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.

This artwork represents a putative event in Guillain–Barré syndrome (GBS) pathogenesis based on molecular mimicry between microbial lipooligosaccharides (LOS) and human peripheral nerve gangliosides. IgG antibodies produced against ganglioside‐like LOSs on bacterial surfaces attack mammalian gangliosides expressed at the node of Ranvier, leading to the onset of GBS causing axonal neuropathy. More information can be found in the Full Paper by A. Imamura, H. Ishida, et al. on page 796.