Synthesis of the title pentasaccharide I, a highly branched pentasaccharide corresponding to structures found in lipopolysaccharides from Moraxella catarrhalis, is described. The best way to introduce the glucopyranosyl groups into the 3-, 4-, and 6-positions of the branched target compds. was a one-step reaction using a 3,4,6-triol as acceptor and 2,3,4,6-tetra-O-benzoyl-D-glucopyranosyl bromide as donor in a silver trifluoromethanesulfonate-promoted coupling. The spacer arm, necessary for the formation of immunoactive glycoconjugates, was introduced into the glucose moiety via a dimethyl(methylthio)sulfonium trifluoromethanesulfonate-promoted reaction using the Et thioglucoside as donor, whereas for Kdo, the acetylated glycal deriv., Me using the Et thioglucoside as donor, whereas for Kdo, the acetylated glycal deriv., Me 4,5,7,8-tetra-O-acetyl-2,6-anhydro-3-deoxy-D-manno-oct-2-enonate, was used as donor and phenylselenyl trifluoromethanesulfonate as a stereo-controlling promoter. [on SciFinder (R)]