The free reducing oligosaccharides of angico branco (Anadenanthera colubrina) gum exudate: an aid for structural assignments in the heteropolysaccharide

A novel method is described for the determination of sequential side-chain structures in the complex, high-arabinose polysaccharide of the gum exudate of angico branco (Anadenanthera colubrina), using as basis the structurall y similar reducing oligosaccharides present in small quantities. Of the ten detected, eight were characterized as disaccharides (2, 3, and 9), linear trisaccharides (1 and 4), branched pentasaccharides (5 and 6), and a doubly branched heptasaccharide (8). The oligosaccharides are substituents of the polysaccharide, which has a (1 --> 3)-linked P-D-galactopyranosyl main cha in, and with two exceptions they had 6-O-substituted galactopyranosyl reduc ing ends, probably corresponding to its main-chain units. Characterization was effected through their 1D and 2D NMR correlation spectra, which were be tter resolved and more readily interpretable than those of the polysacchari de. These spectral data were supported by monosaccharide composition and ro tation values. Controlled Smith degradations and methylation analyses were carried out when it was necessary. These data were confirmed by field-desor ption MS. (C) 1999 Elsevier Science Ltd. All rights reserved.