Structural elucidation of new ferulic acid-containing phenolic dimers and trimers isolated from maize bran

Four new phenolic dimers and trimers that contain ferulic acid moieties were isolated from the alkaline hydrolyzate of insoluble maize bran fiber and their structures were established by 1D/2D NMR and mass spectrometry. The biological role of one dimer remains unclear whereas the dimeric vanillin-ferulic acid-cross-product probably represents an oxidative degradation product from the corresponding diferulate. Both ferulic acid dehydrotrimers are able to cross-link polysaccharide chains. However, the 5-5/ 8-O-4(H2O)-triferulic acid may be a cross-link in its identified structure whereas we assume that the identified 8-O-4/8-5(non-cyclic)triferulic acid arose from a natural 8-O-4/8-5(cyclic)-triferulate analog during the saponification process. 2005 Elsevier Ltd. All rights reserved. Grasses and cereals contain substantial amounts of cell wall-bound hydroxycinnamate esters linked to polysaccharides. Particularly, ferulates play an important role in cross-linking cell wall polysaccharides. Ferulates dehydrodimerize via a radical, oxidative mechanism to form mainly 8-5-, 8-O-4-, 5-5-, 8-8-, and 4-O-5-coupled dehydrodiferulates (often simply referred to as diferulates), thus cross-linking two polysaccharide chains. Polysaccharide cross-linking plays a significant role in the plant and plant derived products, for example, by effecting cell wall strength, fiber degradability, and food textural and processing properties. Furthermore, ferulates and diferulates act as cross-links between polysaccharides and lignin. Recently, three dehydrotriferulic acids have been isolated and identified for the first time, indicating that also higher ferulate oligomers are involved in cross-linking cell wall polysaccharides as proposed by Fry et al. However, to date it is not possible to decide whether triferulates cross-link three polysaccharide chains or whether their cross-link0040-4039/$ see front matter 2005 Elsevier Ltd. All rights reserved. doi:10.1016/j.tetlet.2005.06.140