Structure of the fucose-containing acidic heteroxylan from the gum exudate of Syagrus romanzoffiana (Queen palm)

Abstract

The gum exudate of S. romanzoffiana contained a heteropolysaccharide (SRP), which was isolated in 80% yield, contained Fuc, Ara, Xyl, Gal, Glc and uronic acid in a molar ratio of 23:25:41:1:3:8, and had [ α ] D 25 − 72 ° . It was homogeneous with M w 1.4×10 5 and M w/ M n∼1.0 and formed high viscosity, aqueous solutions. Carboxy-reduction provided neutral material (SRP-CR), having glucose and its 4- O-methyl derivative in a molar ratio of ∼3:1. Methylation analysis of SRP showed a highly branched structure with non-reducing end-units of Ara f (16%), Fuc p (10%) and Xyl p (12%), 3- O- (5%), 2- O- (17%), 3,4- (7%) and 2,4-di- O-substituted Ara f (10%), and 2,3,4-tri- O-susbtituted Xyl p units (21%). The 13C-NMR spectrum of SRP was complex and contained at least 8 C-1 signals. The 13C-NMR spectrum and methylation analysis of Smith-degraded polysaccharide (SRP-SM) were consistent with a (1→4)-linked β-Xyl p main chain. Partial hydrolysis of SRP gave rise to α-Glc pA-(1→2)-β-[Xyl p-(1→4)] 0-1-αβ-Xyl p and 4-Me-α-Glc pA-(1→2)-αβ-Xyl p. Milder hydrolysis conditions gave rise a mixture of oligosaccharides that were fractionated by charcoal–Celite column chromatography. The 10% aq. EtOH fraction (OL-10) gave a main GC spot with R Gal 1.2 and minor ones with R Gal 1.07 and 0.78, and was characterized as a mixture of β-Xylp-(1→2)-αβ-Xyl, Fuc p-(1→4)-αβ-Xyl p, and Fuc p-(1→3)-αβ-Ara. Small amounts of fucobiose were also present.