Block synthesis of Streptococcus pneumoniae type 14 capsular polysaccharide structures

Synthesis of a thioglycoside tetrasaccharide block, beta-D-Galp-(1 -> 4)-beta-DGlcp-(1 -> 6)-[beta-D-Galp-(1 -> 4)]-beta-D-GlcNPhthp-(1 -> SEt, corresponding to the repeating unit of Streptococcus pneumoniae serotype 14 CPS is described. Coupling of this block with a spacer followed by removal of an isopropylidene acetal yielded an acceptor, which was elongated with the donor block to give a protected dimer of the repeating unit. Iteration of this methodology yielded the trimer. Deprotection then produced an octa and a dode-casaccharide derivative ready for conjugation to proteins to afford immunoactive glycoconjugates.