Scheme 1.

The intermediates formed during the cytochrome P450 catalytic cycle (addition of dioxygen, two protons and two electrons, black) and the peroxide shunt mechanism (addition of hydrogen peroxide, blue). Potential active oxidants for sulfoxidation formed during CYP199A4 turnovers are highlighted (Fe(III)‐H₂O₂, Cpd 0 and Cpd I). Shaik and coworkers have also proposed that Cpd I could be formed from the Fe(III)‐H₂O₂ species in hydrogen peroxide‐driven reactions via an O−O homolysis/H‐atom abstraction mechanism.[ ^2a , ⁶ ]