Abstract
2-Aminoethyl glycoside of the pseudotetrasaccharide α-d-Glcp-(1→3)-α-l-Rhap-(1→3)-d-Rib-ol-(5-P-2)-α-d-Galp corresponding to a repeating unit of the Streptococcus pneumoniae type 6A capsular polysaccharide has been synthesized. A suitably protected pseudotrisaccharide α-d-Glcp-(1→3)-α-l-Rhap-(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 via 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 S. pneumoniae 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.
Highlights
Streptococcus pneumoniae is a clinically important bacterial pathogen that causes serious diseases such as pneumonia, bacteremia, meningitis, otitis media, and others in children and adults (Feikin et al, 2000)
Pseudotetrasaccharides 1 and 2 conjugated to bovine serum albumin (BSA) were shown to be immunogenic in mice. Antibodies induced by those conjugates cross-reacted with biotinylated pseudotetrasaccharides 6A 22 and 6B 21. These results indicated the presence of a common epitope in capsular polysaccharides (CPs) of S. pneumoniae serotypes 6A and 6B
We have efficiently synthesized the spacer-armed pseudotetrasacchride corresponding to a repeating unit of the CP of S. pneumoniae serotype 6A
Summary
Streptococcus pneumoniae is a clinically important bacterial pathogen that causes serious diseases such as pneumonia, bacteremia, meningitis, otitis media, and others in children and adults (Feikin et al, 2000). More than 90 serotypes of S. pneumoniae have been identified according to the chemical structure of their capsular polysaccharides (CPs) (Kamerling, 2000). The CPs are considered to be one of the major factors of bacterial virulence. Of the ∼90 serotypes of S. pneumoniae, approximately 20, including the serogroup 6, are responsible for 80–90% of all pneumococcal infections (van Dam et al, 1990). Immunogenic conjugates of the S. pneumoniae serotype 6A CP with carrier proteins were prepared already at an early stage of pneumococcal vaccine development (Chu et al, 1983). The CPs of S. pneumoniae serotypes 6A and 6B are the constituents of the modern 13-valent conjugate pneumococcal vaccine
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