Structures for the N-acetylneuraminic acid (Neu5Ac)-containing O56 and O24 polysaccharides of Escherichia coli have been reported previously. During these studies unusual chemical shifts had been observed for the NMR signals for H-3eq and C-3 of the Neu5Ac residues of both polysaccharides. In further pursuing this phenomenon, we have reinvestigated the O56 and O24 polysaccharides as well as derived oligosaccharides by one- and two-dimensional NMR spectroscopy. The results showed that structures of both polysaccharides (PSs) had to be modified and formulated as [formula: see text] 2D ROESY spectra revealed a strong NOE between H-3eq of Neu5Ac and the protons of the side-chain sugar (H-3 and H-5 of α-D-Galp in the O56 PS and H-3 of α-D-Glcp in the O24 PS) and also between H-3ax of Neu5Ac and H-3 of β-D-Glcp in the main chain. This indicated a close spatial association of the seven-linked α-Neu5Ac and the side-chain residues α-D-Galp (O56 PS) and α-D-Glcp (O25 PS), respectively. The strong long-range spatial contacts caused the unusual chemical shifts of H-3eq and C-3 of Neu5Ac.

Escherichia coli, NMR spectroscopy, polysaccharide structure, 024 and 056 antigens

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6	C7	C8	C9
7,3,2	aDGalp	99.0	69.8	70.6	70.45	72.0	62.0-62.5
7,3	bDGlcp	102.9	78.3	76.1	69.8	77.2	62.0-62.5
7,2	Ac
7	bDGlcpN	101.9	57.7	80.1	70.9	76.6	62.0-62.5
5	Ac
	bXNeup	176.0	97.7	40.6	67.9	55.2	70.5	79.4	72.6	63.9


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
7,3,2	aDGalp	5.37	3.85	3.91	4.02	4.23	3.73
7,3	bDGlcp	4.63	3.49	3.57	3.52	3.47	3.74-3.92
7,2	Ac
7	bDGlcpN	4.90	3.60	4.12	3.52	3.56	3.76-3.99
5	Ac
	bXNeup	-	-	1.86-2.16	4.23	3.81	4.38	3.87	3.82	3.51-3.77


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
7,3,2	aDGalp	99.0/5.37	69.8/3.85	70.6/3.91	70.45/4.02	72.0/4.23	62.0-62.5/3.73
7,3	bDGlcp	102.9/4.63	78.3/3.49	76.1/3.57	69.8/3.52	77.2/3.47	62.0-62.5/3.74-3.92
7,2	Ac
7	bDGlcpN	101.9/4.90	57.7/3.60	80.1/4.12	70.9/3.52	76.6/3.56	62.0-62.5/3.76-3.99
5	Ac
	bXNeup			40.6/1.86-2.16	67.9/4.23	55.2/3.81	70.5/4.38	79.4/3.87	72.6/3.82	63.9/3.51-3.77

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@H]1[C@H](O[C@H]([C@H](O)CO)[C@@H]2O[C@](O)(C(=O)O)C[C@H](O)[C@H]2NC(C)=O)O[C@H](CO)[C@@H](O)[C@@H]1O[C@@H]1O[C@H](CO)[C@@H](O)[C@H](O)[C@H]1O[C@H]1O[C@H](CO)[C@H](O)[C@H](O)[C@H]1O

836.747 g/mol (C₃₁H₅₂N₂O₂₄)