Total Synthesis of Strempeliopidine and Non-Natural Stereoisomers through a Convergent Petasis Borono–Mannich Reaction

Strempeliopidine is a member of the monoterpenoid bisindole alkaloid family, a class of natural products that have been shown to elicit an array of biological responses including modulating protein–protein interactions in human cancer cells. Our synthesis of strempeliopidine leverages palladium-catalyzed decarboxylative asymmetric allylic alkylations to install the requisite all-carbon quaternary centers found in each of the two monomeric natural products, aspidospermidine and eburnamine. Initial studies employing Suzuki–Miyaura cross-coupling followed by diastereoselective hydrogenation provided evidence for a structural reassignment of the natural product. Our final synthetic sequence employs a diastereoselective Petasis borono–Mannich reaction to couple eburnamine to a trifluoroborate aspidospermidine derivative. These convergent approaches enabled the synthesis of eight diastereomers of this heterodimer and offer support for the reassignment of the absolute configuration of strempeliopidine.