Porphyrins and bile pigments from brominated pyrromethenes

Abstract

Aetioporphyrin-I (1a) is obtained in 50–60% yield by heating 5-bromo-3,4′-diethyl-3′,4,5′-trimethylpyrromethene perbromide (4a) under reflux in formic acid, surpassing the yields from the established syntheses using the less accessible 5-bromo-5′-bromomethylpyrromethene hydrobromides (2a, b). The 5-bromo-5′-methylpyrromethene hydrobromides and one equivalent of free bromine can be used as an alternative to the crystalline perbromides; in this way a 50% yield of coproporphyrin-I tetramethyl ester (1b) has been obtained.

Aetiobiliverdin-IVγ(7a) is shown to be a by-product of the aetioporphyrin-I syntheses when 98% formic acid is used as the reaction medium, and the procedure has been modified to give preparatively acceptable yields of this bile pigment.