Biotransformation of organic sulfides.: Part 12.: Conversion of heterocyclic sulfides to chiral sulfoxides by Helminthosporium sp NRRL 4671 and Mortierella isabellina ATCC 42613

The enantioselective oxidation of a series of heterocyclic prochiral sulfides to chiral sulfoxides has been examined using the fungal biocatalysts Helminthosporium species NRRL 4671 and Mortierella isabellina ATCC 42613. Methylthiofuranyl and -thiophenyl substrates gave Q-configuration products in low to moderate enantiomeric purity on biotransformation with H. species, but pyridyl sulfides with the nitrogen atom located at an optimal distance of 8-10 Angstrom from the sulfur centre gave (S) sulfoxides of high enantiomeric purity. The biotransformation of appropriately substituted benzothiane substrates by M. isabellina also gave products of high enantiomeric purity, but with (R) configuration at sulfur. The acceptability of the substrate and the configuration of sulfur oxidation by both H. species and M. isabellina for the range of substrates examined were found to be consistent with predictions based on cubic space models for these oxidations.