ISSN:0749-1581    

DOI:10.1002/mrc.1260301302

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

ISSN:0749-1581    

DOI:10.1002/mrc.1260301303

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractCross‐relaxation interactions between the nicotinamide moiety and the adenine moiety of NAD in D2O solution were unambiguously revealed by steady‐state NOE experiments, transient NOE experiments and synchronous nutation experiments. The experimental results, which allow a concise description in terms of auto‐relaxation and cross‐relaxation, are interpreted as the result of a stacking interaction. Studies of13C relaxation and investigations on ternary mixtures with 6‐methylpurine give evidence for an inter‐ rather than intra‐molecular stack interaction, at least in the NMR concen

ISSN:0749-1581    

DOI:10.1002/mrc.1260301304

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractAnalysis of1H and13C NMR data by 2D NMR techniques was used for the structural identification of triquinanes and bulleranes considered as precursors of complex natural products such as (+)‐cerapicol. The polycyclic molecules are derived from a tandem Norrish Type I photoreaction and intramolecular arene–alkenemetaphotocycloaddition of aryl‐substituted norbornan

ISSN:0749-1581    

DOI:10.1002/mrc.1260301305

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe1H NMR spectrum of the quinolizidine alkaloid lupinine was studied at 200 and 600 MHz. A full assignment of the1H signals was achieved by application of a variety of NMR techniques, including homonuclear1H NOE difference, 2D δH/δHCOSY and direct δC/δHcorrelation 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 the13C NMR spectrum has been confirmed by independent, and more dire

ISSN:0749-1581    

DOI:10.1002/mrc.1260301306

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe full structure of astellatol, a new complex sesterterpene isolated fromAspergillus variecolor, was determined solely by the use of one‐ and two‐dimensional NMR techniques. The carbon skeleton was deduced from a two‐dimensional INADEQUATE spectrum, and the proton shifts were deduced from a two‐dimensional CH correlation (HMQC) experiment. Analysis of a two‐dimensional proton DQFCOSY spectrum and a series of homonuclear NOE difference spectra allowed the determination of the full ster

ISSN:0749-1581    

DOI:10.1002/mrc.1260301307

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractTwo‐dimensional (2D) NMR spectroscopy has become a routine part of molecular structure determination in liquids. In most modern experiments there is some correlation of transition frequencies between the two dimensions, and the mechanism responsible for the correlation dictates the information obtainable from the 2D spectrum. Two distinct mechanisms for magnetization transfer are considered: scalar coupling and cross‐relaxation. The former gives rise to information about the proximity of spins through the electronic framework of the molecule and the latter provides information on spatial proximity and molecular motion. Two‐dimensional experiments of both types are described, concentrating in particular on TOCSY and ROESY. It is shown how polarization transfer can be tailored and controlled, and how the unwanted coherent transfer due toJcoupling can be eliminated in the ROESY experiment. Throughout the discussion, the multiple‐pulse sequence used for each experiment is the central focal point, and its design and analysis are the main conside

ISSN:0749-1581    

DOI:10.1002/mrc.1260301308

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

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 duringt1is replaced by a one‐stepJfilter 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 measurenJ(C,H) (n≤ 2), there are serious limitations to th

ISSN:0749-1581    

DOI:10.1002/mrc.1260301309

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe1H and13C NMR spectra of the pyrrolizidine alkaloid 13‐O‐acetyldicrotaline were studied at 4.7 T. A full assignment of the1H and13C signals was achieved by application of a variety of NMR techniques, including homonuclear1H NOE difference, 2D δH/δHphase‐sensitive COSY and δC/δHdirect and long‐range correlation experiments. The stereochemistry at C‐13 in dicrotaline is confirmed to beS, and the conformation of the elevenmembered macrocycle is compared with that of related pyrrolizid

ISSN:0749-1581    

DOI:10.1002/mrc.1260301310

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY

摘要:

AbstractThe structures of hydrolysable tannins, each existing as an equilibrium mixture due to tautomerization at the sugar core(s) or at the dehydrohexahydroxydiphenoyl group (five‐ and six‐membered hemiacetal forms) in the molecule, were elucidated by NMR, employing 2D NMR techniques (COSY, NOESY,1H13C long‐range COSY, etc.), on derivatives which avoid the spectral complication due to equili

ISSN:0749-1581    

DOI:10.1002/mrc.1260301311

出版商:John Wiley&Sons, Ltd.    

年代:1992

数据来源: WILEY