Synthesis of four spacer-containing 'tetrasaccharides' 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 tetrasaccharides 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)-alpha-D-galactopyranosyl-(1-->3) -alpha-D-glucopyranosyl-(1-->3)-alpha-L-rhamnopyranoside, 3-aminopropyl alpha-L-rhamnopyranosyl-(1-->4)-D-ribityl-5(-->hydrogen phosphate-->2)-alpha-D-galactopyranosyl-(1-->3)-alpha-D-glucopyranoside, 3-aminopropyl alpha-D-glucopyranosyl-(1-->3)-alpha-L-rhamnopyranosyl-(1-->4) -D-ribityl-(5-->hydrogen phosphate-->2) -alpha-D-galactopyranoside, and alpha-D-galactopyranosyl-(1-->3)-alpha-D-glucopyranosyl-(1-->3)-alpha-L -rhamnopyranosyl-(1-->4)-5-O-(3-aminopropyl hydrogen phosphate)-D-ribitol. Phosphorylations were carried out using the H-phosphonate method.