Reactivity of Manganese and Iron Metalloenzyme Models

项目摘要 血红素蛋白参与许多对人类健康重要的基本生物过程， 疾病，并且它们是诊断和治疗治疗的目标。其中一个重要的子集 蛋白质是激活分子氧（O2）或其还原类似物（例如H2 O2）的酶。这些酶利用 相同的铁辅因子介导广泛的反应，包括有机物的单氧化和双氧化 底物、C-H活化、去饱和和C-C键裂解。大自然如何调谐金属中心和活跃 这些酶介导如此广泛功能性的位点是具有根本意义的问题 这继续激励着重要的研究。该建议的重点是合成和反应性的小- 提出了关键中间体的分子模型复合物及其相关的成键/断键事件 在巯基连接血红素酶细胞色素P450（CYP 450）、氯过氧化物酶（CPO）和 芳香族过氧合酶（APO）和非硫醇连接的血红素双加氧酶色氨酸-2，3-双加氧酶 (TDO)和吲哚胺-2，3-双加氧酶（IDO）。巯基连接的血红素酶能够氧化 碳氢化合物C-H键，提出的机制涉及H原子转移（HAT）（质子耦合电子- 转移，PCET）从R-H到称为化合物-I（Fe=O）的中间体，然后进行羟基转移 从质子化的化合物-II（Fe-OH）中分离（“反弹”）以得到ROH产物。然而，反弹步骤可以是 转移到其他途径，导致明显不同的反应结果。许多问题仍然存在， 控制HAT和反弹的基本结构、电子、热力学和动力学因素 步相比之下，TDO/IDO建议依赖于Fe（O2）加合物和化合物-II作为活性氧化剂， 尽管关于这一机制仍有许多东西有待了解。本提案将努力解决这些问题 通过合成和研究仿生M=O，M-OH和M-O2物种，这些物种将用定制的 卟啉类配体设计来稳定这些物种，并允许他们的直接研究。这些配体包括 环收缩的可咯啉（Crl）和可咯嗪（Cz），它们具有修饰的卟啉核， 三阴离子（3-）电荷的金属，类似于硫醇连接血红素活性位点。我们之前的努力表明， Crl和Cz平台提供了获得常规卟啉所未见的新物种的途径，包括 Cpd-I类似物，其具有与在NPO和CPO中发现的相同的自旋基态，并且质子化的Cpd-I类似物的第一个例子是Cpd-I类似物。 Cpd-II模型。可以通过已建立的方法对这些小分子模型进行系统性修改。 合成方法，提供对其几何/电子结构的原子级控制，并提供 一种建立结构-功能关系的方法，这种关系在以下情况下可能具有挑战性或不可能获得： 单独研究酶。拟议工作的长期目标是：1）解决基本问题 有关血红素酶反应性和机制的问题，以及2）建立知识库 关于合成卟啉类配合物在小分子活化和催化中的应用。

Project Summary Heme proteins participate in many essential biological processes that are important to human health and disease, and they are targets of both diagnostic and therapeutic treatments. An important subset of these proteins are enzymes that activate dioxygen (O2) or its reduced analogs (e.g. H2O2). These enzymes utilize the same iron cofactor to mediate a wide range of reactions, including mono- and dioxygenation of organic substrates, C-H activation, desaturation, and C-C bond cleavage. How nature tunes the metal center and active site of these enzymes to mediate such a wide range of functionality is a question of fundamental significance that continues to motivate significant research. This proposal focuses on the synthesis and reactivity of small- molecule model complexes of key intermediates, and their related bond-making/bond-breaking events, proposed in the mechanisms of the thiolate-ligated heme enzymes Cytochrome P450 (CYP), chloroperoxidase (CPO), and aromatic peroxygenase (APO), and the non-thiolate-ligated heme dioxygenases tryptophan-2,3-dioxygenase (TDO) and indoleamine-2,3-dioxygenase (IDO). The thiolate-ligated heme enzymes are capable of oxidizing hydrocarbon C-H bonds, and the proposed mechanism involves H-atom transfer (HAT) (proton-coupled electron- transfer, PCET) from R-H to an intermediate called Compound-I (Fe=O), followed by hydroxyl transfer (“rebound”) from protonated Compound-II (Fe-OH) to give the ROH product. However, the rebound step can be diverted to other pathways, leading to distinctly different reaction outcomes. Many questions remain regarding the fundamental structural, electronic, thermodynamic and kinetic factors that control both HAT and rebound steps. In contrast, TDO/IDO are proposed to rely on an Fe(O2) adduct and Compound-II as active oxidants, although much remains to be learned about this mechanism. Efforts in this proposal will address these questions through the synthesis and study of biomimetic M=O, M-OH, and M-O2 species that will be prepared with tailored porphyrinoid ligands designed to stabilize these species and allow for their direct study. These ligands include ring-contracted corroles (Crl) and corrolazines (Cz), which have a modified porphyrin nucleus which presents a trianionic (3-) charge to the metal, similar to a thiolate-ligated heme active site. Our previous efforts showed that the Crl and Cz platforms provide access to novel species not seen with conventional porphyrins, including a Cpd-I analog with the same spin ground state as found in CYP and CPO, and the first example of a protonated Cpd-II model. Systematic modifications can be made to these small-molecule models through established synthetic methodologies, providing atomic-level control over their geometric/electronic structures, and providing a means to establish structure-function relationships that can be challenging or impossible to obtain when studying the enzymes alone. The long-term goals of the proposed work are: 1) to address fundamental questions related to heme enzyme reactivity and mechanism, and 2) to build the knowledge base regarding synthetic porphyrinoid complexes for applications in small-molecule activation and catalysis.