Shigella flexneri is an important human pathogen causing shigellosis. Strains of S. flexneri are serologically heterogeneous and, based on O-antigens, are currently classified into 14 types. Structures of the O-antigens (O-polysaccharides) of S. flexneri have been under study since 1960s but some gaps still remained. In this work, using one- and two-dimensional (1) H- and (13) C-NMR spectroscopy, the O-polysaccharides of several S. flexneri types were reinvestigated, and their structures were either confirmed (types 2b, 3b, 3c, 5b, X) or amended in respect to the O-acetylation pattern (types 3a, Y, 6, 6a). As a result, the O-acetylation sites were defined in all O-polysaccharides that had not been studied in detail earlier, and the long story of S. flexneri type strain O-antigen structure elucidation is thus completed. New and published data on the S. flexneri O-antigen structures are summarized and discussed in view of serological and genetic relationships of the O-antigens within the Shigella group and between S. flexneri and Escherichia coli.

Shigella flexneri, O-acetylation, serological classification, O-Polysaccharide structure, O-antigen diversity

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3,2,3	30%Ac	175.9	22.0
3,3,2,4	20%Ac	175.8	21.7
3,3,2	aLRhap	102.4	78.4	74.3	71.4	70.7	18.1
3,3	aLRhap	102.2	79.7	71.3	73.6	70.6	18.1
3	aLRhap	102.4	72.0	78.7	73.2	70.5	17.8
2	Ac	175.8	23.7
6	40%Ac	175.8	21.7
	bDGlcpN	103.6	57.0	82.4	69.5	74.7	64.5


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3,2,3	30%Ac	-	2.21
3,3,2,4	20%Ac	-	2.16
3,3,2	aLRhap	5.16	4.25	5.07	?	3.80	1.27
3,3	aLRhap	5.21	4.07	3.93	3.48	3.76	1.31
3	aLRhap	4.90	3.87	3.79	3.55	4.03	1.24
2	Ac	-	2.11
6	40%Ac	-	2.16
	bDGlcpN	4.56	3.85	3.66	3.65	3.47	4.34-4.43


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3,2,3	30%Ac		22.0/2.21
3,3,2,4	20%Ac		21.7/2.16
3,3,2	aLRhap	102.4/5.16	78.4/4.25	74.3/5.07	71.4/?	70.7/3.80	18.1/1.27
3,3	aLRhap	102.2/5.21	79.7/4.07	71.3/3.93	73.6/3.48	70.6/3.76	18.1/1.31
3	aLRhap	102.4/4.90	72.0/3.87	78.7/3.79	73.2/3.55	70.5/4.03	17.8/1.24
2	Ac		23.7/2.11
6	40%Ac		21.7/2.16
	bDGlcpN	103.6/4.56	57.0/3.85	82.4/3.66	69.5/3.65	74.7/3.47	64.5/4.34-4.43

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](COC(C)=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

767.731 g/mol (C₃₂H₄₉R₂NO₂₀, R = next and previous repeats, not counted in mol weight)