Sulphur Trioxide/Thiol: A Novel System for the Reduction of Methionine Sulphoxide
A new method for the effective reduction of methionine sulphoxide in protected peptides with sulphur trioxide and thiol has been developed.In practice, a combination of dimethylformamide-sulphur trioxide complex and ethane-1,2-dithiol was found effective, the presence of pyridine in the reaction medium being found necessary for the reduction to proceed.Methionine sulphoxide in two types of protected methionine-enkephalins was efficiently reduced to methionine by this reduction system at 20 deg C in an hour.The (p-methylsulphinyl)benzyl protecting group was also reduced to (p-methylthio)benzyl simultaneously with the reduction of methionine sulphoxide.Subsequent deprotection afforded methionine-enkephalin of high purity in each case.