Total Synthesis of 12,13‐Dibenzyl‐banistenoside B and Analogs

Abstract

Banistenosides A and B possessing a unique “azepino(1,2‐a)tetrahydro‐β‐carboline” carbon framework were isolated from the stem of Banisteriopsis caapi and showed MAO‐A inhibition. Herein, we report the total synthesis of dibenzyl derivative of the untouched natural product in the last two decades, Banistenoside B. The key steps involve construction of 6.5.6.7 tetracyclic core using Pictet−Spengler reaction and intramolecular amide coupling. The stereoselective glycation was achieved through Hotha's protocol using gold catalyst, and silver triflate in the late stage of synthesis. The stereochemistry of most of the essential compounds were confirmed by X‐ray crystallography.