Sulfur oxidation in supercritical carbon dioxide: dramatic pressure dependant enhancement of diastereoselectivity for sulfoxidation of cysteine derivatives

Abstract

The diastereoselective sulfoxidation of chiral sulfides derived from methionine and cysteine has been investigated in conventional solvents and in supercritical carbon dioxide (scCO₂); use of tert-butyl hydroperoxide and Amberlyst^TM 15 ion exchange resin is particularly effective for sulfoxide formation, and with cysteine derivatives shows a dramatic pressure-dependant increase in diastereoselectivity (up to >95% de) in scCO₂ compared with conventional solvents, where no diastereoselectivity is observed; the stereochemical configuration of the major product of the oxidation of Cbz-CysSMe-OMe has been confirmed as anti using X-ray crystallography.