The synthesis of [10‐13C]bilirubin IXα

The total synthesis of [10-13C]bilirubin IXα, the principal waste product of haem degradation, is described. Site specific labelling was accomplished by the Vilsmeier formylation of one of the dipyrrolic fragments using [1-13C]dimethylformamide. The penultimate dehydrohalogenation reaction was complicated by a competing elimination reaction which yielded a bridged biliverdin derivative. [10-13C]bilirubin IXα was prepared in an overall yield of 6% (from the step where 13C was introduced) with quantitative isotopic incorporation.