Synthesis and Preliminary Immunological Evaluation of a Pseudotetrasaccharide Related to a Repeating Unit of the Serotype 6A Capsular Polysaccharide.

2-Aminoethyl glycoside of the pseudotetrasaccharide α-d-Glc-(1→3)-α-l-Rha-(1→3)-d-Rib-ol-(5-2)-α-d-Gal corresponding to a repeating unit of the type 6A capsular polysaccharide has been synthesized. A suitably protected pseudotrisaccharide α-d-Glc-(1→3)-α-l-Rha-(1→3)-d-Rib-ol with a free 5-OH group in the ribitol moiety and a 2-OH derivative of 2-trifluoroacetamidoethyl α-d-galactopyranoside have been efficiently prepared and then connected a phosphate bridge using the hydrogen phosphonate procedure. Preliminary immunological evaluation of this pseudotetrasaccharide and the previously synthesized pseudotetrasaccharide corresponding to a repeating unit of the capsular polysaccharide of serotype 6B has shown that they contain epitopes specifically recognized by anti-serogroup 6 antibodies and are able to model well the corresponding capsular polysaccharides. Conjugates of the synthetic pseudotetrasaccharides with bovine serum albumin were shown to be immunogenic in mice.