This invention generally relates to the field of phosphoramidite derivatives. In particular, the invention relates to N-Acetylgalactosamine (GalNAc) compounds, in particular phosphoramidite or phosphonoamidite molecules of formula (I) with only one GalNAc moiety (formula II) and to conjugates of nucleic acid molecules with such N-Acetylgalactosamine containing molecules. Also provided are methods for preparation of these molecules and possible uses thereof, in particular in medicine. Wherein R1 is H or C1-6alkyl; R2 is a triphenylmethyl-based hydroxyl protecting group R3 is a phosphorus-containing group, particularly a phosphoramidite or a phosphonoamidite group, and K is represented by the general formula (II).