Voacandial and Voacanginone A, Iboga-Type Monoterpenoid Indole Alkaloids from <i>Voacanga africana</i> Root Bark: Isolation, Structure Elucidation, and Asymmetric Total Syntheses

Two previously undescribed iboga-type monoterpenoid indole alkaloids, voacandial (<b>1</b>) and voacanginone A (<b>2</b>), were isolated from <i>Voacanga africana</i> root bark. Voacandial (<b>1</b>) is a voacangine-derived alkaloid featuring a C-5-C-6 bond cleavage in the voacangine skeleton and bearing two formyl groups at the N-4 and C-7 positions. Voacanginone A (<b>2</b>) has a carbonyl group at the C-6 position of voacangine. Their structures were deduced by spectroscopic analysis and then confirmed by a total asymmetric total synthesis. The total synthesis of catharanthine (+) was also achieved.