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
3,3,5	Ac
3,3	aXNeup	173.9	102.35	37.9	68.9	54.7	72.3	78.9	73.1	63.6
3,2	aDGlcp	96.7	72.95	74.3	71.4	72.65	62.0
3	bDGlcp	104.7	73.1	78.75	70.5	76.6	62.2
2	Ac
	bDGalpN	103.1	53.2	79.8	69.4	75.6	62.9


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
3,3,5	Ac
3,3	aXNeup	-	-	1.99-2.59	4.15	3.77	4.04	3.74	3.81	3.56-3.80
3,2	aDGlcp	5.44	3.49	3.85	3.30	3.88	3.70-3.85
3	bDGlcp	4.74	3.63	4.15	3.52	3.54	3.65-3.77
2	Ac
	bDGalpN	4.61	3.94	4.04	4.15	3.75	3.84


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8	C9/H9
3,3,5	Ac
3,3	aXNeup			37.9/1.99-2.59	68.9/4.15	54.7/3.77	72.3/4.04	78.9/3.74	73.1/3.81	63.6/3.56-3.80
3,2	aDGlcp	96.7/5.44	72.95/3.49	74.3/3.85	71.4/3.30	72.65/3.88	62.0/3.70-3.85
3	bDGlcp	104.7/4.74	73.1/3.63	78.75/4.15	70.5/3.52	76.6/3.54	62.2/3.65-3.77
2	Ac
	bDGalpN	103.1/4.61	53.2/3.94	79.8/4.04	69.4/4.15	75.6/3.75	62.9/3.84

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*O[C@H]([C@H](O)CO)[C@@H]1O[C@@](O[C@H]2[C@H](O)[C@@H](CO)O[C@@H](O[C@@H]3[C@@H](NC(C)=O)[C@H](*)O[C@H](CO)[C@@H]3O)[C@@H]2O[C@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@H]2O)(C(=O)O)C[C@H](O)[C@H]1NC(C)=O

818.732 g/mol (C₃₁H₅₀R₂N₂O₂₃, R = next and previous repeats, not counted in mol weight)