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

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. Herein, we report a practical synthesis of FmocAsn(N-AcGlcNAz)OH, a building block for solid phase peptide synthesis (SPPS). Protecting group manipulations are minimised by taking advantage of the inherent chemoselectivity of phosphine-mediated azide reduction, and the resulting glycosyl amine is employed directly in the opening of Fmoc protected aspartic anhydride.

Rapid synthesis of N-glycan oxazolines from locust bean gum via the Lafont rearrangement.

Enzymatic degradation of locust bean gum provides a Manβ(1 → 4)Man disaccharide, which may be converted into the core Manβ(1 → 4)GlcNAc disaccharide unit of all N-glycans via conversion to a 2-iodo-glycosyl azide, and Lafont rearrangement. The Manβ(1 → 4)GlcNAc disaccharide may be used as a key intermediate for elaboration into more complex N-glycan structures providing a route to N-glycan oxazolines as donor substrates for ENGase enzymes that is considerably shorter than those reported previously.