Toluene and naphthalene dioxygenase-catalysed sulfoxidation of alkyl aryl sulfides

Abstract

A series of alkyl aryl sulfides were metabolised, using selected strains of the soil bacterium Pseudomonas putida containing either toluene dioxygenase (TDO) or naphthalene dioxygenase (NDO), to give chiral sulfoxides. Alkyl aryl sulfoxides 2a–2k, 4a–4j and 4l, having enantiomeric excess (ee) values of >90%, were obtained by use of the appropriate strain of P. putida (UV4 or NCIMB 8859). Enantiocomplementarity was observed for the formation of sulfoxides 2a, 2b, 2d, 2j, 4a, 4b and 4d, with TDO-catalysed (UV4) oxidation favouring the (R) enantiomer and NDO-catalysed oxidation (NCIMB 8859) the (S) enantiomer. Evidence of involvement of the TDO enzyme was obtained using a recombinant strain of Escherichia coli (pKST 11). The marked degree of stereoselectivity appears to be mainly due to enzyme-catalysed asymmetric sulfoxidation, however the possibility of a minor contribution from kinetic resolution, in some cases, cannot be excluded.