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Total Synthesis of Poisonous Aconitum Alkaloids Empowered by a Fragment Coupling Strategy

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co-workers take on this considerable challenge, employing a fragment coupling strategy to synthesize (−)-talatisamine (1), (−)-liljestrandisine (2), and (−)-liljestrandinine (3). A series of highly chemoselective transformations was used to forge… Click to show full abstract

co-workers take on this considerable challenge, employing a fragment coupling strategy to synthesize (−)-talatisamine (1), (−)-liljestrandisine (2), and (−)-liljestrandinine (3). A series of highly chemoselective transformations was used to forge the polycyclic bridged skeleton of the natural products, one of which was structurally revised (2 vs 4). The Aconitum plants are well-known for their ability to biosynthesize neurotoxic C19 DTAs. 2 The plants themselves were used in medicinal preparations or as poison for hunting, due to the properties of the natural products to block cation channels in neurons, and to exhibit antiinflammatory, antihypertensive, pain relief, or antiarrhythmic activities. The structure of these complex compounds results from peculiar biosynthetic transformations, especially a semipinacol rearrangement of the denudatine-type (5) into the aconitine-type (6) skeletons (Figure 2a). This reaction has inspired the synthetic strategy of many chemists, starting with Wiesner’s total synthesis of talatisamine 1 in the 1970s. Besides, the retrosynthetic logic classically advises to unravel the complexity of bridged compounds by disconnecting the maximally bridged cycles. In fact, Reisman et al. solved this synthetic puzzle in a distinctly different manner, by coupling together two complex fragments that were separately assembled (Figure 2b). Such convergent approaches are well-known to empower the total synthesis of complex structures by making the synthetic route more flexible. Fragment A was made from phenol thanks to a stereoselective meta-photocycloaddition, while fragment B was enantioselectively constructed from cyclopentenone. Both intermediates were coupled through a unique sequence of 1,2-addition followed by a high-yielding semipinacol rearrangement to deliver 4 g of intermediate 7, which allows the stereoselective formation of the C-11

Keywords: fragment coupling; coupling strategy; total synthesis; strategy; aconitum

Journal Title: ACS Central Science
Year Published: 2021

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