Chemo- and bio-catalytic methods towards chiral dihalocyclopropanes

近年来，GEM-二卤环丙烷由于其独特的化学性质和生物学性质，具有更高的代谢稳定性、亲脂性和与环氧化物的生物等构性，在医药工业中引起了极大的关注。该项目的主要目标是开发新的合成路线，用于合成难以获得对映体纯的二卤环丙烷。由于对映体富集型GEM-二卤环丙烷的系统方法将对制药、农化和精细化学工业产生重大影响，我们预计，通过开发新型的二卤代卡宾前体，可以一步实现将简单易得的烯烃转化为增值的手性GEM-二卤环丙烷的简化化学和生物催化方法。到目前为止，已经开发了许多高效的二卤环丙烷化烯烃的合成方法，目前最先进的方法主要集中在两个主要方法上：1)自由二卤代卡宾的加成和2)使用三卤甲基阴离子的Michael诱导闭环(MIRC)。尽管有这些有效的方法，但合成手性宝石-二卤代环丙烷的方法很少，这归因于非常快速(和低产)的外消旋背景反应。我们的方法将通过应用两种不同类型的二卤环丙烷试剂来举例说明，这些试剂在Willcox集团内开发；1)新的N-磺酰肼，将作为稳定的重氮前体；2)磺胺试剂，将作为叶立德前体。这两种试剂将分别用于化学催化和生物催化。化学催化方法将重点放在使用经典的卡宾转移试剂(如Rh2(O2CR)4，Fe(TPP)Cl和Co(TPP))[4，5]将二卤卡宾(原位生成于肼)转移到广泛的烯烃上。磺化亚胺叶立德将被用于MIRC化学中，使用有机催化或手性金属催化来促进缺乏电子的烯烃的加成。[6]生物催化方法将使用格林实验室与David Baker教授合作开发的一系列从头开始的血红素酶来探索烯烃二卤代环丙烷反应。同时，我们将探索在设计的酶中加速MIRC反应的几种机理策略：1.Lewis酸催化。2.双氢键催化；3.亚胺离子催化。在这里，我们可以利用在绿色实验室内开发的新的遗传可编码功能组件(例如，自然2019、570、219)。在确定了具有所需活性的有希望的设计后，我们将使用定向进化来优化催化性能和反应选择性。然后，将对优化设计进行结构和生化表征，以深入了解活性提高的根源，从而指导未来的酶设计工作。Willcox集团开展的工作将提供试剂设计、配体设计和合成、新金属络合物的合成、反应优化以及一般合成操作和反应纯化方面的培训。技术包括：Schlenk方法、X射线结晶学、核磁共振、EPR和FTIR光谱、质谱学、过渡金属催化和层析(制备和手性GC/HPLC)。格林小组开展的工作将提供酶设计、定向进化、终止密码子抑制、机械酶学和结构生物学方面的培训。由于缺乏任何有效的化学和生物催化方法来制备对映体富集型二卤环丙烷，这一项目意味着能够获得以前无法获得的手性衍生物。一种新的双卤环丙烷化模式将使英国处于一个新的全球经济部门的前沿，提高这一利基市场的生活质量、健康和创意产出。

In recent years, gem-dihalocyclopropanes have garnered much attention in the pharmaceutical industry due to increased metabolic stability, lipophilicity and being bioisosteric to epoxides attributed to the unique chemical and biological properties. The overarching aim of this project is to develop novel synthetic routes for the synthesis of difficult to access enantiomerically pure dihalocyclopropanes. As systematic methods towards enantioenriched gem-dihalocyclopropanes would be transformative for the pharmaceutical, agrochemical and fine chemical industries, we envisage that through the development of novel dihalocarbene precursors, streamlined chemo- and bio-catalytic approaches converting simple and readily available olefins into value-added chiral gem-dihalocyclopropanes will be achievable in one step. To date many highly efficient synthetic methods for dihalocyclopropanation of olefins have been developed, and current state-of-the-art methodologies centres around two main approaches 1) addition of free-dihalocarbene and 2) Michael-induced ring closure (MIRC) using trihalomethyl anions. Despite these efficient approaches, there is a paucity in the approaches towards the synthesis of chiral gem-dihalocyclopropanes, attributed to the extremely fast (and unproductive) racemic background reaction.Our approach will be exemplified through the application of two different types of dihalocyclopropanation reagents developed within the Willcox group; 1) a novel N-sulfonylhydrazone, which will act as a stable diazo precursor and 2) a sulfoximinium reagent (first reported by Olah) which will act as an ylide precursor. Both of these reagents will be utilized independently in chemo- and bio-catalysis. The chemocatalytic approach will focus on transferring the dihalocarbene (generated in situ from the hydrazone) to a wide range of olefins, using classical carbene transfer reagents (eg Rh2(O2CR)4, Fe(TPP)Cl and Co(TPP)) [4,5]. The sulfoximinium ylide will be employed in MIRC chemistry using either organocatalysis or chiral-at-metal catalysis to facilitate the addition to electron-deficient olefins.[6] The biocatalytic approach will explore olefin dihalocyclopropanations using a series of de novo heme enzymes developed in the Green lab in collaboration with Prof. David Baker. In parallel, we will explore several mechanistic strategies to accelerate the MIRC reaction within designed enzymes; 1. Lewis acid catalysis. 2. Dual hydrogen bonding catalysis and 3. Iminium ion catalysis. Here we can take advantage of new genetically encodeable functional components developed within the Green lab (e.g. Nature 2019, 570, 219). Having identified promising designs with desired activity, we will use directed evolution to optimize catalytic performance and reaction selectivity. Optimized designs will then be structurally and biochemically characterized to gain insights into the origins of improved activity in order to guide future enzyme designs efforts. The work conducted in the Willcox group will provide training in reagent design, ligand design and synthesis, synthesis of new metal complexes, reaction optimization, and general synthetic manipulations and reaction purification. Techniques include: Schlenk methods, X-ray crystallography, NMR, EPR and FTIR spectroscopies, mass spectrometry, transition metal catalysis and chromatography (preparative and chiral GC/HPLC). The work conducted in the Green group will provide training in enzyme design, directed evolution, stop codon suppression, mechanistic enzymology and structural biology.The absence of any effective chemo- and bio- catalytic method to prepare enantiomerically enriched dihalocyclopropance means that this project enables access to previously unattainable chiral derivatives. A new dihalocyclopropanation paradigm would place the UK at the leading edge of a new global economic sector enhancing quality of life, health and creative output in this niche.