Harnessing Polyketide Natural Product Biosynthesis

酶化学是生产复杂分子的有力工具，但它主要用于生成高纯度的异构体中心。酶广泛用于研究和制造的一个主要限制是目前通过酶反应可获得的化学多样性有限。这与合成有机化学形成鲜明对比。为了扩大酶在合成中的应用，必须增加有限的可行酶反应工具箱。天然产物的结构表明，酶促反应可以获得令人难以置信的化学多样性。产生这些天然产物的酶非常适合于满足合成化学家在合成多功能复杂分子时所要求的高度立体、区域和化学选择性的严格要求。我的研究项目考察了负责聚酮天然产物生产的生物合成途径，以识别和利用能够扩展我们酶工具箱的酶。虽然我们的长期目标是利用这些酶在体内和体外快速生产各种分子，但我们的近期目标是专注于开发可用于化学酶合成天然产物的新型催化剂。天然产物全合成是新化学方法的严格试验场，新酶在这一领域的成功整合将促进其在研究和生产中的广泛应用。为了实现扩大可用酶促反应工具箱的长期目标，我们提出了三个短期目标。1)巯基酯酶催化大环化的研究进展。大环化是合成中最具决定性的一步，可以决定任何合成路线的整体效率。目前还没有酶法来合成这个关键的官能团。这一目标使我们能够利用目前可获得的聚酮生物合成酶迅速影响合成界。2)化学酶法合成新榄内酯。这一目标将作为在复杂分子全合成中使用酶的强有力的和首次的演示。这项工作具有转化复杂聚酮合成的潜力，并将证明在全合成的后期阶段使用酶促反应的有效性。3)聚酮生物合成新途径的发现。这一目标有助于我们酶的长期发展，以获得新的化学多样性。在新的生物合成途径中有催化新化学的酶。通过发现这些途径，我们能够开发出新的酶。在短期内，这一目标将影响药理学和药物发现，因为聚酮具有强大的生物活性，可以用来改善人类健康。这些独立但相互关联的方法将扩大通过酶促反应可获得的化学多样性。最初的两个项目侧重于开发基于已知聚酮生物合成酶的新型催化剂，以产生复杂的分子。这使得合成化学家的工具箱中可以短期引入用于大环化和醛醇反应的酶。最后一个项目描述了我们通过发现新的和独特的聚酮生物合成途径来扩大酶化学可获得的化学多样性的长期计划。除了寻找可以利用的新酶之外，该项目还将对发现天然产物的方法产生重大影响，并影响与天然产物直接相关的所有下游发现，包括鉴定新的生物活性化合物、它们的作用机制和靶点，以及开发新药。

Enzymatic chemistry is a powerful tool for the production of complex molecules however it has found use mainly in the generation of high purity strereogenic centers. A major limitation to the broad use of enzymes for research and manufacturing is the restricted chemical diversity currently accessible through enzymatic reactions. This is in stark contrast to synthetic organic chemistry. To expand the use of enzymes in synthesis, the limited toolbox of viable enzymatic reactions must be increased. The structures of natural products show that enzymatic reactions can access incredible chemical diversity. The enzymes that produce these natural products are ideally suited to meet the rigorous demands of high stereo-, regio-, and chemoselectivity that synthetic chemists require for use in the synthesis of polyfunctional complex molecules. My research program examines the biosynthetic pathways responsible for polyketide natural product production to identify and harness enzymes capable of expanding our enzymatic toolbox. While our long-term goal is to use these enzymes to enable rapid production of diverse molecules in vivo and in vitro, our immediate goals are focused on developing new catalysts that can be used in chemoenzymatic synthesis of natural products. Natural product total synthesis is a rigorous testing ground for new chemical methodology and successful integration of new enzymes in this arena will facilitate their broader application in research and manufacturing. To meet our long-term goal of expanding the toolbox of available enzymatic reactions, we propose three short-term objectives. 1) The development of thioesterases to catalyze macrocyclization. Macrocyclization is the most decisive step of a synthesis and can define the overall efficiency of any synthetic route. No enzymatic methodology has been developed to synthesize this key functional group. This objective allows us to rapidly impact the synthetic community with currently accessible enzymes from polyketide biosynthesis. 2) The chemoenzymatic total synthesis of neopeltolide. This objective will serve as a powerful and first of its kind demonstration of the use of enzymes in complex molecule total synthesis. This work has the potential to transform complex polyketide synthesis and will demonstrate the effectiveness of using enzymatic reactions in the late stages of a total synthesis. 3) The discovery of new polyketide biosynthetic pathways. This objective contributes to our long-term development of enzymes to access new chemical diversity. Within new biosynthetic pathways are enzymes that catalyze new chemistry. By discovering these pathways, we enable develop the new enzymes. In the short-term this objective will impact the pharmacology and drug discovery as polyketides have potent bioactivity that can be exploited to improve human health. These separate but interrelated approaches will expand the chemical diversity accessible through enzymatic reactions. The initial two projects focus on developing new catalysts based on known enzymes from polyketide biosynthesis to produce complex molecules. These enable the short-term introduction of enzymes for macrocyclization and aldol reactions into the synthetic chemist’s tool box. The last project describes our long-term plans for expanding the chemical diversity accessible through enzymatic chemistry by discovering new and unique polyketide biosynthetic pathways. In addition to finding new enzymes to harness, this project will have a major impact on approaches to natural product discovery and influence all the downstream discoveries directly related to natural products, including identification of new bioactive compounds, their mechanisms of action and targets, and the development of new drugs.