Structures of mutagens produced by the co-mutagen norharman with o- and m-toluidine isomers

Norharman, abundantly present in cigarette smoke and cooked foods, is not m utagenic to Salmonella typhimurium strains. However, norharman shows mutage nicity to S. typhirnurium TA98 and YG1024 in the presence of S9 mix when co existing with aromatic amines, including aniline, o- and m-toluidines. We p reviously reported that the mutagenicity from norharman and aniline in the presence of S9 mix was due to the formation of a mutagenic compound, 9-(4 ' -aminophenyl)-9H-pyrido[3,4-b]indole (aminophenylnorharman). In the presen t study, we analyzed the mutagens produced by norharman with o- or m-toluid ine in the presence of S9 mix. When norharman and o-toluidine were reacted at 37 degreesC for 20 min, two mutagenic compounds, which were mutagenic wi th and without S9 mix, respectively, were produced, and these were isolated by HPLC. The former mutagen was deduced to be 9-(4 ' -amino-3 ' -methylphe nyl)-9H-pyrido[3,4-b]indole (amino-3 ' -methylphenylnorharman) on the basis of various spectral data, and this new heterocyclic amine was confirmed by its chemical synthesis. The latter mutagen was identified to be the hydrox yamino derivative. Amino-3 ' -methylphenylnorharman induced 41,000 revertan ts of TA98, and 698,000 revertants of YG1024 per mug with S9 mix. Formation of the same DNA adducts was observed in YG1024 when amino-3 ' -methylpheny lnorharman or a mixture of norharman plus o-toluidine was incubated with S9 mix. These observations suggest that norharman reacts with o-toluidine in the presence of S9 mix to produce amino-3 ' -methylphenylnorharman, and thi s compound is metabolically activated to yield its hydroxyamino derivative. After activation by O-acetyltransferase, it might bind to DNA and exert mu tagenicity in S. typhirnurium TA98 and YG1024. When norharman and rn-toluid ine were reacted in the presence of S9 mix, 9-(4 ' -amino-2 ' -methylphenyl )-9H-pyrido[3,4-b]indole (amino-2 ' -methylphenylnorharman) was identified as a mutagen. Thus, the mutagenicity of norharman with m-toluidine may foll ow a mechanism similar to that with o-toluidine. (C) 2001 Elsevier Science B.V. All rights reserved.