Dihydroxylation, of aromatic

Dioxygenases usually contain a tightly bound iron atom and catalyze hydroperoxidation of allylic molecules or carboxylic acids, and dihydroxylation of aromatics (Figure 1.5) [33]. 

Hudlicky, T., Tian, X., Konigsberger, K., Mauiya, R., Rouden, J. and Fan, B. (1996c) Toluene-dioxygenase-mediated as-dihydroxylation of aromatics in enantioselective synthesis. Asymmetric total syntheses of pancratistatin and 7-deoxypancratistatin, promising antitumor agents. J. Am. Chem. Soc., 118, 10752-10765. 

Cis-dihydroxylation of aromatic substrates is catalysed by naphthalene 1,2-dioxygenase (NDO), which comprises a Rieske Fe-S cluster and non-haem iron... 

Hudlicky T, Gonzalez D, Gibson DT (1999) Enzymatic Dihydroxylation of Aromatics in Enantioselective Synthesis Expanding Asymmetric Methodology. Aldrichimica Acta 32 35... 

Hudlicky, T., Gonzalez, D., and Gibson, D. T. 1999. Enzymatic dihydroxylation of aromatics in enantioselective synthesis expanding asymmetric methodology. Aldrichimica Acta, 32(2), 35-62. 

The class of mononuclear dioxygenases [30] can e.g. perform hydroperoxidation of lipids, the cleavage of catechol and dihydroxylation of aromatics. A prominent example is naphthalene dioxygenase, which was the first identified by its crystal structure. It contains iron and a Rieske (2Fe-2S) cluster and is commonly referred to as a Rieske-type dioxygenase [33]. The iron in this case is flanked by two histidines and one aspartic acid residue. Among the mononuclear iron enzymes, the 2-His-l-carboxylate is a common motif, which flanks one-side of the iron in a triangle and plays an important role in dioxygen activation [34] (Fig. 4.17). 

A wide range of soluble redox enzymes contain one or more intrinsic [2Fe-2S]2+ +, [3Fe-4S]+ , or [4Fe S]2+ + clusters that function in electron transport chains to transfer electrons to or from nonheme Fe, Moco/Wco, corrinoid, flavin, thiamine pyrophosphate (TPP), Fe S cluster containing, or NiFe active sites. Many have been structurally and spectroscopically characterized and only a few of the most recent examples of each type are summarized here. Dioxygenases that function in the dihydroxylation of aromatics such as benzene, toluene, benzoate, naphthalene, and phthalate contain a Rieske-type [2Fe-2S] + + cluster that serves as the immediate electron donor to the monomeric nonheme Fe active site see Iron Proteins with Mononuclear Active Sites). The xanthine oxidase family of molybdoenzymes see Molybdenum MPT-containing Enzymes) contain two [2Fe-2S] + + clusters that mediate electron transfer between the Moco active site and the Other soluble molybdoen-... 

Di-oxygenase Dihydroxylation of aromatics Whole-cell systems Isolated enzymes... 

A variety of biochemical pathways are known which may lead to reactive quinoid derivatives. They include dihydroxylation of aromatic or heterocyclic compounds and epoxide formation and hydrolysis to -diphenolic compounds (Booth and Boyland 1957) o- and p-hydroxylations of phenols or arylamines (In-SCOE et al. 1965 Miller et al. 1960 Booth and Boyland 1957) and rearrangement of -hydroxyarylamines to o-aminophenols (Miller and Miller 1960). It now appears that aromatic hydroxylations proceed via highly reactive arene oxides, i.e., compounds in which a formal aromatic double bond has undergone epoxidation. Depending on the compound, arene oxides may give rise to other electrophilic reactive species, including quinoid structures, but react as such readily with nucleophiles and thus provide a basis for understanding covalent attachment of aromatic hydrocarbon derivatives to protein and nucleic acids (Jerina and Daly 1974). 

The development of enzymatic dihydroxylation of aromatics has enabled synthetic access to a large collection of cyclohexadiene diols in enantiopure form. 

While chemical methods for the controlled dihydroxylation of aromatic compounds are still missing, Rieske nonheme iron dioxygenases, are capable of regio- and stereoselective cis-dihydroxylation of aromatic compounds [149, 150]. The mechanism of this demanding oxidation where both atoms of dioxygen are incorporated into the cii-diol product has been carefully investigated [3d, 150a, 151]. 

Arene.. dioxygenases catalyze reactions other than dihydroxylation of aromatics. For example, toluene dioxygenase catalyzes monooxygenation of indene and indan to 1-indenol and 1-indanol, respectively [382], oxidation of polyhalogenated compounds such as trichloroethylene [eq. (24)] [363, 388-390], and stereoselective sulfoxidation of sulfides [391, 392]. 

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