Ricardo Wagner

New structural features of the polysaccharide from gum ghatti (Anogeissus latifola).

Methylation and 13C NMR analyses were carried out on the high-arabinose, acidic heteropolysaccharide of gum ghatti and the products obtained on three successive, controlled Smith degradations. The side chains contained mainly 2-O- and 3-O-substituted Araf units. Of these the second degradation eliminated remaining alpha-Araf units, and their beta anomers became evident. The proportion of Galp units gradually increased in the form of nonreducing end- and Galp units, although 3,6-di-O- and 3,4,6-tri-O-substituted Galp units diminished. After three degradations groups with consecutive 3-O-substituted beta-Galp units were formed. The proportion of periodate-resistant 3-O- and 2,3-di-O-substituted Manp units was maintained. As a guide to side-chain structures in the polysaccharide, seven of the 10 free reducing oligosaccharide fractions (PC) present in the gum were isolated and examined (NMR, ESIMS, and sometimes methylation analysis). Characterized are alpha-Araf-(1 --> 2)-Ara and three Ara-containing oligosaccharide fractions containing 2-O- and 3-O-substituted units. These gave respectively, ESIMS molecular ions arising from Ara(2), beta-Araf oligosaccharides with four units, beta-Araf oligosaccharides with seven units, and Hex(2)-Ara(4). Alpha-Rhap-(1 --> 4)-GlcA, alpha-Rhap-(1 --> 4)-beta-GlcpA-(1 --> 6)-Gal, and alpha-Rhap-(1 --> 4)-beta-GlcpA-(1 --> 6)-beta-Galp-(1 --> 6)-Gal represented other side chains.

Glucuronoarabinoxylan from coconut palm gum exudate: Chemical structure and gastroprotective effect

A glucuronoarabinoxylan (CNAL) was extracted with 1% aq. KOH (25°C) from Cocos nucifera gum exudate. It had a homogeneous profile on HPSEC-MALLS-RI (Mw 4.6 × 10(4)g/mol) and was composed of Fuc, Ara, Xyl, GlcpA (and 4-O-GlcpA) in a 7:28:62:3 molar ratio. Methylation data showed a branched structure with 39% of non-reducing end units, 3-O-substituted Araf (8%), 3,4-di-O- (15%), 2,4-di-O- (5%) and 2,3,4-tri-O-substituted Xylp units (17%). The anomeric region of CNAL (13)C NMR spectrum contained 9 signals, indicating a complex structure. The main chain of CNAL was characterized by analysis of a Smith-degraded polysaccharide. Its (13)C NMR spectrum showed 5 main signals at δ 101.6, δ 75.5, δ 73.9, δ 72.5, and δ 63.1 that were attributed to C-1, C-4, C-3, C-2 and C-5 of (1→4)-linked β-Xylp-main chain units, respectively. CNAL exhibited gastroprotective effect, by reducing gastric hemorrhagic lesions, when orally administered (1 and 3mg/kg) to rats prior to ethanol administration.

Structural characterization of a glucuronoarabinoxylan from pineapple (Ananas comosus (L.) Merrill) gum exudate

Native polysaccharide from pineapple gum (PANP) was obtained following alkaline extraction of gum and fractionation with cetylpyridinium chloride. It was characterized as a glucuronoarabinoxylan using NMR, methylation data, controlled Smith degradation, carboxy-reduction, and ESI-MS of oligosaccharides produced on mild acid hydrolysis of PANP. HSPEC-MALLS-RI of carboxy-reduced fraction showed homogeneous profile (Mw 1.943×10(5) g/mol). PANP was composed of Ara, Xyl, Gal, and GlcpA (40:23:7:30 molar ratio). Its main chain presented (1→4)-linked β-xylan, highly substituted at O-2 and O-3 by side chains of 3-O- and 3,5-di-O-linked α-Araf, 2-O- and 4-O-linked α-GlcpA, and nonreducing end-units of α-Araf, β-Arap, β-Galp, and α-GlcpA. ESI-MS of a mixture of oligosaccharides formed on the mild acid hydrolysis of PANP was consistent with repetitive structures of α-GlcpA O-3 linked at β-Xylp units, whereas in others glucuronoarabinoxylan-type gum exudates, α-GlcpA units had been previously found to be linked at O-2.