Synthesis of a series of 5-nitro-(benzimidazoles and indoles) as novel antimycotics and evaluation as genotoxins in the Ames test.

Nitrobenzimidazole and nitroindole derivatives, related to oxiconazole and characterized by an oxyiminic function, have been synthesized as novel antimycotics and their mutagenic activity tested in Salmonella typhimurium strains TA100 and TA98 with and without an exogenous metabolizing system. TA98NR and TA98/1,8-DNP6 strains were employed to identify a specific metabolic reaction which governs the mutagenic potency. Active compounds are weak direct-acting mutagens. Only derivatives bearing a nitro group on the phenyl ring linked to the oxyiminic function and lacking halogenated substituents show mutagenic activity. Metabolism by bacterial enzyme systems is important to the expression of genotoxicity. The reductive activation of nitrobenzimidazoles and nitroindoles carried out by the 'classical' nitroreductase of Salmonella, which is defective in TA98NR, is required of mutagenicity. Similarly, the O-acetyltransferase defective in TA98/1,8-DNP6 is required for the efficient production of the ultimate electrophilic nitrogen species, which react with DNA. The role of bacterial metabolism in mutation induction needs careful consideration to assess the potential risk to humans from nitrobenzimidazole and nitroindole antimycotics.