Chemoenzymatic Synthesis of Glycosphingolipids Having an HNK-1 Epitope for Erythrocyte Cell Surface Remodeling

Abstract

Several neuropathies, such as Guillain-Barré syndrome and myelin-associated glycoprotein neuropathy (MAG), are caused by antibodies targeting glycosphingolipids. Several studies have indicated that MAG arises from pathogenic IgM autoantibodies targeting sulfoglucuronyl (HNK-1)-containing glycosphingolipids. The exact mechanism by which IgM neuropathy occurs has not been fully elucidated. Furthermore, no appropriate diagnostic tools are available for MAG using sulfoglucuronyl-containing glycosphingolipids. To address these limitations, we describe here a synthetic strategy that makes it possible to prepare sulfoglucuronyl paraglobosides using a neochemoenzymatic approach. It is based on the enzymatic assembly of N-acetyllactosamine (LacNAc) backbones as thioglycosides that were subjected to protecting group manipulations to give glycosyl acceptors for the chemical installation of a sulfated glucuronic acid moiety. A late-stage conversion of the thioglycosides into anomeric fluorides made it possible to enzymatically introduce sphingosine. The resulting compounds were acylated to provide 3-sulfo-glucuronyl- and glucuronyl-containing glycosphingolipids, respectively. The glycosphingolipids were employed to remodel the surface of erythrocytes to examine complement-mediated toxicity by an anti-HNK-1 antibody. It was found that erythrocytes remodeled with exogenously administered HNK-1 containing glycosphingolipid undergo complement-dependent lysis when incubated with an anti-CD57 IgM antibody, whereas a compound lacking a sulfate was not able to induce this effect. The approach could be extended to the gangliosides GM1a and GD1a, which have been implicated in Guillain-Barré syndrome. The results highlight that cell surface remodeling will be attractive for diagnosis, disease monitoring, and immunological research of diseases associated with pathogenic antibodies targeting glycosphingolipids.