Two new flavonoids and other constituents in licorice root. Their relative astringency and radical scavenging effects.

Four compounds, including two new flavonoids, were isolated from Si-pei licorice (licorice from the north-western region of China). The structures of the two new flavonoids, named glycyrrhisoflavanone and glycyrrhisoflavone, were (S)-7, 8'-dihydroxy-2', 2'-dimethyl-5-methoxy-[3, 6'-bi-2H-1-benzopyran]-4(3H)-one (6) and 3-[3, 4-dihydroxy-5-(3-methyl-2-butenyl)phenyl]-5, 7-dihydroxy-4H-1-benzopyran-4-one (9). Glycyrrhisoflavone was found to be one of the tannic substances by the measurement of the binding activity to hemoglobin (relative astringency). Licochalcone B (1) was isolated from the fraction which showed the highest binding activity to hemoglobin among the fractions obtained by centrifugal partition chromatography of the extract of Sinkiang licorice (licorice from Sinkiang in China). Licochalcone B also showed the highest activity as a radical scavenger in the experiment using 1, 1-diphenyl-2-picrylhydrazyl radical, among ten tested compounds obtained from several licorices. The order of the radical scavenging effects was the same as the order of the inhibitory effects on the 5-lipoxygenase-dependent peroxidation in arachidonate metabolism [licochalcone B (1)>licochalcone A (3)>>isoliquiritigenin (14)>liquiritigenin (13)].