Substrate Conformation Masquerades Two different Oxidants in Aromatic C-H and C-F bond activation by Heme-dependent Tyrosine Hydroxylase

A recently discovered heme-dependent enzyme 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 intermediates (Cpd 0 or Cpd I) involved in activating these bonds. Herein, using comprehensive MD Simulations and hybrid QM/MM calculations, we reveal that it is Compound I (Cpd I) that acts as the primary oxidant involved in the functionalization of both the C-F and C-H bonds. Our study shows that the His88 close to the catalytic site acts as a modulator of aromaticity and is essential to initiate the C-H and C-F bond activation. The reaction proceeds via the proton abstraction from the 4-OH group of the substrate by His88, which is coupled with an electron transfer to form a single-electron reduced Cpd I-like intermediate. This species then inserts the oxygen atom into the sp3 hybridized C-H and C-F bond of the substrate. Interestingly, our mechanistic study shows that the two different conformations of the substrate are actually responsible for the C-F and C-H functionalization, which masquerades as two different characters of oxidants involved in the reaction.