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 1 H 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.
Original language | English (US) |
---|---|
Pages (from-to) | 237-245 |
Number of pages | 9 |
Journal | Structural Chemistry |
Volume | 15 |
Issue number | 3 |
DOIs | |
State | Published - Jun 2004 |
Keywords
- Conformations
- Cumambrine
- Dynamic NMR
- Guaianolides
- Low-temperature NMR
- PM3 semiempirical calculations
ASJC Scopus subject areas
- Condensed Matter Physics
- Physical and Theoretical Chemistry