De Novo Chemoenzymatic Synthesis of Asymmetric N-Glycans Empowered by Sulfate and Phosphate as Novel Orthogonal Protecting Groups

Glycoproteins often exist in nature as heterogeneous glycoforms, and it has been difficult to obtain pure homogeneous samples to study the role of specific N-glycans in a glycoprotein. Despite various chemical and enzymatic methods developed for the synthesis of N-glycans, access to highly diverse N-glycans remains a challenge. Herein, we report a concise strategy for the synthesis of multi-antennary N-glycans from designed common core structures with phosphate and sulfate protecting groups, which can be selectively deprotected by respective phosphatase and sulfatase, thereby enabling enzymatic elongation to install a desired glycan chain at a specific antenna. We also explored the directing effect of galactose sulfation for enzymatic fucosylation of the neighboring GlcNAc, further expanding the structural diversity of multi-antennary N-glycans. Starting from sulfate and phosphate-terminated core structures, this synthetic strategy in aqueous solution provides an efficient and practical route for the enzymatic assembly of a diverse array of complex N-glycans for biological study.