Mimicking the Aromatic-Ring-Cleavage Activity of Gentisate-1,2-Dioxygenase by a Nonheme Iron Complex

Gentisate-1,2-dioxygenase (GDO), a nonheme iron enzyme in the cupin superfamily, catalyzes the cleavage of the aromatic-ring of 2,5-dihydroxybenzoic acid (gentisic acid) to form maleylpyruvic acid in the microbial aerobic degradation of aromatic compounds. To develop a functional model of GDO, we have isolated a nonheme iron(II) complex, [(Tp^Ph2)Fe^II(DHN-H)] (Tp^Ph2=hydrotris(3,5-diphenylpyrazole-1-yl)borate, DHN-H=1,4-dihydroxy-2-naphthoate). In the reaction with O₂, the biomimetic complex oxidatively cleaves the aromatic ring of the coordinated substrate with the incorporation of both the oxygen atoms from molecular oxygen into the cleavage product. The presence of para-hydroxy group on the substrate plays a crucial role in directing the aromatic-ring cleaving reaction.