In this unit, a method is described that allows construction of multiantennary oligonucleotide glycoconjugates on a solid support. A bis(hydroxymethyl)malondiamide-based phosphoramidite that contains two phthaloyl-protected aminooxy groups compatible with normal chain assembly is prepared. The aminooxy functions can be deblocked with a hydrazinium acetate treatment and subsequently oximated on-support with fully acetylated 4-oxobutyl alpha-D-mannopyranoside. The resulting reagent is then used to prepare a conjugate containing two non-nucleosidic building blocks (i.e., four alpha-D-mannopyranosyl units) close to the 5' terminus of the oligonucleotide.