A concise synthesis of (+)-batzelladine B from simple pyrrole-based starting materials

Alkaloids, secondary metabolites that contain basic nitrogen atoms, are some of the most well-known biologically active natural products in chemistry and medicine(1). Although the efficient laboratory syntheses of alkaloids would enable researchers to study and optimize their biological properties,(2) the basicity and nucleophilicity of nitrogen, its susceptibility to oxidation, and its ability to alter reaction outcomes in unexpected ways – for example, through stereochemical instability and neighboring group participation – complicates their preparation in the laboratory. Efforts to address these issues have led to the invention of a large number of protecting groups that temper the reactivity of nitrogen(3); however, the use of protecting groups typically introduce additional steps and obstacles into the synthetic route. Alternatively, the use of aromatic nitrogen heterocycles as synthetic precursors can attenuate the reactivity of nitrogen and streamline synthetic strategies(4). In this manuscript, we use such an approach to achieve a synthesis of the complex anti-HIV alkaloid (+)-batzelladine B in nine steps (longest-linear sequence) from simple pyrrole-based starting materials. The route employs several key transformations that would be challenging or impossible to implement using saturated nitrogen heterocycles and highlights some of the advantages conferred by the use of aromatic starting materials.