Alkamides from Anacyclus pyrethrum L. and Their in Vitro Antiprotozoal Activity.

In our ongoing study to evaluate the antiprotozoal activity of alkamides from Asteraceae, a dichloromethane extract from the roots of Anacycluspyrethrum L. showed a moderate in vitro activity against the NF54 strain of Plasmodium falciparum and against Leishmaniadonovani (amastigotes, MHOM/ET/67/L82 strain). Seven pure alkamides and a mixture of two further alkamides were isolated by column chromatography followed by preparative high performance liquid chromatography. The alkamides were identified by mass- and NMR-spectroscopic methods as tetradeca-2E,4E-dien-8,10-diynoic acid isobutylamide (anacycline, 1), deca-2E,4E-dienoic acid isobutylamide (pellitorine, 2), deca-2E,4E,9-trienoic acid isobutylamide (3), deca-2E,4E-dienoic acid 2-phenylethylamide (4), undeca-2E,4E-dien-8,10-diynoic acid isopentylamide (5), tetradeca-2E,4E,12Z-trien-8,10-diynoic acid isobutylamide (6), and dodeca-2E,4E-dien acid 4-hydroxy-2-phenylethylamide (7). Two compounds-undeca-2E,4E-dien-8,10-diynoic acid 2-phenylethylamide (8) and deca-2E,4E-dienoic acid 4-hydroxy-2-phenylethylamide (9)-were isolated as an inseparable mixture (1:4). Compounds 3, 4, and 5 were isolated from Anacycluspyrethrum L. for the first time. While compounds 4 and 5 were previously known from the genus Achillea, compound 3 is a new natural product, to the best of our knowledge. All isolated alkamides were tested in vitro for antiprotozoal activity against Plasmodium falciparum, Trypanosomabruceirhodesiense, Trypanosomacruzi, and Leishmaniadonovani and for cytotoxicity against L6 rat skeletal myoblasts.

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.

Antiprotozoal activity of Buxus sempervirens and activity-guided isolation of O-tigloylcyclovirobuxeine-B as the main constituent active against Plasmodium falciparum.

Buxus sempervirens L. (European Box, Buxaceae) has been used in ethnomedicine to treat malaria. In the course of our screening of plant extracts for antiprotozoal activity, a CH2Cl2 extract from leaves of B. sempervirens showed selective in vitro activity against Plasmodium falciparum (IC50 = 2.79 vs. 20.2 µg/mL for cytotoxicity against L6 rat cells). Separation of the extract by acid/base extraction into a basic and a neutral non-polar fraction led to a much more active and even more selective fraction with alkaloids while the fraction of non-polar neutral constituents was markedly less active than the crude extract. Thus, the activity of the crude extract could clearly be attributed to alkaloid constituents. Identification of the main triterpene-alkaloids and characterization of the complex pattern of this alkaloid fraction was performed by UHPLC/+ESI-QTOF-MS analyses. ESI-MS/MS target-guided larger scale preparative separation of the alkaloid fraction was performed by 'spiral coil-countercurrent chromatography'. From the most active subfraction, the cycloartane alkaloid O-tigloylcyclovirobuxeine-B was isolated and evaluated for antiplasmodial activity which yielded an IC50 of 0.455 µg/mL (cytotoxicity against L6 rat cells: IC50 = 9.38 µg/mL). O-tigloylcyclovirobuxeine-B is thus most significantly responsible for the high potency of the crude extract.