Coordination dynamics of iron enables the selective C–N coupling but bypasses unwanted C–H hydroxylation in Fe(II)/α-ketoglutarate- dependent non-heme enzymes

Abstract

Non-heme Fe(II)/α-ketoglutarate (αKG)-dependent enzymes catalyze numerous C–H activation and functionalization reactions. However, how αKG-dependent non-heme enzymes catalyzed C–H functionalization beyond the hydroxylation is largely unknown. Here, we addressed this issue in Fe(II)/ αKG-dependent oxygenase TqaL_Nc, which catalyzes the selective C–H amination but bypasses the thermodynamically favored C–H hydroxylation. Here, the extensive computational studies have shown that the aziridine formation involves the conformational change of the Fe(IV)=O species from the axial configuration to the equatorial one, the substrate deprotonation of NH₃⁺ group to form the NH-ligated intermediate, the C–H activation by the equatorial Fe(IV)=O species. Such mechanistic scenario has been cross-validated by oxidation of various substrates by TqaL_Nc and its variants, including the available experiments and our new experiments. While the presence of steric hindrance between the substrate and the second-sphere residues would inhibit the aziridination process, the intrinsic reactivity of aziridination vs. hydroxylation is dictated by the energy splitting between two key redox-active dπ* frontier molecular orbitals: dπ*_Fe-N and dπ*_Fe-OH. The present findings highlight the key roles of the coordination change and dynamics of iron cofactor in dictating the catalysis of non-heme enzymes and have far-reaching implications for the other non-heme Fe(II)/αKG-dependent enzymes catalyzed C–H functionalization beyond the hydroxylation.