Absolute configurations of chiral molecules with multiple stereogenic centers without prior knowledge of the relative configurations: A case study of inuloxin C

Electronic circular dichroism (ECD) and discrete wavelength resolved specific optical rotations, referred to as optical rotatory dispersion (ORD), have been remeasured for inuloxin C and analysed with corresponding quantum chemical (QC) predicted data for all diastereomers of inuloxin C. The QC-predicted sign of ORD and of a major ECD band are found to match the experimental observations for more than one diastereomer. However, these ECD and ORD analyses combined with electronic dissymmetry factor analyses narrowed the choices of absolute configuration (AC) of inuloxin C to (5R,7S,8R,10R) and (5S,7S,8S,10S). Supplementing these analyses with corresponding analyses for acetylated inuloxin C resulted in a unique choice for the AC of inuloxin C as (5S,7S,8S,10S). This result is independent of NMR analysis. Furthermore, this AC is in full agreement with previously determined relative configuration by NMR and the AC derived therefrom using ECD and ORD. Therefore, the present study identifies a pathway for determining the ACs of chiral molecules with multiple stereogenic centers when relative configurations are not known, or when it is desired to deduce ACs independent of the known relative configurations.