Structure of an acidic O-specific polysaccharide of the bacterium Providencia alcalifaciens O7

An acidic O-specific polysaccharide was obtained by mild acid degradation o f the lipopolysaccharide of the bacterium Providencia alcalifaciens O7 and purified by gel chromatography followed by anion-exchange chromatography. O n the basis of full acid hydrolysis, methylation, carboxyl reduction, selec tive cleavage with anhydrous hydrogen fluoride, and H-1- and C-13-NMR spect roscopy, including two-dimensional H-1,H-1 homonuclear and H-detected H-1,C -13 heteronuclear correlation spectroscopy and nuclear Overhauser effect sp ectroscopy (NOESY), the following structure of the linear tetrasaccharide r epeating unit of the polysaccharide was established: -->4)beta-D-GlcpNAc-(1-->3)-alpha-D-GlcpA-(1-->4)-alpha-D-GlcpNAc-(1-->3)-b eta-L-Rhap2Ac-(1--> where Rhap2Ac is 2-O-acetylrhamnopyranose.