Screening of ethnomedicinal plants for antimalarial and chemopreventive activities among plants used in Cameroonian folklore medicine to treat fevers, malaria and tumour was conducted on Croton oligandrus (Euphorbiaceae), Justicia hypocrateriformis (Acanthanceae), Pseudospondias microcarpa (Anacardiaceae), Zanthoxylum lepreurii and Zanthoxylum zanthoxyloides (Rutaceae). The selection of plants was based on ethnomedicinal use and literature review. Bioassay-guided isolation of active components from the active plants was performed with the aim to scientifically validate their folklore usage. The plant materials were dried, ground, and Soxhlet-extracted, successively, with n-hexane, dichloromethane (DCM) and methanol (MeOH). The antimalarial and chemopreventive potential of the plants were evaluated using haem polymerisation and the luciferase assays, respectively. The n-hexane and the DCM extracts of C. oligandrus, and the DCM and MeOH extracts of Z. zanthoxyloides were the most active in the luciferase assay causing 18, 21, 34 and 36-fold induction of the level of luciferase in AREc32 cells, respectively. Pseudospondias microcarpa was the most active antimalarial plant with IC50 values of 73.9 ± 25.8, 2.5 ± 1.5 and 4.0 ± 1.7 µM for the stem bark n-hexane, DCM and MeOH extracts, respectively, and 13.0 ± 9.0 µM for the leaves MeOH extract. Fifty-one compounds including eleven novel ones were isolated from active fractions using column chromatography, thin layer chromatography and reversed-phase high-pressure liquid chromatography. Structural elucidation was carried out by spectroscopic means including 1D and 2D NMR and mass spectrometry. Crotonolins A-D, skimmianine, hesperidin and myrtopsine were identified as potent chemopreventive compounds with fold induction greater than 2. None of the isolated compounds demonstrated any inhibition of haem polymerisation. This study generated the first phytochemical report on P. microcarpa, the second of C. oligandrus and the third of J. hypocrateriformis. The biogenesis and chemotaxonomy of isolated compounds have also been discussed
