Abstract
We described the formation of bilirubin from recombination of intermediates formed in the bilirubin diazo coupling reaction. Two types of intermediates formed in the diazo coupling reaction of bilirubin changed to other yellow compounds, whose absorption spectrum was similar to that of bilirubin, during storage after extraction from the reaction mixture. The yellow substance was separated into three yellow compounds by thin layer chromatography. The RI values of these three compounds were similar to those of bilirubin IIIα, IXα and XIIIα. The relative proportions of formation of these three yellow compounds appeared to be 1: 2.6: 2. These substances reacted with the diazonum salt to form an azo dye and formed a green product with the same absorption spectrum as that of biliverdin upon oxidation with a nitrous acid solution. These findings suggested that three isomers, bilirubin IIIα, IXα and XIIIα, are formed by recombination of endovinyl and exovinyl dipyrrole intermediates.
