O‐Specific Polysaccharide of Vibrio cholerae O139: Improved Synthesis and Conjugation to BSA by Squaric Acid Chemistry

• Published in: European journal of organic chemistry Vol. 2018; no. 23; pp. 2944 - 2957
• Main Authors: Lu, Xiaowei, Pfister, Hélène B., Soliman, Sameh E., Kováč, Pavol
• Format: Journal Article
• Language: English
• Published: Weinheim Wiley Subscription Services, Inc 22-06-2018
• Subjects: Antigens; Carbohydrate chemistry; Chemical synthesis; Conjugation; Glycoconjugates; Oligosaccharides; Organic chemistry; Polysaccharides; Proteins; Serum albumin; Vaccine; Vibrio
• ISSN: 1434-193X; 1099-0690
• DOI: 10.1002/ejoc.201800429

The sequence α‐Colp‐(1→2)‐4,6‐P‐β‐d‐Galp‐(1→3)‐[α‐Colp‐(1→4)]‐β‐d‐GlcpNAc‐(1→4)‐α‐d‐GalpA‐(1→3)‐β‐d‐QuipNAc constitutes the complete O‐specific polysaccharide (O‐antigen, O‐SP) of Vibrio cholerae O139. It was chemically synthesized in a linker‐equipped, conjugation‐ready form (7) and conjugated to a model protein carrier, bovine serum albumin. The preparation involved the synthesis of a tetrasaccharide intermediate sequence β‐d‐Galp‐(1→3)‐β‐d‐GlcpNAc‐(1→4)‐α‐d‐GalpA‐(1→3)‐β‐d‐QuipNAc→linker by coupling of two disaccharide intermediates followed by a stepwise, two single‐site colitosylations. The present synthesis is an alternative to the academic, small‐scale synthesis developed earlier where the final hexasaccharide assembly was achieved by simultaneous, two‐sites colitosylation. The approach reported herein comprises a few more synthetic steps but is experimentally less demanding, minimizes separation difficulties and is more convenient when tens of mgs of the final product is required. Syntheses of non‐phosphorylated and methyl ester analogues of 7 are also described.
The shown hexasaccharide is the complete O‐specific polysaccharide of Vibrio cholerae O139. It was chemically synthesized in a linker‐equipped, conjugation‐ready form and conjugated to a model protein carrier, bovine serum albumin. The approach reported herein is experimentally undemanding, minimizes separation difficulties and is suitable for preparation of tens of mgs of the final product.