Chloroperoxidase-catalyzed enantioselective oxidation of methyl phenyl sulfide with dihydroxyfumaric acid oxygen or ascorbic acid oxygen as oxidants

The chloroperoxidase catalyzed oxidation of methyl phenyl sulfide to (R)-me thyl phenyl sulfoxide was investigated, both in batch and membrane reactors , using as oxidant H2O2, or O-2 in the presence of either dihydroxyfumaric acid or ascorbic acid. The effects of pH and nature and concentration of th e oxidants on the selectivity, stability, and productivity of the enzyme we re evaluated. The highest selectivity was displayed by ascorbic acid/O-2, e ven though the activity of chloroperoxidase with this system was lower than that obtained with the others. When the reaction was carried out in a memb rane reactor, it was possible to reuse the enzyme for several conversion cy cles. The results obtained with ascorbic acid/O-2 and dihydroxyfumaric acid /O-2 as oxidants do not seem to be compatible with either a mechanism invol ving hydroxyl radicals as the active species or with the hypothesis that ox idation occurs through the initial formation of H2O2. (C) 1999 John Wiley & Sons, Inc.