Francisco Sánchez-Viesca^1,, Reina Gómez¹

Physostigmine (eserine) is an indole alkaloid isolated from a plant of Western Africa. It is interesting due its striking properties: a potent venom and a drug for open-angle glaucoma treatment. It gives two color reactions, a dark red due to rubreserine, a three ring o-quinone, and a seven ring phenoxazone with a splendid blue color. Though the structures of these compounds have been determined, there is no reaction mechanism related to their formation. We provide the reaction pathway and the electron flow for each reaction. Especially interesting is the case of eserine blue, to know how the molecule is integrated through many reaction intermediates and electron shifts.

Calabar bean, eserine blue, indole alkaloid, physostigmine, reaction intermediates, reaction mechanisms