Absolute configuration of eremophilane sesquiterpenes from Petasites hybridus: Comparison of experimental and calculated circular dichroism spectra |
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Authors: | Antje Bodensieck Walter M.F. Fabian Olaf Kunert Ferdinand Belaj Sajid Jahangir Wolfgang Schühly Rudolf Bauer |
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Affiliation: | 1. Institute of Pharmaceutical Sciences (IPW)—Pharmacognosy, Karl‐Franzens University of Graz, Austria;2. Institute of Chemistry (IfC)—Organic and Bioorganic Chemistry, Karl‐Franzens University of Graz, Austria;3. Institute of Pharmaceutical Sciences (IPW)—Pharmaceutical Chemistry, Karl‐Franzens University of Graz, Austria;4. Institute of Chemistry (IfC)—Inorganic Chemistry, Karl‐Franzens University of Graz, Austria |
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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 8β‐hydroxyeremophilanolide ((8S)‐8‐hydroxyeremophil‐7(11)‐en‐12,8‐olide) ( 1 ) served as starting point for the theoretical conformational calculations of the 8β‐epimers of the eremophilane lactones. Experimental CD spectra as well as 1H NMR spectra of compound 1 in methanol were considerably dependent on sample concentration. Chirality, 2010. © 2009 Wiley‐Liss, Inc. |
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Keywords: | time‐dependent density functional theory rotational strengths CD spectra absolute configuration eremophilane sesquiterpenes Petasites hybridus conformation X‐ray crystallography NMR |
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