An acidic polysaccharide was isolated from Providencia rustigianii O11 by the phenol-water extraction. The polysaccharide was cleaved by solvolysis with triflic acid to yield disaccharides with uronic acid derivatives at the non-reducing end. The polysaccharide and the disaccharides were studied by chemical analyses, high-resolution ESI MS, and 2D (1)H and (13)C NMR spectroscopy, and the following structure of the tetrasaccharide repeating unit of the polysaccharide was established: where GalNAcA stands for 2-acetamido-2-deoxygalacturonic acid, GalNAcA6GluAla for N-(2-acetamido-2-deoxygalacturonoyl)-l-glutam-1-yl-l-alanine, QuiNAc4NAcyl for 2-acetamido-4-[(S)-3-hydroxybutanoylamino]-2,4,6-trideoxyglucose (~75%) or 2,4-diacetamido-2,4,6-trideoxyglucose (~25%); the d configuration of GalNA and QuiN4N was ascribed tentatively. To the best of our knowledge, this is for the first time that an amide of uronic acid with a dipeptide is found in bacterial polysaccharides.

Lipopolysaccharide, bacterial polysaccharide structure, Providencia rustigianii, 2-acetamido-2-deoxygalacturonamide, dipeptide

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,2	Ac	174.7-175.9	23.3-23.9
3	aDGalpNA	98.4	50.1	68.9	70.8	72.9	175.4
2	Ac	174.7-175.9	23.3-23.9
4	lS3HOBut	174.8	46.2	66.0	23.7
	bDQuipN4N	95.7	57.2	76.6	58.1	72.5	17.9


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,2	Ac	-	1.90-2.13
3	aDGalpNA	5.19	4.15	3.77	4.28	4.20	-
2	Ac	-	1.90-2.13
4	lS3HOBut	-	2.32	4.17	1.21
	bDQuipN4N	4.70	3.73	3.84	3.83	3.53	1.18


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,2	Ac		23.3-23.9/1.90-2.13
3	aDGalpNA	98.4/5.19	50.1/4.15	68.9/3.77	70.8/4.28	72.9/4.20	
2	Ac		23.3-23.9/1.90-2.13
4	lS3HOBut		46.2/2.32	66.0/4.17	23.7/1.21
	bDQuipN4N	95.7/4.70	57.2/3.73	76.6/3.84	58.1/3.83	72.5/3.53	17.9/1.18

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

CC(=O)N[C@@H]1[C@@H](O[C@H]2O[C@H](C(=O)O)[C@H](O)[C@H](O)[C@H]2NC(C)=O)[C@H](NC(=O)C[C@H](C)O)[C@@H](C)O[C@H]1O

507.493 g/mol (C₂₀H₃₃N₃O₁₂)