Enantioselective toluene dioxygenase catalysed di- and tri-hydroxylation of monosubstituted benzenes

Asymmetric cis-dihydroxylation to yield diols 2A-2G and sequential benzylic monohydroxylation-cis-dihydroxylation to yield triols 4A-4G (trihydroxylat ion), occurred during biotransformation of a series of monosubstituted alky lbenzene substrates 1A-1G using toluene dioxygenase, a biocatalyst present in Pseudomonas putida UV4. Dioxygenase-catalysed cis-dihydroxylation of the R and S benzylic alcohol enantiomers 3B-3D, 3B'-3D' gave the corresponding enantiopure triols 4B-4D, 4B'-4D'. Biotransformation of substrates 1J-1L y ielded cis-diols 2J-2L and a minor triol metabolite 4A. Benzylic alcohols 3 J-3L were postulated as unstable intermediates yielding triol 4A via benzal dehyde 5 and benzyl alcohol 3A intermediates. cis-Dihydroxylation of monosu bstituted benzylic substrates containing bulky groups (1H, 1I) or 1,4-dialk yl-substituted benzene substrates (10A-10C) gave the corresponding cis-dihy drodiol metabolites (2H, 2I, 11A-11C) exclusively. The cis-diols 2A-2L, 11A -11C and triols 4A-4F, 4B'-4D' were stereochemically assigned as single ena ntiomers of 1S,2R-configuration based on NMR and CD spectroscopy. The absol ute configurations of the exocylic chiral centres in the triol bioproducts 4A-4F, 4B'-4D' were established by stereochemical correlation and aromatisa tion/hydrogenation to yield the corresponding enantiopure phenolic benzylic alcohols having similar CD spectra.