Preparation of carbohydrate–oligonucleotide conjugates using the squarate spacer

Attachment of carbohydrates to oligonucleotides has proven to induce receptor-mediated endocytosis. A facile method for the formation of covalent linkages between glycans and oligonucleotides is herein described. Thus, use of 3,4-diethoxy-3-cyclobutene-1,2-dione as a linking reagent provides easy conjugation between carbohydrates bearing an amino group at the reducing end and oligonucleotides bearing an aminoalkyl modification.