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Research aimed at understanding the specific role of glycosylation patterns in protein function would greatly benefit from additional approaches allowing direct access to homogeneous glycoproteins. Herein the development and application of an efficient approach for the synthesis of complex homogenously glycosylated peptides based on a multifunctional photocleavable auxiliary is described. The presence of a PEG polymer within the auxiliary enables sequential enzymatic glycosylation and straightforward isolation in excellent yields. The auxiliary-modified peptides can be directly used in native chemical ligations with peptide thioesters easily obtained by direct hydrazinolysis of the respective glycosylated peptidyl resins and subsequent oxidation. The ligated glycopeptides can be smoothly deprotected by UV irradiation. We apply this approach to the preparation of variants of the epithelial tumor marker MUC1 carrying one or more Tn, T, or sialyl-T antigens. [ABSTRACT FROM AUTHOR]

A game of tag: N‐Glycans on the surface of living cells were selectively tagged by exogenously administering recombinant ST6Gal I sialyltransferase and azide‐modified CMP‐Neu5Ac. This modification was followed by a strain‐promoted cycloaddition using a biotin‐modified dibenzylcyclooctynol (red star=biotin). The methodology will make it possible to dissect the mechanisms that underlie altered glycoconjugate recycling and storage in disease. [ABSTRACT FROM AUTHOR]