A. Dondoni Research

It is well established that protein glycosylation is a post-translational modification that profoundly affects the protein structure, stability and biological properties and activities. As native glycoproteins are isolated as mixtures of glycoforms, there is a pressing need to make available by chemical synthesis glycopeptides and glycoproteins with a well established structure and composition. These compounds may serve as probes for studies of biological events as well as for the discovery of leads toward the development of new drugs. The developments of methods for the glycosylation of peptides and proteins by efficient and site-specific ligation tools is at the forefront in biotechnology and proteomics. We have developed a method that is based on the free-radical hydrothiolation of allyl glycosides by cysteine-containing peptides and the model protein bovine serum albumin (BSA). This reaction, currently known as thiol-ene coupling, is especially appealing because being thermally or photochemically induced is not metal-based catalyst dependent and is compatible with oxygen and water. Hence in a first instance we have set out the photoinduced glycosylation of glutathione and a cysteine-containing synthetic nonapeptide by a C-allyl galactoside. The mild reaction conditions employed in this exploratory study (room temperature, irradiation at 365 nm, aqueous solvent) were then adopted for the glycosylation of BSA. In this case, however, a multiple glycosylation did in fact occur due to the photochemically induced cleavage of cystine residues (Scheme 8). It is noteworthy that this protein was employed in its native form without any chemical modification/activation. Moreover, the observed hyperglycosylation constituted the first example of site- selective protein modification induced by a photocleavage reaction