First synthesis of beta-D-Galf-(1-->3)-D-Galp--the repeating unit of the backbone structure of the O-antigenic polysaccharide present in the lipopolysaccharide (LPS) of the genus Klebsiella.

beta-D-Galactofuranosyl-(1-->3)-D-galactopyranose (1), the repeating unit of the backbone structure of the O-antigenic polysaccharide present in the lipopolysaccharide (LPS) of the genus Klebsiella, has been efficiently synthesized using 1,2:5,6-di-O-isopropylidine-alpha-D-galactofuranose (3) as the glycosyl acceptor and 2,3,5,6-tetra-O-benzoyl-beta-D-galactofuranosyl trichloroacetimidate (6) as the glycosyl donor with TMSOTf as catalyst by the well-known Schmidt glycosylation method. The preparation of 3 was improved by increasing the ratio of DMF to acetone and employing a solid-supported catalyst.