Non-enzymatic Stereoselective S-glycosylation of Polypeptides and Proteins

Abstract Glycosylation (1-4) is an essential and powerful technique that Nature employs to regulate the properties and functions of proteins and polypeptides. Our capacity to emulate Nature’s power, however, is limited by the methods available (5) to perform glycosylation on these complex biomolecules. So far, very few glycosylation reactions could operate under the conditions tolerated by biomolecules (e.g., aqueous media, mild pH, and ambient temperature), and the need to install glycosyl groups in a stereo-controlled fashion poses additional, significant challenges. Here we report a non-enzymatic glycosylation reaction that builds axial S-glycosidic bonds under biorelevant conditions. Our strategy exploits the exceptional functional group tolerance of radical processes, and is enabled by the design and use of allyl glycosyl sulfones as precursors to glycosyl radicals. Our method could introduce a variety of glycosyl units to the cysteine residues of polypeptides in a highly selective fashion. The power of this method is further demonstrated in the direct glycosylation of bioexpressed proteins. Computational and experimental studies provide insights into the reaction mechanism.