An Fmoc-protected L-threonine building block carrying an α-D-GalNAc residue, designed for solid-phase peptide synthesis (SPPS) of glycopeptides. The Nα-Fmoc group is removed under standard base conditions (piperidine) during chain elongation, while the free α-carboxylic acid is available for coupling to the growing resin-bound peptide. The sugar hydroxyl groups are protected as three acetate esters (Ac3), which keep the glycan inert during synthesis and are removed under mild base (e.g., sodium methoxide / hydrazine) after assembly. The installed glycan is the Tn antigen (GalNAcα-O-Ser/Thr), the simplest mucin-type O-glycan and a tumor-associated carbohydrate antigen, widely used to build glycopeptides for cancer vaccine, anti-Tn antibody, and lectin (e.g., MGL/CLEC10A) research.