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

The competition between monomolecular and bimolecular reactions of alkyl radicals of artemisinin is considered theoretically. The enthalpies of these reactions are calculated. The activation energies and rate constants of intramolecular hydrogen atom transfer, of the decyclization of the alkyl radicals of artemisinin, and of the bimolecular reactions of these radicals with C-H, S-H, and O-H bonds of biological substrates and their analogues are calculated in the framework of the parabolic model. The intramolecular hydrogen transfer reactions proceed at the highest rate. The bimolecular reactions occur somewhat less rapidly. The fastest of them are the reactions of the alkyl radicals with the thio groups of cysteine. The decyclization reactions of all artemisinin alkyl radicals are very slow.