The structure of the repeating unit of the O-antigenic polysaccharide from Plesiomonas shigelloides strain AM36565 has been determined. Component analysis and (1)H and (13)C NMR spectroscopy experiments were employed to elucidate the structure. Inter-residue correlations were determined by (1)H,(13)C heteronuclear multiple-bond correlation, (1)H,(1)H-NOESY, and (1)H,(13)C-HSQC-(1)H,(1)H-NOESY experiments. The O-antigen polysaccharide is composed of repeating units with the following structure: →3)-α-L-Rhap-(1→2)-α-L-Rhap-(1→4)[β-D-GalpNAc-(1→3)]-α-d-GlcpNAc-(1→, in which the monosaccharide side-chain substitutes the backbone in half of the repeating units. A matrix-assisted laser desorption/ionization mass spectrometry experiment suggested that the polysaccharide consists of two regions, one with tetrasaccharide repeating units and one with trisaccharide repeating units.

Lipopolysaccharide, NMR, biological repeating unit, MALDI-TOF MS, Plesiomonas shigelloides, SDS-PAGE

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4,2	aDRhap	102.9	67.6	76.1	71.2	70.1	17.7
4	aLRhap	100.2	79.5	70.8	72.8	70.0	17.3
2	Ac	175.3	22.7
	aDGlcpN	95.0	54.8	70.4	78.3	72.0	60.8


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4,2	aDRhap	5.01	4.22	3.82	3.54	3.78	1.33
4	aLRhap	5.04	4.00	3.86	3.48	4.04	1.2
2	Ac	-	2.06
	aDGlcpN	5.07	3.98	3.90	3.68	4.08	3.75-3.85


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4,2	aDRhap	102.9/5.01	67.6/4.22	76.1/3.82	71.2/3.54	70.1/3.78	17.7/1.33
4	aLRhap	100.2/5.04	79.5/4.00	70.8/3.86	72.8/3.48	70.0/4.04	17.3/1.2
2	Ac		22.7/2.06
	aDGlcpN	95.0/5.07	54.8/3.98	70.4/3.90	78.3/3.68	72.0/4.08	60.8/3.75-3.85

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

495.478 g/mol (C₂₀H₃₃R₂NO₁₃, R = next and previous repeats, not counted in mol weight)