In this study the in vitro antiplasmodial activities of extracts from Cussonia spicata (Araliaceae), Artemisia afra, Vernonia colorata, V. natalensis (Asteraceae), Parinari curatellifolia (Chrysobalanaceae), Clutia hirsuta, Flueggea virosa, (Euphorbiaceae), Adenia gummifera (Passifloraceae) and Hymenodictyon floribundum, (Rubiaceae) were evaluated. The lipophilic extracts from the aerial parts of Artemisia afra and Vernonia colorata proved to be the most active against the chloroquine-sensitive strain PoW and against the chloroquine-resistant clone Dd2 of Plasmodium falciparum. Bioassay-guided fractionation of the extract of A. afra yielded seven flavonoids, from which acacetin, genkwanin and 7-methoxyacacetin showed in vitro activity; the IC(50) values ranged from 4.3 microgram/mL to 12.6 microgram/mL. In addition, several sesquiterpene lactones could be obtained from the most active fractions. Whereas eudesmaafraglaucolide proved to be inactive, the guaianolides 1-desoxy-1alpha-peroxy-rupicolin A-8-O-acetate, 1alpha,4alpha-dihydroxybishopsolicepolide and rupicolin A-8-O-acetate revealed in vitro antiplasmodial activity. Evaluation of V. colorata gained four sesquiterpenes 11beta,13-dihydrovernodalin, vernodalol, 11beta,13-dihydrovernolide and 11beta,13,17,18-tetrahydrovernolide, from which the first two constituents exhibited the strongest antiplasmodial activity (IC(50) values: 1.1-4.8 microgram/mL).

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Different extracts from 11 West African plants traditionally used against malaria in Ghana were tested against both the chloroquine-sensitive strain PoW and the chloroquine-resistant clone Dd2 of Plasmodium falciparum. Due to the promising in vitro activity of the lipophilic extract [IC50: 10.5 μg/ml (PoW); 13.1 μg/ml (Dd2)], Microglossa pyrifolia (Lam.) Kuntze (Asteraceae) was chosen for further phytochemical investigation. From active fractions 13 compounds were isolated; their structures were established on the basis of spectroscopic methods. 1-Acetyl-6E-geranylgeraniol-19-oic acid and sinapyl diangelate represent new natural compounds. The two diterpenes E-phytol [IC50: 8.5 μм (PoW); 11.5 μм (Dd2)], and 6Egeranylgeraniol- 19-oic acid [IC50: 12.9 μм (PoW); 15.6 μм (Dd2)] proved to be the most active constituents in our test system.