General last-step labeling of biomolecule-based substrates by [12C], [13C], and [11C] carbon monoxide.

Alkaloid-, steroid-, biotin-, carbohydrate-, nucleoside-, and peptide-based bioconjugates are easily labeled with CO by a last-step palladium-catalyzed carbonylation. The choice of the [12C], [13C], or [11C] isotope opens the way to a new class of potential tracers or ligands easily available for various applications.