Strategies for the synthesis of Stemona alkaloids

The extracts of several plants of the Stemonaceae family have long been used in Asian countries against different diseases and for their antiparasitic properties. Significant constituents of these extracts are a series of structurally related secondary metabolites named Stemona alkaloids. All the Stemona alkaloids are polycyclic and contain multiple stereocenters. Most of them present a central pyrrolo[1, 2-a]- azepine system and the majority also incorporate at least one a-methyl-y-butyrolactone substructure. Their challenging molecular architectures have motivated the development of new strategies for the construction of their skeletons, but only a small number of total syntheses have been published and they are still limited to quite a small number of targets. This microreview briefly examines most of the synthetic approaches to these alkaloids, according to the strategies devised to assemble their intricate structures, stressing the main similarities and differences encountered in the work developed by different laboratories, as well as the variations introduced along the synthetic route when pursuing different alkaloids through a common strategy. © Wiley-VCH Verlag GmbH & Co. KGaA.