Structure of a heteroxylan of gum exudate of the palm Scheelea phalerata (uricuri)
2004
Simas, F.F. | Gorin, P.A.J. | Guerrini, M. | Naggi, A. | Sassaki, G.L. | Delgobo, C.L. | Iacomini, M.
The polysaccharide isolated from the gum exudate of palm Scheelea phalerata (SPN) was water-insoluble and composed of Fuc, Ara, Xyl, and uronic acid moieties in a 5:34:54:7 molar ratio: 12% of phenolics were also present. A soluble polysaccharide (SPNa) was obtained after alkaline treatment, which contained Fuc, Ara, Xyl and uronic acid in a 7:44:42:7 molar ratio, with only 2% phenolics. SPNa had an Mw approximately 1.04 x 10(5) g mol-1 and was almost monodisperse (Mw/Mn:1.25 ± 0.22). It had a branched structure with side chains of 2-O-substituted Xylp (approximately 8%) and 3-O-substituted Araf (12%) units, and a large proportion of nonreducing end-units of Araf (15%), Fucp (10%), Xylp (4%), and Arap (6%). The (1 to 4)-linked beta-Xylp main-chain units were 3-O- (9%), 2-O- (13%), and 2,3-di-O- (13%) substituted. Its 13C NMR spectrum contained at least 9 C-1 signals, those at 108.6 and 107.7 arising from alpha-Araf units. Others were present at delta 175.4 from C-6 of alpha-GlcpA and delta 15.6 from C-6 of Fucp units. The main chain of SPNa was confirmed by analysis of a Smith-degraded polysaccharide (SPDS): methylation analysis provided a 2,3-Me2-Xyl (65%) derivative and its 13C NMR spectrum showed five main signals typical of a (1 to 4)-linked beta-Xylp units. Methylation analysis of a carboxy-reduced polysaccharide (SPN-CR) revealed a 2,3,4,6-Me4-Glc derivative (4%) arising from nonreducing end-units of GlcpA. alpha-GlcpA-(1 to 2)-alphabeta-Xylp and alpha-GlcpA-(1 to 2)-beta-Xylp-(1 to 4)-alphabeta-Xylp were obtained via partial acid hydrolysis of SPN, showing the structure of side-chain substituents on O-2 of the main-chain units.
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