Peptide and Protein Cysteine Modification Enabled by Hydrosulfuration of Ynamide

Efficient functionalization of peptides and proteins has widespread applications in chemical biology and drug discovery. However, the chemoselective and site-selective modification of proteins remains a daunting task. Herein, a highly efficient chemo-, regio-, and stereoselective hydrosulfuration of ynamide was identified as an efficient method for the precise modification of peptides and proteins by uniquely targeting the thiol group of cysteine (Cys) residues. This novel method could be facilely operated in aqueous buffer and was fully compatible with a wide range of proteins, including small model proteins and large full-length antibodies, without compromising their integrity and functions. Importantly, this reaction provides the <i>Z</i>-isomer of the corresponding conjugates exclusively with superior stability, offering a precise approach to peptide and protein therapeutics. The potential application of this method in peptide and protein chemical biology was further exemplified by Cys-bioconjugation with a variety of ynamide-bearing functional molecules such as small molecule drugs, fluorescent/affinity tags, and PEG polymers. It also proved efficient in redox proteomic analysis through Cys-alkenylation. Overall, this study provides a novel bioorthogonal tool for Cys-specific functionalization, which will find broad applications in the synthesis of peptide/protein conjugates.