Stereoselective oxidation of gem-disulphides with aspergillus niger

A strain of Aspergillus niger was used to prepare optically active gem-disulphide S-oxides 2 and 3 and the (s)-meso-disulphoxide 4. The structural assignment was made by intercorrelating the senses of NMR non-equivalence in pseudoasymmetric disulphoxides 4 and 5 of established configurations with the configurationally related monosulphoxides 2 and 3. The enantiomeric composition and absolute configurations were determined using the chiral solvent NMR method. The stereoselectivity in the microbial oxidation was found to be independent of the configuration of the incipient chiral centre at carbon.