Artemisinin assay

The peroxide group is essential for neurotoxicity, and, depending on the assay, artemisinin could be considered relatively nontoxic or quite toxic. Removal of the oxygen atom at C-10 (10-deoxoartemisinin) resulted in a marked reduction in neurotoxicity. 

An additional step in the radical mechanism has been suggested namely, that collapse of C-4 radical intermediate 234 to a neutral but highly reactive alkoxy-epoxide 235 occurs (Scheme 5).104 Protein alkylation then presumably occurs via 235 and not radical intermediates such as 234. Unfortunately, epoxide 235 is probably too unstable to be handled or identified. In the case of 258 however, we were granted the opportunity to test the hypothesis that an intermediate epoxide was responsible for the mode of action. Of the series of three tetracycles, 258 retained nearly two-thirds of the activity of artemisinin. The Fe(II)-induced rearrangement product 281, a quite stable epoxide was submitted for antimalarial assay and found to be completely devoid of activity. As 258 is a potent antimalarial but the epoxide 281 is not, it seems reasonable to suggest that the antimalarial activity of 258 is unrelated to epoxy intermediates. 

In parallel, extensive studies on P. falciparum field isolates in Gabon [140-142], Senegal [143], Cambodia [118, 119, 144], and the Thailand Burmese border [145] corroborated the efficacy of FQ on the parasite whatever its resistance level to chloroquine or to other commonly used antimalarials mefloquine, quinine, halofantrine, and artemisinin derivatives [146, 147]. The cross reactivity observed in some studies with CQ was limited and it was demonstrated that it was caused by differences in initial parasitemia among isolates at the start of the assays [141]. Independance of susceptibility of P. falciparum with phenotypic variation of pfcrt gene, responsible for CQ resistance, could be suspected from these results, but this was demonstrated at the molecular level on Cambodia isolates [148] and extended further on other genes currently involved in resistance to aminoquinoline antimalarials [89, 90]. 

M.A. van Agtmael, J.J. Butter, E.J.G. Portier and C.J. van Boxtel, Validation of an improved reversed-phase high-performance liquid chromatography assay with reductive electrochemical detection for the determination of artemisinin derivatives in man, Ther. Drug Monit., 1998, 20, 109-116. 

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