Chemoenzymatic Synthesis of Unnatural Nucleotide Sugars for Enzymatic Bioorthogonal Labeling

Abstract

In recent years, the development of the enzymatic bioorthogonal labeling strategy has offered exciting possibilities in the probing of structure-defined glycan epitopes. This strategy takes advantage of relaxed donor specificity and strict acceptor specificity of glycosyltransferases to label target glycan epitopes with bioorthogonal reactive groups carried by unnatural nucleotide sugars in vitro. The subsequent covalent conjugation by bioorthogonal chemical reactions with either fluorescent or affinity tags allows further visualization, quantification, or enrichment of target glycan epitopes. However, the application and development of the enzymatic labeling strategy have been hindered due to the limited availability of unnatural nucleotide sugars. Herein, a platform that combines chemical synthesis and enzymatic synthesis for the facile preparation of unnatural nucleotide sugars modified with diverse bioorthogonal reactive groups is described. By this platform, a total of 25 UDP-GlcNAc and UDP-GalNAc derivatives, including the most well explored bioorthogonal functional groups, were successfully synthesized. Furthermore, the potential application of these compounds for use in enzymatic bioorthogonal labeling reactions was also evaluated.