Abstract

Synthesis of the trisaccharide, benzyl 2-acetamido-3,6-di-O-benzyl-2-deoxy-β-Dglucopyranosyl-(1→3)-2,4,6-tri-O-benzyl-β-D-galactopyranosyl-(1→4)-2,3,6-tri-O-benzyl-β-Dglucopyranoside (9), was achieved from building block derivatives of the component mono- and disaccharide units. Initially the benzyl lactoside acceptor 3, which has a free hydroxyl group at position O-3`, was prepared via selective opening of the 3',4'-cyclic orthoester derivative 2. The glucosaminyl donor, 2-methyl (3,4,6-tri-O-acetyl-l,2-dideoxy-(α-D-glucopyrano)-[2`,1`:4,5]-2-oxazoline (4), was coupled to 3 affording the trisaccharide glycoside 5 in a good yield. Successive de-O-acetylation (5→6), benzylidenation (6→7), benzylation (7→8) and reductive opening of the benzylidene acetal function of 8 gave the target trisaccharide 9, which is a useful building block for the construction of complex oligosaccharides.

Keywords: Carbohydrates, Building block, Oxazoline coupling, Cyclic orthoester, Sialyl Le^x.

Graphical Abstract