Structure of the O-polysaccharide of Proteus mirabilis O38 containing 2-acetamidoethyl phosphate and N-linked D-aspartic acid

The O-antigen of Proteus mirabilis O38 was found to be unique among bacterial polysaccharides and to have the following structure: AcEtnP|6 → 3)-α-D-GlcpNAc-(1 → 3)-β-D-Quip4N(Ac-D-Asp)-(1 → 6)-α-D-Glcp-(1 → 4)-α-D-GalpA-(1 → where D-Qui4N(Ac-D-Asp) is 4-(N-acetyl-D-aspart-4-ylamino)-4,6-dideoxy-D-glucose and AcEtnP is 2-acetamidoethyl phosphate. Neither of these entities have been hitherto found in natural polysaccharides. Structural studies were performed using 1D and 2D NMR spectroscopy, including experiments run in an H₂O/D₂O mixture to reveal correlations for NH protons. In addition, dephosphorylation, carboxyl reduction and selective cleavages were applied. Solvolysis of the polysaccharide with anhydrous HF gave an α-D-GlcNAc-(1 → 3)-D-Qui4N(Ac-D-Asp) disaccharide. Solvolysis with trifluoromethanesulfonic (triflic) acid afforded D-GlcNAc6(AcEtnP), thus showing the suitability of this reagent for the preparation of phosphorylated sugar derivatives.