Synthesis of a thioglycoside tetrasaccharide block, b-D-Galp-(1->4)-b-DGlcp-(1->6)-[b-D-Galp-(1->4)]-b-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 methodol. yielded the trimer. Deprotection then produced an octa and a dodecasaccharide deriv. ready for conjugation to proteins to afford immunoactive glycoconjugates. [on SciFinder (R)]