title: Structural identification of dehydrotriferulic and dehydrotetraferulic acids isolated from insoluble maize bran fiber.
abstract: Two new dehydrotriferulic acids and two dehydrotetraferulic acids were isolated from saponified maize bran insoluble fiber using size exclusion chromatography on Bio-Beads S-X3 followed by Sephadex LH-20 chromatography and semipreparative phenyl-hexyl reversed phase high-performance liquid chromatography. On the basis of UV spectroscopy, mass spectrometry, and one- and two-dimensional NMR experiments, the structures were identified as 8-5(noncyclic)/5-5-dehydrotriferulic acid, 8-8(tetrahydrofuran)/5-5-dehydrotriferulic acid, and 4-O-8/5-5/8-O-4-dehydrotetraferulic acid. The second tetramer was tentatively identified as 4-O-8/5-5/8-5(noncyclic)-dehydrotetraferulic acid. Compounds containing an 8-5(noncyclic)-coupled dimeric unit probably do not exist in planta but are formed from their phenylcoumaran precursors containing an 8-5(cyclic)-coupled dimeric unit during saponification. The presented dehydrotrimers are the first dehydrotriferulates that do not contain an 8-O-4-coupled dimeric unit. The ferulate dehydrotetramers that are reported for the first time are presumed, like the dimers and trimers, to cross-link polysaccharides in the plant. Because both tetramers contain a 5-5/8-O-4-dehydrotriferulate moiety, the predominant dehydrotrimer in maize bran, it is not possible to deduce whether tetramers are formed by coupling of a fourth unit to a preformed dehydrotriferulate or by 5-5-coupling of preformed 8-O-4- and 8-5-dehydrodiferulates. Nevertheless, such compounds document expanded roles for ferulates in cross-linking polysaccharides in plant cell walls.
authors.affiliation: Institute of Biochemistry and Food Chemistry, Department of Food Chemistry, University of Hamburg, Grindelallee 117, 20146 Hamburg, Germany. mirko.bunzel@uni-hamburg.de
authors.forename: Mirko
authors.initials: M
authors.lastname: Bunzel
authors.forename: John
authors.initials: J
authors.lastname: Ralph
authors.forename: Philipp
authors.initials: P
authors.lastname: Brüning
authors.forename: Hans
authors.initials: H
authors.lastname: Steinhart
mesh_terms: D002473:Cell Wall / Q000737:chemistry; D002850:Chromatography, Gel; D002851:Chromatography, High Pressure Liquid; D003373:Coumaric Acids / Q000032:analysis* / Q000737:chemistry*; D004043:Dietary Fiber / Q000032:analysis; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D015394:Molecular Structure; D012995:Solubility; D003313:Zea mays / Q000737:chemistry*
chemical_list: D003373:Coumaric Acids; D004043:Dietary Fiber; C004999:ferulic acid