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Abstract：
Phenoxy radical coupling reactions are widely used in nature for the synthesis of complex molecules such as lignin. Their use in the laboratory has great potential for the production of high value compounds from the polyphenol family. While the enzymes responsible for the generation of the radicals are well known, the behavior of the latter is still enigmatic and difficult to control in a reaction flask. Previous work in our laboratory using the enzymatic secretome of B. cinerea containing laccases has shown that incubation of stilbenes leads to dimers, while incubation of phenylpropanoids leads to dimers as well as larger coupling products. Building on these previous studies, this paper investigates the role of different structural features in phenoxy radical couplings. We first demonstrate that the presence of an exocyclic conjugated double bond plays a role in the generation of efficient reactions. In addition, we show that the formation of phenylpropanoid trimers and tetramers can proceed via a decarboxylation reaction that regenerates this reactive moiety. Lastly, this study investigates the reactivity of other phenolic compounds: stilbene dimers, a dihydro-stilbene, a 4-O-methyl-stilbene and a simple phenol with the enzymatic secretome of B. cinerea. The observed efficient dimerization reactions consistently correlate with the presence of a para-phenol conjugated to an exocyclic double bond. The absence of this structural feature leads to variable results, with some compounds showing low conversion or no reaction at all. This research has allowed the development of a controlled method for the synthesis of specific dimers and tetramers of phenylpropanoid derivatives and novel stilbene derivatives, as well as an understanding of features that can promote efficient radical coupling reactions.
摘要：
苯氧基自由基偶联反应在自然界中广泛用于合成复杂分子如木质素。它们在实验室中的使用对于从多酚家族生产高价值化合物具有巨大的潜力。虽然负责产生自由基的酶是众所周知的，后者的行为仍然是神秘的，难以在反应烧瓶中控制。在我们的实验室中使用含有漆酶的B.cinerea酶促分泌组的先前工作表明，二苯乙烯的孵育会导致二聚体，而苯基丙烷类的孵育会导致二聚体以及更大的偶联产物。在这些先前研究的基础上，本文研究了不同结构特征在苯氧基自由基偶联中的作用。我们首先证明了环外共轭双键的存在在产生有效反应中起作用。此外,我们表明，苯丙素类三聚体和四聚体的形成可以通过脱羧反应再生该反应性部分进行。最后,这项研究调查了其他酚类化合物的反应性：二苯乙烯二聚体，一种二氢二苯乙烯,一种4-O-甲基-二苯乙烯和一种具有灰霉病菌酶促分泌组的简单酚。观察到的有效二聚反应始终与共轭到环外双键的对酚的存在相关。缺乏这种结构特征会导致不同的结果，一些化合物显示低转化率或根本没有反应。这项研究允许开发一种可控的方法来合成苯丙素衍生物和新型二苯乙烯衍生物的特定二聚体和四聚体，以及对可以促进有效自由基偶联反应的特征的理解。
