Stereoselective enzyme-catalysed oxidation–reduction reactions of thioacetals–thioacetal sulphoxides by fungi

Abstract

Enzymes present in the fungus Mortierella isabellina catalyse the transfer of an oxygen atom to the cyclic thioaceta 1,3-dithian and from 1,3-dithian 1-oxide, 1,3,5-trithian 1-oxide, and cis-1,3-dithian 1,3-dioxide. The oxidation of 1,3-dithian and the acyclic thioacetal bis-(p-tolythio)methane to form the corresponding monosulphoxides occurred in the presence of growing cultures of Aspergillus foetidus and a Helminthosporium species. The degree and preferred direction of stereoselectivity occurring during the asymmetric oxidation and reduction steps was deduced from the enantiomeric excess (e.e.) and absolute stereochemistry of the isolated 1,3-dithian 1-oxide and p-tolythio-(p-tolylsulphinyl)methane.