First determination of the standard potential for the dissociative reduction of the antimalarial agent artemisinin

The reduction of the known antimalarial agent Artemisinin (ART) has been studied in N,N-dimethylformamide (DMF) by cyclic voltammetry and other electrochemical techniques. ART undergoes an irreversible, dissociative reduction with an anodic peak potential (E-p) that varies with scan rate and is -1.68 V vs SCE at 1 V/s. Direct electrochemical reduction of ART is subject to a large activation overpotential, and thus the E-p's do not provide an accurate value of the standard reduction potential (E-diss(ART(o))) required for the determination of the free energy of electron transfer from possible biological electron donors (Delta G(ET)(o) = F(E-D(o).+(/D) - E-diss(ART(o)))). Using careful heterogeneous electrochemical methods with convolution analysis, the standard potential of the dissociative reduction of ART (E-diss(ART(o))) has been determined for the first time to be -0.89 V versus SCE in DMF. This value is ca. 0.8 V more positive than the irreversible direct reduction observed using cyclic voltammetric measurements. In addition, the value E-diss(ART(o)) allows the estimation of the O-O bond dissociation energy. The thermochemical values determined are important to understanding ART's biological activity and investigating its potential for undergoing electron-transfer-initiated processes with biological donors.