A new, improved synthesis of the trisaccharide repeating unit of the O-antigen from Xanthomonas campestris pv. campestris 8004

Abstract Recent studies have revealed that lipid-A and core fragments of the lipopolysaccharide from Xanthomonas campestris pv. campestris 8004 ( Xcc ), a phytopathogenic Gram-negative bacterium, are able to elicit plant immunity with two independent mechanisms. To date, nothing is known about the effect of the O -antigen portion. Since its separation from the core region by selective chemical degradation is very difficult, the chemical synthesis of related oligosaccharides is strictly necessary. In this paper a new, improved synthesis of the O -antigen repeating unit is presented. The main improvements in the synthesis are: (1) a shorter, high-yielding preparation of an efficient glycosyl donor of the rare sugar 3-acetamido-3,6-dideoxy- d -galactopyranose (3-acetamido- d -fucose, d -Fuc p 3NAc); (2) a new protecting group pattern, which is demonstrated to open a path to the future synthesis of higher oligomers.