Recently, ether-linked diastereomeric 2,4-dihydroxypentanoic acids have been reported as new components of bacterial glycans [Shashkov, A. S. et al.Nat. Prod. Commun.2008, 3, 1625-1630]. In this work, an ether of (2R,4R)-2,4-dihydroxypentanoic acid (Dhpa) with d-mannose was identified in the O-polysaccharide of Providencia alcalifaciens O31, and the polysaccharide structure was elucidated. Studies by NMR spectroscopy confirmed the ether linkage between O-2 of Dhpa and O-4 of Man, and the absolute configuration of Man was determined after ether cleavage with boron trichloride. In the polysaccharide, Dhpa was found to exist partially in the form of 1,4-lactone. Using sugar and methylation analyses along with (1)H and (13)C NMR spectroscopy, including 2D (1)H,(1)H COSY, TOCSY, ROESY, H-detected (1)H,(13)C HSQC, and gHMBC experiments, the following structure of the tetrasaccharide repeating unit of the polysaccharide was established: [carbohydrate structure: see text]

structure, O-antigen, Providencia alcalifaciens, 2, NMR analysis, 4-dihydroxypentanoic acid, lipolysaccharide, baterial polysaccharide structure

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,4,4,4	lXRRDhpa?	?	71.6	73.7	67.2	23.4
3,4,4	bDManp	101.7	72.5	73.9	78.0	76.3	61.5
3,4	aDGalp	102.1	69.9	78.9	77.5	71.5	61.5
3,2	Ac	175.4	23.8
3	bDGalpN	104.6	53.8	71.5	78.0	76.3	61.5
2	Ac	176.2	23.9
	bDGalpN	104.6	52.7	80.8	69.5	75.9	62.5


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,4,4,4	lXRRDhpa?	-	4.37	1.79-1.89	4.05	1.25
3,4,4	bDManp	5.03	4.07	3.84	3.71	3.46	3.79-3.96
3,4	aDGalp	4.95	3.96	4.16	4.43	4.40	3.62-3.75
3,2	Ac	-	2.03
3	bDGalpN	4.59	3.95	3.84	4.04	3.74	3.82-3.87
2	Ac	-	2.06
	bDGalpN	4.67	4.05	3.86	4.16	3.71	3.79-3.79


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,4,4,4	lXRRDhpa?		71.6/4.37	73.7/1.79-1.89	67.2/4.05	23.4/1.25
3,4,4	bDManp	101.7/5.03	72.5/4.07	73.9/3.84	78.0/3.71	76.3/3.46	61.5/3.79-3.96
3,4	aDGalp	102.1/4.95	69.9/3.96	78.9/4.16	77.5/4.43	71.5/4.40	61.5/3.62-3.75
3,2	Ac		23.8/2.03
3	bDGalpN	104.6/4.59	53.8/3.95	71.5/3.84	78.0/4.04	76.3/3.74	61.5/3.82-3.87
2	Ac		23.9/2.06
	bDGalpN	104.6/4.67	52.7/4.05	80.8/3.86	69.5/4.16	75.9/3.71	62.5/3.79-3.79

The spectrum also has 1 signal at unknown position (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

846.786 g/mol (C₃₃H₅₄R₂N₂O₂₃, R = next and previous repeats, not counted in mol weight)