Naphthalene, dihydrodiol oxidation

Multistep biocatalysis for the preparation of optically pure epoxides was applied by Sello and coworkers [24, 25]. The commercially available 3-vinyl benzaldehyde was the substrate of choice for the synthesis of 3-(oxiran-2-yl) benzoic acid in high yields and optical purity by solely employing enzyme catalysis (Scheme 3.6). This goal was achieved by applying a mixed culture approach with different recombinant E. coli strains expressing, individually, both oxidizing biocatalysts. One strain contained a native ADH and a SMO from Pseudomonas Jiuorescens ST, while a second one expressed a naphthalene dihydrodiol dehydrogenase (NDDH) from P. Jiuorescens N3. 

Althongh the degradation of naphthalene-2-carboxylate by Burkholderia sp. strain JT 1500 involves the formation of 1-hydroxy naphthalene-2-carboxylate, this is not formed from the expected (l/ ,25)-di-l,2-dihydrodiol-2-naphthoate. Possibly, therefore, the reaction is carried out by a monooxygenase, or a dehydration step is involved. Subsequent reactions produced pyruvate and o-phthalate that was degraded via 4,5-dihydroxyphthalate (Morawski et al. 1997). Degradation of naphthalene carboxylates formed by oxidation of methyl groups has already been noted. 

Like for benzene, the cytotoxicity of naphthalene is not due to the epoxide but to the quinone metabolites, namely 1,2-naphthoquinone and 1,4-naphthoquinone [85], As shown in Table 10.1, naphthalene 1,2-oxide (10.2) is a better substrate than benzene oxide for epoxide hydrolase. Its rapid isomerization to naphthalen-l-ol, facile enzymatic hydration to the dihydrodiol and lack of reactivity toward nucleophiles such as glutathione may explain its absence of direct toxicity [85],... 

Fig. 10.9. Stereoselective formation of the 1,2-dihydrodiols of naphthalene and anthracene from their precursor 1,2-oxides, 10.2 and 10.24, respectively (modified from [86])... 

P. J. van Bladeren, J. M. Sayer, D. E. Ryan, P. E. Thomas, W. Levin, D. M. Jerina, Differential Stereoselectivity of Cytochrome P450b and P450c in the Formation of Naphthalene and Anthracene 1,2-Oxides. The Role of Epoxide Hydrolase in Determining the Enantiomer Composition of the 1,2-Dihydrodiols Formed ,. /. Biol. Chem. 1985, 260, 10226- 10235. 

The oxidation of naphthalene was one of the earliest examples of an epoxide as an intermediate in aromatic hydroxylation. The epoxide can rearrange nonenzymatically to yield predominantly 1-naph-thol, interact with the enzyme epoxide hydrolase to yield the dihydrodiol, or interact with glutathione S-transferase to yield the glutathione conjugate, which is ultimately metabolized to a mer-capturic add. 

Touring studies at NIH, it was discovered that enzymatic hydroxyla-tion of (deuterated or tritiated) substrates leads to a novel and mechanistically important shift of the deuterium or tritium from the point of substitution by oxygen to an adjacent position in the aromatic ring (12). [It has been found recently that arene oxides are likely intermediates in the metabolism of aromatic compounds. They rearrange to phenols with concomitant NIH Shift, and they are enzymatically converted to dihydrodiols and premercapturic acids. In addition, naphthalene oxide has now been demonstrated as an intermediate in the conversion of naphthalene to a-naphthol, frari5-l,2-dihydro-I,2-dihydroxynaphthalene, and... 

The conversion of toluene to the cw-dihydrodiol has been examined using inunobilized P. putida UV4, and a dramatic increase in production observed under defined conditions of aeration in a fluidized-bed reactor [48]. The naphthalene dioxygenase enzyme from Pseudomonas fluorescens has been expressed in E. coli, and the resulting biocatalyst used for the conversion of a series of substituted naphthalenes to the diols shown in Fig. 29 [49], while Pseudomonas testosteroni ACS converts 2-naphthoic acid to the diol 40 shown in Fig. 30 [50]. Substituted biphenyls are also substrates for TDO oxidation (Fig. 31) using E. coli JM109 expressing this enzyme [51]. 

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