Absolute Configurations of (+/-)-Glabridin Enantiomers

Abstract

Concerned with ambiguous stereochemistry assignment of natural (+)-glabridin, absolute configurations of (+/-)-glabridin enantiomers were studied with synthetic glabridin. Synthetic glabridin enantiomers were separated by semi-preparative Sumi-chiral column chromatography, and characterized by UV-Vis and NMR spectroscopy. Three-dimensional molecular structure of glabridin was obtained as equatorial Ph-3 half chair chroman ring from semi-empirical PM3 calculation, and refined by coupling constants in H-1 NMR spectrum. Finally, absolute configurations of two enantiomers were determined by circular dichroism spectroscopy based on the empirical helicity rules. Absolute configuration of natural (+)-glabridin was confirmed as (R)-glabridin, as known.