Pyrano-isoflavans from Glycyrrhiza uralensis with Antibacterial Activity against Streptococcus mutans and Porphyromonas gingivalis

Continuing investigation of fractions from a supercritical fluid extract of Chinese licorice (Glycyrrhiza uralensis) roots has led to the isolation of 12 phenolic compounds, of which seven were described previously from this extract. In addition to these seven metabolites, four known components, 1-methoxyerythrabyssin II (4), 6,8-diprenylgenistein, gancaonin G (5), and isoglycyrol (6), and one new isoflavan, licorisoflavan C (7), were characterized from this material for the first time. Treatment of licoricidin (1) with palladium chloride afforded larger amounts of 7 and also yielded two new isoflavans, licorisoflavan D (8), which was subsequently detected in the licorice extract, and licorisoflavan E (9). Compounds 1-9 were evaluated for their antibacterial activities against the cariogenic Streptococcus mutans and the periodontopathogenic Porphyromonas gingivalis. Licoricidin (1), licorisoflavan A (2), and 7-9 showed antibacterial activity against P. gingivalis (MICs of 1.56-12.5 μg/mL). The most potent activity against S. mutans was obtained with 7 (MIC of 6.25 μg/mL), followed by 1 and 9 (MIC of 12.5 μg/mL). This study provides further evidence for the therapeutic potential of licorice extracts for the treatment and prevention of oral infections.