528814-97-3Relevant articles and documents
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).
Salen complexes with bulky substituents as useful tools for biomimetic phenol oxidation research
Haikarainen, Anssi,Sipil?, Jussi,Pietik?inen, Pekka,Pajunen, Aarne,Mutikainen, Ilpo
, p. 1633 - 1638 (2007/10/03)
The catalytic properties of bulky water-soluble Co-, Cu-, Fe- and Mn-salen complexes in the oxidation of phenolic lignin model compounds have been studied in aqueous water-dioxane solutions (pH 3-10). Mn catalysts were found to oxidize coniferyl alcohol in a same reaction time as horseradish peroxidase (HRP) enzyme and Mn and Co catalysts showed different regioselectivity suggesting a different substrate to catalyst interaction in the oxidative coupling. When the oxidation of material more relevant to plant polyphenolics was studied, the results indicated that the complexes catalyze one- and two-electron oxidations depending on the bulk of the substrate. Copyright
Regioselectivity in lignin biosynthesis. The influence of dimerization and cross-coupling
Syrjaenen, Kaisa,Brunow, Goesta
, p. 183 - 187 (2007/10/03)
We have studied the regioselectivity of oxidative phenol coupling in lignin formation using an oxidation system that distinguishes between dimerization reactions and cross-coupling reactions. We found that the regioselectivity of coupling was different in the two reactions. For instance, in coniferyl alcohol dimerization the formation of β-5 coupling product has a slight prevalence over the formation of β-O-4 product; in cross-coupling the β-0-4 mode is favoured in a ratio of ≈10:1. This ratio is higher than that found in isolated softwood lignins. The degree of cross-coupling was influenced only to a small extent by changes in the rates of conventional addition of coniferyl alcohol (Zulauf versus Zutropf conditions). We found that diffusion through a dialysis membrane did effectively suppress the dimerization of coniferyl alcohol. Of the different oxidants investigated, manganese triacetate in acetic acid yielded the highest proportion of cross-coupling product. The Royal Society of Chemistry 2000.
