Spacer-equipped dimers and trimers of the repeating units of the capsular polysaccharide of Haemophilus influenzae type c, -4)-3-O-Ac-b-D-GlcpNAc-(1->3)-a-D-Galp-(1-OPO3--, and type f, -3)-b-D-GalpNAc-(1->4)-3-O-Ac-a-D-GalpNAc-(1-OPO3--, have been synthesized for use in immunol. studies. H-Phosphonate chem. was used for the formation of the interglycosidic phosphate diester linkages. Two types of building blocks, a spacer glycoside disaccharide starting monomer and an anomeric monoester a-H-phosphonate disaccharide elongating monomer, were built up for each serotype structure from properly protected monosaccharide precursors using mainly thioglycosides as glycosyl donors. Stereospecificity in the formation of the a-linked monoester H-phosphonate was possible in type c through crystn. of the pure a-anomer of the precursor hemiacetal from an a/b-mixt., whereas in type f, the hemiacetal was isolated directly as exclusively the a-anomer. Subsequent phosphonylation using triimidazolylphosphine was performed without anomerization. Formation of the anomeric phosphate diester linkages was performed using pivaloyl chloride as coupling reagent followed by I2/H2O oxidn. of the formed diester H-phosphonates. Original expts. afforded no diester product at all, but optimization of the oxidn. conditions (lowering the temp. and diln. with pyridine prior to I2 addn.) gave the dimers in good yields (71% and 81%) and, subsequently, after removal of a temporary silyl protecting group in the dimers, the trimers in fair yields (36% and 37%), accompanied by hydrolysis of the dimer phosphate linkage. One-step deprotection through catalytic hydrogenolysis efficiently afforded the target dimer and trimer structures. The synthetic scheme allows for further elongation to give higher oligomers. [on SciFinder (R)]