The sequential use of Cys(Acm)/Cys(Acm)(O) (first step) and Cys(MBzl)/Cys(MBzl)(O) (second step) pairs, with control of acidity in the presence of chloride anion, allowed onepot/stepwise interchain disulfide formation. This led to the development of an unprecedented strategy for synthesizing insulin. The strategy features an acid-controllable redox reaction that occurs between an S-protected cysteine and the corresponding sulfoxide pair. Furthermore, conducting disulfidebond formation and lipidation sequences utilizing an acidactivated cysteine sulfoxide permitted the one-pot synthesis of lipidated insulin. The methodology that we present herein should pave the way not only for insulin synthesis, but also for insulinlike peptides, including relaxins. Concerning the encountered side reaction in utilizing the isopeptide for disulfide formation, studies on exploring the cause and proposing potential solutions to overcome it will be presented in due course.