Chemoenzymatic synthesis of deca and dodecasaccharide N-glycans of the ‘bisecting’ type

The synthesis of N-glycans carrying the ‘bisecting’ GlcNAc modification is difficult due to steric hindrance at the central β-mannoside. A facile introduction of a ‘bisecting’ GlcNAc residue was accomplished by using an excess of a glucosaminyl fluoride. After deprotection of the resulting octasaccharide a 6-aminohexanoyl spacer was attached. Enzymatic elongation of the carbohydrate chains using three different glycosyltransferases gave full length ‘bisecting’ N-glycans of the complex type terminating with galactose, α-2,6 or α-2,3 linked sialic acid.