Gold‐Promoted Biocompatible Selenium Arylation of Small Molecules, Peptides and Proteins

Abstract

AbstractA low pKa (5.2), high polarizable volume (3.8 Å), and proneness to oxidation under ambient conditions make selenocysteine (Sec, U) a unique, natural reactive handle present in most organisms across all domains of life. Sec modification still has untapped potential for site‐selective protein modification and probing. Herein we demonstrate the use of a cyclometalated gold(III) compound, [Au(bnpy)Cl2], in the arylation of diselenides of biological significance, with a scope covering small molecule models, peptides, and proteins using a combination of multinuclear NMR (including 77Se NMR), and LC–MS. Diphenyl diselenide (Ph−Se)2 and selenocystine, (Sec)2, were used for reaction optimization. This approach allowed us to demonstrate that an excess of diselenide (Au/Se−Se) and an increasing water percentage in the reaction media enhance both the conversion and kinetics of the C−Se coupling reaction, a combination that makes the reaction biocompatible. The C−Se coupling reaction was also shown to happen for the diselenide analogue of the cyclic peptide vasopressin ((Se−Se)‐AVP), and the Bos taurus glutathione peroxidase (GPx1) enzyme in ammonium acetate (2 mM, pH=7.0). The reaction mechanism, studied by DFT revealed a redox‐based mechanism where the C−Se coupling is enabled by the reductive elimination of the cyclometalated Au(III) species into Au(I).