Conformational analysis of (+)-germacrene A by variable-temperature NMR and NOE spectroscopy

(+)- Germacrene A, an important intermediate in sesquiterpene biosynthesis, was isolated in pure form from a genetically engineered yeast and was characterized by chromatographic properties (TLC, GC), MS, optical rotation, UV, IR, H-1 NMR, and C-13 NMR data. Variable-temperature 500 MHz H-1 NMR spectra in CDCl3 showed that this flexible cyclodecadiene ring exists as three NMR-distinguishable conformational isomers in a ratio of about 5: 3: 2 at or below ordinary probe temperature ( 25 degrees C). The conformer structures were assigned by H-1 NMR data comparisons, NOE experiments, and vicinal couplings as follows: 1a (52%, UU), 1b (29% UD), and 1c (19%, DU). (c) 2007 Elsevier Ltd. All rights reserved.