Concise chemoenzymatic synthesis of N-glycans

Structure-defined N-glycans are essential tools to uncover the molecular basis of N-glycan functions. However, the difficulty in obtaining diverse collections of well-defined N-glycans has always been an obstacle that greatly hampers progress in glycoscience. Here, we developed a general platform for the concise total synthesis of N-glycans. Using the designed strategy, the general N-glycan precursors, including core pentasaccharide and core tetrasaccharide, were successfully assembled from common starting materials in only a few facile chemical and enzymatic steps. Starting from core pentasaccharide and core tetrasaccharide, a variety of biantennary N-glycans were prepared successfully in large quantities by taking advantage of enzymatic diversification. In particular, reverse galactosylation was employed as a selective protecting strategy, by which complex asymmetric N-glycans could be obtained easily and efficiently.