Efficient synthesis and enzymatic extension of an N -GlcNAz asparagine building block

Abstract

N-Azidoacetyl-D-glucosamine (GlcNAz) is a particularly useful tool in chemical biology as the azide is a metabolically stable yet accessible handle within biological systems. In this work [1], we recently reported a practical synthesis of FmocAsn(N-Ac3GlcNAz)OH, a building block for solid phase peptide synthesis (SPPS). Protecting group manipulations were minimised by taking advantage of the inherent chemoselectivity of phosphine-mediated azide reduction, and the resulting glycosyl amine was employed directly in the opening of Fmoc protected aspartic anhydride. We demonstrated one potential application of the building block by establishing it as a substrate for enzymatic glycan extension using sugar oxazolines of varying size and biological significance with several endo-β-Nacetylglucosaminidases (ENGases). The added steric bulk resulting from incorporation of the azide was shown to have no or a minor impact on the yield of enzymatic glycan extension.