Chemistry of phenolic compounds of licorice (Glycyrrhiza species) and their estrogenic and cytotoxic activities

The genus Glycyrrhiza consists of about 30 species in which G. glabra, G. uralensis, G. inflata, G. aspera, G. korshinskyi, and G. eurycarpa are generally recognized as licorice because of their sweet taste. Except G. korshinskyi, we examined isoprenoid-substituted phenols of these licorices. Each plant could be characterized by some isoprenoid phenols. We also investigated the biological activities of the Glycyrrhiza phenols. In the course of screening phytoestrogen in medicinal plants, six Glycyrrhiza phenols exhibited the binding affinities for the bovine uterine estrogen receptor. The affinity of a dihydrostilbene with two 3-methyl-2-butenyl (prenyl) groups, gancaonin R, was higher than those of isoflavone phytoestrogens (genistein and daidzein) in dietary foods. The affinities of the other five phenols, a flavanone (liquiritigenin), two prenylflavanones (isobavachin and sigmoidin 13), a prenylated coumestan (glycyrol), and a pyranoisoflav-3-ene (glabrene), were similar to that of the dietary isoflavone, genistein or daidzein. Cytotoxic activities of the Glycyrrhiza phenols against human oral tumor cell lines and HIV-infected MT-4 cells were also reviewed.