Mechanism for the synthesis of medium-chain 1-alkenes from fatty acids catalyzed by binuclear iron UndA decarboxylase

Terminal olefins synthesized by the decarboxylation of fatty acids are important platform chemicals. PfUndA is a nonheme di-iron oxidase capable of converting medium-chain (C10 ∼ C14) fatty acids into the corresponding 1-alkenes. Using density functional theory calculations, it is demonstrated that the PfUndA-catalyzed lauric acid decarboxylation is initiated by introducing one pair of H+/e−. The subsequent reaction mainly involves the O − O bond dissociation, the partial interconversion between active high-spin Fe(III)-O• and inactive medium-spin Fe(IV) = O, the formation of triple-hydroxyl intermediates and substrate Cβ radical resulted from successive hydrogen transfers, the stepwise decarboxylation of substrate radical, and the protonation of Fe-bound hydroxides with H+ and e− added. Other mechanistic possibilities have been excluded. It is further found that the low catalytic efficiency of UndA may be due to the energy penalty caused by the drop of active high-spin Fe(III)-O• to a deeper minimum (inert medium-spin Fe(IV) = O).