The homogeneous extracellular polysaccharide, AW1, was obtained from the fermented broth of the fungus Aspergillus ochraceus derived from coral Dichotella gemmacea. AW1 was a galactomannan with a molar ratio of mannose and galactose of 2.16:1.00 and a molecular weight of about 29.0kDa. The structure of AW1 was investigated by chemical and spectroscopic methods, including methylation analysis, one- and two-dimensional nuclear magnetic resonance (1D, 2D NMR) and electrospray mass spectrometry with collision-induced dissociation (ES-CID MS/MS) spectroscopic analyses. The results showed that the backbone of AW1 consisted of (1⟶2)-linked α-d-mannopyranose residues. The mannopyranose residues in the backbone were substituted at C-6 by the (1⟶)-linked α-d-mannopyranose units and (1⟶5)-linked β-D-galactofuranose oligosaccharides with different degrees of polymerization. The investigation demonstrated that AW1 was a novel galactomannan with different structural characteristics from other fungal galactomannans, and could be a potential resource of the (1⟶5)-linked β-D-galactofuranose oligosaccharides.

NMR, extracellular polysaccharide, Aspergillus ochraceus, ES-CID MS/MS, galacto-oligosaccharide

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

OC[C@@H](O)[C@@H]1O[C@@H](O[C@H](CO)[C@@H]2O[C@@H](O[C@H](CO)[C@@H]3O[C@@H](O[C@H](CO)[C@@H]4O[C@@H](O[C@H](CO)[C@@H]5OC(O)[C@H](O)[C@H]5O)[C@H](O)[C@H]4O)[C@H](O)[C@H]3O)[C@H](O)[C@H]2O)[C@H](O)[C@H]1O

828.72 g/mol (C₃₀H₅₂O₂₆)

The homogeneous extracellular polysaccharide, AW1, was obtained from the fermented broth of the fungus Aspergillus ochraceus derived from coral Dichotella gemmacea. AW1 was a galactomannan with a molar ratio of mannose and galactose of 2.16:1.00 and a molecular weight of about 29.0kDa. The structure of AW1 was investigated by chemical and spectroscopic methods, including methylation analysis, one- and two-dimensional nuclear magnetic resonance (1D, 2D NMR) and electrospray mass spectrometry with collision-induced dissociation (ES-CID MS/MS) spectroscopic analyses. The results showed that the backbone of AW1 consisted of (1⟶2)-linked α-d-mannopyranose residues. The mannopyranose residues in the backbone were substituted at C-6 by the (1⟶)-linked α-d-mannopyranose units and (1⟶5)-linked β-D-galactofuranose oligosaccharides with different degrees of polymerization. The investigation demonstrated that AW1 was a novel galactomannan with different structural characteristics from other fungal galactomannans, and could be a potential resource of the (1⟶5)-linked β-D-galactofuranose oligosaccharides.

NMR, extracellular polysaccharide, Aspergillus ochraceus, ES-CID MS/MS, galacto-oligosaccharide

13C NMR data:
Linkage	Residue	C1	C2	C3	C4	C5	C6
2,6,5	bDGalf	107.08	81.36	76.39	81.36	75.56	61.09
2,2,2,2,6	aDManp	102.21	70.51	69.98	66.84	73.21	?
2,2,2,2	aDManp	98.20	78.51	70.51	66.84	70.51	65.51
2,2,2,6	aDManp	102.21	70.51	69.98	66.84	73.21	?
2,2,2	aDManp	98.20	78.51	70.51	66.84	70.51	65.51
2,2	aDManp	100.65	77.79	69.98	66.84	73.21	?
2,6,5,5	bDGalf	107.70	81.36	76.39	82.57	71.14	61.09
2,6	bDGalf	107.08	81.36	76.39	81.36	75.56	61.09
2	aDManp	98.20	78.51	70.51	66.84	70.51	65.51
	aDManp	100.65	77.79	69.98	66.84	73.21	?


1H NMR data:
Linkage	Residue	H1	H2	H3	H4	H5	H6
2,6,5	bDGalf	5.03-5.05	3.98	3.95	3.98	3.79	3.64
2,2,2,2,6	aDManp	5.02	3.99	3.78	3.67	3.57	?
2,2,2,2	aDManp	4.90	3.99	3.91	3.67	3.68	3.57
2,2,2,6	aDManp	5.02	3.99	3.78	3.67	3.57	?
2,2,2	aDManp	4.90	3.99	3.91	3.67	3.68	3.57
2,2	aDManp	5.06	3.99	3.91	3.67	3.57	?
2,6,5,5	bDGalf	4.86-4.92	3.97	3.95	3.97	3.84	3.64
2,6	bDGalf	5.03-5.05	3.98	3.95	3.98	3.79	3.64
2	aDManp	4.90	3.99	3.91	3.67	3.68	3.57
	aDManp	5.06	3.99	3.91	3.67	3.57	?


1H/13C HSQC data:
Linkage	Residue	C1/H1	C2/H2	C3/H3	C4/H4	C5/H5	C6/H6
2,6,5	bDGalf	107.08/5.03-5.05	81.36/3.98	76.39/3.95	81.36/3.98	75.56/3.79	61.09/3.64
2,2,2,2,6	aDManp	102.21/5.02	70.51/3.99	69.98/3.78	66.84/3.67	73.21/3.57	?/?
2,2,2,2	aDManp	98.20/4.90	78.51/3.99	70.51/3.91	66.84/3.67	70.51/3.68	65.51/3.57
2,2,2,6	aDManp	102.21/5.02	70.51/3.99	69.98/3.78	66.84/3.67	73.21/3.57	?/?
2,2,2	aDManp	98.20/4.90	78.51/3.99	70.51/3.91	66.84/3.67	70.51/3.68	65.51/3.57
2,2	aDManp	100.65/5.06	77.79/3.99	69.98/3.91	66.84/3.67	73.21/3.57	?/?
2,6,5,5	bDGalf	107.70/4.86-4.92	81.36/3.97	76.39/3.95	82.57/3.97	71.14/3.84	61.09/3.64
2,6	bDGalf	107.08/5.03-5.05	81.36/3.98	76.39/3.95	81.36/3.98	75.56/3.79	61.09/3.64
2	aDManp	98.20/4.90	78.51/3.99	70.51/3.91	66.84/3.67	70.51/3.68	65.51/3.57
	aDManp	100.65/5.06	77.79/3.99	69.98/3.91	66.84/3.67	73.21/3.57	?/?

The spectrum also has 4 signals at unknown positions (not plotted).

There is only one chemically distinct structure:

SVGMWSMILES3D molIonize

 

Warning = sub-repeat ending at bDGalf: variable unit count (0-7) was assumed to be 0
[*]O[C@H]1[C@@H](O)[C@H](O)[C@@H](CO[C@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@@H]2O)O[C@@H]1O[C@H]1[C@@H](O)[C@H](O)[C@@H](CO[C@H]2O[C@H](CO)[C@@H](O)[C@H](O)[C@@H]2O)O[C@@H]1O[C@H]1[C@@H](O)[C@H](O)[C@@H](CO)O[C@@H]1O[C@H]1[C@@H](O)[C@H](O)[C@@H](CO[C@@H]2O[C@@H]([C@@H](CO)O[C@@H]3O[C@@H]([C@@H](CO)O[C@@H]4O[C@@H]([C@H](O)CO)[C@H](O)[C@H]4O)[C@H](O)[C@H]3O)[C@H](O)[C@H]2O)O[C@@H]1O[C@H]1[C@@H](O)[C@H](O)[C@@H](CO)O[C@@H]1[*]

1621.41 g/mol (C₆₀H₁₀₀R₂O₅₀, R = next and previous repeats, not counted in mol weight)