Flavonoids isolated from the flowers of Pulsatilla flavescens and their anti-piroplasm activity.

Pulsatilla species are known as "Yargui", and their flowers are traditionally used in Mongolia as a tonic and for the treatment of inflammatory diseases. By chemical investigation of P. flavescens flowers, 21 flavonoids, including a new chalcone C-glucoside, chalconaringenin 2'-O-β-D-glucopyranosyl-5'-β-D-glucopyranoside, and two new flavanone C-glucosides, (2R)- and (2S)-naringenin 8-β-D-glucopyranosyl-4'-O-β-D-glucopyranoside, were isolated. The absolute configurations of the seven flavanone glucosides were elucidated by ECD spectra. For the isolated compounds, inhibitory activity against Babesia caballi and Theileria equi, which cause fatal diseases in horses, was estimated. Although most of the isolated chalcone and flavanone derivatives did not show any anti-piroplasm activity, all the isolated flavone and flavonol derivatives showed moderate effects against B. caballi and/or T. equi.