Efficient and Reproducible Synthesis of an Fmoc-protected Tn Antigen

The total synthesis of the Thomsen-nouveau (Tn) antigen, a tumour-associated O-linked mucin glycopeptide, was achieved through a concise route. The key glycosylation step proved challenging to reproduce from the literature precedents and was most reliably accomplished using a palladium-catalyzed coupling between the glycosyl donor and Fmoc-functionalized serine acceptor to form the target in moderate yields. This is, to the best of our knowledge, the shortest synthesis reported from galactose for preparing this essential building block for large-scale solid phase peptide synthesis.