Substrate Conformation Regulates Aromatic C–H Vs C–F Bond Activation in Heme-Dependent Tyrosine Hydroxylase

A recently discovered heme-dependent enzyme tyrosine hydroxylase (TyrH) offers a green approach for functionalizing the high-strength C–H and C–F bonds in aromatic compounds. However, there is ambiguity regarding the nature of the oxidant (compound 0 or compound I) involved in activating these bonds. Herein, using comprehensive molecular dynamics (MD) simulations and hybrid quantum mechanical/molecular mechanical calculations, we reveal that it is compound I (Cpd I) that acts as the primary oxidant involved in the functionalization of both C–F and C–H bonds. The energy barrier for C–H and C–F activation using compound 0 (Cpd 0) as an oxidant was very high, indicating that Cpd 0 cannot be an oxidant. Consistent with the previous experimental finding, our simulation shows two different conformations of the substrate, where one orientation favors the C–H activation, while the other conformation prefers the C–F activation. As such, our mechanistic study shows that nature utilizes just one oxidant, that is, Cpd I, but it is the active site conformation that decides whether it selects C–F or C–H functionalization which may resemble involvement of two different oxidants.