Cepacian is an exopolysaccharide produced by the majority of the isolates belonging to the Burkholderia cepacia complex bacteria, a group of 17 species, some of which infect cystic fibrosis patients, sometime with fatal outcome. The repeating unit of cepacian consists of a backbone having a trisaccharidic repeating unit with three side chains, as reported in the formula below. The exopolysaccharide is also acetylated, carrying from one to three acetyl esters per repeating unit, depending on the strain examined. The consequences of O-acetyl substitution in a polysaccharide are important both for its biological functions and for industrial applications, including the preparation of conjugated vaccines, since O-acetyl groups are important immunogenic determinants. The location of acetyl groups was achieved by NMR spectroscopy and ESI mass spectrometry and revealed that these substituents are scattered in non-stoichiometric ratio on many sugar residues in different positions, a feature which adds to the already unique carbohydrate structure of the polysaccharide.

NMR, polysaccharide structure, ESI-MS, cystic fibrosis, O-Acetyl groups, Burkholderia cepacia complex

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
3,3	bDGlcp	105.22	74.26	85.54	73.20	78.01	62.94
3,2	aDGalp	98.88	70.70	71.66	71.65	73.36	63.41
3	aD4dthrHexp4enA	100.45	74.92	76.10	108.99	147.40	171.19
6	bDGalp	105.83	72.00	74.98	71.06	77.43	?
	aDManp	103.40	72.15	81.42	67.70	74.23	70.66


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
3,3	bDGlcp	4.75	3.42	3.61	3.59	3.50	3.76-3.93
3,2	aDGalp	5.31	3.86	4.00	3.91	4.21	3.76
3	aD4dthrHexp4enA	5.59	4.19	4.76	6.00	-	-
6	bDGalp	4.45	3.60	3.68	3.94	3.71	?
	aDManp	5.18	4.20	4.12	3.99	4.16	3.93-4.17


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
3,3	bDGlcp	105.22/4.75	74.26/3.42	85.54/3.61	73.20/3.59	78.01/3.50	62.94/3.76-3.93
3,2	aDGalp	98.88/5.31	70.70/3.86	71.66/4.00	71.65/3.91	73.36/4.21	63.41/3.76
3	aD4dthrHexp4enA	100.45/5.59	74.92/4.19	76.10/4.76	108.99/6.00		
6	bDGalp	105.83/4.45	72.00/3.60	74.98/3.68	71.06/3.94	77.43/3.71	?/?
	aDManp	103.40/5.18	72.15/4.20	81.42/4.12	67.70/3.99	74.23/4.16	70.66/3.93-4.17

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](CO)O[C@@H](O[C@@H]2C=C(C(=O)O)O[C@H](O[C@@H]3[C@H](O)[C@@H](*)O[C@H](CO[C@@H]4O[C@H](CO)[C@H](O)[C@H](O)[C@H]4O)[C@H]3O)[C@H]2O[C@H]2O[C@H](CO)[C@H](O)[C@H](O)[C@H]2O)[C@@H]1O

806.673 g/mol (C₃₀H₄₆R₂O₂₅, R = next and previous repeats, not counted in mol weight)