Oligomerization of indole derivatives with incorporation of thiols

Abstract

Two molecules of indole derivative, e.g. indole-5-carboxylic acid, reacted with one molecule of thiol, e.g. 1,2-ethanedithiol, in the presence of trifluoroacetic acid to yield adducts such as 3-[2-(2-amino-5-carboxyphenyl)-1- (2-mercaptoethylthio)ethyl]-1H-indole-5-carboxylic acid. Parallel formation of dimers, such as 2,3-dihydro-1H,1′H-2,3′-biindole-5,5′- dicarboxylic acid and trimers, such as 3,3′-[2-(2-amino-5-carboxyphenyl) ethane-1,1-diyl]bis(1H-indole-5-carboxylic acid) of the indole derivatives was also observed. Reaction of a mixture of indole and indole-5-carboxylic acid with 2-phenylethanethiol proceeded in a regioselective way, affording 3-[2-(2-aminophenyl)-1-(phenethylthio)ethyl]-1H-indole-5-carboxylic acid. An additional product of this reaction was 3-[2-(2-aminophenyl)-1-(phenethylthio) ethyl]-2,3-dihydro-1H,1′H-2,3′-biindole-5′-carboxylic acid, which upon standing in DMSO-d6 solution gave 3-[2-(2-aminophenyl)-1- (phenethylthio)ethyl]-1H,1′H-2,3′-biindole-5′-carboxylic acid. Structures of all compounds were elucidated by NMR, and a mechanism for their formation was suggested. © 2008 by the authors; licensee Molecular Diversity Preservation International.