Dynamic Relationships between Bioactive 2'-Hydroxychalcones and their Flavanone Isomers in Licorice (Glycyrrhiza glabra L. and Glycyrrhiza uralensis Fisch. ex DC.)

Flavanones and their 2'-hydroxychalcones isomers are biosynthetically related and chemically interchangeable. This relationship is defined as a dynamic equilibrium, exemplifying the notion of residual complexity in natural compounds.¹ We demonstrated recently that the interconversion between the flavanone liquiritigenin (LigF) and its chalcone isomer, isoliquiritigenin (LigC), can occur during bioassays, reaching a final LigF/LigC proportion of 9:1.¹ The LigF/LigC equilibrium also affects their glycosides derivatives, which are the major phenolic compounds in licorice roots.² Together, these flavanones/chalcones (F/C) pairs support the overall estrogenicity of licorice extracts.³ Hence, the determination of all major F/C pairs is proposed as an important parameter for the characterization of licorice preparations used to alleviate menopausal symptoms. Extracts from three batches of DNA-authenticated G. glabra L., and G. uralensis Fisch. ex DC. (Fabaceae) were analyzed by orthogonal UHPLC-UV and qHNMR methods. It was observed that each entity of all glycosylated LigF/LigC pair coexists in the extract, and that their equilibration rate depends on the site of glycosidation. Interestingly, extracts from G. glabra could be differentiated from those obtained from G. uralensis according to their F/C composition.

(1) Simmler, C. et al. JAFC, 2013 (2) Nomura, T. et al. Pure Appl Chem.2002, (3) Hajirahimkhan, A.et al. PLoS One, 2013, in press