Non-enzymatic reduction of quinone methides during oxidative coupling of monolignols: implications for the origin of benzyl structures in lignins
Non-enzymatic reduction of quinone methides during oxidative coupling of monolignols: implications for the origin of benzyl structures in lignins
复制标题
DOI：
10.1039/b606369a
复制
发表时间：
2006-01-01
影响因子：
3.2
通讯作者：
Ralph, John
中科院分区：
文献类型：
--
作者：
Holmgren, Anders;Brunow, Goesta;Ralph, John
木质素被认为是通过4-羟基苯基丙烷类的氧化偶联合成的。在天然木质素中，存在某些类型的还原结构，其不能仅通过氧化偶联来解释。在目前的工作中，我们表明，通过仿生模型实验，烟酰胺腺嘌呤二核苷酸（NADH），在非催化过程中，还原β-芳基醚醌甲基化物的苄基衍生物。许多其他具有生物学意义的还原剂，包括纤维二糖脱氢酶，未能产生还原结构。在还原剂NADH的存在下合成的松柏醇的合成脱氢聚合物（在氧化条件下）产生与模型实验中相同种类的还原结构，表明氧化和还原过程可以在相同的环境中发生，并且原位生成的醌甲基化物的还原与水的加入具有足够的竞争力。在本研究中未实现β-β-醌甲基化物的原位还原。因此，木质素中外消旋苄基结构的起源仍然未知，但这里证明了简单化学还原的潜力。
Lignin is believed to be synthesized by oxidative coupling of 4-hydroxyphenylpropanoids. In native lignin there are some types of reduced structures that cannot be explained solely by oxidative coupling. In the present work we showed via biomimetic model experiments that nicotinamide adenine dinucleotide ( NADH), in an uncatalyzed process, reduced a beta-aryl ether quinone methide to its benzyl derivative. A number of other biologically significant reductants, including the enzyme cellobiose dehydrogenase, failed to produce the reduced structures. Synthetic dehydrogenation polymers of coniferyl alcohol synthesized ( under oxidative conditions) in the presence of the reductant NADH produced the same kind of reduced structures as in the model experiment, demonstrating that oxidative and reductive processes can occur in the same environment, and that reduction of the in situ-generated quinone methides was sufficiently competitive with water addition. In situ reduction of beta - beta-quinone methides was not achieved in this study. The origin of racemic benzyl structures in lignins therefore remains unknown, but the potential for simple chemical reduction is demonstrated here.