Abstract: A method of forming a conjugate of a sulfonamide and a polypeptide, the method comprising: a) Providing an activated sulfonamide, wherein the activated sulfonamide corresponds to Formula (I); b) Providing an aqueous solution of a polypeptide having a free amino group, wherein the aqueous solution optionally comprises an alcohol; c) Contacting the aqueous solution of b) with the activated sulfonamide of a); and d) Reacting the activated sulfonamide with the polypeptide having a free amino group, obtaining a solution comprising the conjugate of a sulfonamide and a polypeptide, wherein the sulfonamide is covalently bonded to the polypeptide. Also associated conjugates, processes, procedures, proinsulins and the like.