Isolation and Antiprotozoal Effects of Two Sesquiterpene Lactones from Ptilostemon chamaepeuce subsp. cyprius (Asteraceae)

In continuation of our recent report on the antileishmanial activity of an ethanolic extract from leaves of Ptilostemon chamaepeuce subsp. cyprius (Pcc, Asteraceae), we have now isolated the main sesquiterpene lactone, deacylcynaropicrin, along with a minor derivative, 13-hydroxy-11β,13-dihydro-deacylcynaropicrin. The main constituent was tested for antileishmanial activity against promastigotes and amastigotes of Leishmania infantum (Lin), the causative agent of visceral leishmaniasis. Both STLs were tested against additional protozoan pathogens, including L. donovani, Trypanosoma brucei rhodesiense (Tbr), and Plasmodium falciparum. The STL cynaropicrin from Artichoke (Cynara cardunculus), a congener of deacylcynaropicrin with a hydroxymethacrylate ester group, previously known to possess antiprotozoal activity, was retested against Lin for direct comparison. Cynaropicrin was found to be much more potent than either its deacyl congener or the hydroxylated derivative from Pcc against all tested parasites and also against an isolated parasite enzyme, Tbr pteridine reductase (TbPTR1). The ester moiety of cynaropicrin significantly enhances the antiprotozoal activity of this STL. Since cynaropicrin also displayed significant cytotoxicity against mammalian cells (L6 and J774A.1 cell lines), its utility as candidate for further development appears limited. However, this study provides valuable new insight into the structure–activity relationships of these compounds.