Chemoenzymatic Preparation of a Lipid-Linked Heptasaccharide on an Azide-Linked Polyisoprenoid.

Complex poly- and oligosaccharides on the surface of bacteria provide a unique fingerprint to different strains of pathogenic and symbiotic microbes that could be exploited for therapeutics or sensors selective for specific glycans. To discover reagents that can selectively interact with specific bacterial glycans, a system for both the chemoenzymatic preparation and immobilization of these materials would be ideal. Bacterial glycans are typically synthesized in nature on the C55 polyisoprenoid bactoprenyl (or undecaprenyl) phosphate. However, this long-chain isoprenoid can be difficult to work with in vitro. Here, we describe the addition of a chemically functional benzylazide tag to polyisoprenoids. We have found that both the organic-soluble and water-soluble benzylazide isoprenoid can serve as a substrate for the well-characterized system responsible for -linked heptasaccharide assembly. Using the organic-soluble analogue, we demonstrate the use of an -acetyl-glucosamine epimerase that can be used to lower the cost of glycan assembly, and using the water-soluble analogue, we demonstrate the immobilization of the heptasaccharide on magnetic beads. These conjugated beads are then shown to interact with soybean agglutinin, a lectin known to interact with -acetyl-galactosamine in the heptasaccharide. The methods provided could be used for a wide variety of applications including the discovery of new glycan-interacting partners.