Absolute Configuration of (−)-Centratherin, a Sesquiterpenoid Lactone, Defined by Means of Chiroptical Spectroscopy

(−)-Centratherin is a bioactive sesquiterpenoid lactone, whose absolute configuration (AC) was not established, but has been proposed based on those of germacrane precursors. To verify this proposal, the experimental electronic circular dichroism (ECD), electronic dissymmetry factor (EDF), optical rotatory dispersion (ORD), vibrational circular dichroism (VCD), and vibrational dissymmetry factor (VDF) spectra of (−)-centratherin have been analyzed with the corresponding density functional theoretical predictions. These analyses suggest the AC of naturally occurring (−)-centratherin to be (6R,7R,8S,10R,2′Z).