Robust and General Procedure for Carbon Isotope Labeling of Linear Urea Derivatives with Carbon Dioxide

Carbon isotope labeling is a traceless technology, which allows tracking the fate of organic compounds either in the environment or in living organisms. Despite recent advances in the field, the development of robust and general technologies remains a significant task. This full article reports on a general approach to label urea derivatives with all carbon isotopes, including ¹⁴C and ¹¹C. Based on a Staudinger aza-Wittig sequence, it provides access to all aliphatic/aromatic urea combinations as well as to semicarbazides, sulfonylureas, hydroxyl ureas, and simple terminal ureas. A de-risking approach was developed to evaluate the robustness of the reaction. This technology is based on [¹⁴C]CO₂ screening that allowed to investigate the tolerance of the procedure with most representative heterocycles and functional groups found in FDA approved drugs.