4-Chloro-6-methoxyindole is the precursor of a potent mutagen (4-chloro-6-methoxy-2-hydroxy-1-nitroso-ndolin-3-one oxime) that forms during nitrosation of the fava bean (Vicia faba)

Abstract

Fava beans (Vicia faba) upon treatment with nitrite under simulated gastric conditions, form a direct-acting bacterial mutagen, comparable in specific activity to the most potent known mutagens for several strains of Salmonella typhimurium. The precursor of the mutagen was isolated and identified as 4-chloro-6-methoxyindole by u.v., i.r., m.s. and n.m.r. The precursor was dechlorinated with NaBH4 and PdCl2 as the catalyst and the product obtained from this reaction was identified as 6-methoxyindole. Since synthetic 4-chloro-6-methoxyindole was not available, structure activity studies were conducted on substituted indoles. Nitrosation of 4-chloroindole closely follows the results for nitrosation of 4-chloro-6-methoxyindole. The major product of nitrosation of 4-chloroindole is 4-chloro-2-hydroxy-N1-nitroso-indolin-3-one oxime. Thus, it appears that the major nitrosation product of 4-chloroindole and of 4-chloro-6-methoxyindole is a stable alpha-hydroxy N-nitroso compound. This is the first reported case of stable alpha-hydroxy N-nitroso compounds. In the presence of N-(1-naphthyl)ethylenediamine dihydrochloride (NEDD), the alpha-hydroxy N-nitroso compound rearranges to an aromatic diazonium ion which couples with the diamine to form an azo dye. Studies on nitrosation kinetics indicate that the nitrosation of indoles are relatively fast reactions. Both the structural and rate studies give strong support to the hypothesis that intragastric nitrosation of fava beans yield the putative gastric carcinogen in the high-risk area in Colombia.

Past, present, and future of mutagens in cooked foods.

“…The mutagen precursor was later identified as 4-chloro-6-methoxyindole by Yang et al. (67). Soybeans were treated by nitrite but did not exhibit any mutagenic activity, while fermented products of soybeans showed mutagenic activity after nitrite treatment.…”

In vitro testing and the carcinogenic potential of several nitrosated indole compounds

“…It was identified as 4-chloro-6-methoxyindole (4C6MI), from which 4-chloro-2-hydroxy-Nl-nitroso-3H-indoline-3-one-oxime was formed upon nitrosation (Btichi et al, 1985) (Figure 1). The nitrosated compound was highly mutagenic to S. typhimurium TA1535, inducing comparable numbers of revertents as aflatoxin B1 (Yang et al, 1984). To our knowledge, no other studies on the mutagenicity or carcinogenicity of nitrosated 4C6MI have been reported.…”

“…Because significantly high nitrate levels were found in Narifio's drinking water , Tannenbaum et al, 1979, it was hypothesized that the formation of mutagenic NOC in the stomach from the precursor present in fava beans, could be a causative factor in the etiology of gastric cancer (Correa et al, 1983). Yang et al (1984) isolated the compound occurring in fava beans. It was identified as 4-chloro-6-methoxyindole (4C6MI), from which 4-chloro-2-hydroxy-Nl-nitroso-3H-indoline-3-one-oxime was formed upon nitrosation (Btichi et al, 1985) (Figure 1).…”

1-Nitrosoindole-3-acetonitrile, a mutagen produced by nitrite treatment of indole-3-acetonitrile.

“…*) (Communicated April 12, 1985) Secondary amines and amides react with nitrite yielding mutagenic and carcinogenic N-nitroso compounds in vitro and in vivo (Sander and Burkle, 1969;Mirvish, 1975) . Various naturally occurring indole derivatives, such as 1-methyl-1,2,3,4-tetrahydro--carboline-3-carboxylic acid isolated from soy sauce (Wakabayashi et al, 1983), 4-chloro-6-methoxyindole from fava beans (Yang et al, 1984), L-tryptophan and tryptamine (Ohta et al, 1981;Gatehouse and Wedd, 1983), are nitrosable precursors of direct-acting mutagens on Salmonella typhimurium.…”

“…4-Chloro-6-methoxy-2-hydroxy-1-nitroso-indolin-3-one oxime was proposed to be a nitrosated mutagenic product of 4-chloro-6-methoxyindole (Yang et al, 1984).…”