Bilirubin (BR) is a water-insoluble product of heme catabolism in mammals. Elevated blood concentrations of BR, especially in the neonatal period, are treated with blue-green light phototherapy. The major mechanism of BR elimination during phototherapy is photoisomerization, while a minor, less studied mechanism of degradation is oxidation. In this work, we studied the oxidation of the bilirubin model tetramethyl-dipyrrinone (Z-13) by singlet oxygen in methanol using UV-vis and ESI-MS spectroscopy, resulting in propentdyopents as the main oxidation products. We also identified two additional intermediates that were formed during the reaction (hydroperoxide 21a and imine 17). The structure of the hydroperoxide was confirmed by helium-tagging IR spectroscopy. Such reaction intermediates formed during the oxidation of BR or bilirubin models have not been described so far. We believe that this work can be used as a first step in studying the complex oxidation mechanism of BR during phototherapy.

Department of Chemistry Faculty of Science Masaryk University Kamenice 5 Brno 625 00 Czech Republic

Institute for Molecules and Materials Faculty of Science Radboud University Heyendaalseweg 135 Nijmegen 6525 AJ Netherlands

RECETOX Faculty of Science Masaryk University Kamenice 5 Brno 625 00 Czech Republic

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