Synthesis of trisaccharide 6’ SiaLec and its 6-O-Su derivative

The synthetic approach to 6 ' SiaLe c and its 6-O-Su derivative comprised α-sialylation of a protected Le c derivative, 2,3-di-OAcGalβ1-3(3-OAc-6-OBn)GlcNAcβ1-Osp (68% yield) as the key stage. Deprotection of the obtained trisaccharide (three stages, 79% overall yield) led to Neu5Acα2-6Galβ1-3GlcNAcβ1-Osp; partial deprotection followed by selective sulfation and total deprotection – to Neu5Acα2-6Galβ1-3(6-O-Su)GlcNAcβ1-Osp (four stages, 72% overall yield).