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	102.4	37.75	69.6	?	72.5	78.9	73.0	63.7
3,2	aDGalp	97.2	69.6	70.6	70.5	71.55	62.4
3	bDGlcp	103.3	73.6	78.7	69.9	76.75	62.4
2	Ac
	bDGlcpN	102.2	57.3	80.8	70.6	76.3	62.45


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8	H9
3,3,5	Ac
3,3	aXNeup	-	-	2.0-2.51	4.05	3.91	3.88	3.72	3.78	3.50-3.80
3,2	aDGalp	5.52	3.83	3.92	4.00	4.13	3.75
3	bDGlcp	4.70	3.66	4.15	3.54	3.50	3.73-3.90
2	Ac
	bDGlcpN	4.74	3.68	4.08	3.52	3.53	3.79-4.00


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			37.75/2.0-2.51	69.6/4.05	?/3.91	72.5/3.88	78.9/3.72	73.0/3.78	63.7/3.50-3.80
3,2	aDGalp	97.2/5.52	69.6/3.83	70.6/3.92	70.5/4.00	71.55/4.13	62.4/3.75
3	bDGlcp	103.3/4.70	73.6/3.66	78.7/4.15	69.9/3.54	76.75/3.50	62.4/3.73-3.90
2	Ac
	bDGlcpN	102.2/4.74	57.3/3.68	80.8/4.08	70.6/3.52	76.3/3.53	62.45/3.79-4.00

The spectrum also has 1 signal at unknown position (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

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