Biocatalytic Oxidation of Sulfides to Sulfones

Abstract

This paper describes a method for the biocatalytic oxidation of sulfides. During the screening of microorganisms using pure cultures of Bacteria and Fungi for the oxidation of sulfides, it was observed that a number of strains of microorganisms, were able to oxidize various sulfides (1-4), but the desired sulfoxide was either not obtained or obtained only as a minor product. A close observation of the reaction showed complete oxidation and thus sulfone (5-8) formation had occurred in these cases.Sulfones are used to stabilize intermediates like α-radicals, α-anionsetc. and also used as cationic synthons in many known reactions.This prompted us to explore the sulfone synthesis by biocatalytic route.Approximately 20% of the strains tested (400 bacterial and 200 fungal) showed the formation of sulfone with conversion rate varying from 3 to 100% based on TLC analysis. There were two strains of fungi, Aspergillus ochraceus MTCC 5245 and Penicillium Funiculosum MTCC 5246 which showed excellent biocatalytic activity for oxidation sulfides to corresponding sulfones in high yield. In all these strains, the product was different from corresponding standard sulfoxide prepared by oxidation with m-chloroperbenzoic acid but well corresponded with the standard sample of sulfone prepared by oxidation of the corresponding sulfides with oxone®. The identity of sulfones in all cases was confirmed by 1H NMR.