Antibacterial compounds from Glycyrrhiza uralensis

From the roots of Glycyrrhiza uralensis, two new pterocarpenes, glycyrrhizol A (1) and glycyrrhizol B (2), along with four known isoflavonoids, 5-O-methylglycryol (3), isoglycyrol (4), 6,8-diisoprenyl-5,7,4'-trihydroxyisoflavone (5), and gancaonin G (6), were isolated using a bioassay-guided fractionation method. The structures of the new compounds (1and 2) were elucidated by spectroscopic data interpretation. The known compounds (3-6) were identified by comparison of their spectroscopic data with reported values in the literature. Glycyrrhizol A (1) and 6,8-diisoprenyl-5,7,4'-trihydroxyisoflavone (5) exhibited potent antibacterial activity against Streptococcus mutans with minimum inhibitory concentrations of 1 and 2 microg/mL, respectively, while glycyrrhizol B (2) and gancaonin G (6) showed more moderate activity.