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Chemical Synthesis Elucidates the Key Antigenic Epitope of the Autism‐Related Bacterium Clostridium bolteae Capsular Octadecasaccharide
Author(s) -
Cai Juntao,
Hu Jing,
Qin Chunjun,
Li Lingxin,
Shen Dacheng,
Tian Guangzong,
Zou Xiaopeng,
Seeberger Peter H.,
Yin Jian
Publication year - 2020
Publication title -
angewandte chemie international edition
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 5.831
H-Index - 550
eISSN - 1521-3773
pISSN - 1433-7851
DOI - 10.1002/anie.202007209
Subject(s) - tetrasaccharide , glycan , glycoconjugate , epitope , chemistry , antigen , microbiology and biotechnology , glycosylation , biochemistry , bacteria , stereochemistry , biology , glycoprotein , polysaccharide , genetics
The gut pathogen Clostridium bolteae has been associated with the onset of autism spectrum disorder (ASD). To create vaccines against C. bolteae , it is important to identify exact protective epitopes of the immunologically active capsular polysaccharide (CPS). Here, a series of C. bolteae CPS glycans, up to an octadecasaccharide, was prepared. Key to achieving the total syntheses is a [2+2] coupling strategy based on a β‐ d ‐Rha p ‐(1→3)‐α‐ d ‐Man p repeating unit that in turn was accessed by a stereoselective β‐ d ‐rhamnosylation. The 4,6‐ O ‐benzylidene‐induced conformational locking is a powerful strategy for forming a β‐ d ‐mannose‐type glycoside. An indirect strategy based on C2 epimerization of β‐ d ‐quinovoside was efficiently achieved by Swern oxidation and borohydride reduction. Sequential glycosylation, and regioselective and global deprotection produced the disaccharide and tetrasaccharide, up to the octadecasaccharide. Glycan microarray analysis of sera from rabbits immunized with inactivated C. bolteae bacteria revealed a humoral immune response to the di‐ and tetrasaccharide, but none of the longer sequences. The tetrasaccharide may be a key motif for designing glycoconjugate vaccines against C. bolteae .