Chemo- and bio-catalytic methods towards chiral dihalocyclopropanes

近年来，宝石-二卤环丙烷由于其独特的化学和生物学特性而具有较高的代谢稳定性、亲脂性和与环氧化物的生物等同性，在制药工业中引起了广泛的关注。该项目的总体目标是开发新的合成路线，以合成难以获得的对映体纯二卤环丙烷。由于对映体富集的宝石-二卤环丙烷的系统方法将对制药、农化和精细化工行业产生革命性的影响，我们设想，通过开发新型二卤碳烯前体，简化的化学和生物催化方法将可一步实现将简单易得的烯烃转化为增值的手性宝石-二卤环丙烷。迄今为止，已经开发了许多高效的烯烃二卤环丙烷化合成方法，目前最先进的方法主要集中在两种方法上：1)加入游离二卤羰基和2)使用三卤甲基阴离子的迈克尔诱导环闭合（MIRC）。尽管有这些有效的方法，但由于手性宝石-二卤环丙烷的外消旋背景反应速度极快（且产量极低），因此合成手性宝石-二卤环丙烷的方法很少。我们的方法将通过威尔科克斯集团开发的两种不同类型的二卤环丙烷化试剂的应用来举例说明；1)一种新的n -磺酰腙，它将作为一个稳定的重氮前驱体；2)一种磺酰亚胺试剂（由Olah首次报道），它将作为一个酰基前驱体。这两种试剂将在化学和生物催化中独立使用。化学催化方法将侧重于使用经典的碳转移试剂(如Rh2(O2CR)4, Fe（TPP)Cl和Co(TPP)）将二卤碳（从腙原位生成）转移到各种烯烃[4,5]。亚砜酰亚胺将用于MIRC化学中，使用有机催化或手性金属催化来促进对缺电子烯烃的加成生物催化方法将使用Green实验室与David Baker教授合作开发的一系列全新血红素酶来探索烯烃二卤环丙烷化。同时，我们将探索几种机制策略来加速设计酶内的MIRC反应；1. 路易斯酸催化。2. 双氢键催化和3。离子催化。在这里，我们可以利用绿色实验室开发的新的基因可编码功能组件（例如Nature 2019, 570,219）。在确定了具有期望活性的有前途的设计之后，我们将使用定向进化来优化催化性能和反应选择性。优化后的设计将在结构上和生物化学上进行表征，以深入了解改善活性的起源，从而指导未来的酶设计工作。Willcox小组开展的工作将提供试剂设计、配体设计和合成、新金属配合物合成、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射线晶体学，核磁共振，EPR和FTIR光谱，质谱，过渡金属催化和色谱（制备和手性GC/HPLC）。Green小组开展的工作将提供酶设计、定向进化、停止密码子抑制、机制酶学和结构生物学方面的培训。缺乏任何有效的化学和生物催化方法来制备对映体富集的二卤环丙烷意味着该项目使以前无法获得的手性衍生物成为可能。新的二卤环丙烷化模式将使联合王国处于新的全球经济部门的前沿，从而提高这一利基市场的生活质量、健康和创造性产出。

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.