Structure-activity relationship studies on the mutagenicity of some azo dyes in the Salmonella/microsome assay

Analogs of Direct Black 19 and Direct Black 38 were synthesized and tested in the Salmonella/microsome assay. Those dyes which gave positive responses in strains TA98 and TA1538 would be expected to be metabolized to p-phenylenediamine by the liver microsomal enzymes (S9). Pure p-phenylenediamine is non-mutagenic in this assay but becomes mutagenic after it is oxidized. Thus the positive response of our synthetic azo compounds are most likely due to the formation of oxidized p-phenylenediamine. Modification of the moieties that can be metabolized to p-phenylenediamine by sulfonation, carboxylation or copper complexation eliminated the mutagenic responses.