160097-39-2Relevant academic research and scientific papers
NMR Assignment for Diaryl Ether Structures (4-O-5 Structures) in Pine Wood Lignin
Li, Yanding,Akiyama, Takuya,Yokoyama, Tomoya,Matsumoto, Yuji
, p. 1921 - 1929 (2016)
A 4-O-5-tetramer lignin model compound carrying β-O-4 linkages on each of the side-chain moieties was synthesized, as well as 4-O-5-coupled dehydrodiconiferyl alcohol. By comparison with their NMR data, two cross-signals in the HSQC spectrum of pine milled wood lignin recorded in DMSO-d6 were assigned to H2/C2 and H6/C6 correlations on the aromatic rings of 4-O-5-linked units. Although the H2/C2 correlation peak appeared in the same region as syringyl units, nitrobenzene oxidation of the pine lignin did not yield any syringyl-type product, but did release a 4-O-5-type product.
Synthesis and characterization of new 5-linked pinoresinol lignin models
Yue, Fengxia,Lu, Fachuang,Sun, Runcang,Ralph, John
supporting information, p. 16402 - 16410 (2013/02/23)
Pinoresinol structures, featuring a β-β′-linkage between lignin monomer units, are important in softwood lignins and in dicots and monocots, particularly those that are downregulated in syringyl-specific genes. Although readily detected by NMR spectroscopy, pinoresinol structures largely escaped detection by β-ether-cleaving degradation analyses presumably due to the presence of the linkages at the 5 positions, in 5-5′- or 5-O-4′-structures. In this study, which is aimed at helping better understand 5-linked pinoresinol structures by providing the required data for NMR characterization, new lignin model compounds were synthesized through biomimetic peroxidase-mediated oxidative coupling reactions between pre-formed (free-phenolic) coniferyl alcohol 5-5′- or 5-O-4′-linked dimers and a coniferyl alcohol monomer. It was found that such dimers containing free-phenolic coniferyl alcohol moieties can cross-couple with the coniferyl alcohol producing pinoresinol-containing trimers (and higher oligomers) in addition to other homo- and cross-coupled products. Eight new lignin model compounds were obtained and characterized by NMR spectroscopy, and one tentatively identified cross-coupled β-O-4′-product was formed from a coniferyl alcohol 5-O-4′-linked dimer. It was demonstrated that the 5-5′- and 5-O-4′-linked pinoresinol structures could be readily differentiated by using heteronuclear multiple-bond correlation (HMBC) NMR spectroscopy. With appropriate modification (etherification or acetylation) to the newly obtained model compounds, it would be possible to identify the 5-5′- or 5-O-4′-linked pinoresinol structures in softwood lignins by 2D HMBCN MR spectroscopic methods. Identification of the cross-coupled dibenzodioxocin from a coniferyl alcohol 5-5′-linked moiety suggested that thioacidolysis or derivatization followed by reductive cleavage (DFRC) could be used to detect and identify whether the coniferyl alcohol itself undergoes 5-5′-cross-linking during lignification. Super model: In this study, aimed at helping to better understand 5-linked pinoresinol structures by providing the required data for NMR structural characterization, new lignin model pinoresinol compounds were synthesized through biomimetic peroxidase-mediated oxidative coupling between pre-formed (free-phenolic) 5-5′- or 5-O-4′-linked coniferyl alcohol dimers and a coniferyl alcohol monomer (examples with 5-O-4′-linked dimers are shown in the scheme).
Identification and Synthesis of New Ferulic Acid Dehydrodimers Present in Grass Cell Walls
Ralph, John,Quideau, Stephane,Grabber, John H.,Haffield, Ronald D.
, p. 3485 - 3498 (2007/10/02)
Seven isomeric dehydrodimers of ferulic acid (4-hydroxy-3-methoxycinnamic acid) have been synthesized and identified in extracts of saponified cell walls of cocksfoot, switchgrass, and suspension-cultured corn.Dehydrodimers (E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnamic acid, trans-5--2-(4-hydroxy-3-methoxyphenyl)-7-methoxy-2,3-dihydrobenzofuran-3-carboxylic acid, (Z)-β--2-methoxyphenoxy>-4-hydroxy-3-methoxycinnamic acid, (E)-3--2-methoxyphenoxy>-4-hydroxy-5-methoxycinnamic acid, (E,E)-4,4'-dihydroxy-3,5'-dimethoxy-β,3'-bicinnamic acid, 4,4'-dihydroxy-3,3'-dimethoxy-β,β'-bicinnamic acid, and trans-7-hydroxy-1-(4-hydroxy-3-methoxyphenyl)-6-methoxy-1,2-dihydronaphthalene-2,3-dicarboxylic acid, all arise from oxidative coupling of ferulate esters in cell walls and represent products of 8-5, 8-8, 8-O-4, 4-O-5, and 5-5 radical coupling.Prior literature has acknowledged only the presence of the 5-5 coupled dehydrodimer (E,E)-4,4'-dihydroxy-5,5'-dimethoxy-3,3'-bicinnamic acid.Consequently, by measuring only a single dehydrodimer and assuming inappropriate response factors, ferulate dehydrodimers have been underestimated by factors of up to 20.Synthetic routes to all seven isomers have been developed to provide structural authentication and determination of GC response factors.
