Biomimetic Oxidative Coupling of Sinapyl Acetate by Silver Oxide: Preferential Formation of β-O-4 Type Structures
Biomimetic Oxidative Coupling of Sinapyl Acetate by Silver Oxide: Preferential Formation of β-O-4 Type Structures
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DOI：
10.1021/jf506111q
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发表时间：
2015-03-04
影响因子：
6.1
通讯作者：
Nakajima, Noriyuki
中科院分区：
文献类型：
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作者：
Kishimoto, Takao;Takahashi, Nana;Nakajima, Noriyuki
为了更好地理解高度酰化天然木质素中高频率的β-O-4结构，用Ag 2 O进行了芥子醇和乙酸芥子酯的仿生氧化。芥子醇的Ag 2 O氧化的主要产物是芥子醛（14%产率）、β-O-4-偶联二聚体（32%产率）和β-β-偶联二聚体（3%产率）。相比之下，乙酸芥子酯的Ag 2 O氧化以66%的产率产生β-O-4-偶联二聚体。还以18%的产率获得了主要具有β-O-4结构的低聚产物。乙酸芥子酯的β-O-4-偶联产物的产率远高于芥子醇。基于密度泛函理论的计算表明，γ-乙酰基基团显著减少了C β上的负电荷。计算结果表明，乙酸芥子酯自由基中的C β和O-4之间的库仑排斥作用被γ-乙酰基显著降低，从而导致乙酸芥子酯优先形成β-O-4结构。
Biomimetic oxidations of sinapyl alcohol and sinapyl acetate were carried out with Ag2O to better understand the high frequency of beta-O-4 structures in highly acylated natural lignins. The major products from the Ag2O oxidation of sinapyl alcohol were sinapyl aldehyde (14% yield), beta-O-4-coupled dimer (32% yield), and beta-beta-coupled dimer (3% yield). In contrast, the Ag2O oxidation of sinapyl acetate produced beta-O-4-coupled dimer in 66% yield. Oligomeric products with predominantly beta-O-4 structures were also obtained in 18% yield. The yield of the beta-O-4-coupled products from sinapyl acetate was much higher than that from sinapyl alcohol. Computational calculations based on density functional theory showed that the negative charge at C beta was significantly reduced by the gamma-acetyl group. The computational calculations suggest that the Coulombic repulsion between C beta and O-4 in sinapyl acetate radicals was significantly reduced by the gamma-acetyl group, contributing to the preferential formation of beta-O-4 structures from sinapyl acetate.