From the medicinal plant Rudbeckia fulgida, var. sillivantii (Boynton et Beadle) a low-molecular-mass (4-O-methyl-alpha-D-glucurono)-D-xylan was isolated by alkaline extraction, followed by ethanol precipitation, ion-exchange chromatography and gel filtration. The results of compositional and linkage analyses, supported by those of 1H and 13C NMR measurements of oligomers generated on partial acid hydrolysis, showed the (1-->4)-linked beta-D-xylopyranosyl backbone with about 18% of 4-O-methyl-D-glucuronic acid attached to O-2 of the xylose residues. From the mean distance of adjacent carboxyl groups, obtained from experimentally determined single-ion activity coefficients of calcium counterions, it followed that the uronic acid units are separated and distributed regularly along the xylan chain, i.e. approximately each sixth D-xylose unit bears a 4-O-methyl-D-glucuronic acid residue.

Structure determination, Rudbeckia fulgida, (4-O-methyl-alpha-D-glucurono)-D-xylan, H-1 and C-13 NMR spectroscopy

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
4,4	bDXylp	102.6	73.6	74.6	77.2	63.9
4	bDXylp	102.6	73.6	74.6	77.2	63.9
2,4	Me	60.8
2	aDGlcpA	98.5	73.1	?	83.3	72.9	177.5
	bDXylp	102.3	77.7	72.1	76.9	?


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
4,4	bDXylp	4.45	3.26	3.56	3.77	3.37-4.09
4	bDXylp	4.45	3.26	3.56	3.77	3.37-4.09
2,4	Me	3.46
2	aDGlcpA	5.27	3.56	3.74	3.20	4.31	-
	bDXylp	4.61	3.45	3.61	3.79	3.42-4.13


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
4,4	bDXylp	102.6/4.45	73.6/3.26	74.6/3.56	77.2/3.77	63.9/3.37-4.09
4	bDXylp	102.6/4.45	73.6/3.26	74.6/3.56	77.2/3.77	63.9/3.37-4.09
2,4	Me	60.8/3.46
2	aDGlcpA	98.5/5.27	73.1/3.56	?/3.74	83.3/3.20	72.9/4.31	
	bDXylp	102.3/4.61	77.7/3.45	72.1/3.61	76.9/3.79	?/3.42-4.13

The spectrum also has 2 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

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

586.496 g/mol (C₂₂H₃₄R₂O₁₈, R = next and previous repeats, not counted in mol weight)