Competition of monomolecular and bimolecular reactions of the alkyl radicals of artemisinin

Intramolecular chain reaction of artemisinin oxidation

“…A comparison of the rate constants showed that for radicals R(5a) • and R(12) • the intramolecular hydrogen atom abstraction reactions R(5a) • R(8a) • (k = 1.30•10 9 s -1 ) and R(12) • R(8a″) • (k = 6.05•10 7 s -1 ) occur more rapidly. 7 Only after completion of these reactions, new alkyl radicals add oxygen with the specific rate k О 2 [О 2 ] = 3.5•10 6 s -1 to form peroxy radicals RO 2 • . For other alkyl radicals, namely, R(4) • , R(7) • , R(5a) • , and R(8a´) • , the oxygen addition reaction predominates.…”

“…6,7 In the case of the alkoxy radicals, the reactions involving the intramolecu lar hydrogen transfer and decyclization of these radicals were shown to prevail. 6 As a result, the free valence is retained on artemisinin as one of its alkyl radicals.…”

“…Under anaerobic conditions, the intramolecular reactions of the alkyl radicals of artemisinin also prevail over their bimo lecular reactions with the substrates. 7 The C centered radicals of artemisinin formed in these reactions are capable of fast adding oxygen to trans form into peroxy radicals. These reactions occur in the liquid phase with a diffusion controlled rate constant of 10 9 -10 10 L mol -1 s -1 .…”

Artemisinin as a self-propagating radical initiator under aerobic conditions

“…6,7 For alkoxy radicals, intramolecular hydrogen transfer and decyclisation predominate; as a result, a free valence is retained on artemisinin in the form of its alkyl radical. For alkyl radicals of artemisinin, intramolecular reactions also predominate over bimolecular reactions with substrates under anaerobic conditions.…”

Reactions of alkoxy and peroxy radicals formed upon the decomposition of hydroxyperoxide groups in the artemisinin derivatives

“…In our previous studies 7, 8 the problems of competition of intramolecular and bimolecular reactions of alkoxy and alkyl radicals generated from artemisinin were considered at the quantitative level. It was found 7,8 that the alkoxy radical formed upon the cleavage of the peroxide bridge react very rapidly in intramolecular reactions with hydro gen atom transfer and decyclization, transforming into the C centered radicals.…”