Synthesis of four spacer-containing `tetrasaccharidesʹ that represent four possible repeating units of the capsular polysaccharide of Streptococcus pneumoniae type 6B

In the framework of studies towards oligosaccharide-conjugate based vaccines against Streptococcus pneumoniae, the synthesis is reported of four spacer-containing `tetrasaccharidesʹ that each can be conceived as representing a repeating unit of the capsular polysaccharide of S. pneumoniae serotype 6B, namely, 3-aminopropyl d-ribityl-(5→hydrogen phosphate→2)-α-d-galactopyranosyl-(1→3)-α-d-glucopyranosyl-(1→3)-α-l-rhamnopyranoside, 3-aminopropyl α-l-rhamnopyranosyl-(1→4)-d-ribityl-(5→hydrogen phosphate→2)-α-d-galactopyranosyl-(1→3)-α-d-glucopyranoside, 3-aminopropyl α-d-glucopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→4)-d-ribityl-(5→hydrogen phosphate→2)-α-d-galactopyranoside, and α-d-galactopyranosyl-(1→3)-α-d-glucopyranosyl-(1→3)-α-l-rhamnopyranosyl-(1→4)-5-O-(3-aminopropyl hydrogen phosphate)-d-ribitol. Phosphorylations were carried out using the H-phosphonate method.