Chemical synthesis of glycans up to a 128-mer relevant to the O-antigen of Bacteroides vulgatus.

Glycans are involved in various life processes and represent critical targets of biomedical developments. Nevertheless, the accessibility to long glycans with precise structures remains challenging. Here we report on the synthesis of glycans consisting of [→4)-α-Rha-(1 → 3)-β-Man-(1 → ] repeating unit, which are relevant to the O-antigen of Bacteroides vulgatus, a common component of gut microbiota. The optimal combination of assembly strategy, protecting group arrangement, and glycosylation reaction has enabled us to synthesize up to a 128-mer glycan. The synthetic glycans are accurately characterized by advanced NMR and MS approaches, the 3D structures are defined, and their potent binding activity with human DC-SIGN, a receptor associated with the gut lymphoid tissue, is disclosed. Glycans are abundant biomolecules that mediate essential biological processes, but their chemical synthesis is challenging. Here, the authors report the synthesis of glycans up to a 128-mer, which represents the O-antigen of Bacteroides vulgatus lipopolysaccharide and one of the longest synthetic glycans to date.