Oxidation of the Neurotoxin 6-Nitrodopamine and Related 4-Nitrocatechols Under Biomimetic Conditions

Oxidation of 6-nitrodopamine (1) with horseradish peroxidase (HRP)/H2O2 in 0.05 M phosphate buffer, pH 7.4 afforded as main product the novel 5-[4-(2-aminoethyl)-2-hydroxy-5-nitrophenoxy]-6,7-dihydroxy-4-nitro-2,3-dihydroindole (4). Similar oxidation of the 4-nitrocatechols 2 and 3 with HRP/H2O2 or K3Fe(CN)6 gave chiefly the dimers 5/6 and 7/8. These products arise probably via 4-nitro-o-quinone or 4-nitro-2,3-dihydroindole-6,7-dione intermediates which are trapped by the starting nitrocatechols.