Photo-oxidation of bilirubin in hydroxylic solvents

Abstract

Photo-oxidation of bilirubin in methanol containing anhydrous ammonia (0·2%) rapidly destroys the substrate. Methylvinylmaleimide, three methanol–propentdyopent adducts, and a water–propentdyopent adduct have been isolated. Arguments are presented which allow structures to be assigned to the propentdyopent adducts, and the absence of a fourth methanol–propentdyopent isomer is rationalised. Equilibration between a pair of unsymmetrically substituted methanol–propentdyopent adducts occurs on irradiation (of the free acids), on treatment with zinc acetate, and on treatment with 10% acetic acid in chloroform. A dipyrrylmethane dialdehyde obtained from an aqueous photolysate of bilirubin has been characterised. Mechanistic aspects of the photo-oxidation are discussed.