Synthesis of Imidazo[1′,5′:1,2]pyrido[3,4-b]indole Derivatives

Summary.  The reactions of 1,2,3,4-tetrahydro-β-carboline-1-carboxylic acid and its ethyl ester with alkyl and aryl isothiocyanates under mild conditions resulted in the corresponding thiohydantoin-fused tetrahydro-β-carbolines. Treatment of the ethyl ester with isocyanates furnished ethyl 2-alkyl- or arylcarbamoyl-1,2,3,4-tetrahydro-β-carboline-1-carboxylates which were transformed to hydantoin-fused tetrahydro-β-carbolines. The structures of the thiohydantoin compounds, involving two conformers and the presence of keto-enol tautomerism, were determined by NMR spectroscopy. Corresponding author. E-mail: fulop@pharma.szote.u-szeged.hu Received February 2, 2002. Accepted (revised) March 4, 2002