Pyrano-isoflavans from <i>Glycyrrhiza uralensis</i> with Antibacterial Activity against <i>Streptococcus mutans</i> and <i>Porphyromonas gingivalis</i>

Continuing investigation of fractions from a supercritical fluid extract of Chinese licorice (<i>Glycyrrhiza uralensis</i>) 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 (<b>4</b>), 6,8-diprenylgenistein, gancaonin G (<b>5</b>), and isoglycyrol (<b>6</b>), and one new isoflavan, licorisoflavan C (<b>7</b>), were characterized from this material for the first time. Treatment of licoricidin (<b>1</b>) with palladium chloride afforded larger amounts of <b>7</b> and also yielded two new isoflavans, licorisoflavan D (<b>8</b>), which was subsequently detected in the licorice extract, and licorisoflavan E (<b>9</b>). Compounds <b>1</b>–<b>9</b> were evaluated for their antibacterial activities against the cariogenic <i>Streptococcus mutans</i> and the periodontopathogenic <i>Porphyromonas gingivalis</i>. Licoricidin (<b>1</b>), licorisoflavan A (<b>2</b>), and <b>7</b>–<b>9</b> showed antibacterial activity against <i>P. gingivalis</i> (MICs of 1.56–12.5 μg/mL). The most potent activity against <i>S. mutans</i> was obtained with <b>7</b> (MIC of 6.25 μg/mL), followed by <b>1</b> and <b>9</b> (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