Expanding the terpenome: complementary approaches to novel terpenoids
Expanding the terpenome: complementary approaches to novel terpenoids
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扩展萜类化合物：新型萜类化合物的补充方法
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发表时间：
2015
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通讯作者：
Daniel J Grundy
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作者：
Daniel J Grundy
萜类和萜类化合物构成天然产物中最大和结构最多样化的家族之一，已知化合物的数量在数万种。相当大比例的萜类化合物是次级代谢产物，其显示出广泛的生物活性，因此许多已被发现用作治疗药物，最值得注意的是抗癌剂紫杉醇;和抗疟疾疗法中的关键药物青蒿素。由于以令人满意的产率合成这些高度复杂的化合物的挑战，这些药物的大部分供应仍然是从天然来源提取的或从天然提取的化合物半合成地生产的。
萜烯脱氢酶将线性异戊二烯基二磷酸（所有萜类化合物的前体）转化为复杂的烃骨架，其通常天然地被P450细胞色素进一步衍生。最近，在利用萜烯脱氢酶生产萜类化合物前体方面取得了进展，但尽管有这些进展，烃骨架的选择性衍生化仍然是将这些骨架转化为治疗上可行的化合物的主要障碍。
本论文主要研究了利用萜烯糖苷酶合成简单萜类化合物的方法。该项目分为两个部分，旨在研究简单萜类化合物的生成方法。第一部分集中在germacradien-4-ol synthase（GdolS），最近发现的细菌倍半萜合酶，它将水的环化级联产生一个单一的萜烯醇。这种酶的特点和机制探测使用底物类似物和单点突变，以阐明GdolS是如何能够将水纳入其产品，同时仍然保护高活性的碳阳离子中间体。我们的数据表明，germacradien-4-ol合酶催化的损失的二磷酸基团和环闭合在一个逐步的方式，然后由1，3-氢化物移位，以产生一个长寿命的烯丙基碳正离子中间体。我们建议，这种碳正离子，然后淬火水进入活性位点，由于循环运动。
该项目的第二部分涉及一系列法呢基二磷酸类似物的合成，旨在提供一系列倍半萜烯脱氢酶催化作用中捕获碳阳离子中间体的方法。这些类似物主要是环氧-FDPs，设计用于产生具有羟基和环氧官能团的简单萜类化合物。虽然许多制备的类似物被测试的倍半萜烯脱氢酶转化，但10，11-环氧-FDP和10-羟基-11-烯-FDP能够在失去二磷酸基团时拦截法尼基阳离子，以产生新的大环醚。
Terpenes and terpenoids make up one of the largest and most structurally diverse families of natural products with known compounds numbering in the tens of thousands. A significant proportion of terpenoids are secondary metabolites, which display a wide range of biological activities, and consequently many have found uses as therapeutic drugs, most notably paclitaxel, the anti-cancer agent; and artemisinin, a key drug in anti-malarial therapies. Due to the challenges in synthesising these highly complex compounds in satisfactory yields the majority of the supply of these drugs is still extracted from natural sources or produced semi-synthetically from naturally extracted compounds.
Terpene synthases convert the linear isoprenyl diphosphates, precursors of all terpenoids, into complex hydrocarbon skeletons, which are often naturally further derivatised by P450 cytochromes. Recently there have been advances in exploiting terpene synthases for the production of terpenoid precursors, but despite these advances selectively derivatising the hydrocarbon skeleton remains the major barrier to the conversion of these skeletons to therapeutically viable compounds.
This thesis focuses on exploring methods of generating simple terpenoids from terpene synthases. The project is divided into two parts both designed to investigate methods of generating simple terpenoids. The first part focuses on germacradien-4-ol synthase (GdolS), a recently discovered bacterial sesquiterpene synthase, which incorporates water in the cyclisation cascade to generate a single terpene alcohol. This enzyme was characterised and the mechanism probed using substrate analogues and single-point mutations to elucidate how GdolS is able to incorporate water into its product while still protecting the highly reactive carbocation intermediates. Our data indicated that germacradien-4-ol synthase catalyses the loss of the diphosphate group and ring closure in a stepwise manner, followed by a 1,3-hydride shift to generate a long-lived allylic-carbocation intermediate. We propose this carbocation is then quenched by water ingress into the active site due to loop movement.
The second part of the project involved the synthesis of a range of farnesyl diphosphate analogues designed to offer means of trapping carbocation intermediates in the catalysis by a range of sesquiterpene synthases. These analogues were primarily epoxy-FDPs, designed to produce simple terpenoids with hydroxy- and epoxy-functionalities. While a number of the prepared analogues were turned over by the tested sesquiterpene synthases two, 10,11-epoxy-FDP and 10-hydroxy-11-ene-FDP, were able to intercept the farnesyl cation upon loss of the diphosphate group, to generate a novel macrocyclic ether.