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	98.9	50.2	68.7	70.8	72.9	175.4
2	Ac	174.7-175.9	23.3-23.9
4	Ac	174.7-175.9	23.3-23.9
	aDQuipN4N	92.1	54.2	74.3	58.2	67.9	17.9


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,2	Ac	-	1.90-2.13
3	aDGalpNA	5.18	4.15	3.79	4.28	4.20	-
2	Ac	-	1.90-2.13
4	Ac	-	1.90-2.13
	aDQuipN4N	5.10	4.03	3.99	4.03	3.97	1.13


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	98.9/5.18	50.2/4.15	68.7/3.79	70.8/4.28	72.9/4.20	
2	Ac		23.3-23.9/1.90-2.13
4	Ac		23.3-23.9/1.90-2.13
	aDQuipN4N	92.1/5.10	54.2/4.03	74.3/3.99	58.2/4.03	67.9/3.97	17.9/1.13

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

463.44 g/mol (C₁₈H₂₉N₃O₁₁)