Antiprotozoal activity of Achillea ptarmica (Asteraceae) and its main alkamide constituents

In the course of our ongoing screening of plants of the family Asteraceae for antiprotozoal activity, a CH2Cl2-extract from the flowering aerial parts of Achillea ptarmica L. (sneezewort yarrow) was found to be active in vitro against Trypanosoma brucei rhodesiense (IC50 = 0.67 µg/mL) and Plasmodium falciparum (IC50 = 6.6 μg/mL). Bioassay guided fractionation led to the isolation and identification of five alkamides from the most active fractions. Pellitorine and 8,9-Z-dehyropellitorine are the main components of the extract. Beside these olefinic acid amides, four alkamides with diene-diyne structures were isolated. All alkamides were tested for antiprotozoal activity in vitro. Pellitorine was the most active compound so far within this study against P. falciparum (IC50 = 3.3 µg/mL), while 8,9-Z-dehydropellitorine was most active against T. b. rhodesiense (IC50 = 2.0 µg/mL). The activity of pure pellitorine against Plasmodium is higher than that of the crude extract and thus explains the activity of the latter. None of the isolated alkamides, however, was as active against T. b. rhodesiense as the crude extract whose antitrypanosomal activity must therfore be due to a synergistic effect of the isolated compounds or to more active yet to be identified constituents.