Total Synthesis of (±)-Rhynchine E

Key words

(±)-rhynchine E - Pictet–Spengler reaction - 1,2-migration - aldol addition - C–H oxidation - Krapcho decarboxylation

Significance

In 2021, a new class of structurally unique monoterpene indole alkaloids was isolated from Uncaria rhynchophylla, rhynchines A–E. Zhao and co-workers now report the first racemic total synthesis of rhynchine E as well as rhynchine A–D. A biosynthetic relationship of the rhynchines natural products to hirsuteine, which is also commonly found in the isolation plant, was proposed.

Comment

The synthesis commenced with the formation of tetracyclic triester E from pyridinium salt C, through a Pictet–Spengler reaction. Subsequent treatment with NaBH₃CN in AcOH, triggered conjugated reduction and a 1,2-migration, forming the core tetrahydroazepine G. The tetrahydrofuran ring of (±)-rhynchine E was formed via C–H oxidation using K₃[Fe(CN)₆].

Publikationsverlauf

Artikel online veröffentlicht:
14. Juni 2024