An Fmoc-protected L-serine building block carrying a branched Galβ1-3[GlcNAcβ1-6]GalNAcα trisaccharide, 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 core 2 structure (Galβ1-3[GlcNAcβ1-6]GalNAcα-O-Ser/Thr), a branched mucin-type O-glycan core that serves as a scaffold for extended and sialylated/fucosylated O-glycans, used in mucin and selectin-ligand research.