Structural characterization of novel l-galactose-containing oligosaccharide subunits of jojoba seed xyloglucans

Jojoba seed xyloglucan was shown to be a convenient source of biologically active xyloglucan oligosaccharides that contain both l- and d-galactosyl residues [E. Zablackis et al., Science, 272 (1996) 1808–1810]. Oligosaccharides were isolated by liquid chromatography of the mixture of oligosaccharides generated by treating jojoba seed xyloglucan with a β-(1 → 4)-endoglucanase. The purified oligosaccharides were reduced with NaBH4, converting them to oligoglycosyl alditol derivatives that were structurally characterized by a combination of mass spectrometry and 2-dimensional NMR spectroscopy. This analysis established that jojoba xyloglucan oligosaccharides contain the novel side-chain [α-l-Gal p-(1 → 2)-β-d-Galp-(1 → 2)-α-d-Xyl p-(1 → 6)-], which is structurally homologous to the fucose-containing side-chain [α-l-Fucp-(1 → 2)-β-d-Galp-(1 → 2)-α-d-Xyl p-(1 → 6)-] found in other biologically active xyloglucan oligosaccharides.