Synthesis and Immunological Characterization of Modified Hyaluronic Acid Hexasaccharide Conjugates

• Published in: Journal of organic chemistry Vol. 78; no. 16; pp. 8004 - 8019
• Main Authors: Gu, Guofeng, Adabala, Pal John Pal, Szczepina, Monica G, Borrelli, Silvia, Pinto, B. Mario
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 16-08-2013
• Subjects: Humans; Hyaluronic Acid - chemistry; Hyaluronic Acid - immunology; Hyaluronic Acid - pharmacology; Microbial Sensitivity Tests; Molecular Structure; Oligosaccharides - chemistry; Oligosaccharides - immunology; Oligosaccharides - pharmacology; Serum Albumin - chemistry; Serum Albumin - immunology; Streptococcal Infections - immunology; Streptococcal Infections - prevention & control; Streptococcal Vaccines - chemistry; Streptococcal Vaccines - immunology; Streptococcal Vaccines - pharmacology; Streptococcus - drug effects; Streptococcus - immunology; Tetanus Toxoid - chemistry; Tetanus Toxoid - immunology
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo4012442

The synthesis of a tetanus toxoid (TT)-conjugate of a hyaluronic acid (HA) hexasaccharide is described. The compound was intended for use in monitoring HA levels as a disease marker and as a potential vaccine against Group A Streptococcus (GAS) infections. We also report the synthesis of a chemically modified HA-hexasaccharide-TT conjugate in which the N-acetyl moiety of the N-acetyl-d-glucosamine residue is replaced with an N-propionyl unit in order to enhance immunogenicity. The oligosaccharides are synthesized in a convergent manner. The TT-conjugate syntheses rely on the reaction of the amines on the 6-aminohexyl aglycon of the hexasaccharides with diethyl squarate to give the monoethyl squarate adducts. Subsequent reactions with lysine ε-amino groups on TT then give the glycoconjugates containing an average of 8 hexasaccharide haptens per TT molecule. Immunological studies in mice show very similar antibody responses with both conjugates, suggesting that the N-acetyl groups of the glucosaminyl residues of the HA-hexasaccharide are not a critical part of the epitope recognized by the anti-HA polyclonal immune response. Furthermore, it would appear that the N-acyl moieties are not in close contact with the amino acid residues of the antibody combining sites.