Method for preparing oligoreptide-aldehyde

Preparation of a reversibly protected oligopeptide aldehyde (I) comprises: (a) dissolving an N-terminal-end reversibly protected oligopeptide alcohol in a buffered solvent mixture containing a non-oxidisable, polar, water immiscible solvent and a small amount of water; (b) adding a stoichiometric amount of sodium bromide; (c) oxidising the alcohol under cooling using a catalytic amount of 2,2,6,6-tetramethylpiperidinoxyl (TEMPO) and/or its derivative; (d) adding an aqueous sodium hypochlorite solution to the reaction suspension; and (e) ending the reaction by adding a reducing agent.