Biocatalytic asymmetric dihydroxylation of conjugated mono- and poly-alkenes to yield enantiopure cyclic cis-diols

Dioxygenase-catalysed asymmetric dihydroxylation, of a series of conjugated monoalkenes and polyenes, was found to yield the corresponding monols and 1,2-dihydrodiols. The diol metabolites were obtained from monosubstituted, gem-disubstituted, cis-disubstituted, and trisubstituted alkene substrates, using whole cells of Pseudomonas putida strains containing toluene and naphthalene dioxygenases. Dioxygenase selection and alkene type were established as important factors, in the preference for dioxygenase-catalysed 1,2-dihydroxylation of conjugated alkene or arene groups, and monohydroxylation at benzylic or allylic centres. Competition from allylic hydroxylation of methyl groups was observed only when naphthalene dioxygenase was used as biocatalyst. The structures, enantiomeric excess values and absolute configurations of the bioproducts, were determined by a combination of stereochemical correlation, spectroscopy (NMR and CD) and X-ray diffraction methods. cis-1,2-Diol metabolites from arenes, cyclic alkenes and dienes were generally observed to be enantiopure (> 98% ee), while 1,2-diols from acyclic alkenes had lower enantiomeric excess values (< 88% ee). The enantiopure cis-diol metabolite of a gem-disubstituted fulvene was used as precursor in a new chemoenzymatic route to a novel C-2-symmetrical ketone.