Nature's Ingenuity in Stereoselective (Phenol) Coupling

立体选择性（苯酚）偶联中的大自然智慧

• 批准号: 9631980
• 负责人: Norman Lewis
• 金额: --
• 依托单位: Washington State University
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 1996
• 资助国家: 美国
• 起止时间: 1996-09-01 至 1999-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9631980&HistoricalAwards=false
• 关键词: Nature; Ingenuity; Stereoselective; Phenol; Coupling

9631980 Lewis One of the most important yet poorly understood biological events in nature is that of bimolecular phenoxy radical coupling. Surprisingly, phenoxy radical coupling reactions have long been imperfectly characterized, and are frequently described as lacking stereoselectivity based on their catalytic properties in vitro. Yet even a cursory analysis of such reactions in nature indicates that some mechanism for conferring stereospecificity must exist, since the products are stereospecific. Seeking to understand how this stereoselectivity is produced, the investigators examined the coupling of two achiral molecules of E-coniferyl alcohol to give (+)-pinoresinol, one of the simplest dimeric lignan products known in nature. They established that a 78kDa protein is necessary to confer both regio- & stereospecificity on the products. This stereoselective coupling only occurs when auxiliary oxidative capacity is provided through the addition of either an oxidase or a free-radical initiator, such as ammonium peroxydisulfate or FMN. This investigation will seek to define the biochemical mechanism of this unique mode of control. The relationships between the 78 kDa protein, the substrate and an auxiliary oxidase/oxidant will be studied. That is, does the operative mechanism involve initial binding of two E-coniferyl alcohol molecules to the 78 kDa protein, or is the substrate for binding actually the free-radical species obtained via one electron oxidation? A third possibility is that some charge-transfer mechanism is in place, although the absence of any detectable active site (prosthetic group) makes this unlikely. The investigators will conduct a detailed kinetic anaylsis of the coupling reaction as well as defining the substrate specificity for binding/coupling and the effect of putative inhibitors. In this way the mechanism for conferring stereoselectivity in phenoxy radical coupling will be determined and will serve as a starting point to determine the generality of this m echanism in nature. %%% One of the most important, and yet most poorly understood, biological events in nature is that of bimolecular phenoxy radical coupling, the joining of two molecules containing phenol moieties. It is highly significant, since it eventually leads to the formation of woody and cork tissues, insect cuticles, fungal fruiting bodies, aphid pigments, and a host of defense molecules, particularly in plants. Taken together, phenolic coupling reactions account for roughly 35-40% of all organic plant material. Two phenol moieties can often be joined in numerous ways, with the individual products being mirror images of each other. Before the advances by these investigators, in vitro reactions only yielded mixtures of various mirror image products. In vivo reactions, however, often yield only one product and in one mirror image form. How is that specificity attained? The investigators have isolated a protein, which they have called a "specifier", which confers such specificity on the reactions. The goal of this project is to define the biochemical mechanism of this novel protein. ***

刘易斯自然界中最重要但知之甚少的生物学事件之一是双分子苯氧基自由基偶联。 令人惊讶的是，苯氧基自由基偶联反应长期以来一直不完善的特点，并经常被描述为缺乏立体选择性的基础上，在体外的催化性能。然而，即使粗略地分析自然界中的这种反应，也表明一定存在某种赋予立体特异性的机制，因为产物是立体特异性的。 为了了解这种立体选择性是如何产生的，研究人员研究了E-松柏醇的两个非手性分子的偶联，得到（+）-松醇，这是自然界中已知的最简单的二聚木脂素产物之一。 他们确定了78 kDa蛋白质是赋予产物两种区域立体特异性所必需的。 这种立体选择性偶联仅在通过添加氧化酶或自由基引发剂（如过二硫酸铵或FMN）提供辅助氧化能力时发生。 这项研究将试图确定这种独特的控制模式的生化机制。 将研究78 kDa蛋白质、底物和辅助氧化酶/氧化剂之间的关系。 也就是说，其作用机制是否涉及两个E-松柏醇分子的初始结合 还是用于结合的底物实际上是通过一个电子氧化获得的自由基物质？ 第三种可能性是存在某种电荷转移机制，尽管缺乏任何可检测到的活性位点（辅基）使这种可能性不大。 研究者将对偶联反应进行详细的动力学分析，并确定结合/偶联的底物特异性和推定抑制剂的作用。 以这种方式，将确定在苯氧基自由基偶联中赋予立体选择性的机制，并将作为确定该机制在自然界中的一般性的起点。 在自然界中，最重要的生物学事件之一是双分子苯氧基自由基偶联，即两个含有苯酚部分的分子的连接。 这是非常重要的，因为它最终导致木质和软木组织，昆虫表皮，真菌子实体，蚜虫色素和许多防御分子的形成，特别是在植物中。 总的来说，酚偶联反应约占所有有机植物材料的35-40%。 两个酚部分通常可以以多种方式连接，其中各个产物彼此成镜像。在这些研究人员取得进展之前，体外反应只能产生各种镜像产物的混合物。然而，体内反应通常只产生一种产物，并且呈一种镜像形式。 这种特异性是如何实现的？ 研究人员已经分离出一种蛋白质，他们称之为“特异性”，它赋予反应这种特异性。 该项目的目标是确定这种新型蛋白质的生化机制。 ***