The (H+-K+)-ATPase inhibiting sulfoxides la, b undergo acid-induced transformations into the cyclic sulfenamides 2a, b via the putative sulfenic acids 4a, b. At high concentrations mixtures of 2a, b and thiosulfinates 5a, b were obtained. In contrast, IC, which cannot form 2, is completely transformed under similar conditions into 5c, the anhydride of 4c. The temperature-dependent equilibrium between 2a and 5a and the kinetics of the ring ...