A β-D-maltose (Glcα1-4Glc) ligand equipped with a terminal carboxylic acid through a hydrophilic PEG4 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 a maltose (Glcα1-4Glc) building block, a model α-glucan disaccharide for glycoconjugate synthesis and glycosidase studies.