title: Hydroxycinnamic acids are ester-linked directly to glucosyl moieties within the lignan macromolecule from flaxseed hulls.
abstract: In flaxseed hulls, lignans are present in an oligomeric structure. Secoisolariciresinol diglucoside (SDG), ester-linked to hydroxy-methyl-glutaric acid (HMGA), forms the backbone of this lignan macromolecule. The hydroxycinnamic acids p-coumaric acid glucoside (CouAG) and ferulic acid glucoside (FeAG) are also part of the lignan macromolecule. However, their position and type of linkage are still unknown. The aim of this study was to investigate how CouAG and FeAG are linked within the lignan macromolecule from flaxseed hulls. Fragments of the lignan macromolecule were obtained by partial saponification. After isolation of the fragments by preparative RP-HPLC, several key structures were identified by MS and NMR. Within the lignan macromolecule, CouAG is attached to the C-6 position of a glucosyl moiety of SDG. FeA is linked to the C-2 position of a glucosyl moiety of SDG. FeAG is ester-linked within the lignan macromolecule with its carboxyl group, but it remains unclear whether FeAG links to the C-2 or C-6 position of SDG. Attachment of HMGA to the glucosyl moiety of CouAG or FeAG was not observed. The results clearly show that within the lignan macromolecule, the hydroxycinnamic acids are linked directly via an ester bond to the glucosyl moiety of SDG.
authors.affiliation: Laboratory of Food Chemistry, Wageningen University, PO Box 8129, 6700 EV Wageningen, The Netherlands.
authors.forename: Karin
authors.initials: K
authors.lastname: Struijs
authors.forename: Jean-Paul
authors.initials: JP
authors.lastname: Vincken
authors.forename: René
authors.initials: R
authors.lastname: Verhoef
authors.forename: Alphons G J
authors.initials: AG
authors.lastname: Voragen
authors.forename: Harry
authors.initials: H
authors.lastname: Gruppen
mesh_terms: D002851:Chromatography, High Pressure Liquid / Q000379:methods; D003373:Coumaric Acids / Q000737:chemistry*; D004952:Esters / Q000737:chemistry* / Q000302:isolation & purification; D019597:Flax / Q000737:chemistry*; D005960:Glucosides / Q000737:chemistry* / Q000302:isolation & purification; D017705:Lignans / Q000737:chemistry* / Q000302:isolation & purification; D046911:Macromolecular Substances / Q000737:chemistry / Q000302:isolation & purification; D009682:Magnetic Resonance Spectroscopy / Q000379:methods / Q000592:standards; D013058:Mass Spectrometry / Q000379:methods; D015394:Molecular Structure; D012015:Reference Standards; D012639:Seeds / Q000737:chemistry
chemical_list: D003373:Coumaric Acids; D004952:Esters; D005960:Glucosides; D017705:Lignans; D046911:Macromolecular Substances