Total Syntheses of (−)‐Strictosidine and Related Indole Alkaloid Glycosides
Jukiya Sakamoto, Yuhei Umeda, Kenta Rakumitsu, Michinori Sumimoto, Hayato Ishikawa
Abstract
A collective synthesis of glycosylated monoterpenoid indole alkaloids is reported. A highly diastereoselective Pictet-Spengler reaction with α-cyanotryptamine and secologanin tetraacetate as substrates, followed by a reductive decyanation reaction, was developed for the synthesis of (-)-strictosidine, which is an important intermediate in biosynthesis. This two-step chemical method was established as an alternative to the biosynthetically employed strictosidine synthase. Furthermore, after carrying out chemical and computational studies, a transition state for induction of diastereoselectivity in our newly discovered Pictet-Spengler reaction is proposed. Having achieved the first enantioselective total synthesis of (-)-strictosidine in just 10 steps, subsequent bioinspired transformations resulted in the concise total syntheses of (-)-strictosamide, (-)-neonaucleoside A, (-)-cymoside, and (-)-3α-dihydrocadambine.