Iboga-Type Alkaloids from Ervatamia officinalis.
Seven new iboga-type alkaloids, ervaoffines A-D (1-4), (7S)-3-oxoibogaine hydroxyindolenine (5), ibogaine-5,6-dione (6), and 19-epi-5-oxovoacristine (7), and 10 known alkaloids were isolated from Ervatamia officinalis. The absolute configurations of 1-7 were determined through X-ray diffraction and electronic circular dichroism (ECD) analyses. Ervaoffines A and B represent the first iboga-type pseudoindoxyl alkaloids in which the C-2 spiro carbon configuration is opposite to that of other members of this class, such as iboluteine (8). The relationship between the absolute configuration of the spiro carbons and the Cotton effect in the ECD spectrum is established for the first time for iboga-type pseudoindoxyl and oxindole alkaloids. Additionally, a plausible biogenetic pathway for these alkaloids is proposed.