Reactions of 1-methyl-2-mercaptoimidazole with hypochlorous acid and superoxide.

Reactions of thioureylene antithyroid drugs (1-methyl-2-mercaptoimidazole and carbimazole) with hypochlorous acid (HOCl) and superoxide were followed optically and products were analyzed by mass spectrometry. 1-methyl-2-mercaptoimidazole (MMI) and carbimazole reacted rapidly with HOCl with a rate constant of 1 x 10(7) and 7 x 10(6) M(-1)s(-1), respectively. The characteristic spectrum assigned to MMI disulfide appeared immediately after addition of HOCl, followed by a slow conversion to a final spectrum. The conversion was dependent upon the ratio of HOCl to MMI and both antithyroid drugs uptake 3 moles HOCl for complete conversion. A similar sequence of spectral changes was also observed when the HOCl was replaced by myeloperoxidase (MPO)/H2O2/Cl- system. The final oxidation product of MMI and carbimazole with HOCl and superoxide was 1-methylimidazole.