Nuclear Magnetic Resonance Experiments Applicable to the Elucidation and Characterization of Alkaloid Structures Part I: Direct 1H–13C Heteronuclear Shift Correlation and Establishing Contiguous Protonated Carbon Spin Systems

Josep Sauri, Gary E. Martin

Research output: Book chapterChapterpeer-review

1 Citation (Web of Science)

Abstract

Characterization of alkaloid structures begins with the preparation of the sample, which is discussed first, followed by probe and parameter choices. In parallel, it is assumed that an investigator will also acquire mass spectral data to help define the empirical formula of the molecule. A proton reference spectrum initiates the pursuit of the structure of the molecule. If there is sufficient material available, a 1D 13C spectrum might also be acquired at that time. The variants of acquiring an HSQC heteronuclear shift correlation spectrum are discussed, including multiplicity editing and what are generally referred to as pure shift HSQC spectra. In sample-limited situations, investigators may wish to consider intentionally folding their heteronuclear shift correlation spectra into the second or F1 frequency domain, which is considered next, followed by non-uniform sampling. Both of these techniques can lead to considerable savings of spectrometer time. Next, we favor the acquisition of long-range heteronuclear shift correlation data to supplement the HSQC spectrum. In sample-limited situations, where there is insufficient material to allow for the convenient acquisition of a 13C reference spectrum, the acquisition of HMBC data can provide access to non-protonated carbon resonances that would otherwise be derived from a carbon reference spectrum. Beyond this array of experiments, the authors generally undertake defining the proton–proton connectivity network using COSY or TOCSY spectra. In many cases, the ensemble of data described in this chapter will be sufficient to define the structure of the molecule in question.
Original languageEnglish
Title of host publicationModern Nmr Approaches To The Structure Elucidation Of Natural Products, Vol 2: Data Acquisition And Applications To Compound Classes
EditorsAJ Williams, GE Martin, D Rovnyak
PublisherRoyal Soc Chemistry
Chapter9
Pages315-357
Number of pages43
Volume2
ISBN (Electronic)978-1-84973-468-4
ISBN (Print)978-1-84973-393-9
DOIs
Publication statusPublished - Dec 2016
Externally publishedYes

Keywords

  • Bond correlation spectroscopy
  • Indirect covariance nmr
  • C-13 nmr
  • Connectivity networks
  • Polarization transfer
  • Coupling-constants
  • Natural-products
  • N-adequate
  • 2d nmr
  • Hmbc

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