HPLC separation of naringin, neohesperidin and their C-2 epimers in commercial samples and herbal medicines.

Flavanone glycosides, such as naringin and neohesperidin, are distributed in some Citrus species and have a chiral center in the C-2 position of the flavanone moiety. Naringin and neohesperidin (2S-form) were separated from the corresponding C-2 epimers (2R-epi-form) by normal-phase HPLC using a polysaccaride-derived chiral stationary phases (CSPs), CHIRALPAK IB. The analyses of commercial samples of naringin revealed that the relative ratios of naringin to the C-2 epimer were 29-89%. In the case of a commercial sample of neohesperidin, the relative ratio of the neohesperidin (2S-form) is 84%. The HPLC application to Citrus species used as crude drugs in Japan (Kijitsu, Kikoku and Tohi) showed that the relative ratios of naringin to the C-2 epimer were 75-93% in Kijitsu, 74-79% in Kikoku and 54-64% in Tohi. However, there is a quite small ratio of the (2R)-epi-neohesperidin in Citrus. This result suggested that the averages of relative ratio of (2S)-naringin in Citrus species reduced according to the maturity of fruits (Kijitsu<Kikoku<Tohi). Since the relative ratios of (2S)-naringin of dry extracts of 5 Kampo formulations (including Kijitsu or Kikoku) decreased to 42-54%, the conversion from naringin to the (2R)-epimer might be enhanced during the decoction process of the formulations.