Synthesis-driven mapping of the dictyodendrin alkaloids

The dictyodendrin alkaloids have been described as the first telomerase inhibitors of marine origin. As such they represent interesting lead compounds in the quest for small molecule inhibitors of this tumor-marker enzyme. Described herein is the preparation of a collection of dictyodendrin-like compounds that hinges on the formation of their indole subunit by reductive cyclization of appropriate keto-amide precursors mediated by low valent titanium. It is shown that the underlying concept can be extended from the synthesis of heterocycles to the preparation of phenol and aniline derivatives using oxo-acid, oxo-nitrile or oxo-lactam derivatives as the substrates; such arene formations can even be carried out in cascade. Exploratory studies into the closure of the B-ring of the dictyodendrins with the aid of electrophilic reagents such as Ph3PAuCl/AgSbF6 or I+ revealed the bias of these polycyclic heteroarenes to undergo unusual skeletal rearrangements. It is demonstrated that the individual dictyodendrins and analogues are capable of cleaving double stranded DNA under oxidative conditions, provided that they exhibit at least one unprotected phenol group in their periphery.