The structure of the O-antigen polysaccharide (PS) from Escherichia coli O175 has been elucidated. Component analysis together with (1)H and (13)C NMR spectroscopy experiments were used to determine the structure. Inter-residue correlations were determined by (1)H,(1)H-NOESY, and (1)H,(13)C-heteronuclear multiple-bond correlation experiments. The PS is composed of pentasaccharide repeating units with the following structure: →2)-α-D-Glcp-(1→4)-α-D-GlcpA-(1→3)-α-D-Manp-(1→2)-α-D-Manp-(1→3)-β-D-GalpNAc-(1→. Cross-peaks of low intensity from an α-linked glucopyranosyl residue were present in the (1)H,(1)H-TOCSY NMR spectra. The α-D-Glcp residue is suggested to originate from the terminal part of the polysaccharide and consequently the biological repeating unit has a 3-substituted N-acetyl-D-galactosamine residue at its reducing end. The repeating unit of the E. coli O175 O-antigen is similar to those from E. coli O22 and O83, both of which carry an α-D-Glcp-(1→4)-D-GlcpA structural element, thereby explaining the reported cross-reactivities between the strains.

Lipopolysaccharide, NMR, Escherichia coli, biological repeating unit

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,2,3,4	aDGlcp	98.93	81.36	72.49	70.62	72.41	61.12
3,2,3	aDGlcpA	101.03	72.33	74.43	77.98	73.94	176.17
3,2	aDManp	103.03	70.66	78.86	67.35	74.29	62.10
3	aDManp	95.64	79.85	70.94	67.52	74.29	61.92
2	Ac	175.26	23.32
	bDGalpN	103.62	51.87	75.75	64.68	75.94	62.05


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,2,3,4	aDGlcp	5.62	3.63	3.78	3.41	3.74	3.77-3.80
3,2,3	aDGlcpA	5.27	3.64	4.05	3.82	4.14	-
3,2	aDManp	5.04	4.23	3.92	3.83	3.82	3.74-3.90
3	aDManp	5.24	4.00	3.81	3.72	3.55	3.80-3.86
2	Ac	-	2.06
	bDGalpN	4.76	4.04	3.86	4.16	3.67	3.77-3.87


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,2,3,4	aDGlcp	98.93/5.62	81.36/3.63	72.49/3.78	70.62/3.41	72.41/3.74	61.12/3.77-3.80
3,2,3	aDGlcpA	101.03/5.27	72.33/3.64	74.43/4.05	77.98/3.82	73.94/4.14	
3,2	aDManp	103.03/5.04	70.66/4.23	78.86/3.92	67.35/3.83	74.29/3.82	62.10/3.74-3.90
3	aDManp	95.64/5.24	79.85/4.00	70.94/3.81	67.52/3.72	74.29/3.55	61.92/3.80-3.86
2	Ac		23.32/2.06
	bDGalpN	103.62/4.76	51.87/4.04	75.75/3.86	64.68/4.16	75.94/3.67	62.05/3.77-3.87

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

*O[C@@H]1[C@@H](O)[C@H](O)[C@@H](CO)O[C@@H]1O[C@@H]1[C@@H](C(=O)O)O[C@H](O[C@@H]2[C@H](O)[C@@H](O[C@@H]3[C@@H](O[C@@H]4[C@@H](NC(C)=O)[C@H](*)O[C@H](CO)[C@@H]4O)O[C@H](CO)[C@@H](O)[C@@H]3O)O[C@H](CO)[C@H]2O)[C@H](O)[C@H]1O

865.741 g/mol (C₃₂H₅₁R₂NO₂₆, R = next and previous repeats, not counted in mol weight)