An Fmoc-protected L-serine building block carrying a β-D-xylose 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 a xylose residue (O-xylosylation), the initiating sugar of glycosaminoglycan biosynthesis on Ser, used to build proteoglycan-related glycopeptides.