Functional model oxygenations by nonheme iron complexes - Advances in Catalytic Activation of Dioxygen by Metal Complexes - page 162

that are ligated by 2 His and 1 Glu residues, 58, 59 but some enzymes are
known also to catalyze the extradiol cleavage of some type of catechols. 60-62

-

containing enzymes are known to catalyze the extradiol cleavage. 63,64

There is another group of catechol 1,2-dioxygenases, i.e. chlorocatechol
dioxygenases. Compared with ordinary catechol dioxygenases ( e.g. catechol 1,2-
dioxygenase, protocatechuate 3,4-dioxygenase), these enzymes exhibit the higher
activities and affinities toward chlorinated catechols, the higher selective intradiol
cleavage, and the higher affinities towards a wide range of substituted catechols
bearing electron-donating and -withdrawing groups. The presence of high-spin
Fe(III) in a rhombic environment with tyrosine coordination has been reported, but
evidence for the histidine coordination has not been obtained. 65, 66 Once chlorinated
aromatic compounds are converted to chlorocatechols, these enzymes oxygenate
them to chloromuconic acids that are dechlorinated to non-chlorinated acids by
cycloisomerases. This indicates that the enzymes can be good targets of the model
chemistry for development of catalysts that degrade halogenated pollutants.

3.1.1 Intradiol Cleavage Oxygenations
Functional model oxygenations were performed by using activated oxygen
species until early 80's in the absence of metals, singlet
and peroxo compounds 75-79 or in the presence of metals other