Chemoenzymatic synthesis of a MUC1 glycopeptide carrying non-natural sialyl TF-β O-glycan

Abstract

A MUC1 type of glycopeptide was synthesized by the 9- fluorenylmethoxycarbonyl (Fmoc) solid-phase peptide synthesis (SPPS) protocol using benzyl and benzylidene-protected β-D-Gal-(1→3)-β-D-GalNAc- Ser/Thr (TF-β: a stereoisomer of the Thomsen-Friedenreich antigen). The synthetic glycopeptide was released from the resin with reagent K, and the resulting benzylated glycopeptide was deprotected under conditions of low-acidity trifluoromethanesulfonic acid (TfOH). The glycopeptide carrying duplicate non-natural O-glycans was dominant in the products, but was accompanied by a considerable amount of the glycopeptide missing one of the O-glycans. In contrast, the native α-glycoside was relatively stable under the acidic debenzylation conditions as shown by a parallel experiment with the glycopeptide involving α-D-GalNAc-Ser/Thr linkage. Enzymatic glycosylation with CMP-NeuAc was successful with both natural and non-natural O-glycans of the synthetic glycopeptide.