New Strategies for the Synthesis of Monoterpene Indole Alkaloids

The synthetic efforts of the author's research team in several areas within the monoterpene indole alkaloid family are summarized. Most of the work was accomplished in the field of the Aristotelia alkaloids, where some 25 natural products were synthesized for the first time. Systematic investigations on the oxidative rearrangement of indoles to oxindoles and pseudoindoxyl derivatives led to control over the chemoselectivity and stereoselectivity of this process, which served for enantioselective preparations of the simple alkaloids horsfiline and elacomine. In addition, recent developments in a novel approach to Iboga alkaloids containing a hydroxyl group at C(19) are presented. The key steps involved a self-immolating 1,4-chirality transfer in an Ireland-Claisen rearrangement and an intramolecular nitrone-olefin [2+3]-cycloaddition to give the aliphatic isoquinuclidine core of the target molecules. The first synthesis of (19R)- hydroxyibogamine was completed by grafting a 3-ethylindole unit onto the aliphatic nitrogen, followed by closing the 7- membered ring.