Is 18α-Glycyrrhizin a real natural product? Improved preparation of 18α-Glycyrrhizin from 18β-Glycyrrhizin as a positive standard for HPLC analysis of licorice extracts.

Kritamorn Jitrangsri, Kazuaki Kamata, Mana Akiba, Yoshie Yajiri, Masami Ishibashi, Jin Tatsuzaki, Tsutomu Ishikawa

Journal of natural medicines 2022 Mar

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18α-Glycyrrhizin is an epimer of 18β-glycyrrhizin, a major component of licorice (Glycyrrhiza sp.), which is widely used as a traditional medicine. Whether 18α-glycyrrhizin is a real natural product has been debated in the long history of glycyrrhizin chemistry because 18β-glycyrrhizin is epimerizable to a more thermodynamically stable 18α-glycyrrhizin under aqueous alkali conditions. We improved the preparation of 18α-glycyrrhizin from 18β-glycyrrhizin by successive epimerization reactions of 18β-glycyrrhizin, trimethyl esterification of the resulting epimerized mixture, and alkaline hydrolysis of a purified 18α-glycyrrhizin trimethyl ester. Approaches to the possible presence of 18α-glycyrrhizin in licorice extracts by HPLC using synthetic 18α-glycyrrhizin as a positive standard strongly suggested that 18α-glycyrrhizin could naturally exist as a minor congener of glycyrrhizin derivatives in Glycyrrhiza species. © 2021. The Japanese Society of Pharmacognosy.

Citation

Kritamorn Jitrangsri, Kazuaki Kamata, Mana Akiba, Yoshie Yajiri, Masami Ishibashi, Jin Tatsuzaki, Tsutomu Ishikawa. Is 18α-Glycyrrhizin a real natural product? Improved preparation of 18α-Glycyrrhizin from 18β-Glycyrrhizin as a positive standard for HPLC analysis of licorice extracts. Journal of natural medicines. 2022 Mar;76(2):367-378