Acinetobacter baumannii is a gram-negative bacterium emerged in the last decade as cause of severe nosocomial infections, especially in intensive care units1. Interest in Acinetobacter is increased over recent years, for its outstanding resistance to any antibiotic therapy. The mechanism by which Acinetobacter is able to express its pathogenicity has not yet been completely elucidated, but a crucial role is played by the lipopolysaccharide portion of the outer membrane, making this structure a candidate for vaccine development. In particular we focused our attention on the extremely virulent strain ATCC 17961. The structure of the repeating unit of its O-chain LPS has been identified2 by NMR with the branched pentasaccharide reported in Fig.1.
This pentasaccharide contains a very rare monosaccharide residue, namely the 2,3-diacetamido-2,3- dideoxy-D-glucuronic acid. Since unusual saccharide branches in the framework of pathogen-associated surface polysaccharides have usually strong antigenic properties and they are often essential components of the epitope, the present research project is focused on the synthesis of three fragments of this repeating unit, bearing the β-D-GlcpNAc3NAcA moiety, in order to evaluate their immunogenicity. This monosaccharide has been therefore selected as initial synthetic target, to be used also as a glycosyl donor for the preparation of di- and trisaccharide fragments (Fig. 2).
In this communication, we report on the first synthesis of fragments 1-3 and preliminary data of their biological characterization
1. Nature Review. 2007, 5, 939
2. Carbohydr. Research. 2009, 344, 474
