Cytochrome P450 enzymes catalyze a number of oxidations in nature including hydroxylation of hydrocarbons.  The iron-oxo species, oxygen bound to iron in the formal oxidation state of Fe(V), has long been thought to be the electrophilic oxidant, but multiple reaction pathways appear to be necessary to explain the results of mechanistic probe studies.  Recent kinetic isotope effect studies in our lab demonstrated that a second oxidizing species (presumed to be a hydroperoxy-iron complex or iron-complexed hydrogen peroxide) effects oxidations P450.

Radical Cation Clocks were recently developed for kinetic studies of enol ether radical cations and the reaction that form these species.  The work involved using laser flash photolysis to make radicals that cleave heterolytically to give radical cations.  The radical cations then cyclized to give distonic radical cations that have a strong chromophore in the UV.  Scheme 1 below shows one series of reactions. 

Coenzyme B-12-dependent enzymes catalyze a number of radical conversions in nature.  The synthetic sequence in Scheme 2 below gives a radical precursor for laser flash photolysis studies of the reaction catalyzed by methylmalonyl Co-A mutase, a reversible radical isomerization of succinyl-CoA to methylmalonyl-CoA.  The SePh group in the precursor can be cleaved by laser irradiation or in a radical chain reaction.  The diphenylcyclopropyl group is a “reporter” that will give a diphenylalkyl radical that can be detected by UV as in the reaction in Scheme 1.

Scheme 2.  Synthetic sequence for a radical precursor for use in studies of the radical rearrangement catalyzed by methylmalonyl-CoA mutase.