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 synthesizedand tested in the Salmonella/microsome assay. Those dyes whichgave positive responses in strains TA98 and TA1538 would beexpected to be metabolized to p-phenyl-enediamine by the livermicrosomal enzymes (S9). Pure p-phenylenediamine is non-mutagenicin this assay but becomes mutagenic after it is oxidized. Thusthe positive response of our synthetic azo compounds are mostlikely due to the formation of oxidized p-phenylenediamine.Modification of the moieties that can be metabolized to p-phenylenediamineby sulfonation, carboxylation or copper complexation eliminatedthe mutagenic responses.