2-O-beta-D-xylopyranosyl-(5-O-feruloyl)-L-arabinose, a widespread component of grass cell walls

Graminaceous cell walls contain arabinoxylans in which some of the Araf residues are 5-O-feruloylated. In the present study, mild acid hydrolysis of (pentosyl-H-3)-labelled Festuca arundinacea cell walls yielded the well-characterized 5-O-Fer-L-Ara (1) and at least seven new (E)-feruloylated oligosaccharides, 2-8. Compound 2 was a feruloylated disaccharide, Fer-(D-Xylp --> L-Ara); electrophoresis in molybdate buffer, Smith degradation and methylation analysis showed a (1 --> 2)-linkage. H-1 and C-13 NMR data and susceptibility to commercial beta-D-xylosidase indicated a beta-linkage. Graded alkaline hydrolysis of 2 showed no evidence for more than one ester group. Hydrolysis with commercial beta-xylosidase yielded 5-O-feruloyl-L-arabinose. Compound 2 was thus 2-O-beta-D-xylopyranosyl-(5-O-feruloyl)-L-arabinose. We propose that 2 was furanose-linked to a xylan backbone in the intact polymer. Compounds 3-8 also appeared to be O-feruloyl oligosaccharides with a former Araf residue at the reducing terminus. Mild acid hydrolysis of cell walls from twenty other species of grass and one palm also yielded compounds 1-3, and most or all of 4-8. Therefore, these complex feruloylated side-chains of arabinoxylans are widespread or universal in the Gramineae. Their possible biological roles are discussed. Copyright (C) 1997 Elsevier Science Ltd.