Peptide and Protein\nCysteine Modification Enabled\nby Hydrosulfuration of Ynamide

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