The structures of the carbohydrate backbones of the lipopolysaccharides from Escherichia coli rough mutants F470 (R1 core type) and F576 (R2 core type)

The lipopolysaccharides (LPS) from Escherichia coli rough mutant strains F4 70 (R1 core type) and F576 (R2 core type) were deacylated yielding in each case a mixture of oligosaccharides with one predominant product which was i solated using high-performance anion-exchange chromatography. In addition, one oligosaccharide present in minor quantities was isolated from LPS of E. coli strain F576 (R2 core type). The structures of the oligosaccharides we re determined by chemical analyses and NMR spectroscopic experiments. Furth ermore, de-O-acylated and dephosphorylated LPS preparations were investigat ed by fast-atom bombardment and collision induced dissociation tandem mass spectrometry. The combined data allow us to deduce the following carbohydra te backbones of the E. coli Ri and R2 core types which share the following structure (Scheme 1): [GRAPHICS] but differ in the substituents R-1 and R-2 which for the R1 core type are p redominantly: [GRAPHICS] and to a minor extent: [GRAPHICS] and for the R2 core type predominantly: [GRAPHICS]