Isolation, antihypertensive activity and structure activity relationship of flavonoids from three medicinal plants

Abstract

Eight flavonoids, namely naringenin <b>1</b>, 3-β-hydroxynaringenin designated as isoaromadendrin <b>2</b>, taxifolin <b>3</b>, isoaromadendrin-7-O-β-D-glucopyranoside designated as isosinensin <b>4</b> have been isolated from <i>Euphorbia cuneata</i> Vahl; 5-hydroxy-3, 4′, 7-trimethoxyflavone <b>5</b>, 5-hydroxy-3, 3′, 4′, 7-tetramethoxyflavone (retusin) <b>6</b>, 4′, 5-dihydroxyflavone-5-O-β-D-glucopyranoside named as verbenacoside <b>7</b> are obtained from <i>Salvia verbenaca</i> L; and epicatchin <b>8</b> is isolated from <i>Osyris abyssinica</i>. Their structures have been established by spectral and chemical methods, whereupon the compounds <b>2</b>, <b>4</b> and <b>7</b> are found to be new flavonoids. Compounds <b>1-5, 7, 8</b> and alcoholic extract of <i>Salvia verbenaca</i> have also been screened biologically for antihypertensive activity in normotensive albino rats, which showed a varied degree in the decrease of blood pressure and heart rate. The flavonoids <b>2, 3</b> and <b>5</b> are found most potent exhibiting the decrease in blood pressure 36.5, 20.0 and 30.0 (mmHg) respectively in comparison to normal values. Other compounds also exhibit a good activity. The structure activity relationship (SAR) has also been discussed.