Spin labels as a tool to identify and characterize protein-ligand interactions by NMR spectroscopy.

NMR spectroscopy based discovery and optimization of lead compounds for a given molecular target requires the development of methods with maximum sensitivity and robustness. It is shown here that organic nitroxide radicals ("spin labels") can be used to boost the sensitivity of NMR spectroscopic screening in drug discovery research. The concept of utilizing spin labels in NMR spectroscopy is summarized, examples for successful first-site and second-site NMR spectroscopic screens are given, and guidelines for linker design are presented.