Techniques to glycosylation are described, and more particularly to the production of glycosylation structures that are resistant to enzymatic degradation, thereby modulating one or more of their biological properties or those of therapeutic moieties incorporating them, and in particular to reacting activated carbohydrate substrates containing fluorine, such as 3-fluoro sialic acid compounds, with sugar acceptors to produce covalent conjugates of the sugar acceptor and one or more of the sialic acid compounds.