An Fmoc-protected L-serine building block carrying a Galβ1-3GalNAcα disaccharide, 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 acetate esters (peracetate), 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 T antigen / core 1 structure (Galβ1-3GalNAcα-O-Ser/Thr), a tumor-associated carbohydrate antigen and ligand for galectins and the macrophage galactose lectin, used to build glycopeptides for cancer immunology and O-glycobiology research.