Separation and structure determination of two diastereomeric pairs of enantiomers from Dracocephalum rupestre by high-performance liquid chromatography with circular dichroism detection

All of the four stereoisomers of an unprecedented type of flavanones, the dracorupesins, were separated from the aerial parts of Dracocephalum rupestre simultaneously. The dracorupesins were characterized as two diastereomeric pairs of enantiomers by on-line chiral high-performance liquid chromatography-circular dichroism (HPLC-CD) analysis, which was a reliable stereoanalytical tool for natural products. The planar structures of the compounds were elucidated by means of spectroscopic methods including IR, MS, one-dimensional NMR (1D-NMR) and two-dimensional NMR (2D-NMR) techniques.