Synthesis of erythropoietins site‐specifically conjugated with complex‐type N‐glycans

: The biological activity of the glycoprotein hormone erythropoietin (EPO) is dependent mainly on the structure of its N-linked glycans. We aimed to readily attach defined N-glycans to EPO through copper-catalyzed azide alkyne cycloaddition. EPO variants with an alkyne-bearing non-natural amino acid (Plk) at the N-glycosylation sites 24, 38, and 83 were obtained by amber suppression followed by protein purification and refolding. Click conjugation of the alkynyl EPOs with biantennary N-glycan azides provided biologically active site-specifically modified EPO glycoconjugates.