cis-Dihydrodiol metabolites were obtained from dioxygenase-catalysed asymmetric dihydroxylations of five monocyclic (azabiphenyl) and four tricyclic (azaphenanthrene) azaarene substrates. Enantiopurity values and absolute configuration assignments were determined using a combination of stereochemical correlation, X-ray crystallography and spectroscopy methods. The degree of regioselectivity found during cis-dihydroxylation of monocyclic azaarenes (2,3 bond >> 3,4 bond) and of tricyclic azaarenes (bay region > non-bay region bonds) was dependent on the type of dioxygenase used. The cis-dihydrodiol metabolite from an azaarene (3-phenylpyridine) was utilised in the chemoenzymatic synthesis of the corresponding trans-dihydrodiol.

A series of ten cis-dihydrodiol metabolites has been obtained by bacterial biotransformation of the corresponding 1,4-disubstituted benzene substrates using Pseudomonas putida UV4, a source of toluene dioxygenase (TDO). Their enantiomeric excess (ee) values have been established using chiral stationary phase HPLC and 1H NMR spectroscopy. Absolute configurations of the majority of cis-dihydrodiols have been established using stereochemical correlation and X-ray crystallography and the remainder have been tentatively assigned using NMR spectroscopic methods but finally confirmed by circular dichroism (CD) spectroscopy. These configurational assignments support and extend the validity of an empirical model, previously used to predict the preferred stereochemistry of TDO-catalysed cis-dihydroxylation of ten 1,4-disubstituted benzene substrates, to more than twenty-five examples.

Enantiopure trans-dihydrodiols have been obtained by a chemoenzymatic synthesis from the corresponding cis-dihydrodiol metabolites, obtained by dioxygenase-catalysed arene cis-dihydroxylation at the 2,3-bond of monosubstituted benzene substrates. This generally applicable, seven-step synthetic route to trans-dihydrodiols involves a regioselective hydrogenation and a Mitsunobu inversion of configuration at C-2, followed by benzylic bromination and dehydrobromination steps. The method has also been extended to the synthesis of both enantiomers of the trans-dihydrodiol derivatives of toluene, through substitution of a vinyl bromine atom of the corresponding trans-dihydrodiol enantiomers derived from bromobenzene. Through incorporation of hydrogenolysis and diMTPA ester diastereoisomer resolution steps into the synthetic route, both trans-dihydrodiol enantiomers of monohalobenzenes were obtained from the cis-dihydrodiols of 4-haloiodobenzenes.

Summary. The mammalian enzymes oxidizing ethylene glycol to glycolaldehyde were investigated with homogenates of horse liver and of rat tissues. The oxidation was followed by measuring either pyridine nucleotide reduction by fluorometry or glycolaldéhyde with diphenylamine. The reaction required either NAD^+ or a biological source of H(2)0(2); NADP^+ was ineffective. In the presence of NAD^+, crude horse liver demonstrated the same relative rates for ethylene glycol oxidation, ethanol oxidation, and acetaldehyde reduction as did crystalline horse liver alcohol dehydrogenase. The oxidation of many flavoprotein oxidoreductase substrates (including glycolic acid, a metabolite of ethylene glycol) could be coupled to that of ethylene glycol, presumably by providing a source of H(2)0(2) for the oxidation of ethylene glycol via tissue catalase. Partially purified L-gulonate: NADP oxidoreductase and glycerol: NADP oxidoreductase (D-glyceraldehyde forming) oxidized ethylene glycol poorly. The results suggest that the important enzymes in the first step of ethylene glycol oxidation are the same as those for ethanol oxidation, namely alcohol dehydrogenase and catalase.

Summary. Ethanol inhibits the oxidation of ethylene glycol by horse liver alcohol dehydrogenase, beef liver catalase, and crude rat liver homogenates. The inhibition of alcohol dehydrogenase is of the competitive type, with a K(r) of 1.9 mM at pH 8.0, at which the K(m) for ethylene glycol is 38 mM. Theoretically, the generation of H(2)0(2), a by-product of the oxidation of ethanol by liver homogenates, could increase the oxidation of ethylene glycol via catalase, but this tendency is outweighed by the inhibitory effect of ethanol on this reaction. The results provide a theoretical basis for the use of ethanol in ethylene glycol intoxication in humans.