A novel dimeric flavonol glycoside from <i>Cynanchum acutum</i> subsp. <i>sibiricum</i>

<p>A novel dimeric flavonol glycoside, Cynanflavoside A (<b>1</b>), together with six analogues, kaempferol-3-<i>O</i>-<i>α</i>-L-rhamnopyranosyl-(1→2)-<i>β</i>-D-glucopyranoside (<b>2</b>), quercetin-3-<i>O</i>-<i>α</i>-L-rhamnopyranosyl-(1→2)-<i>β</i>-D-glucopyranoside (<b>3</b>), kaempferol-3-<i>O</i>-<i>α</i>-L-rhamnopyranosyl-(1→2)-<i>β</i>-D-xylopyranoside (<b>4</b>), quercetin-3-<i>O</i>-<i>α</i>-L-rhamnopyranosyl-(1→2)-<i>β</i>-D-xylopyranoside <b>(5)</b>, kaempferol-3-<i>O</i>-<i>β</i>-D-glucopyranosyl-7-<i>O</i>-<i>α</i>-L-rhamnopyranoside (<b>6</b>), and quercetin-3-<i>O</i>-galactoside (<b>7</b>) were isolated from the <i>n</i>-butyl alcohol extract of <i>Cynanchum acutum</i> subsp. <i>sibiricum</i>. Their structures were determined spectroscopically and compared with previously reported spectral data. All compounds were evaluated for their anti-complementary activity <i>in vitro</i>, and only compound <b>5</b> exhibited anti-complement effects with CH₅₀ value of 0.33 mM.