Highly Chemo-, Regio- and Stereoselective Cysteine Modification of Peptides and Proteins with Ynamides

Chemoselective modification of peptides and proteins has wide applications in chemical biology and pharmaceutical development. An efficient cysteine (Cys) precise modification protocol via rationally designed β-addition of ynamides is reported. The strong electron-withdrawing triflyl group on the nitrogen atom of ynamides plays a crucial role for controlling the chemo-, stereo- and regioselectivities of this protocol. Another substituent of the terminal ynamides offers a handle for functionality diversification. This Cys modification with ynamides proceeds efficiently in a slightly basic aqueous media (pH 8) to provide a series of Z-isomer of the corresponding conjugated products with excellent stereoselectivity (> 99%) and superior stability. All the reactive peptide side chain functional groups such as amino, carboxyl, primary amide, and hydroxyl groups, as well as the unprotected imidazole and indole rings are compatible. This method displays a broad substrates scope including linear and cyclic peptides and proteins. The potential application of this method in peptide and protein chemical biology was exemplified by Cys-bioconjugation with ynamides containing different functional molecules, including drug, fluorescent and affinity tags. In addition, this strategy is also compatible with click chemistry (performed in one pot), which remarkably extends the toolbox for further applications. The chemoselective biotinylation of ubiquitin(G47C) variant with a biotinylated ynamide, as well as the regioselective modification of Cys14 and Cys38 in bovine pancreatic trypsin inhibitor (BPTI) were accomplished under the optimized conditions and in high yield, without perturbation of disulfide bonds.