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
7,3	bDGlcp	104.35	74.2	76.8	70.0	77.2	61.9
7,2	Ac
7	bDGlcpN	102.3	56.3	84.1	69.9	76.5	62.2
5	Ac
	bDSugp	174.4	96.7	40.0	67.85	54.35	71.05	79.1	61.9


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6	H7	H8
7,3	bDGlcp	4.45	3.29	3.47	3.49	3.44	3.68-3.87
7,2	Ac
7	bDGlcpN	4.79	3.72	3.82	3.49	3.75	3.73-3.93
5	Ac
	bDSugp	-	-	1.84-2.14	4.07	3.75	4.10	3.94	3.64


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6	C7/H7	C8/H8
7,3	bDGlcp	104.35/4.45	74.2/3.29	76.8/3.47	70.0/3.49	77.2/3.44	61.9/3.68-3.87
7,2	Ac
7	bDGlcpN	102.3/4.79	56.3/3.72	84.1/3.82	69.9/3.49	76.5/3.75	62.2/3.73-3.93
5	Ac
	bDSugp			40.0/1.84-2.14	67.85/4.07	54.35/3.75	71.05/4.10	79.1/3.94	61.9/3.64

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

644.58 g/mol (C₂₄H₄₀N₂O₁₈)