Convenient Synthesis of an N-Glycan Octasaccharide of the Bisecting Type

Convenient synthesis of an N-glycan octasaccharide (A) of the bisecting type was described. The stable and easily prepared orthoester F, 3 ''-O-chloroacetyl-4 '',6 ''-O-benzylidene-alpha-D-glucopyranose 1 '',2 ''-(chloromethyl 3',6'-di-O-benzyl-2'-deoxy-2'-phthalimido-beta-D-glucopyranosyl-(1 -> 4)-3,6-di-O-benzyl-2-deoxy-2-phthalimido-beta-D-glucopyranosylazide-4'-yl orthoacetate), was designed as the key intermediate with two advantages: (1) distinguishing OH-2 '' from OH-3 '' in beta-D-glucopyranoside to construct the central beta-D-mannopyranoside by inverting the configuration of OH-2 '' in beta-D-glucopyranoside and (2) distinguishing OH-4 '' and OH-6 '' from OH-3 '' in the beta-D-mannopyranoside to introduce the bisecting GlcNAc residue.