A novel process for enantioselective synthesis of single enantiomers of omeprazole or its alkaline salts, of other optically pure substituted 2-(2-pyridinylmethyl-sulphinyl) -1H-benzimidazoles as well as of other structurally related sulphoxides or their alkaline salts. The claimed process is an asymmetric oxidation of a pro-chiral sulphide to the single enantiomers or an enantiomerically enriched form of the corresponding sulphoxide. The application also claims the enantiomeric sulphoxide products produced by the process and their use in medicine