N-arylhydroxamic acid N,O-acyltransferase. Positional requirements for the substrate hydroxyl group

N-Arylhydroxamic acid N,O-acyltransferase (AHAT) is a cytosolic enzyme system that is capable of converting toxic and carcinogenic N-arylhydroxamic acids into electrophilic reactants and of catalyzing the transacetylation of arylamines. The role of the N-hydroxyl group in promoting AHAT-catalyzed transacetylation of arylamines was investigated by the synthesis and biochemical evaluation of a series of o-hydroxyaryl amides and N-arylglycolamides. Several of these compounds are metabolites of carcinogenic aryl amides in vivo. 3-Hydroxy-4-acetamidobiphenyl (8) was weakly effective as an acetyl donor when partially purified preparations of hamster or rat hepatic AHAT were used to catalyze the transacetylation of 4-aminoazobenzene. 1-Hydroxy-2-acetamidofluorene (1), 3-hydroxy-2-acetamidofluorene (2), 2-glycolamidofluorene (3), 4-glycolamidobiphenyl (9), and trans-4-glycolamidostilbene (5) were less effective acyl donors than 4-acetamidobiphenyl (7) itself. The compounds were also assayed for their abilities to participate in the AHAT-catalyzed conveydroxy-2-acetamidofluorene (1), 3-hydroxy-2-acetamidofluorene (2), 2-glycolamidofluorene (3), 4-glycolamidobiphenyl (9), and trans-4-glycolamidostilbene (5) were less effective acyl donors than 4-acetamidobiphenyl (7) itself. The compounds were also assayed for their abilities to participate in the AHAT-catalyzed conveydroxy-2-acetamidofluorene (1), 3-hydroxy-2-acetamidofluorene (2), 2-glycolamidofluorene (3), 4-glycolamidobiphenyl (9), and trans-4-glycolamidostilbene (5) were less effective acyl donors than 4-acetamidobiphenyl (7) itself. The compounds were also assayed for their abilities to participate in the AHAT-catalyzed conversion of N-arylhydroxylamines to electrophilic intermediates that form methylthio adducts upon reaction with N-acetylmethionine. None of the compounds exhibited more than 4% of the activity of the prototype compound, N-hydroxy-4-acetamidobiphenyl (10). These results indicate that the presence of an hydroxyl group on the ring position ortho to the amide group or on the alpha-position of the acyl group is not sufficient to confer significant acyltransferase activity with AHAT.