Department of Chemistry and Chemical Biology, University of New Mexico, Albuquerque, New Mexico 87131, United States.
J Org Chem. 2011 Apr 15;76(8):2840-52. doi: 10.1021/jo200253v. Epub 2011 Mar 18.
New types of tetrameric lignin model compounds, which contain the common β-O-4 and β-1 structural subunits found in natural lignins, have been prepared and carbon-carbon bond fragmentation reactions of their cation radicals, formed by photochemical (9,10-dicyanoanthracene) and enzymatic (lignin peroxidase) SET-promoted methods, have been explored. The results show that cation radical intermediates generated from the tetrameric model compounds undergo highly regioselective C-C bond cleavage in their β-1 subunits. The outcomes of these processes suggest that, independent of positive charge and odd-electron distributions, cation radicals of lignins formed by SET to excited states of sensitizers or heme-iron centers in enzymes degrade selectively through bond cleavage reactions in β-1 vs β-O-4 moieties. In addition, the findings made in the enzymatic studies demonstrate that the sterically large tetrameric lignin model compounds undergo lignin peroxidase-catalyzed cleavage via a mechanism involving preliminary formation of an enzyme-substrate complex.
已经制备了新的四聚体木质素模型化合物，其中包含天然木质素中常见的β-O-4 和 β-1 结构单元，并探索了它们的阳离子自由基的碳-碳键断片反应，这些阳离子自由基是通过光化学（9,10-二氰基蒽）和酶促（木质素过氧化物酶）SET 促进方法形成的。结果表明，来自四聚体模型化合物的阳离子自由基中间体在其β-1 亚基中经历高度区域选择性的 C-C 键断裂。这些过程的结果表明，独立于正电荷和奇数电子分布，通过敏化剂或酶中血红素铁中心的激发态进行 SET 形成的木质素阳离子自由基通过β-1 与β-O-4 部分的键断裂反应选择性地降解。此外，在酶研究中发现，空间位阻较大的四聚体木质素模型化合物通过涉及酶-底物复合物初步形成的机制经历木质素过氧化物酶催化的裂解。
