Stereochemistry and conformations of natural 1,2-epoxy-guaianolides based on 1D and 2D NMR data and semiempirical calculations

Snežana Trifunović, Slobodan Milosavljević, Vlatka Vajs, Slobodan Macura, Nina Todorovic

Research output: Contribution to journalArticlepeer-review

10 Scopus citations

Abstract

From detailed study of ID and 2D NMR spectra of ten natural 1,2-epoxyguaianolides (bis-1,2:3,4-epoxyguaianolides and guaianolide-1,2- epoxychlorohydrins), we identified general spectral traits helpful for stereochemical assignment of such sesquiterpene lactones. We found that the chemical shifts of certain 1H and 13C nuclei are consistently dependent on the configuration of 1,2-epoxy-ring which could be used as a simple rule for establishing this configuration. Then, from 1D and 2D (COSY, NOESY, HMQC, HMBC) NMR data, applying the observed rule, the structure and stereochemistry of two new, diastereomeric guaianolide-1,2- epoxychlorohydrins, isolated from Achillea serbica, are determined. The NMR data, namely, nuclear overhauser enhancement (NOE) correlations, pointed out two conformations of guaianolide's cycloheptane ring. The semiempirical calculations (AMI and PM3 methods), performed inordertogainadditional information regarding conformations, resulted in three geometries of investigated lactones. Even so, the conformations derived from the NMR data agreed well with those calculated by semiempirical methods.

Original languageEnglish (US)
Pages (from-to)427-431
Number of pages5
JournalMagnetic Resonance in Chemistry
Volume46
Issue number5
DOIs
StatePublished - May 1 2008

Keywords

  • 2D NMR
  • Achillea L
  • C NMR
  • Conformational analysis
  • Guaianolide-1,2-epoxychlorohydrins
  • H NMR
  • Sesquiterpene lactones

ASJC Scopus subject areas

  • Chemistry(all)
  • Materials Science(all)

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