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

The enantioselective oxidation of a series of heterocyclic prochiral sulfid es to chiral sulfoxides has been examined using the fungal biocatalysts Hel minthosporium species NRRL 4671 and Mortierella isabellina ATCC 42613. Meth ylthiofuranyl and -thiophenyl substrates gave Q-configuration products in l ow to moderate enantiomeric purity on biotransformation with H. species, bu t pyridyl sulfides with the nitrogen atom located at an optimal distance of 8-10 Angstrom from the sulfur centre gave (S) sulfoxides of high enantiome ric 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 a nd the configuration of sulfur oxidation by both H. species and M. isabelli na for the range of substrates examined were found to be consistent with pr edictions based on cubic space models for these oxidations.