The structure of the O-specific polysaccharide (O-antigen) from Escherichia coli O92 was established. The acid-labile polysaccharide was produced by O-deacylation of the lipopolysaccharide under mild alkaline conditions. The methylation analysis combined with 1D and 2D 1H and 13C NMR spectroscopy demonstrated that the O-specific polysaccharide chain of the lipopolysaccharide is a linear fructan composed of mono-O-acetylated disaccharide repeating units having the structure →1)-b-d-Fruf3Ac-(2→3)-b-d-Fruf-(2→. To the best of our knowledge, this fructan has been hitherto unknown in bacteria.

Escherichia coli, ipopolysaccharide, O-antigen gene cluster, fructan, structure of the O-specific polysaccharide

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3	Ac	173.8	21.2
3	bDFruf	61.6	103.8	78.9	72.5	82.2	61.5
	bDFruf	63.6	105.4	78.1	75.5	82.3	63.0


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3	Ac	-	2.13
3	bDFruf	3.56-3.70	-	5.42	4.40	3.91	3.75-3.86
	bDFruf	3.76-3.76	-	4.48	4.14	3.86	3.63-3.85


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3	Ac		21.2/2.13
3	bDFruf	61.6/3.56-3.70		78.9/5.42	72.5/4.40	82.2/3.91	61.5/3.75-3.86
	bDFruf	63.6/3.76-3.76		78.1/4.48	75.5/4.14	82.3/3.86	63.0/3.63-3.85

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

366.319 g/mol (C₁₄H₂₂R₂O₁₁, R = next and previous repeats, not counted in mol weight)