A β-D-N-acetyllactosamine (LacNAc) ligand equipped with a terminal carboxylic acid through a hydrophilic PEG3 spacer. The carboxylic acid can be activated to NHS, sulfo-NHS, or pentafluorophenyl esters and reacted with amine-functionalized platforms or lysine residues on proteins and peptides to form amide bonds. This compound provides an N-acetyllactosamine (LacNAc; Galβ1-4GlcNAc) building block, a core disaccharide of N- and O-glycans and a galectin ligand; it is a substrate for sialyltransferases and fucosyltransferases, enabling extension to sialylated and fucosylated structures.