A conserved tetrasaccharide structure, L-glycero-a-D-manno-heptopyranosyl-(1->2)-(6-O-aminoethylphosphono-L-glycero-a-D-manno-heptopyranosyl)-(1->3)-[b-D-glucopyranosyl-(1->4)]-L-glycero-a-D-manno-heptopyranose, from the LPS inner core of Haemophilus influenzae has been synthesized as its ethylamino glycosides to allow later conjugations. Starting from a previously synthesized suitably protected trisaccharide intermediate, the third heptose and subsequently the spacer were introduced using thioglycoside donor chem. The phosphoethanolamine was formed employing a Boc-protected phosphoamidite. Final deprotection and conjugation to biotin gave conjugates that will be used to study the specificity of MAbs raised against native LPS structures. [on SciFinder (R)]