Shigella flexneri type 2a is the first, and type 1b is the second, most prevalent isolates from patients with shigellosis in Russia. The O-specific polysaccharides (OPSs, O-antigens) of S. flexneri types 1-5 possess a common →2)-α-L-RhapIII-(1→2)-α-L-RhapII-(1→3)-α-L-RhapI-(1→3)-β-D-GlcpNAc-(1→ backbone and differ from each other in its glucosylation or/and O-acetylation at various positions, the modifications being responsible for various O-factors. It was suggested that O-factor 6 expressed by type 1b is associated with O-acetylation of RhaI at position 2 but more than one O-acetyl group has been detected in the type 1b OPS [Kenne, L. et al. Eur. J. Biochem.1978, 91, 279-284]. In this work, O-acetylation of RhapI in the type 1b OPS was confirmed by NMR spectroscopy and location of an additional O-acetyl group at position either 3 (major) or 4 (minor) of RhapIII was determined. Type 1a differs from type 1b in the lack of O-acetylation of RhapI only. In type 2a, in addition to two reported major O-acetyl groups at position 6 of GlcNAc and position 3 of RhapIII [Kubler-Kielb, J. et al. Carbohydr. Res.2007, 342, 643-647], a minor O-acetyl group was found at position 4 of RhaIII. Therefore, RhapIII is O-acetylated in the same manner in all three S. flexneri serotypes studied.

O-antigen, Shigella flexneri, O-specific polysaccharide, O-acetylation, bacterial polysaccharide structure

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,2,3	65%Ac	174.8	21.9
3,3,2,4	25%Ac	174.8	21.8
3,3,2	aLRhap	102.6	78.1	74.2	71.5	70.5	18.1
3,3	aLRhap	101.8	79.9	71.3	73.6	70.6	18.2
3	aLRhap	100.0	71.9	77.8	72.6	71.3	18.0
2	Ac	175.5	23.7
4	aDGlcp	98.2	73.3	74.3	70.7	74.2	61.9
	bDGlcpN	104.3	55.0	80.2	71.5	77.4	62.6


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,2,3	65%Ac	-	2.21
3,3,2,4	25%Ac	-	2.17
3,3,2	aLRhap	5.17	4.27	5.08	3.56	3.79	1.29
3,3	aLRhap	5.26	4.09	3.95	3.51	3.78	1.34
3	aLRhap	5.12	4.00	3.81	3.55	3.78	1.28
2	Ac	-	2.09
4	aDGlcp	5.42	3.60	3.69	3.45	3.65	3.78-3.86
	bDGlcpN	4.59	4.14	4.04	4.03	3.72	3.84-3.84


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,2,3	65%Ac		21.9/2.21
3,3,2,4	25%Ac		21.8/2.17
3,3,2	aLRhap	102.6/5.17	78.1/4.27	74.2/5.08	71.5/3.56	70.5/3.79	18.1/1.29
3,3	aLRhap	101.8/5.26	79.9/4.09	71.3/3.95	73.6/3.51	70.6/3.78	18.2/1.34
3	aLRhap	100.0/5.12	71.9/4.00	77.8/3.81	72.6/3.55	71.3/3.78	18.0/1.28
2	Ac		23.7/2.09
4	aDGlcp	98.2/5.42	73.3/3.60	74.3/3.69	70.7/3.45	74.2/3.65	61.9/3.78-3.86
	bDGlcpN	104.3/4.59	55.0/4.14	80.2/4.04	71.5/4.03	77.4/3.72	62.6/3.84-3.84

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

887.835 g/mol (C₃₆H₅₇R₂NO₂₄, R = next and previous repeats, not counted in mol weight)