Toshiaki Nishida

Long‐range proton–carbon coupling constants in conformational analysis of oligosaccharides

Long‐range heteronuclear coupling constants, 3J(C,H), were measured across glycosidic linkages in β‐linked disaccharides and also for vicinally disubstituted trisaccharides. One‐dimensional multiple‐site 13C excitation experiments using Hadamard spectroscopy and band‐selective 1H decoupling during the acquisition period were used in conjunction with pulsed field gradients for coherence selection in the 1H detected experiment. For one dihedral angle the 3J(C,H) value could only be unambiguously determined utilizing the band‐selective 1H decoupling. The 2D EXSIDE was also used for the measurement of 3J(C,H) values and the results showed excellent agreement with those of the 1D measurements. The influence of solvent, water and water–dimethyl sulfoxide (7:3), on conformation was investigated, but showed only small changes in 3J(C,H) values. In general, the long‐range heteronuclear coupling constants related to the ϕ dihedral angles (3.6–4.3 Hz) were smaller than those of the ψ dihedral angles (4.3–5.3 Hz). A comparison with 3J(C,H) values from Monte Carlo or Langevin dynamics simulations showed better agreement for the ψ dihedral angles than for the ϕ dihedral angles as calculated using a Karplus relationship.

NMR spectroscopy of 13C‐enriched polysaccharides: application of 13C–13C TOCSY to sugars of different configuration

13C–13C 2D TOCSY experiments were applied, with both carbon‐13 and proton detection, to alleviate the problem of limited 1H–1H coherence transfer in certain sugars, e.g. those with the manno or galacto configuration. The 13C–13C couplings are not as dependent on the different sugar geometries and can be up to 50 times larger, i.e. 1JCC vs. 3JHH. For bacterial polysaccharides, Mr ca. 104–105, loss of magnetization can be severe owing to long delays in 1H–1H TOCSY experiments, and these are circumvented by applying the spin lock on the 13C nuclei.

7,8-epoxy-4-basmen-6-one, a tobacco diterpenoid having a novel skeleton, having a novel skeleton

Abstract A dieterpenoid, probably cembrane-derived and having an novel skeleton, has been isolated from Greek tobacco. Its structure has been determined by spectroscopic methods and X-ray analysis.

The association reactions of ion radicals with neutral molecules. I: Thermodynamic parameters for the association of benzaldehyde anion radical with alcohols in N,N-dimethylformamide

Parametres thermodynamiques, ΔH°, ΔS°, ΔG°, K pour la liaison H des alcools (methanol, ethanol, t-butanol) avec le radical anionique du benzaldehydre dans DMF

Diagonal-peak patterns in double-quantum-filtered COSY

Two-dimensional correlation spectroscopy with double-quantum filtration (DQCOSY) is now widely used by NMR spectroscopists because it facilitates examination of cros peaks close to the diagonal (1, 2). For a coupled two-spin system, the double-quantum-filtered spectrum resembles the conventional COSY spectrum except that the diagonal peaks are in the (antiphase) absorption mode and responses from uncoupled spins have been suppressed

Long-range proton–carbon chemical shift correlation by 1D and 2D n.m.r. spectroscopy: structure of a sucrose ester

The structure of an octa-acylated derivative of a disaccharide isolated from oriental tobacco has been confirmed with the aid of long-range proton–carbon-13 shift correlation by 2D n.m.r. spectroscopy using a 10 mg sample.

Application of 2d-nmr spectroscopy in the structural determination of a new tobacco cembranoid

Abstract Proton-proton shift correlated 2D-NMR spectroscopy has been used to determine the structure of a new tobacco cembranoid as (1 S ,2 E ,4 S ,6 R ,7 E )-4,6-dihy-droxy-2,7,12(20)-cembratrien-11-one (1). This assignment has been verified by chemical means.

An Unusual Cyclic System: Derivatives of N-Acetyl [2-Deoxy-β-D-Mannopyranosid]Urono-6,2-Lactam

ABSTRACT Syntheses are described of a new ring system, namely derivatives of N-acetyl [2-deoxy-β-D-mannopyranosid]urono-6,2-lactam. These were formed by participation of a 2-acetamido-2-deoxy group in the oxidation using pyridinium dichromate of a 6-hydroxyl group in a mannopyranosidic system The structures of the new compounds were determined mainly by NMR experiments inter alia by HMBC techniques.

Towards the understanding of aromatic solvent induced chemical shifts. A multivariate data analysis of 1H ASIS of cyclic ethers and thioethers

Les deplacements chimiques de 1 H, induit par des solvants aromatiques, pour une serie de solutes etheres, sont analyses en distinguant les effets moyens specifiques et generaux sur le solute. Discussion

A sensitive and convenient method for the determination of multiplicities of lines in 13C n.m.r. spectra

Mutiplicity determination from an optimized heteronuclear J-spectrum is shown to have several significant advantage over spectrual editing techniques; despite the experiment being two-dimensional it is of comparable sensitivity with equivalent one-dimensional techniques and involves little extra data processing.