The Second-Generation Electrochemical Labeling of Hydroxyindoles with Chemoselectivity (eCLIC) for Site-Specific Protein Bioconjugation

Abstract

Electrochemistry has gained recognition for its precise control over reactions, mild conditions, and scalability in small molecule synthesis. However, its application in modifying complex biomolecules, including proteins, specifically through electrochemical site-specific labeling, is still relatively unexplored. The eCLIC, electrochemically-promoted coupling reaction, developed by the Chatterjee group enables the selective labeling of proteins using 5-HTP and aromatic amines under mild conditions. By incorporating 5-HTP through genetic code expansion, eCLIC allows for specific labeling of recombinant proteins. Although the technique offers advantages such as high conversion rates, broad substratescope, cost-effectiveness, and compatibility with existing labeling methods, its optimization for incorporating hydrophobic molecules is essential. Initial attempts to conjugate 5-HTP with hydrophobic molecules through eCLIC were challenging, but the incorporation of negatively charged functional groups, such as carboxylic acids, has shown to be promising in enhancing the reactivity of eCLIC reactions. This study investigates the use of tertiary aniline warheads with negatively charged functional groups in conjunction with hydrophobic molecules to improve reaction efficiency and stability. The results demonstrate that these functional groups facilitate more efficient carbon-carbon bond formation, leading to stable conjugation between the warhead and the target protein. The findings emphasize the potential of incorporating negatively charged functional groups in designing eCLIC reactions and their role in developing effective and versatile site-specific labeling strategies for complex biomolecules.