Submitted to: Organic and Biomolecular Chemistry
Publication Type: Peer reviewed journal
Publication Acceptance Date: 5/24/2006
Publication Date: 8/1/2006
Citation: Schatz, P.F., Ralph, J., Lu, F., Guzei, I.A., Bunzel, M. 2006. Synthesis and identification of 2,5-bis-(4-hydroxy-3-methoxyphenyl)-tetrahydrofuran-3,4-dicarboxylic acid, an unanticipated ferulate 8-8-coupling product acylating cereal plant cell walls. Organic and Biomolecular Chemistry. 4(14):2801-2806. Interpretive Summary: A plant's fiber component provides a great deal of structural strength as well as considerable nutrition to ruminant animals. Grain fiber also has significant human health benefits. The fiber is reinforced in the plant by cross-linking of the polysaccharide polymers, on a micro-scale rather akin to the cross-bracing we use when building wooden structures. Some time ago we discovered new mechanisms by which wall cross-linking could be achieved by chemical coupling of two so-called ferulate molecules (that were each tied to one polysaccharide chain) to create ferulate dimers. Such findings have opened up avenues of research into improving the utilization of large classes of plant fiber and other food commodities. Here we report a new cross-linking structure derived from ferulate that has escaped researchers' attention due to its unanticipated structure. We synthesized the compound and confirmed that the structure released from grass cell walls was the same, and quantified it relative to the other dimers in dietary fiber. The significance is that cross-linking is even more prevalent than we previously thought, and that ferulates are capable of creating the cross-links in a variety of ways. Future efforts are aimed at minimizing this cross-linking in forage plants to improve ruminant digestibility, and to ascertain the human and animal health benefits of the ferulates in cereal grains.
Technical Abstract: A new product implicated in cereal grain polysaccharide cross-linking has been authenticated by independent synthesis. Saponification of cereal grain fiber releases the RRRS/SSSR-isomer of 2,5-di-(4´-hydroxy-3´-methoxyphenyl)-2,3,4,5-tetrahydrofuran-3,4-dicarboxylic acid. The parent ester logically derives from 8-8-coupling of ferulate followed by water addition to one of the incipient quinone methide moieties and internal trapping of the other. The finding adds complexity to the analysis of plant cell wall cross-linking, but provides clues to important polysaccharide cross-linking pathways occurring in planta.