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 038 was found to be unique among bacterial polysaccharides and to have the following structure: AcEtnP \ 6 --> 3)-alpha-D-GlcpNAc-(1 --> 3)-beta-D-Quip4N(Ac-D-Asp)-(1 --> 6)-alpha-D-Glcp-(1 --> 4)-alpha-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 113 and 213 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 alpha-D-GlcNAc-(1 --> 3)-D-Qui4N(Ac-D-Asp) disaccharide. Solvolysis with trifluoromethanesulfonic (triflic) acid afforded DG1cNAc6(AcEtnP), thus showing the suitability of this reagent for the preparation of phosphorylated sugar derivatives. (C) 2003 Elsevier Ltd. All rights reserved.