title: Absolute configuration of eremophilane sesquiterpenes from Petasites hybridus: comparison of experimental and calculated circular dichroism spectra.
abstract: In-depth conformational analyses of 10 known eremophilane (= (1S,4aR,7R,8aR)-decahydro-1,8a-dimethyl-7-(1-methylethyl)napththalene) sesquiterpenes, 1-10, from Petasites hybridus were performed with molecular mechanics as well as density functional theory methods. Electronic transition energies and rotational strengths of these eight eremophilane lactones and two petasins were calculated by time-dependent density functional theory (B3PW91/TZVP). The absolute configurations of the constituents could be assigned by comparison of their simulated and experimental circular dichroism (CD) spectra in methanol as (4S,5R,8S,10R) (1, 2), (2R,4S,5R,8S,10R) (3, 4, 5), (2R,4S,5R,8R,9R,10R) (6), (2R,4S,5R,8R,10R) (7, 8), and (3R,4R,5R) (9, 10). Single-crystal X-ray diffraction data of 8beta-hydroxyeremophilanolide ((8S)-8-hydroxyeremophil-7(11)-en-12,8-olide) (1) served as starting point for the theoretical conformational calculations of the 8beta-epimers of the eremophilane lactones. Experimental CD spectra as well as (1)H NMR spectra of compound 1 in methanol were considerably dependent on sample concentration.
authors.affiliation: Institute of Pharmaceutical Sciences (IPW)-Pharmacognosy, Karl-Franzens University of Graz, Austria.
authors.forename: Antje
authors.initials: A
authors.lastname: Bodensieck
authors.forename: Walter M F
authors.initials: WM
authors.lastname: Fabian
authors.forename: Olaf
authors.initials: O
authors.lastname: Kunert
authors.forename: Ferdinand
authors.initials: F
authors.lastname: Belaj
authors.forename: Sajid
authors.initials: S
authors.lastname: Jahangir
authors.forename: Wolfgang
authors.initials: W
authors.lastname: Schühly
authors.forename: Rudolf
authors.initials: R
authors.lastname: Bauer
mesh_terms: D002942:Circular Dichroism / Q000379:methods*; D041621:Eremophila Plant / Q000737:chemistry*; D009682:Magnetic Resonance Spectroscopy / Q000379:methods; D008956:Models, Chemical; D008968:Molecular Conformation; D015394:Molecular Structure; D036901:Petasites / Q000737:chemistry*; D011487:Protein Conformation; D012717:Sesquiterpenes / Q000737:chemistry*; D013237:Stereoisomerism; D013329:Structure-Activity Relationship; D013379:Substrate Specificity
chemical_list: D012717:Sesquiterpenes