Synthesis of Monovalent N-Acetylgalactosamine Phosphoramidite for Liver-Targeting Oligonucleotides

Ligand-targeted drug delivery (LTDD) has emerged as an attractive option in the field of oligonucleotide drugs following the great success of N-acetylgalactosamine (GalNAc)–conjugated siRNA and antisense oligonucleotides. GalNAc is a well-known ligand of the asialoglycoprotein receptor (ASGPR), and is classified as a C-type lectin associated with the metabolism of desialylated glycoproteins. This article describes the synthesis of a non-nucleosidic monovalent GalNAc phosphoramidite—a useful reagent for facilitating the conjugation of GalNAc epitopes into oligonucleotides using DNA synthesizers—together with some important caveats. The monomeric GalNAc consists of three parts: (1) a GalNAc moiety, (2) a linker moiety, and (3) a trans-4-hydroxyprolinol (tHP) branch point. The GalNAc moiety and the tHP moiety are coupled via a condensation reaction to prepare the monovalent GalNAc phosphoramidite. © 2019 by John Wiley & Sons, Inc.

Basic Protocol 1: Synthesis of N-acetylgalactosamine ligand

Basic Protocol 2: Preparation of trans-4-hydroxyprolinol building block

Basic Protocol 3: Preparation of GalNAc phosphoramidite