(-)-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).

To determine the absolute configuration of 3-ishwarone, 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 (+)-3-ishwarone are analyzed with the corresponding density functional theoretical predictions for different diastereomers. ECD and ORD spectra by themselves could not facilitate the determination of the absolute configuration of this molecule. However, the magnitude of the experimental EDF of (+)-3-ishwarone is found to match better with that predicted for the (1R,2S,4S,5R,9R,11R) diastereomer. The analyses of similarity measures between experimental and predicted spectra for VCD and VDF clearly suggested that the absolute configuration of (+)-3-ishwarone is (1R,2S,4S,5R,9R,11R).

The first natural occurrence in optically active form of the dimeric flavonoid agathisflavone and definition of its axial chirality using chiroptical spectroscopic methods are described. The experimental electronic circular dichroism, electronic dissymmetry factor, optical rotatory dispersion, vibrational circular dichroism (VCD), and vibrational dissymmetry factor spectra of agathisflavone are presented and analyzed with their corresponding quantum chemical predictions to definitively assign the axial chirality of (-)-agathisflavone as (aS).

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