Perfect Partners: Biocatalytic Halogenation and Metal Catalysis for Protein Bioconjugation.

Flavin-dependent halogenases (FDHs) are the most extensively researched halogenases and show great potential for biotransformation applications. These enzymes use chloride, bromide, or iodide ions as halogen donors to catalyze the oxygen-dependent halogenation of electron-rich aryl moieties, requiring stochiometric amounts of FADH in the process. This makes FDH-catalyzed aryl halogenation a highly selective and environmentally friendly tool for the synthesis of aryl halides. The latter in turn serve as valuable intermediates for transition metal catalyzed cross coupling reactions for C-C bond formation. Previous research made extensive use of this approach to halogenate small molecules as building blocks for late-stage functionalization by transition-metal catalyzed cross-coupling reactions. Based on these results, several groups have managed to expand this research to protein targets over the past two years. Their work indicates an emerging methodology for bioconjugation using late-stage biocatalytic halogenation in conjunction with biorthogonal Suzuki-Miyaura cross-coupling. This strategy could present an attractive alternative to existing approaches due to the stability of the C-C bond bridging the generated biaryl moiety and the ease of late-stage enzymatic modification while maintaining excellent selectivity under mild conditions.