The present invention relates to a process for the production of a conjugate from a polynucleotide and a polysaccharide comprising the steps: a) provision of an aldonic acid of the polysaccharide or of a derivative thereof b) reaction of the aldonic acid with an alcohol derivative, preferably a carbonate derivative of an alcohol, to an aldonic acid ester, preferably to an activated aldonic acid ester and c) reaction of the aldonic acid ester with the polynucleotide, wherein the polynucleotide exhibits a functional amino group, wherein the reaction of the aldonic acid with the alcohol derivative in step b) takes place in a dry aprotic polar solvent.
