Scalable Total Syntheses of <i>N</i>-Linked Tryptamine Dimers by Direct Indole−Aniline Coupling: Psychotrimine and Kapakahines B and F

This report details the invention of a method to enable syntheses of psychotrimine (1) and the kapakahines F and B (2, 3) on a gram scale and in a minimum number of steps. Mechanistic inquiries are presented for the key enabling quaternization of indole at the C3 position by electrophilic attack of an activated aniline species. Excellent chemo-, regio-, and diastereoselectivities are observed for reactions with o-iodoaniline, an indole cation equivalent. Additionally, the scope of this reaction is broad with respect to the tryptamine and aniline components. The anti-cancer profiles of 1−3 have also been evaluated.