Synthesis of the glycan moiety of ganglioside HPG-7 with an unusual trimer of sialic acid as the inner sugar residue

The glycan moiety of ganglioside HPG-7, isolated from the sea cucumber (Holothuria pervicax), was synthesized for the first time. The characteristic substructure, a trisialic acid sequence embedded in the glycan, was deliberately constructed by utilizing suitably differentiated sialyl units for various synthetic purposes. Finally, a pentasaccharide was successfully delivered as the hexyl glycoside.