A facile synthesis of sialylated oligolactosamine glycans from lactose via the Lafont intermediate

The 2-aminophosphonium iodide lactosamine glycoside (Lafont intermediate) readily obtained from lactose has been previously shown not to be amenable to derivatization for oligosaccharide synthesis, but has now been successfully converted via the salicylaldehyde imine into suitably protected lactosamine building blocks (13-16) for glycosylation. The titled strategy has enabled us to rapidly synthesize the Neu5Ac-alpha-2,3LacNAc-beta-1,3LacNAc pentasaccharide and Neu5Ac-alpha-2,3LacNAc-beta-1,3LacNAc-beta-1,3LacNAc heptasaccharide. Furthermore, this strategy has been adopted for the synthesis of other 2-amino sugars (e.g., 23-27), which provides a useful method for the preparation of 2-amino sugar building blocks.