Oligosaccharide–Peptide Ligation of Glycosyl Thiolates with Dehydropeptides: Synthesis of S‐Linked Mucin‐Related Glycopeptide Conjugates

A chemoselective strategy for oligosaccharide-peptide ligation is described in which α-thio analogues of mucin-related glycoconjugates can be readily accessed through site-selective conjugate addition of complex oligosaccharide thiolates to dehydroalanine-containing peptides. The efficiency of the ligation is highlighted by the rapid convergent assembly of thio-isosteres of the four tumor-associated carbohydrate antigens, T N , T, ST N , and 2,6-ST, as a pair of diastereoisomers at the newly formed cysteine stereocenter. The process proceeds in high yield and with complete retention of the α-anomeric configuration.