ON THE ROLE OF SINGLET OXIGEN IN THE SELF-SENSITIZED PHOTO-OXYGENATION OF BILIRUBIN AND ITS PYRROMETHENONE MODELS

Article abstract of DOI:10.1016/S0040-4020(01)88703-2

4-Ethyl-3-methyl-5-(4-ethyl-3,5-dimethylpyrrolyl-2-methylidene)-3-pyrrolin-2-one (1), 3,4-diethyl-5-(4-ethyl-3,5-dimethylpyrrolyl-2-methylidene)-3-pyrrolin-2-one (2) and xanthobilirubinic acid (XBR) undergo self-sensitized photo-oxygenation, as does bilirubin.The reaction products of 1 consist of methylethylmaleimide, kryptopyrrole aldehyde and its photo-oxygenation product and oxygenated dipyrroles.The same products are formed from 2, except xeronimide is found instead of methylethylmaleimide.Kinetic studies indicate that singlet oxygen is not necessarily involved in the photo-oxygenation reactions.Geometric photoisomerization (Z<*>E) of 1 and 2, and XBR proceeds at an even faster rate than photosensitized oxygenation.