A long journey toward structure revision and total synthesis of amphidinol 3

Amphidinol 3 (AM3) is a super-carbon-chain compound isolated from the dinoflagellate Amphidinium klebsii. Although the absolute configuration of AM3 was determined in 1999 by instrumental analysis in combination with degradation of the natural product, it was a daunting task because of its limited availability from natural sources and presence of around 70% of chiral centers on the acyclic carbon chain. During the course of our synthetic studies of AM3, the originally proposed structure was revised, which was confirmed by the first total synthesis of AM3 in 2020, more than 20 years since its first discovery. A highly convergent strategy via the fragment assembly using Suzuki-Miyaura coupling and Julia-Kocienski olefination led to the successful total synthesis; however, it was not an easy task to assemble large segments by the Suzuki-Miyaura coupling. A number of experiments optimizing the reaction conditions including model systems revealed that the concentration of the aqueous cesium carbonate is crucial for the key step Suzuki-Miyaura coupling to proceed effectively.