Synthesis of the tetrasaccharide outer core fragment of Burkholderia multivorans lipooligosaccharide.

The first synthesis of the outer core fragment of Burkholderia multivorans lipooligosaccharide [ß-D-Glc-(1→3)-α-D-GalNAc-(1→3)-ß-D-GalNAc-(1→3)-L-Rha] as α-allyl tetrasaccharide was accomplished. The glycosylations involving GalNAc units were studied in depth testing them under several conditions. This allowed the building of both the α- and the ß-configured glycosidic bonds by employing the same GalNAc glycosyl donor, thus considerably shortening the total number of synthetic steps. The target tetrasaccharide was synthesized with an allyl aglycone to allow its future conjugation with an immunogenic protein en route to the development of a synthetic neoglycoconjugate vaccine against the Burkholderia cepacia pathogens.