N-terminal protein-macrocycles enabled by conjugate addition/ring expansion cascade reactions

Site selective protein modification is a vital tool in chemical biology and associated biomedical research. In this manuscript, simple, easy-to-prepare acryloyl imides are revealed as novel reagents for selective N-terminal protein bioconjugation, using conjugate addition/ring expansion (CARE) cascade reactions. Advantages of the CARE approach include high selectivity for N-terminal modification over lysine side chains, the formation of stable bioconjugates driven by irreversible ring expansion, and the ability to generate proteins modified with relatively complex, functionalized macrocycles. The selective N-terminal modification of a series of medicinally relevant proteins is demonstrated, allowing the imaging of prostate cancer tissue slices and the modulation of cell surface chemokine receptors.