Submitted to: Phytochemistry
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/4/2004
Publication Date: 1/1/2005
Citation: Allerdings, E., Ralph, J., Schatz, P.F., Gniechwitz, D., Steinhart, H., Bunzel, M. 2004. Isolation and structural identification of diarabinosyl 8-o-4 dehydrodiferulate from maize bran insoluble fibre. Phytochemistry. 66:113-124. Interpretive Summary: Plant cell walls are rich in polysaccharides that provide considerable nutrition to ruminant animals and are part of the indigestible fiber component valuable in the human diet. Very small amounts of cross-linking agents in the walls tie polysaccharides together, reducing their digestibility in ruminants, but possibly providing health benefits to humans and animals. To date, a natural cross-linking agent, ferulate, has been well implicated to operate by cross-linking in a variety of ways. Only one of these cross linking structures has been definitively established by isolating that component still tethered to small pieces of the polysaccharide after most of the cell wall has been selectively removed with enzymes. In order to demonstrate that the other cross-linking mechanisms by ferulate do indeed cross-link polysaccharides, at least one other product of this type needed to be found. The isolation turns out to be extremely difficult, but collaborators at the University of Hamburg succeeded in isolating a compound which we showed by NMR to be the "di-5-O-L-arabinosyl ester of 8-O-4-dehydrodiferulic acid." Its existence provides the required evidence that these other cross-linking mechanisms are operating in cell walls. Such cross-linking has profound effects on the structure of plant cell walls, influencing the physical and possibly physiological properties of cereal grain fibers in general. In the paper we speculate further on the nature of the coupling of polysaccharide chains mediated by ferulate.
Technical Abstract: The first saccharide ester of a dehydrodiferulic acid (DFA) other than 5-5-DFA has been isolated from maize bran insoluble fibre after acidic hydrolysis and fractionation by gel chromatography and semi-preparative RP-HPLC. HPLC-MS along with 1D, 2D and 3D NMR spectra provided the requisite structural evidence that it is the di-5-O-L-arabinosyl ester of 8-O-4-DFA. Although a range of DFAs have been well authenticated as components released from the cell walls of grasses, the only structural evidence for a DFA attached to polysaccharides had been from 5-5-DFA. The isolation of the 8-O-4-ester demonstrates that polysaccharides in maize cell walls, and presumably in all grasses, are intermolecularly cross-linked through dehydrodiferulates other than 5-5-dehydrodiferulate.