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 prochiral sulfides by hydrogen peroxide, revealed that substrates having a cis-positioned carboxyl group are oxidized rapidly, giving the sulfoxide 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 corresponding, non-protolytic, methyl esters were not catalyzed by the enzyme. Rapid loss of stereoselectivity was found to occur when VBrPO-catalyzed oxidation was carried out in the presence of bromide ions. This has been interpreted as being due to the intervention of a competing reaction involving oxidation of bromide and the subsequent formation of a bromosulfonium ion intermediate. (C) 1998 Elsevier Science Ltd. All rights reserved.