NPs perform the reversible phosphorolysis of nucleosides to pentose-1-phosphates and nucleobases. By coupling the enzymatic phosphorolysis of a sugar donor with the glycosylation of a free nucleobase in situ, nucleosides can formally be synthesized directly from their corresponding nucleobases. The application of these enzymes resolves the need for protecting groups, laborious preparation as well as isolation of sugar synthons, and furthermore greatly reduces the use of toxic organic solvents by employing aqueous systems (for reviews, see ).