ASYMMETRIC SULFOXIDATION CATALYZED BY A VANADIUM BROMOPEROXIDASE - SUBSTRATE REQUIREMENTS OF THE CATALYST

An investigation of the catalytic effect of vanadium bromoperoxidase ( VBrPO, from Corallina officinalis) on the oxidation of a series of pro chiral sulfides by hydrogen peroxide, revealed that substrates having a cis-positioned carboxyl group are oxidized rapidly, giving the sulfo xide in >95% e.e. The pH-rate profile shows a typical sharp sigmoidal curve, indicative of a deprotonation event at around pH 6.4. The corre sponding, non-protolytic, methyl esters were not catalyzed by the enzy me. Rapid loss of stereoselectivity was found to occur when VBrPO-cata lyzed oxidation was carried out in the presence of bromide ions. This has been interpreted as being due to the intervention of a competing r eaction involving oxidation of bromide and the subsequent formation of a bromosulfonium ion intermediate. (C) 1998 Elsevier Science Ltd. All rights reserved.