Structural Determination of the O-Chain Moieties of the Lipopolysaccharide Fraction from Agrobacterium radiobacter DSM 30147

Two O-chain structures were identified after acid hydrolysis of the lipopolysaccharide fraction of Agrobacterium radiobacter (type strain). The first is constituted by the linear tetrasaccharide repeating unit [2)-a-L-Rhap-(1 3)-a-L-Rhap- (1 3)-a-L-Rhap-(1 2)-a-L-Rhap-(1 ]n and the second by the (1 2)-branched repeating unit a-D-Manp-(1 2)-[3)-a-DFucp-( 1 3)-a-D-Fucp-(1 ]n.The two structures were determined mainly by 1D- and 2D NMR spectroscopy together with chemical-degradation methods. A detailed analysis of the NOESY spectrum, supported by molecular dynamics calculations, suggested that some unexpected NOEs were due to the sum of many small dipolar effects, whose identification was possible only by considering the 3D structure of an Ochain oligosaccharide bigger than the repeating unit.