STEREOCHEMICAL STUDIES OF ISOPRENOID BIOSYNTHESIS

烯丙基焦磷酸盐，法尼基香叶基焦磷酸盐，是 倍半萜和单萜的通用无环前体， 分别进行了分析。使用多种单萜和倍半萜合成酶 从真菌和高等植物中分离出来，我们计划研究关键的环化作用 这些广泛存在的类异戊二烯天然化合物的反应 产品是生物合成的。 六元化合物形成的立体化学模型 含环倍半萜类化合物，涉及叔基中间体 烯丙基焦磷酸盐橙花油基焦磷酸盐将通过使用 毛状二烯合成酶和适当的~3H和~(14)C标记的法尼基和 橙花酯焦磷酸底物，使我们能够定义构象 环化底物以及焦磷酸盐所起的作用 离子。提出的异构化反应机理--环化反应序列 导致三环二烯形成的原因将由 三环二烯合成酶与三环己烯合成酶作用机制的比较 法尼基焦磷酸异构酶。后一种酶催化 橙花酯焦磷酸的法尼基异构化。通过使用一系列 选择底物类似物，我们将尝试将三环二烯因子 合成酶反应转化为其组分的异构化和 骑自行车。我们计划研究第二个立体化学的细节 法尼基的酶促转化-环化反应 一种分离的环化酶催化焦磷酸合成顺式胡萝卜烯 来自Sage的。我们一直在测试单萜的立体化学模型 生物合成，使用各种单萜烯合成酶。成立为法团 包括焦磷酸芳樟酯在内的各种标记前体的计划 这将使我们能够阐明其详细的结构和构象 单萜生物合成的活性中间体。这是意料之中的 所提出的工作将导致新技术的发展 天然产物生物合成的研究和所获得的信息 这些研究将适用于对催化作用的理解 生物碳-碳键的形成。

The allylic pyrophosphates, farnesyl geranyl pyrophosphate, are the universal acyclic procursors of sesquiterpenes and monoterpenes, respectively. Using a number of monoterpene and sesquiterpene synthetases isolated from fungi and higher plants, we plan to study the key cyclization reactions by which these widely occurring classes of isoprenoid natural products are biosynthesized. A proposed stereochemical model for the formation of six-membered ring-containing sesquiterpenes, involving the intermediacy of the tertiary allylic pyrophosphate nerolidyl pyrophosphate will be tested by the use of trichodiene synthetase and appropriately 3H- and 14C-labeled farnesyl and nerolidyl pyrophosphate substrates, allowing us to define the conformation of the cyclizing substrates as well as the role played by the pyrophosphate ion. The mechanism of the proposed isomerization--cyclization sequence leading to formation of trichodiene will be further investigated by comparing the mechanism of action of trichodiene synthetase with that of farnesyl pyrophosphate isomerase. The latter enzyme catalyzes the isomerization of farnesyl of nerolidyl pyrophosphate. By using a series of selected substrate analogs, we will attempt to factor the trichodiene synthetase reaction into its component transformations of isomerization and cyclization. We plan to study the stereochemical details of a second cyclization reaction, the enzymatic transformation of farnesyl pyrophosphate to the sequiterpene humulene, catalyzed by a cyclase isolated from sage. We have been testing a stereochemical model of monoterpene biosynthesis, using a variety of monoterpene synthetases. Incorporations of various labeled precursors, including linalyl pyrophosphate, are planned which will allow us to elucidate the detailed structure and conformation of the reactive intermediates of monoterpene biosynthesis. It is expected that the work proposed will lead to the development of new techniques for the study of natural products biosynthesis and that the information gained from these studies will be applicable to an understanding of the catalysis of biological carbon-carbon bond formation in general.