Structural Chemistry

, Volume 15, Issue 3, pp 237–245

Conformational Analysis of Guaianolide-Type Sesquiterpene Lactones by Low-Temperature NMR Spectroscopy and Semiempirical Calculations

Authors

  • Slobodan Milosavljević
    • Faculty of ChemistryUniversity of Belgrade
  • Ivan Juranić
    • Faculty of ChemistryUniversity of Belgrade
  • Vanja Bulatović
    • Institute for Medicinal Plant Research “Dr. Josif Pančić
  • Slobodan Macura
    • Department of Biochemistry and Molecular BiologyMayo Foundation
  • Nenad Juranić
    • Department of Biochemistry and Molecular BiologyMayo Foundation
  • Hans-Heinrich Limbach
    • Institut für ChemieFreie Universität Berlin
  • Klaus Weisz
    • Institut für ChemieFreie Universität Berlin
  • Vlatka Vajs
    • Institute for Chemistry, Technology and Metallurgy
    • Institute for Chemistry, Technology and Metallurgy
Article

DOI: 10.1023/B:STUC.0000021533.65546.57

Cite this article as:
Milosavljević, S., Juranić, I., Bulatović, V. et al. Structural Chemistry (2004) 15: 237. doi:10.1023/B:STUC.0000021533.65546.57

Abstract

Conformational analysis of 9α-acetoxycumambrine A 1 and 8-O-isobutiryl-9α-acetoxycumambrine B 2 was carried out by low-temperature NMR studies. Results suggested that lactones 1 and 2 are mixtures of two distinctive conformers, I and II. Based on low-temperature 1H NMR spectra, in four solvents, the thermodynamic parameters of I ⇌ II exchange process were assessed. Energy of activation of I → II reaction was obtained by dynamic NMR simulations for both compounds. Results revealed that conformational exchange of lactones 1 and 2 occurs due to “chair ⇌ twisted chair” interconversion of a heptane ring. The same PM3 semiempirical method was applied for geometry optimization of lactones 1 and 2, as well as of 9α-hydroxycumambrine A 3, 9α-acetoxycumambrine B 4, and cumambrine B 5.

Guaianolidescumambrineconformationslow-temperature NMRdynamic NMRPM3 semiempirical calculations

Copyright information

© Plenum Publishing Corporation 2004