Glyco oligonucleotide conjugates, each exhibiting two mannose and two galactose residues, were efficiently synthesized by two successive 1,3-dipolar cycloadditions (click chemistry). Two phosphoramidite derivatives were used: one bearing a bromoalkyl group as a precursor to azide functionalization and another bearing a propargyl group. After a first cycloaddition with a mannosyl-azide derivative, the bromine atoms were substituted with NaN(3) and a second click reaction was performed with a 1'-O-propargyl galactose, affording the heteroglyco oligonucleotide conjugate.

A solid support bearing an azido linker was used to synthesize a 3'-azido-alkyl-oligonucleotide by phosphoramidite chemistry. The resulting oligonucleotide was either conjugated by 1,3-dipolar cycloaddition on solid support or in solution with mannose-propargyl derivative and in solution with dansyl propargyl. Besides, after introduction of an alkyne function at the 5'-end, the resulting oligonucleotide bearing both 3'-azide and 5'-alkyne functions was circularized.