(H+-K+)-ATPase Inhibiting 2-benzimidazoles. 3. Evidence for the Involvement of a Sulfenic Acid in Their Reactions

Article abstract of DOI:10.1021/jo00300a038

The (H⁺-K⁺)-ATPase inhibiting sulfoxides 1a,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, 1c, 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 opening of 2a by water provide evidence for the sulfenic acid 4 as an intermediate involved in the pH-dependent transformations of 1.The thiosulfinate 5 decompose mainly to the disulfides 6 at a rate depending on the solvent and conditions and are also reduced to 6 by thiols.The dimeric ylide 7a could be isolated from 6a (prepared in situ from 1a as well as from 2a).The symmetrical disulfides 6 and 7 are cleaved by thiols to yield the mixed disulfides 3 and the thiols 8.Similarly, cleavage of 3 liberates an additional equivalent of 8.Finally, the unstable thiols 8 are removed from the thiol-disulfide interchange equilibrium by irreversible rearrangment to the sulfides 9.