Aryl Hydroxylation of Aminoazo Dyes and 3-Acetaminotoluene by Several Model Systems

Enzymic hydroxylation of 3'-methyl-4-(dimethylamino) azobenzene [4'-2H, 4'-3H, or 5'-3H] or 3'-methyl-4-(methylamino) azobenzene [4'-2H] and the reactions of deuterated aminoazo dyes or 3-acetaminotoluene with several model hydroxylating systems were investigated in order to elucidate the NIH shift in these hydroxylations. The values of retention of isotopic hydrogen (43%) were closely comparable in all hydroxylated metabolites produced from 4'-deuterated aminoazo dyes. Accordingly, it was confirmed that the enzymic hydroxylation of aminoazo dyes or 3-acetaminotoluene showed the characteristic NIH shift in each substrate. The retention values during hydroxylation of these compounds by photolysis of hydrogen peroxide, the Udenfriend or Hamilton system, and m-Cl-perbenzoic acid were lower in any cases than those by photolysis of pyridine-N-oxide. Deuterium retention during these hydroxylations with pyridine-N-oxide was the same level as those obtained with rat in vivo and in vitro. Deuterium retention during all the oxidations of aminoazo dyes with the model systems used was higher than those of 3-acetaminotoluene. These results indicate the close analogy between the NIH shift recognized in the enzyme systems and that in the model hydroxylating systems.