A spacer-equipped tetrasaccharide, p-aminocyclohexylethyl a-L-Colp-(1->2)-b-D-Galp-(1->3)-[a-L-Colp-(1->4)]-b-D-GlcpNAc, contg. a 4,6-cyclic phosphate in the galactose residue, has been synthesized. The structure corresponds to a part of the repeating unit of the capsular (and lipo-) polysaccharide of the endemic bacteria Vibrio cholerae type O139 synonym Bengal. The synthetic strategy allows continuous syntheses of the complete O139 hexasaccharide repeating unit as well as of the structurally related repeating unit of serotype O22. Starting from Et 2-azido-4,6-O-benzylidene-2-deoxy-1-thio-b-D-glucopyranoside, a thioglycoside tetrasaccharide donor block was constructed through two orthogonal glycosylation with glycosyl bromide donors. First, a properly protected galactose moiety was introduced using silver triflate as promoter and subsequently the two colitose residues, carrying electron-withdrawing protecting groups for stability reasons, under halide-assisted conditions. The tetrasaccharide block was then linked to the spacer in a NIS-TMSOTf-promoted coupling. Transformation of the azido group into an acetamido group using H2S followed by removal of temporary protecting acetyl groups gave a 4',6'-diol, which was next phosphorylated with Me dichloro-phosphate and deprotected to yield the 4,6-cyclic phosphate tetrasaccharide target structure. [on SciFinder (R)]