Isolation and identification of a ferulic acid dehydrotrimer from saponified maize bran insoluble fiber

Abstract

Following saponification of maize bran insoluble fiber a ferulic acid dehydrotrimer was isolated using Sephadex LH-20 chromatography. Structural identification was carried out using UV-spectroscopy, mass spectrometry and 1D and 2D NMR experiments (1H, 13C, DEPT, COSY, TOCSY, 13C-1H HSQC, HMBC). UV-spectroscopy indicated characteristics of ferulate structures, mass spectrometry showed a trimeric ferulate structure, and the NMR spectra provided diagnostic evidence for its being a 5-5/8-O-4-coupled dehydrotrimer. Ferulic acid dehydrodimers are mainly derived from diferulates which cross-link polysaccharides. Because of the involvement of a 5-5-dehydrodiferulic acid unit in the identified trimer, this novel dehydrotriferulic acid from cereal grain fiber need not imply the cross-linking of three polysaccharide chains; molecular modeling of the ferulate dehydrodimerization in earlier studies showed that the 5-5-diferulate, uniquely, can form intramolecularly. This first identified ferulic acid dehydrotrimer nevertheless reveals that polysaccharide chains can be more extensively cross-linked than previously recognized.