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首页> 外文期刊>Chemistry: A European journal >Synthesis and characterization of new 5-linked pinoresinol lignin models
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Synthesis and characterization of new 5-linked pinoresinol lignin models

机译：新型5连接松脂醇木质素模型的合成与表征

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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).
机译：在木质素单体单元之间具有β-β'键的松脂醇结构在软木木质素以及双子叶植物和单子叶植物中，特别是在丁香烯基特异性基因中被下调的那些中，是重要的。尽管可以通过NMR光谱轻松地检测到，但由于5-5'-或5-O-4'-结构中的5个位置均存在连接键，因此松脂醇结构很大程度上无法通过β-醚裂解降解分析进行检测。在这项研究中，旨在通过提供NMR表征所需的数据来帮助更好地理解5-连接的松脂醇结构，通过仿生过氧化物酶介导的预先形成的（游离酚）松柏树醇之间的氧化偶联反应合成了新的木质素模型化合物。 5-5'-或5-O-4'-连接的二聚体和松柏醇单体。发现含有游离酚类松柏油醇部分的二聚体可以与产生松柏油醇的含松脂醇的三聚体（和高级低聚物）交叉偶联，此外还具有其他均聚和交联产物。获得了八种新的木质素模型化合物，并通过NMR光谱进行了表征，并从一种针叶醇5-O-4'连接的二聚体中初步鉴定出一种交叉偶联的β-O-4'-产物。已经证明，通过使用异核多键相关（HMBC）NMR光谱可以轻松地区分5-5'-和5-O-4'-连接的松脂醇结构。通过对新获得的模型化合物进行适当的修饰（醚化或乙酰化），可以通过2D HMBCN MR光谱法鉴定软木木质素中5-5'-或5-O-4'-连接的松脂醇结构。从针叶树醇5-5'-连接的部分交叉偶联的二苯并二恶英的鉴定表明，硫代酸解或衍生化然后进行还原裂解（DFRC）可用于检测和鉴定针叶树醇本身是否经过5-5'-交叉在木质化过程中连接。超级模型：在这项研究中，旨在通过提供NMR结构表征所需的数据来帮助更好地理解5-连接的松脂醇结构，通过仿生过氧化物酶介导的预先形成的（游离酚）之间的氧化偶合反应合成了新的木质素模型松脂醇化合物。 ）5-5′-或5-O-4′-连接的松柏醇二聚体和松柏醇单体（具有5-O-4′-连接的二聚体的实例显示在方案中）。

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