Synthesis of the Core Oligosaccharides of Lipooligosaccharides from Campylobacter jejuni: A Putative Cause of Guillain–Barré Syndrome

Abstract

The chemical synthesis of the highly branched core oligosaccharides of lipooligosaccharides (LOSs) found in Campylobacter jejuni, which causes Guillain–Barré syndrome by a preceding infection, is described. The target LOS mimics, consisting of eight or nine monosaccharides, were classified into three groups as key building blocks: ganglioside‐core tetra‐/pentasaccharides (GM1‐/GD1a‐like), l‐glycero‐d‐manno‐heptose‐containing trisaccharides, and 3‐deoxy‐d‐manno‐2‐octulosonic acid (KDO) residues. These synthetic fragments were obtained from commercially available monosaccharides. Less obtainable l‐glycero‐d‐manno‐heptose and KDO residues, as key components of the LOSs, were synthesized from p‐methoxyphenyl d‐mannoside and di‐O‐isopropylidene‐protected d‐mannose, respectively. The synthesis of α‐KDO glycoside, as one of the most difficult stereocontrolled glycosidic constructions, was achieved by treating a 2,3‐ene derivative of KDO with phenylselenyl trifluoromethanesulfonate as a suitable α‐directing reagent. All synthetic blocks were constructed through a convergent synthetic route, which resulted in the first synthesis of structurally challenging LOS core glycans containing ganglioside GM1 and GD1a‐core sequences.

Chemoenzymatic Synthesis of Campylobacter jejuni Lipo-oligosaccharide Core Domains to Examine Guillain–Barré Syndrome Serum Antibody Specificities

“…The chemical synthesis of the inner core hexasaccharide 1 is challenging due to the low acceptor reactivity of the C5-hydroxyl of Kdo-α-(2→4)-Kdo acceptor 29 − and the need to install glycosidic bonds to form a highly crowded 3,4-branched heptoside. , We envisaged that fully protected hexasaccharide 1 could be synthesized by a convergent and stereocontrolled [4 + 2] approach (Scheme ) relying on the use of flexible disaccharide intermediate 26 , which is modified by the orthogonal protecting groups 2-naphthylmethyl (Nap) ether, chloroacetyl (ClAc) ester, and allyl (All) ether. The ability to remove the Nap ether and ClAc ester protecting groups in different orders made it possible to establish the optimal glycosylation sequence, using glycosyl 27 and 28 , to prepare tetrasaccharide 41 having a crowded 3,4-branched heptoside.…”

“…Here, we introduce a synthetic strategy that addressed the latter deficiency and made it possible to prepare an unprecedented collection of ganglio-oligosaccharides ( 14 – 25 ). It was expected that the galactosyl moiety of inner-core oligosaccharide 1 would provide a proper starting structure for extension by the glycosyltransferases ,− and was amenable to our strategy to give access to ganglioside mimics 2 – 12 .…”

“…Finally, we examined WGA, which preferentially binds GlcNAc moieties and also interacts with glycoproteins via terminal sialic acid residues. As expected, only the ganglioside oligosaccharides having a terminal α(2,3)Neu5Ac moiety (14,17,22,24) and the corresponding mimics (2,5,10,12) showed binding (Figure 2D).…”

“…In each sample, IgM and/or IgG antibodies were observed that bound one or more of the ganglioside oligosaccharides (14−25). Anti-GM1a ( 16), anti-GM1b (24), and anti-GD1a (17) antibodies have been associated with the motor form of GBS after C. jejuni infection. 11,12,52 The array data showed that the majority of the patients had elicited IgM and/or IgG antibodies targeting GM1a.…”

Identifying the targets and functions of N-linked protein glycosylation in Campylobacter jejuni

“…10,11 The basis for these post-acute immune-mediated disorders is thought to be largely based on cross-reactivity between antibodies directed against C. jejuni surface lipooligosaccharide (LOS) and human cell surface gangliosides, and this relationship has been reviewed extensively. [12][13][14] Several C. jejuni genomes have been sequenced from laboratory-adapted and clinical strains and several features remain consistent; the organism encodes B1620-1650 genes, a large proportion of which encode membrane-associated proteins that are poorly functionally annotated. [15][16][17] Human infection is not completely understood but involves bacterial adherence to gut epithelial cells, followed by invasion and subsequent toxin production.…”