Stereoselective separation, configuration determination, and quantification of flavanone glycosides in Citrus using chiral HPLC-UV in combination with CD spectra

Abstract

Flavanone glucosides, such as naringin and neohesperidin, are present in specific Citrus species and manifest a chiral center at the C-2 position of their flavanone moiety. This study successfully achieved the simultaneous stereoselective separation of the C-2 diastereomers of naringin, neohesperidin and hesperidin, as well as the partial separation of narirutin using a chiral high performance liquid chromatography with ultraviolet detection method with cellulose tris(3,5-dichlorophenylcarbamate) as the stationary phase under normal-phase mode. The mobile phase comprised n-hexane and ethanol (containing 0.25% formic acid) at a proportion of 65 : 35 (v/v) with a flow rate of 0.6 mL min⁻¹. Each single epimer of chiral flavanone glycosides was prepared using chiral semi-preparative chromatography, and the absolute configuration was then characterized by combining the experimental electronic circular dichroism detection and time-dependent density functional theory calculations. The epimer composition of each chiral flavonoid glycoside in Fructus aurantii (Zhiqiao) and Fructus aurantii immaturus (Zhishi) was determined revealing variations among herbs collected from different production regions. Additionally, the epimer composition was found to be related to the harvesting time of the herbs. Considering the safety and efficacy, the existence of epimers of different stereo-configurations should be given more attention in the quality evaluation of natural drugs.