Chemistry of Bifunctional Photoprobes. 1. Perfluoroaryl Azido Functionalized Phosphorus Hydrazides as Novel Photoreactive Heterobifunctional Chelating Agents:  High Efficiency Nitrene Insertion on Model Solvents and Proteins

Synthesis and evaluation of a new class of photochemically activated heterobifunctional chelating agents for protein modification is described. Selective functionalization of perfluoroaryl azides by versatile phosphorus hydrazide ligating systems 2 and 3 for the complexation of transition metals and analogous radiometals form the basis for these new agents. The utility of the photogenerated precursors from these bifunctional agents to form covalent attachments is demonstrated through examination of C−H bond insertion on cyclohexane. Representative amide-coupled phosphorus hydrazides 5 and 6 provide >78% insertion of the probe into unactivated C−H bonds of cyclohexane with short photolysis times. Photoconjugation of the photoactivable heterobifunctional chelating agent 6 and its Pd metalated analog 7 with HSA is also evaluated. The uncomplexed chelate appears to add to HSA with high efficiency, consistent with the observed 82% bond insertion into model solvents. Covalent attachment of 7, evaluated through the use of 109Pd, was estimated to be between 49% and 74% with the uncertainty arising because of prephotolysis association of the 109Pd complex with HSA. The application of in situ 19F NMR to distinguish between bond insertion and noninsertion processes is demonstrated. These results suggest that functionalized perfluoroaryl azido phosphorus hydrazides may find utility as heterobifunctional photolabeling agents for attaching radionuclides to proteins and antibodies.