Conformational analysis of an anti-androgenic, (E,E)-8-hydroxygermacrene B, using NOESY and dynamic NMR spectroscopy

(E,E)-8-Hydroxygermacrene B was prepared by ketone reduction of germacrone, a naturally occurring compound from Curcuma aeruginosa Roxb. with NaBH4 at low temperature (4 °C). This compound showed remarkable in vitro anti-androgenic activity (IC50 0.15 ± 0.022 mM) applicable to male baldness treatments. NMR analysis at −50 °C indicated that there were four conformational isomers of (E,E)-8-hydroxygermacrene B in a ratio of 48:40:8:4. The major conformers were assigned by 1H NMR and 2D-NOESY NMR spectroscopy as having methyl groups at C-10 and C-4 in up-down (UD) orientations (48% predominance) and UU (40%). 1H NMR spectra implied another two minor conformers with these methyls having DU (8%) and DD (4%) orientations.