2-Mercaptothiazolo[5,4-b]pyridine (I) is treated with chloroacetic acid butyl ester (II) in the presence of potassium carbonate in DMF to give 2-[(butoxycarbonylmethyl)thio]thiazolo[5,4-b]pyridine (III), which is oxidized with m-chloroperbenzoic acid in dichloromethane.