Site-directed spin labelling of proteins by Suzuki-Miyaura coupling via a genetically encoded aryliodide amino acid

We report site-directed protein spin labelling via Suzuki-Miyaura coupling of a nitroxide boronic acid label with the genetically encoded amino acid 4-iodo-L-phenylalanine. The resulting spin label bears a rigid biphenyl linkage with lower flexibility than spin label R1. It is suitable to obtain defined electron paramagnetic resonance distance distributions and to report protein-membrane interactions and conformational transitions of alpha-synuclein.