Brønsted Acid Catalyzed Bisindolization of α-Amido Acetals: Synthesis and Anticancer Activity of Bis(indolyl)ethanamino Derivatives

A Bronsted acid catalyzed bisindolization reaction with suitable α-amido acetals that tolerates a wide range of indoles is reported. The method allows rapid access to the biologically relevant bisindolyl ethanamine scaffold in good to excellent yields upon mild amide basic hydrolysis. In preliminary pharmacological studies, some of these compounds display cytotoxic activity in U937 cancer cells. The marine natural alkaloid 2,2-di(6′-bromo-3′-indolyl)-ethylamine was the most active compound and could be a lead candidate for further optimization. For the first time, the biological role of this brominated bisindole marine alkaloid is presented.