The present invention relates to a supported oxidation reactant of formula (I): R-[Met(O)k]n-X- (I) in which: - R represents a hydrogen atom or an amine function-protecting group, -[Met(O)] represents an oxidized methionine residue of formula - k is 1 or 2 - represents a solid or soluble support used in organic synthesis, - X represents a radical derived from a function of the type amine or hydroxyl, or halogeno, capable of anchoring methionine, it being understood that this function capable of anchoring methionine can be separated from the support by means of a functionalized arm or a spacer, and - n is an integer greater than or equal to 1. The invention also relates to the use of a supported oxidation reactant of formula (I), for the formation of intramolecular disulfide bridges, in particular in peptides and/or proteins.