Mild acid hydrolysis of the lipopolysaccharide of Escherichia coli O57 afforded an O-polysaccharide, which was isolated by gel permeation chromatography (GPC) and studied by sugar analysis, Smith degradation and solvolysis with trifluoroacetic acid, along with 2D 1H and 13C NMR spectroscopy. The O-polysaccharide was found to contain d-Glc, d-Gal, d-GalA, d-GlcNAc, and l-FucNAc, as well as O-acetyl groups. Smith degradation of the O-deacetylated polysaccharide destroyed side-branch β-Glсp and α-GalpA to give a modified linear polysaccharide. Solvolysis cleaved selectively the linkage of α-l-FucpNAc to give a pentasaccharide corresponding to the O-polysaccharide repeat. A comparison of the NMR spectra of the initial and O-deacetylated polysaccharides showed that α-GalpA is non-stoichiometrically O-acetylated at position either 2 (~30%) or 3 (~40%). The following structure of the O-polysaccharide was established, which is unique among known bacterial polysaccharide structures.

O-antigen, Escherichia coli, O-polysaccharide, bacterial polysaccharide structure, CF3CO2H solvolysis

← originally published structure   Show legend

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3	aDGalp	101.9	68.2	75.9	67.2	72.5	62.6
3,2	Ac	175.0-175.7	23.1-24.1
3	aLFucpN	98.9	49.6	76.9	72.4	68.0	16.5
2	Ac	175.0-175.7	23.1-24.1
	aDGlcpN	96.7	54.7	77.1	69.5	73.2	61.6


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3	aDGalp	5.12	3.87	3.90	4.48	4.65	3.69-3.74
3,2	Ac	-	1.96-2.09
3	aLFucpN	5.02	4.32	4.01	4.00	4.46	1.18
2	Ac	-	1.96-2.09
	aDGlcpN	4.95	4.12	3.91	3.61	3.97	3.81-3.85


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3	aDGalp	101.9/5.12	68.2/3.87	75.9/3.90	67.2/4.48	72.5/4.65	62.6/3.69-3.74
3,2	Ac		23.1-24.1/1.96-2.09
3	aLFucpN	98.9/5.02	49.6/4.32	76.9/4.01	72.4/4.00	68.0/4.46	16.5/1.18
2	Ac		23.1-24.1/1.96-2.09
	aDGlcpN	96.7/4.95	54.7/4.12	77.1/3.91	69.5/3.61	73.2/3.97	61.6/3.81-3.85

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

552.53 g/mol (C₂₂H₃₆R₂N₂O₁₄, R = next and previous repeats, not counted in mol weight)