Chemical and Chemoenzymatic Synthesis of S‐Linked Ganglioside Analogues and Their Protein Conjugates for Use as Immunogens

Abstract

Analogues of the tumor-associated gangliosides GM(3) and GM(2) containing terminal S-linked neuraminic acid residues and an amino terminated, truncated ceramide homologue have been synthesized and conjugated to a protein. The synthesis involved coupling of a S-linked sialyl alpha(2-->3) galactose disaccharide with a glucosyl sphingosine analogue, followed by elaboration and deprotection to give amino-terminated glycosyl ceramide 1. Glycosyltransferase-catalyzed extension of the trisaccharide 1 provided access to the modified GM(2) tetrasaccharide 2 or sulphur-containing GD(3) analogue 30. Owing to their potentially enhanced resistance to endogenous exo-glycoside hydrolases and their inherent non-self character, carbohydrate antigens containing non-reducing terminal thioglycosidic linkages may be more immunogenic than O-linked antigens and may stimulate the production of antibodies capable of recognizing naturally occurring oligosaccharides. Our initial results suggest that in fact these antigens are viable immunogens and furthermore, that immune sera cross reacts with O-gangliosides in the context of a heterologous glycoprotein conjugate.

A nonself sugar mimic of the HIV glycan shield shows enhanced antigenicity

“…It should be noted that previous examples of glycoconjugates designed as vaccines [containing, e.g., S-linked gangliosides (38) or N-propionylated polysialic acids (39)] have led to antibodies being generated that were highly complementary to the modification in preference to the unmodified sugar. Although here HIV-reactive antibodies were not elicited, higher titers of self-D1 arm (3) reactive antibodies were elicited by immunization with the nonself glycoconjugate compared to the self glycoconjugate; it also cannot be discounted that other differences such as loading distribution may play a role.…”

Synthesis and Immunochemical characterization of S‐linked Glycoconjugate Vaccines against Candida albicans

“…[8] We have demonstrated that thiooligosaccharide conjugate vaccines could evoke antibodies specific for native antigens in mice. [9,10] For example synthetic ganglioside antigens containing a terminal S-linked sialic acid were able to generate antibodies that recognized the corresponding O-linked antigen. As part of a detailed study of the immunochemistry of the protective (1!2)-b-mannan antigen of Candida albicans we have investigated the synthesis of C. albicans trisaccharide vaccine candidates composed of oligosaccharides containing terminal and an internal interglycosidic S-linkages.…”

Glycosylation of a Neoglycoprotein by Using Glycosynthase and Thioglycoligase Approaches: The Generation of a Thioglycoprotein

“…This work thereby complements the recent demonstration of the synthesis of thioglycoside-containing glycolipids by using the very low inherent activities of a few glycosyltransferases to catalyze thioglycoside formation. [26,27] The resistance of this thioglycoprotein, but not of its oxygen analogue, to glycosidase digestion and the further glycosylation of both structures by glycosyl transferases directly demonstrates the potential of this approach for generating metabolically stable glycoprotein structures. Work is currently underway to extend this strategy with other glycosynthases and thioglycoligases to other glycosylated structures, particularly those which terminate in a thiosialoside, and to install these in natural glycoproteins.…”