title: Biomimetic oxidative coupling of sinapyl acetate by silver oxide: preferential formation of β-O-4 type structures.
abstract: Biomimetic oxidations of sinapyl alcohol and sinapyl acetate were carried out with Ag2O to better understand the high frequency of β-O-4 structures in highly acylated natural lignins. The major products from the Ag2O oxidation of sinapyl alcohol were sinapyl aldehyde (14% yield), β-O-4-coupled dimer (32% yield), and β-β-coupled dimer (3% yield). In contrast, the Ag2O oxidation of sinapyl acetate produced β-O-4-coupled dimer in 66% yield. Oligomeric products with predominantly β-O-4 structures were also obtained in 18% yield. The yield of the β-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 Cβ was significantly reduced by the γ-acetyl group. The computational calculations suggest that the Coulombic repulsion between Cβ and O4 in sinapyl acetate radicals was significantly reduced by the γ-acetyl group, contributing to the preferential formation of β-O-4 structures from sinapyl acetate.
authors: Bioorganic Chemistry Laboratory, Department of Biotechnology, Faculty of Engineering, Toyama Prefectural University , Imizu 939-0398, Japan.
authors: Takao
authors: T
authors: Kishimoto
authors: Nana
authors: N
authors: Takahashi
authors: Masahiro
authors: M
authors: Hamada
authors: Noriyuki
authors: N
authors: Nakajima
mesh_terms: D000085:Acetates / Q000737:chemistry*; D032701:Biomimetics; D008031:Lignin / Q000737:chemistry; D015394:Molecular Structure; D058451:Oxidative Coupling; D010087:Oxides / Q000737:chemistry*; D010696:Phloroglucinol / Q000031:analogs & derivatives* / Q000737:chemistry; D018030:Silver Compounds / Q000737:chemistry*
chemical_list: D000085:Acetates; D010087:Oxides; D018030:Silver Compounds; C533261:sinapyl acetate; C040225:disilver oxide; D008031:Lignin; D010696:Phloroglucinol
keywords: Coulombic repulsion; DFT; acylated lignin; sinapyl alcohol; β-O-4