Isotope labeling is a crucial tool in drug discovery. Therefore, expanding the toolbox of a radiochemist with methods that allow late-stage labeling is highly important. The work presented in this thesis describes the development and utilization of late-stage labeling methods with carbon and fluorine. Carbonylation reactions with carbon monoxide are particularly known as mild and compatible with the late-stage labeling. The first part of the thesis describes the development of visible-light mediated palladium-catalysis using alkyl iodides as the coupling partner for the carbonylation. The mild and versatile radical aminocarbonylation protocol has shown good substrate compatibility. The use of 9-Methylfluorene-9-carbonyl chloride (COgen) allowed easy translation between unlabeled and labeled reaction. In order to bypass the synthesis of COgen which proceeds in two steps plus one step for the liberation of CO, we focused our efforts towards the one step reduction of labeled CO₂ to labeled CO using disilanes catalyzed by fluorides. The last part of this thesis discusses the development of a new positron emission tomography (PET) radiotracer for P-glycoprotein (P-gp), an active transporter at the blood-brain barrier. Crizotinib is an approved treatment for non-small cell lung carcinoma and its brain accumulation is restricted by P-gp. Crizotinib was successfully labeled with ¹⁸F, and rodent studies to map P-gp and improve the delivery of crizotinib to the brain are ongoing.