NMR Techniques (nmr + techniques)

Distribution by Scientific Domains
Distribution within Chemistry

Kinds of NMR Techniques

  • two-dimensional nmr techniques

  • Selected Abstracts

    NMR studies of chiral organic compounds in non-isotropic phases

    Marek J. Potrzebowski
    Abstract In this article, new applications and perspectives of one- and two-dimensional NMR spectroscopy for study of chiral organic compounds in the non-isotropic phases (solid state and liquid crystals) are presented. The review is organized into five sections. In the first part, theoretical background and short introduction to solid state NMR are shown. The second part presents how NMR isotropic chemical shift can be used for distinguishing of racemates and enantiomers. In the third section, the power of the ODESSA pulse sequence for investigation of racemates, enantiomers and establishing of enantiomeric excess are discussed. The fourth part shows the application of analysis of principal elements of chemical shift tensors obtained by means of 2D NMR techniques for searching of absolute configuration and conformational changes in the solid state. The final part presents recent achievements of chiral liquid crystals NMR methodology for study of chiral compounds. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A:201,218, 2008. [source]

    High-precision measurement of internuclear distances using solid-state NMR

    Jae-Seung Lee
    Abstract Today, nuclear magnetic resonance (NMR) is among the most efficient tools in structural studies. Measurement of interatomic distances is the most common way of determining high-resolution structures of molecules using NMR techniques. In this article, we describe NMR techniques for static powder samples, based on a two-dimensional single-echo scheme, enhanced with adiabatic cross-polarization. They can significantly increase the accuracy of measuring internuclear distances and turn NMR into a high-precision crystallographic technique, complementing the X-ray, and neutron-scattering methods. Experimental examples are presented for intramolecular CN and CC distances in ,-crystalline form of glycine. © 2008 Wiley Periodicals, Inc. Concepts Magn Reson Part A 32A: 56,67, 2008. [source]

    NMR methods for studying membrane-active antimicrobial peptides

    Erik Strandberg
    Abstract NMR is a versatile tool for studying interactions between antimicrobial peptides and lipid membranes. Different approaches using both liquid state and solid state NMR are outlined here, with an emphasis on solid state NMR methods, to study the structures of antimicrobial peptides in lipid bilayers as well as the effect of these peptides on model membranes. Different NMR techniques for observing both peptides and lipids are explained, including 2H, 13C, 15N, and 19F labels, or natural abundance 1H, 13C, or 31P. Previous studies in the field are extensively reviewed in easily accessible tables. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 23A: 89,120, 2004. [source]

    NMR studies of surfactants

    Olle Söderman
    Abstract Surfactant molecules are amphipathic and posses complicated solution chemistry and self-assembly properties. In addition to being of enormous practical significance, the physical characterization of surfactant systems presents a rich area of condensed matter physics. This article focuses on the application and interpretation of the commonly used NMR approaches for probing these systems. In particular, the use of NMR relaxation, diffusometry and, more briefly, electrophoretic NMR to determine characteristics such as micellar size and structure, ion-binding and solubilization are considered. The application of these NMR techniques is illustrated by a number of pertinent examples. © 2004 Wiley Periodicals, Inc. Concepts Magn Reson 23A:, 121,135, 2004. [source]

    Designing the Host-Guest Properties of Tetranuclear Arene Ruthenium Metalla-Rectangles to Accommodate a Pyrene Molecule

    Nicolas P. E. Barry
    Abstract Cationic tetranuclear arene ruthenium complexes of the general formula [Ru4(p -cymene)4(N,N)2(dhnq)2]4+ comprising rectangular structures are obtained in methanol from the reaction of the dinuclear arene ruthenium precursor [Ru2(p -cymene)2(dhnq)2Cl2] (dhnq = 5,8-dihydroxy-1,4-naphthoquinonato) with pyrazine or bipyridine linkers [N,N = pyrazine, 1; 4,4,-bipyridine, 2; 1,2-bis(4-pyridyl)ethylene, 3] in the presence of AgCF3SO3. All complexes 1,3, isolated in good yield as triflate salts, have been characterised by NMR and IR spectroscopy. The interaction of these rectangular complexes with pyrene as a guest molecule has been studied in solution by various NMR techniques (1D, DOSY, ROESY). In [D3]acetonitrile, the pyrazine-containing metalla-rectangle 1 shows no meaningful interactions with pyrene. On the other hand, the 4,4,-bipyridine- and 1,2-bis(4-pyridyl)ethylene-containing metalla-rectangles 2 and 3 clearly interact with pyrene in [D3]acetonitrile. DOSY measurements suggest that, in the case of [Ru4(p -cymene)4(4,4,-bipyridine)2(dhnq)2]4+ (2), the interactions occur on the outside of the rectangular assembly, while in the case of [Ru4(p -cymene)4{1,2-bis(4-pyridyl)ethylene}2(dhnq)2]4+ (3), the pyrene molecule is found inside the hydrophobic cavity of the metalla-rectangle, thus giving rise to a host-guest system. [source]

    Adducts of Schiff Bases with Tris(,-diketonato)lanthanide(III) Complexes: Structure and Liquid-Crystalline Behaviour

    Koen Binnemans
    Abstract Adducts of the Schiff base 2-hydroxy- N -octadecyloxy-4-tetradecyloxybenzaldimine with tris(,-dibenzoylmethanato)lanthanide(III) complexes are described. The stoichiometry of the complexes is [Ln(dbm)3Lx], where Ln is a trivalent lanthanide ion (all lanthanides except Ce and Pm), Hdbm is dibenzoylmethane and L is the Schiff base; x = 2 for Ln = La,Er and x = 1 for Ln = Tm,Lu. The Schiff-base ligands are in a zwitterionic form and coordinate through the phenolic oxygen only. The X-ray single-crystal structure of [La(dbm)3L,2] with L, = N -butyl-2-hydroxy-4-methoxybenzaldimine is described. The solution structure of lanthanum(III) complexes has been investigated by 1D and 2D 1H NMR techniques. Although the long-chain Schiff-base ligand and the tris(,-dibenzoylmethanato)lanthanide(III) complexes are non-mesomorphic, some of the adducts exhibit a monotropic smectic A phase. The mesomorphic behaviour depends on the lanthanide ion, in the sense that only a mesophase is observed for the series Ln = La,Eu, not for the heavier lanthanides. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003) [source]

    Oxidation of ,4 - and ,5 -Steroids with Hydrogen Peroxide Catalyzed by Porphyrin Complexes of MnIII and FeIII

    Susana L. H. Rebelo
    Abstract In this paper we describe a new environmentally friendly method to promote the stereoselective epoxidation of ,4 - and ,5 -steroids. Metalloporphyrins efficiently catalyze the epoxidation reactions of 17,-acetoxy-4-androstene (1), 4-cholestene (2) and 3,-acetoxy-5-cholestene (3) in the presence of H2O2 as oxygen donor. Modeling the molecular structure of the porphyrin as well as the central metal allows the control of the preferential formation of ,- or ,-epoxides. Porphyrins with bulky, electron-withdrawing groups in the ortho positions of the meso phenyls and with MnIII as the central metal ion, such as [Mn(TDCPP)Cl], gave preferentially the ,-epoxide of ,4 - and ,5 -steroids. [Fe(TPFPP)Cl] catalyzes preferentially the ,-epoxidation of ,4 -steroids and also increases the stereoselectivity for the ,-epoxide in ,5 -steroids, similar to the results obtained with m -CPBA (m -chloroperbenzoic acid) as oxidant. The substrate structure strongly influences the chemoselectivity of the reactions. The X-ray structures of two main products were determined, and two-dimensional NMR techniques allowed the full assignment of 1H and 13C NMR resonances as well as the stereochemistry of these products. A mechanistic proposal involving oxo species for the ,-approach and peroxy species for the ,-approach is proposed. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    The Synthesis of the Dimethyl Ester of Quino[4,4a,5,6- efg]-Annulated 7-Demethyl-8-deethylmesoporphyrin and Three of Its Isomers with Unprecedented peri -Condensed Quinoline Porphyrin Structures.

    Molecules with Outstanding Properties as Sensitizers for Photodynamic Therapy in the Far-Red Region of the Visible Spectrum
    Abstract The mesoporphyrin dimethyl ester nickel complex has been formylated via the Vilsmeier method. The four possible mono meso-formyl derivatives were isolated and characterized. Wadsworth,Emmons coupling with the anion of (diethylphosphono)acetonitrile converted these aldehydes into the four novel meso acrylonitriles. Brief treatment of these acrylonitrile systems in hot trichloroacetic acid resulted in the formation of four achiral porphyrin derivatives with unprecedented nickel complexes of quino-fused porphyrins. Subsequent removal of the nickel gave four quino-porphyrin free bases: quino[4,4a,5,6- efg]-annulated 7-demethyl-8-deethylmesoporphyrin dimethyl ester 6a, 2,-(methoxycarbonyl)quino[4,4a,5,6- jkl]-annulated 12-demethyl-13-de[2,-(methoxycarbonyl)ethyl]mesoporphyrin dimethyl ester 6b, 2,-(methoxycarbonyl)quino[4,4a,5,6- qrs]-annulated 18-demethyl-17-de(2,-methoxycarbonylethyl)mesoporphyrin dimethyl ester 6c and quino[4,5,6,7- abt]-annulated 2-demethyl-3-deethylmesoporphyrin dimethyl ester 6d. The structures of these systems were unambiguously determined via mass spectroscopy and a plethora of NMR techniques. In the same way, etioporphyrin and octaethylporphyrin were converted into the corresponding peri -condensed quinoporphyrins as products, which shows that the formation of novel pericondensed quino-porphyrins is a general reaction in the porphyrin series and will have a wide scope in this field. Also, a plausible reaction mechanism for the formation of the quinoporphyrin systems was derived. As a first test for the use of these systems as sensitizers in far-red phototherapy, the quantum yield of singlet oxygen generation by 6a in toluene was studied. This quantum yield is 0.77, which is even higher than the singlet oxygen generation by sensitized meso-tetraphenylporphyrin. Secondly, when Chinese Hamster ovary (CHO) cells were incubated in medium which contained up to 15 ,g/ml of 6a, the survival rate of the cells in the dark is complete within experimental error, showing that under these conditions, 6a is not toxic to CHO cells. When CHO cells incubated in medium containing 6a in concentrations of 1 ,g/ml and higher were treated with white light of intensity 30 mW/cm2 for 15 minutes, complete cell death was observed. Based on these facts, we expect that all four achiral systems will show very promising properties to form the basis of a photodynamic therapy in far-red light. The fact that these systems are achiral is an additional bonus for medical applications. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004) [source]

    Structural analysis of the lipopolysaccharide from nontypeable Haemophilus influenzae strain 1003

    FEBS JOURNAL, Issue 3 2002
    Martin Månsson
    Structural analysis of the lipopolysaccharide (LPS) of nontypeable Haemophilus influenzae strain 1003 has been achieved by the application of high-field NMR techniques, ESI-MS, capillary electrophoresis coupled to ESI-MS, composition and linkage analyses on O-deacylated LPS,and core oligosaccharide material. It was found that,the LPS contains the common structural element of,H. influenzae, l -,- d -Hepp -(1,2)-[PEtn,6]- l -,- d -Hepp -(1,3)-[,- d -Glcp -(1,4)]- l -,- d -Hepp -(1,5)-[PP Etn,4]-,-Kdop -(2,6)-Lipid A, in which the ,- d -Glcp residue is substituted by phosphocholine at O-6 and an acetyl group at O-4. A second acetyl group is located at O-3 of the distal heptose residue (HepIII). HepIII is chain elongated at O-2 by either a ,- d -Glcp residue (major), lactose or sialyllactose (minor, i.e. ,-Neu5Ac-(2,3)-,- d -Galp -(1,4)-,- d -Glcp), where a third minor acetylation site was identified at the glucose residue. Disialylated species were also detected. In addition, a minor substitution of ester-linked glycine at HepIII and Kdo was observed. [source]

    Response of native and denatured hen lysozyme to high pressure studied by 15N/1H NMR spectroscopy

    FEBS JOURNAL, Issue 6 2001
    Yuji O. Kamatari
    High-pressure 15N/1H NMR techniques were used to characterize the conformational fluctuations of hen lysozyme, in its native state and when denatured in 8 m urea, over the pressure range 30,2000 bar. Most 1H and 15N signals of native lysozyme show reversible shifts to low field with increasing pressure, the average pressure shifts being 0.069 ± 0.101 p.p.m. (1H) and 0.51 ± 0.36 p.p.m. (15N). The shifts indicate that the hydrogen bonds formed to carbonyl groups or water molecules by the backbone amides are, on average, shortened by ,,0.02 Å as a result of pressure. In native lysozyme, six residues in the , domain or at the ,/, domain interface have anomalously large nonlinear 15N and 1H chemical-shift changes. All these residues lie close to water-containing cavities, suggesting that there are conformational changes involving these cavities, or the water molecules within them, at high pressure. The pressure-induced 1H and 15N shifts for lysozyme denatured in 8 m urea are much more uniform than those for native lysozyme, with average backbone amide shifts of 0.081 ± 0.029 p.p.m. (1H) and 0.57 ± 0.14 p.p.m. (15N). The results show that overall there are no significant variations in the local conformational properties of denatured lysozyme with pressure, although larger shifts in the vicinity of a persistent hydrophobic cluster indicate that interactions in this part of the sequence may rearrange. NMR diffusion measurements demonstrate that the effective hydrodynamic radius of denatured lysozyme, and hence the global properties of the denatured ensemble, do not change detectably at high pressure. [source]

    The helix nucleation site and propensity of the synthetic mitochondrial presequence of ornithine carbamoyltransferase

    FEBS JOURNAL, Issue 18 2000
    Harmen H. J. De Jongh
    This study describes the helix nucleation site and helix propagation of the amphiphilic helical structure of the mitochondrial presequence of rat ornithine carbamoyltransferase. We investigated this property of the 32-residue synthetic presequence using CD and 2D-HR NMR techniques by determining the structure as a function of the concentration of trifluoroethanol. It was found that the hydrophobic cluster Ile7-Leu8-Leu9 forms the helix nucleation site, expanding to include residues Asn4 to Lys16 when the concentration of trifluoroethanol is increased from 10 to 30%. At higher trifluoroethanol concentrations an increased ,stiffening' of the polypeptide backbone (to Arg26) is observed. In addition, by recording CD spectra at different trifluoroethanol concentrations as a function of temperature, it was found that the equilibrium constant between helix and random coil formation for this peptide exhibits a strong temperature dependence with maximum values between 20 and 30 °C. Comparison of these equilibrium constants with those of homopolymers stressed the unique character of the mitochondrial presequence. The findings are discussed in relation to the molecular recognition events at different stages of the transport process of this protein into mitochondria. [source]

    Characterization of active-site mutants of Schizosaccharomyces pombe phosphoglycerate mutase

    FEBS JOURNAL, Issue 24 2000
    Elucidation of the roles of amino acids involved in substrate binding, catalysis
    The roles of a number of amino acids present at the active site of the monomeric phosphoglycerate mutase from the fission yeast Schizosaccharomyces pombe have been explored by site-directed mutagenesis. The amino acids examined could be divided broadly into those presumed from previous related structural studies to be important in the catalytic process (R14, S62 and E93) and those thought to be important in substrate binding (R94, R120 and R121). Most of these residues have not previously been studied by site-directed mutagenesis. All the mutants except R14 were expressed in an engineered null strain of Saccharomyces cerevisiae (S150-gpm::HIS) in good yield. The R14Q mutant was expressed in good yield in the transformed AH22 strain of S. cerevisiae. The S62A mutant was markedly unstable, preventing purification. The various mutants were purified to homogeneity and characterized in terms of kinetic parameters, CD and fluorescence spectra, stability towards denaturation by guanidinium chloride, and stability of phosphorylated enzyme intermediate. In addition, the binding of substrate (3-phosphoglycerate) to wild-type, E93D and R120,121Q enzymes was measured by isothermal titration calorimetry. The results provide evidence for the proposed roles of each of these amino acids in the catalytic cycle and in substrate binding, and will support the current investigation of the structure and dynamics of the enzyme using multidimensional NMR techniques. [source]

    Composition of the essential oil of flowers of Chloranthus spicatus (Thunb.) Makino

    Hailemichael Tesso
    Abstract The composition of the essential oil of the flowers of Chloranthus spicatus (Thunb.) Makino (Chloranthaceae) was investigated using capillary GC-GC/MS, preparative GC and NMR techniques. Forty-seven compounds were identified either by comparing their retention indices and mass spectra with a library of authentic samples established under identical experimental conditions or, by isolating the compounds and deriving their structures by one- and two-dimensional NMR investigations. Thus, four minor components, viz. chloranthalactone A (0.5%), isogermafurenolide (0.7%), eudesma-4(15),7(11),9-trien-12-olide (0.5%), and 7, -hydroxyeudesm-4-en-6-one (3.3%), were isolated for the first time as constituents of the essential oil of the flowers of C. spicatus and their structures established. The major components of the oil include (Z)- , -ocimene (6.3%), allo-aromadendrene (6.2%), sarisane (2-allyl-4,5-methylenedioxyanisol, 4.2%) and selina-4(15),7(11)-diene (6.4%). Copyright © 2006 John Wiley & Sons, Ltd. [source]

    2,3-,-Epoxyjaeschkeanadiol 5-benzoate from Ferula hermonis Boiss

    Youssef Diab
    Abstract The new 2,3-,-epoxyjaeschkeanadiol 5-benzoate has been isolated and its 1H- and 13C-NMR signals were completely assigned by the application of the modern NMR techniques. Its conformations are discussed on the basis of molecular modelling calculations and nuclear Overhauser effect spectroscopy (NOESY) spectra. Copyright © 2001 John Wiley & Sons, Ltd. [source]

    Four New Lignans with a Bicyclo[3.3.1]nonadienemethanol Skeleton from Cunninghamia lanceolata

    Ching-Kuo Lee
    Abstract Four unique bicyclo[3.3.1]nonadienemethanol lignans, designated lanceolatanins A (1), B (2), C (3), and D (4), along with one previously known compound, isolariciresinol (5), were isolated from the MeOH extracts of the heartwood of Cunninghamia lanceolata. Their structures were elucidated by application of various spectroscopic methods, including 1D- and 2D-NMR techniques, to their acetylated derivatives 1a, 2a, 3a, and 4a. Their possible biosynthetic formations are also discussed. [source]

    Cathepsin B Inhibitory Tetraene Lactones from the Fungus Talaromyces wortmannii

    Yuesheng Dong
    Abstract Wortmannilactones E,H (1,4), four new cathepsin B inhibitors, were produced and isolated from the culture of the soil filamentous fungus Talaromyces wortmannii. Their structures and relative configurations were elucidated on the basis of 1D- and 2D-NMR techniques, three of them (1, 2, and 4) posses an oxabicyclo[2.2.1]heptane moiety. Compounds 1,4 showed inhibitory activities against cathepsin B with IC50 values of 4.3, 6.5, 13.0, and 6.0,,M, respectively. [source]

    New Sesquiterpenoids from Ligularia duciformis

    Wen-Shu Wang
    Abstract From the whole plants of Ligularia duciformis, four new sesquiterpenoids, 3, -acetoxy-6, -methoxyeremophila-7(11),9(10)-dien-12,8, -olide (1), 3, -acetoxy-8, -hydroxy-6, -methoxyeremophila-7(11),9(10)-dien-12,8, -olide (2), 3, -acetoxy-10, -hydroxy-6,,8, -dimethoxyeremophil-7(11)-en-12,8, -olide (3), and 3, -acetoxy-6,,8,,10, -trihydroxyeremophil-7(11)-en-12,8, -olide (4) were isolated. Their structures were established by high-field NMR techniques (1H,1H-COSY, 13C-APT, HMQC, HMBC, and NOESY) and HR-ESI-MS analysis, together with comparison of the spectroscopic data with those of structurally related compounds. In addition, the cytotoxicity of the new compounds against human hepatic cancer cells Bel-7402, human pneumonic cancer cells A-549, and human colonic cancer cells HCT-8 were evaluated, the new compounds showed no cytotoxicity against the three tumor cells (all IC50 values >200,,M). [source]

    Synthesis and Conformational Analysis of Pentapeptides Containing Enantiomerically Pure 2,2-Disubstituted Glycines

    Abstract The synthesis and conformational analysis of model pentapeptides with the sequence Z-Leu-Aib-Xaa-Gln-Valol is described. These peptides contain two 2,2-disubstituted glycines (,,, -disubstituted , -amino acids), i.e., Aib (aminoisobutyric acid), and a series of unsymmetrically substituted, enantiomerically pure amino acids Xaa. These disubstituted amino acids were incorporated into the model peptides via the ,azirine/oxazolone method'. Conformational analysis was performed in solution by means of NMR techniques and, in the solid state, by X-ray crystallography. Both methods show that the backbones of these model peptides adopt helical conformations, as expected for 2,2-disubstitued glycine-containing peptides. [source]

    Alkaloids from Fruits of Daphniphyllum oldhamii

    Li-She Gan
    Abstract Seventeen Daphniphyllum alkaloids, including two new pentacyclic alkaloids, yuzuric acid (1) and daphnezomic acid (2), and 15 known ones, were isolated from the fruits of Daphniphyllum oldhamii. The structures and configuration of the two new alkaloids were determined on the basis of spectroscopic methods, especially 2D NMR techniques. [source]

    2-Hydroxytorularhodin, a New Xanthophyll from the Red Yeast Sporobolomyces coprosmae

    A new hydroxylated carotenoic acid was isolated from the red yeast Sporobolomyces coprosmae and unambiguously identified as 2-hydroxytorularhodin (1), i.e., (all-E)-3,,4,-didehydro-2-hydroxy- ,,, -caroten-16,-oic acid, by application of extensive 1D and 2D NMR techniques (gCOSY, gHSQC, gHMBC, DQS, gTOCSY, and ROESY). Hydroxylation of carotenoids at C(2) is uncommon in nature, very rare in fungi, and unprecedented for torularhodin. [source]

    Longistylumphyllines A,C, Three New Alkaloids from Daphniphyllum longistylum

    Xin Chen
    Three new alkaloids, longistylumphyllines A,C (1,3), together with the six known alkaloids deoxycalyciphylline B, deoxyisocalyciphylline B, methyl homosecodaphniphyllate, daphnicyclidin A, daphnicyclidin B, and daphnicyclidin F, were isolated from the stems and leaves of Daphniphyllum longistylum. Their structures and relative configuration were elucidated on the basis of spectroscopic data, especially 1D and 2D NMR techniques. [source]

    Three New Urea Derivatives from Pliocene-Fossil Pinus armandii

    You-Xing Zhao
    Three new urea derivatives, isolated from the Pliocene lignified wood of Pinus armandii, were identified as carbonylbis[imino(6-methyl-3,1-phenylene)]bis[carbamic acid] dimethyl ester (1), and as the corresponding dibutyl ester 2 and bis(2-methylpropyl) ester 3. Their structures were elucidated by spectroscopic methods, including MS and 1D- and 2D-NMR techniques. [source]

    Two Novel Triterpenes from the Leaves of Ficus microcarpa

    Yueh-Hsiung Kuo
    Two novel triterpenes, 29(20,19)abeolupane-3,20-dione (4) and 19,20-secoursane-3,19,20-trione (5), besides (3,)-3-hydroxy-29(20,19)abeolupan-20-one (2), lupenone, and , -amyrone (6), were isolated from the leaves of Ficus microcarpa and were characterized by spectroscopic means, including 2D-NMR techniques and chemical methods. Compound 4 is the second derivative having the 29(20,19)abeolupane skeleton, and 5 is a novel skeleton. A biosynthetic pathway to 5 is proposed (Scheme). [source]

    Chemical Constituents from the Fruits of Madhuca latifolia


    From the fruit coats of the medicinal plant Madhuca latifolia were isolated three new compounds, the triterpenoid madhucic acid (=3,- (octanoyloxy)-11-oxoolean-12-en-28-oic acid; 1), the untypical isoflavone madhushazone (=9-methoxy-7-(2,3,6-trimethoxyphenyl)-[1,3]dioxolo[4,5- g][1]benzopyran-8(8H)-one; 2), and a bis(isoflavone) named madhusalmone (=5,14-dimethoxy-3,12-bis(3,4,5-trimethoxyphenyl)-1,6,8,10,15,17-hexaoxanaphtho[2,,3,:,6,7]cyclodeca[1,2- b]naphthalene-4,13(4H,13H)-dione; 3), as well as eight known constituents, and their structures were elucidated by spectral analysis, including 2D-NMR techniques. [source]

    Five New Sesquiterpenoids from Parasenecio petasitoides

    Hua Zhang
    From the whole plants of Parasenecio petasitoides, five new sesquiterpenoids were isolated, (E,E)-3,,9, -dihydroxy-6,H,11,H-13-norgermacra-1(10),4-dien-11,6-carbolactone (2), (E,E)-2,,9, -dihydroxy-6,H,11,H-13-norgermacra-1(10),4-dien-11,6-carbolactone (3), (E,E)-2,,9, -dihydroxy-6,H,11,H-13-norgermacra-1(10),4-dien-11,6-carbolactone (4), (E)-15-hydroxy-2-oxo-6,H,11,H-13-norguaia-3-ene-11,6-carbolactone (7), and (E)-11,,15-dihydroxy-2-oxo-6,H-13-norguaia-3-ene-11,6-carbolactone (8), together with three known compounds, deacetyl herbolide A (1), jacquilenin (5), and (E)-15-hydroxy-2-oxo-6,H,11,H-13-norguaia-3-ene-11,6-carbolactone (6). The structures of these natural products were elucidated spectroscopically, especially by 1D- and 2D-NMR techniques, in combination with high-resolution mass spectroscopy. [source]

    Two Novel 14-Nor-13,14-secopodocarpanes from the Bark of Taiwania cryptomeriodes

    Shih-Chang Chien
    The two novel compounds cryptomelactones A (3) and B (4) were isolated from the bark of Taiwania cryptomeriodes, besides the two known podocarpane derivatives 1,,13,14-trihydroxypodocarpa-8,11,13-trien-7-one (1) and 3,,13,14-trihydroxypodocarpa-8,11,13-trien-7-one (2), and were characterized by spectroscopic means including 2D-NMR techniques. Compounds 3 and 4 are novel-14-nor-13,14-seco-podocarpanes. The absolute configurations of 3 and 4 were determined by the modified Mosher method. The biotransformation mechanism of 3 and 4 is proposed. [source]

    Two New and a Known Compound from Lawsonia inermis


    A new obtusafuran derivative, lawsonicin (1), and a new naphthaquinone, lawsonadeem (2), along with a known constituent, vomifoliol (3), were isolated from the aerial parts of Lawsonia alba and characterized by chemical transformation and spectroscopic experiments, including 2D-NMR techniques. [source]

    N - and C -acyclic thionuleoside analogues of 1,2,3-triazole

    Najim A. Al-Masoudi
    Cycloaddition of the azide derivative 5 with 1,4-dihydroxybutyne afforded the N -thio-acyclic nucleoside 6, which prepared alternatively from coupling of the bromo derivative 8 with 2-acetoxy-ethylmercaptan. Deblocking of 6 gave the free nucleoside 7. Mesylation of 6 furnished the dimesylate 9, which gave three rearranged products 14,16 on treatment with chloride anion. These compounds might be obtained via the episulfonium ion 10, which is subjected to nucleophilic displacement and further sulfur participation. Deblocking of 14,16 afforded the free nucleoside analogues 17,19, and their structures were confirmed by COSY, ROESY, HMQC, and HMBC NMR techniques. Compound 16 was prepared alternatively from chlorination of alcohol 6 with Ph3P-CCl4. Carbomoylation of 6 led to the carbamate 20, which gave the free nucleoside analogue 21 on deblocking. © 2004 Wiley Periodicals, Inc. Heteroatom Chem 15:380,387, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/hc.20030 [source]

    Cold-adapted signal proteins: NMR structures of pheromones from the antarctic ciliate Euplotes nobilii

    IUBMB LIFE, Issue 8-9 2007
    William J. Placzek
    Abstract Cell type-specific signal proteins, known as pheromones, are synthesized by ciliated protozoa in association with their self/nonself mating-type systems, and are utilized to control the vegetative growth and mating stages of their life cycle. In species of the most ubiquitous ciliate, Euplotes, these pheromones form families of structurally homologous molecules, which are constitutively secreted into the extracellular environment, from where they can be isolated in sufficient amounts for chemical characterization. This paper describes the NMR structures of En-1 and En-2, which are members of the cold-adapted pheromone family produced by Euplotes nobilii, a species inhabiting the freezing coastal waters of Antarctica. The structures were determined with the proteins from the natural source, using homonuclear 1H NMR techniques in combination with automated NOESY peak picking and NOE assignment. En-1 and En-2 have highly homologous global folds, which consist of a central three-,-helix bundle with an up-down-up topology and a 310-helical turn near the N-terminus. This fold is stabilized by four disulfide bonds and the helices are connected by bulging loops. Apparent structural specificity resides in the variable C-terminal regions of the pheromones. The NMR structures of En-1 and En-2 provide novel insights into the cold-adaptive modifications that distinguish the E. nobilii pheromone family from the closely related E. raikovi pheromone family isolated from temperate waters. [source]

    Solid-state NMR Structure Determination

    IUBMB LIFE, Issue 9 2003
    Alison Drechsler
    Abstract Biological applications of solid-state NMR (SS-NMR) have been predominantly in the area of model membrane systems. Increasingly the focus has been membrane peptides and proteins. SS-NMR is able to provide information about how the peptides or proteins interact with the lipids or other peptides/proteins in the membrane, their effect on the membrane and the location of the peptides or proteins relative to the membrane surface. Recent developments in biological SS-NMR have been made possible by improvements in labelling and NMR techniques. This review discusses aligned systems and magic angle spinning techniques, bilayers and bicelles, and measurement of chemical shift anisotropy and dipolar coupling. A number of specific experiments such as cross polarization, rotational resonance, REDOR, PISEMA, MAOSS and multidimensional experiments are described. In addition to 2H, 13C and 15N, recent solid-sate 1H, 19F and 17O NMR work is discussed. Several examples of the use of SS-NMR to determine the structure of membrane peptides and proteins are given. IUBMB Life, 55: 515-523, 2003 [source]