group does not exhibit prototropic tautomerism in the crystalline state. This is in agreement with the small variation in the 15N NMR chemical shifts of the pyridine nitrogen, which excludes the prevalence of pyridinium ions. Among the four NMR nuclei studied, 15N seems to possess the best predictive power regarding the exceptional properties of the nitramino group.
31P and 13C NMR spectra of cyclohexylphenylphosphines, tricyclohexylphosphine and triphenylphosphine
Authors: Schraml Jan , Čapka Martin , Blechta Vratislav
Published: May 2005

13C and 31P NMR chemical shifts and coupling constants are reported and assigned for the two cyclohexylphenylphosphines, tricyclohexylphosphine and triphenylphosphine. The 13C NMR spectra of all compounds except dicyclohexylphenylphosphine could be assigned on the basis of APT experiments, substituent effects on the chemical shifts and the values of the 13C31P spin–spin coupling constants. The 13C NMR spectrum of dicyclohexylphenylphosphine, which shows six non‐equivalent (both in chemical shift and in spin–spin coupling) cyclohexyl carbons, was completely assigned on the basis of one‐bond and long‐range 13C13C 2D INADEQUATE experiments. The variable‐temperature spectra indicate a hindered motion in this compound. The one‐bond 13C13C spin–spin coupling constants of the cyclohexyl carbons vary only slightly with the distance from the substituent. An increase in the 31P chemical shift with an increasing number of cyclohexyl groups parallels the increasing catalytic activity of rhodium complexes containing the studied molecules as ligands.
15N NMR study of tetrazoles
Authors: Naumenko Valentina N. , Koren Andrei O. , Gaponik Pavel N.
Published: May 2005

A natural abundance 15N NMR study was carried out on a series of 1‐ and 2‐mono‐ and 1,5‐ and 2,5‐disubstituted tetrazoles in different media. An erroneous assignment given in the literature for 2,5‐disubstituted tetrazoles was corrected using MNDO molecular orbital calculations and the analysis of changes in the 15N chemical shifts on protonation. Earlier assignments for 1‐ and 2‐mono‐ and 1,5‐disubstituted tetrazoles were confirmed by the same means and by the use of 15N,H couplings. Direct proof that N‐4 is the protonation site is presented, to our knowledge for the first time.
Phenindamine and its analogues and precursors: NMR evidence of structure and configuration
Authors: Casy Alan F. , Hussain Rohannah B. , Upton Christopher
Published: May 2005

The 1H and 13C NMR spectra of analogues of the antihistaminie agent phenindamine and its precursors are interpreted in terms of structure and geometry. Points of interest are the conformations of 4‐piperidinol and dihydro‐1‐pyrindene(diene) intermediates, and the configuration of the hexahydro analogue of phenindamine and its corresponding product of equilibration. Results of an antihistamine evaluation test are presented.
High‐resolution proton‐detected 2D HEHAHA correlation experiments with spin–echo discrimination of long‐range correlations
Authors: Gibbs Andrew , Morris Gareth A.
Published: May 2005

Recent work has shown that broadband heteronuclear Hartmann—Hahn coherence transfer is an efficient alternative to pulsed coherence transfer methods. A new technique for heteronuclear long‐range correlation between 13C and protons, making use of proton detection and an extended mixing period, is described, which can have sensitivity and resolution advantages over current techniques. Efficient regiospecific correlation is shown in a model system, menthol, and the use of a modulated spin‐‐echo for the simultaneous determination of one‐bond and long‐range correlations is demonstrated.
Complete assignment of the 1H, 13C and 15N spectra of bradykinin derivatives
Authors: Zerbe Oliver , Welsh John H. , Robinson John A. , Von Philipsborn Wolf‐Gang
Published: May 2005

The complete assignment of the 1H, 13C and 15N spectra of bradykinin derivatives is presented. The proton assignments were performed using COSY, TOCSY and ROESY experiments, whereas the heteronuclei were assigned using inverse correlation experiments.
NMR and 14N NQR spectra. Structure of the crystalline products from the nitrosation of phosphorylacetaldehydes
Authors: Pavlov Valeriy A. , Smith John A. S. , Zjablikova Tatjana A.
Published: May 2005

14N NQR and NMR spectroscopy were used to show that, in the solid phase, the products of nitrosation of phosphorylacetaldehydes are a mixture of dimers of 1‐(dialkoxyphosphoryl)‐1‐nitrosoethen‐2‐ols and dialkoxyphosphorylacetaldnitrones. The stabilization of the nitrone form is probably made possible by a high degree of conjugation and by the way the dimeric molecules are packed in the crystal, which causes them to be held in fixed positions. When the dimeric 1‐(dialkoxyphosphoryl)‐1‐nitrosoethen‐2‐ols and dialkoxyphosphorylacetaldnitrones are dissolved, they undergo aldo‐enol, nitroso‐oxime and nitrone‐oxime tautomerism, converting gradually into monomeric aldehyde oximes which exist in E‐ and Z‐isomeric forms. The ratios of dimeric nitroso‐enol, nitrone‐enol and monomeric aldehyde oxime forms can be measured by NMR and depend on the solvent, concentration and temperature.
Synthesis and evaluation of fluorinated calcium chelators with enhanced relaxation characteristics
Authors: Levy Louis A. , Murphy Elizabeth , Raju Bore , London Robert E.
Published: May 2005

The fluorinated calcium ion chelator 5F BAPTA [1,2‐bis(2‐amino‐5‐fluorophenoxy)ethane‐N, N, N′, N′‐tetra‐acctic acid] was used for the determination of cytosolic Ca2+ ion levels in cells and tissues by 19F NMR. The possibility of enhancing the sensitivity of these measurements by modifying the relaxation behavior of the chelator was evaluated. These strategies involved the design of a chelator with reduced T1 value viz. 5F RBAPTA {1,2‐bis [2‐amino‐4‐(1‐carboxy‐2‐methyl‐2‐propyl)‐5‐fluorophenoxy]ethane‐N, T, N′, N‐tetraacetic acid}, and the evaluation of chelator with slower exchange characteristics, viz 5F BenzEGTA [1‐(2‐amino‐5‐fluorophenoxy)‐2‐(2‐aminoethoxy)ethane‐N, N, N′, N′‐tetraacetic acid]. Both analogs exhibit chemical shift differences on calcium complexation which are similar to those of the parent compound, 5F BAPTA. In the case of BenzEGTA, a considerably greater pH dependence of the apparent calcium, dissociation constant, KD, also results from the presence of a tertiary amine with a pK value above the physioligical range. Additionally, the synthetic approach used for RBAPTA can lead to wide variety of derivatives with variable chemical, biochemical and NMR properties.
Applications of gradient‐selective COSY and DQCOSY to brucine and gibberellic acid
Authors: Carpenter T. A. , Colebrook L. D. , Hall L. D. , Pierens G. K.
Published: May 2005

High‐quality gradient‐selective COSY spectra were recorded at 300 MHz for brucine and gibberellic acid and double‐quantum filtered gradient‐selective COSY spectra for brucine, using a single‐frequency, high‐resolution 1H probe modified by the addition of an unshielded z‐gradient coil set. Data were efficiently recorded using buffered acquisition with a single transient per increment in 1t, in times much lower than those required for phase‐cycled COSY, and with no loss of information. Gradient‐selective COSY90, COSY45 and long‐range COSY45 experiments, and the correlations leading to chemical shift assignments for gibberellic acid, are reported.
Assignment of the 1H and 13C NMR spectra of naphtho [1′,2′:4,5]thieno[2,3‐c]quinoline using two‐dimensional NMR spectroscopy
Authors: Castle Lyle W. , Zektzer Andrew S. , Johnston Milton D.
Published: May 2005

The 1H NMR spectrum of naphtho [1′,2′:4,5]thieno[2,3‐c]quinoline is highly congested because all the protons are in an aromatic environment, and the structure of the molecule is nearly symmetric. With this in mind, the assignment of the 1H and 13C NMR spectra of this compound obtained using two‐dimensional NMR spectroscopy is reported.
Deuterium isotope effects on 13C nuclear shielding of amino and acetamido compounds. Tautomerism and intramolecular hydrogen bonding
Authors: Hansen Poul Erik , Kolonicny Alois , Lycka Antonin
Published: May 2005

Deuterium isotope effects on 13C nuclear shielding were investigated for a series of o‐amino and acetamido azo compounds and for amino‐ and acetamido‐9,10‐anthra‐ and leucoanthraquinones. A variety of these compounds form intramolecular hydrogen bonds and are possibly tautomeric in nature. Deuterium isotope effects on 13C chemical shifts were used to probe both the tautomerism and the nature of the hydrogen bond. Deuterium isotope effects over two bonds reflect the strength of the hydrogen bond. In general, isotope effects do not depend on the solvent and, in this study, are independent of temperature. In the acetamido compounds isotope effects on the internal aromatic carbons, 2ΔCar(ND), vary much more than the 2ΔCO(ND) values of the external carbonyl carbon. Plots of 2Δ vs. δ(H) accordingly show different slopes. Investigations of these types of compounds allow a correlation between the hydrogen‐bond enthalpy and 2ΔCO(ND) of amides. 2ΔCO(ND) values therefore form a basis for extending the use of deuterium isotope effects to, for example, biomolecules. Diamino‐9,10‐leucoanthraquinone represents, to our knowledge, the first case of a compound in which isotope effects from both a hydrogen‐bonded and a free ND deuterium can be observed. Bis(phenylamino)leucoanthraquinone exhibits interesting equilibrium isotope effects over many bonds. Many of these isotope effects are non‐additive. Hydrogen bonding is discussed in general, based on these observations.
Structural elucidation of disubstituted nortricyclenes through vicinal 13C, 1H coupling constants
Authors: Gridnev I. D. , Leshcheva I. F. , Sergeyev N. M. , Chertkov V. A.
Published: May 2005

Vicinal 13C, 1H coupling constants were used to establish the configuration of a 3,5‐disubstituted notricyclene. The assignment procedure is supported by independent measurements of 13C, 2H coupling constants in 3‐ deuterionortricyclene and confirmed by 1H, 1H NOE data for exo‐3‐N‐acetylamino‐exo‐5‐pivaloylnortricyclene.
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

The 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

Two‐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

Long‐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

Driven 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

The 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

The 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

Several 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

A 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

A 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

A 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

The 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

The 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

Perindopril, 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

The 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

The 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

The 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

Carbon‐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

Isotope 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

The 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

Stereochemical 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

13C, 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

Eight 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

The 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

A 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

The 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.
13C NMR data for labdane diterpenoids
Authors: Barrero Alejandro F. , Altarejos Joaquin
Published: May 2005

The analysis of the 13C NMR spectra of 91 labdane‐type compounds, classified into ten different series, is reported.
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

The 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

The 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

The 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

The 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.
1H NMR of acetylated β‐ether/β‐ether lignin model trimers
Authors: Ralph John
Published: May 2005

Detailed examination of the 1H NMR spectra of acetylated β‐ether/β‐ether lignin model trimers, particularly those synthesized with partially defined stereochemistry, revealed that all of the eight chemically distinct isomers (sixteen optical isomers from four optical centers) are detectable. These compounds provide excellent models for both internal (etherified) and terminal (free‐phenolic) units in lignin and clearly delineate the chemical shifts for each isomer. High‐field two‐dimensional TOCSY or relayed coherence transfer NMR experiments allow correlation of all the side‐chain protons in each isomer, while J‐resolved experiments clearly show the presence of all expected isomers. The degree of complexity already encountered with these simple compounds points to the overwhelming improbability of finding even small crystalline regions in lignin.
1H NMR lanthanide‐induced shift (LIS) investigations of highly flexible molecules—a new approach. Part II
Authors: Lehmann J. , Kleinpeter E.
Published: May 2005

A new method and computer program for LIS calculations of highly flexible molecules was developed using molecular geometries obtained by randomly varied dihedral angles (up to ten angles rotating freely and independently from each other are possible) as start conformations for a STEEpest Descent (STEED) search algorithm to find minima characterized by the R factor at the ‘LIS R factor hyper surface.’ This STEED–LIS method allows easy, accurate and rapid access to the probable global minimum of the R factor depending on up to ten variable dihedral angles. This means that LIS investigations of highly flexible molecules with more than one freely rotating dihedral angle are no longer complicated and time consuming, but can be carried out automatically using the developed programs [JLLISSD (with interactive parameter dialogue) and LISSDEMU (using parameter input files prepared by LISSDINP)]. The results obtained are in very good agreement with known or reported preferred conformations of the investigated test compounds, propan‐1‐ol, butan‐1‐ol and ethyl p‐methoxycinnamate.