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Spiro- and Dispiro-1,2-dioxolanes:  Contribution of Iron(II)-Mediated One-Electron vs Two-Electron Reduction to the Activity of Antimalarial Peroxides

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journal contribution
posted on 15.11.2007, 00:00 by Xiaofang Wang, Yuxiang Dong, Sergio Wittlin, Darren Creek, Jacques Chollet, Susan A. Charman, Josefina Santo Tomas, Christian Scheurer, Christopher Snyder, Jonathan L. Vennerstrom
Fourteen spiro- and dispiro-1,2-dioxolanes were synthesized by peroxycarbenium ion annulations with alkenes in yields ranging from 30% to 94%. Peroxycarbenium ion precursors included triethylsilyldiperoxyketals and -acetals derived from geminal dihydroperoxides and from a new method employing triethylsilylperoxyketals and -acetals derived from ozonolysis of alkenes. The 1,2-dioxolanes were either inactive or orders of magnitude less potent than the corresponding 1,2,4-trioxolanes or artemisinin against P. falciparum in vitro and P. berghei in vivo. In reactions with iron(II), the predominant reaction course for 1,2-dioxolane 3a was two-electron reduction. In contrast, the corresponding 1,2,4-trioxolane 1 and the 1,2,4-trioxane artemisinin undergo primarily one-electron iron(II)-mediated reductions. The key structural element in the latter peroxides appears to be an oxygen atom attached to one or both of the peroxide-bearing carbon atoms that permits rapid β-scission reactions (or H shifts) to form primary or secondary carbon-centered radicals rather than further reduction of the initially formed Fe(III) complexed oxy radicals.

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