The direct-acting mutagenicity of nitroimidazo[2,1-b]thiazoles in Salmonella typhimurium.

A series of nitroimidazo[2,1-b]thiazole derivatives was investigated for direct-acting mutagenic potency with the Salmonella assay. All of the nine derivatives tested were mutagenic. The compounds induced predominantly base displacements resulting in frame-shift mutations. The mutagenic activity did not require the S9 fraction but was largely dependent on "classical" bacterial nitroreductase. The primary basis of the mutagenic activity of nitroimidazo[2,1-b]thiazoles appears to be a reduction of the nitro-function to the corresponding hydroxylamine. Mutagenicity seems to be paralleled by an increase of the nitro groups: dinitroderivatives were more active than nitroderivatives. Other electrophiles and sterically constrained nitro groups could account for differences in genotoxicity.