An α-L-rhamnose ligand equipped with a terminal carboxylic acid through a short butyl spacer. The carboxylic acid can be activated to NHS, sulfo-NHS, or pentafluorophenyl (PFP) esters and reacted with amine-functionalized platforms or lysine residues on proteins and peptides to form stable amide bonds. This compound provides an α-L-rhamnose building block for glycoconjugate synthesis and the construction of probes that exploit naturally occurring anti-rhamnose antibodies, with applications in antibody-recruiting molecule and immunotherapy research.