Reactivity of Manganese and Iron Metalloenzyme Models

项目概要 血红素蛋白参与许多对人类健康和健康至关重要的重要生物过程。 疾病，它们是诊断和治疗的目标。其中一个重要的子集 蛋白质是激活双氧 (O2) 或其还原类似物（例如 H2O2）的酶。这些酶利用 相同的铁辅助因子可介导多种反应，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。大自然如何调节金属中心和活性 这些酶介导如此广泛的功能的位点是一个具有根本意义的问题 这继续激励着重要的研究。该提案重点关注小分子的合成和反应性 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 硫醇连接血红素酶细胞色素 P450 (CYP)、氯过氧化物酶 (CPO) 和 芳香族过氧化酶 (APO) 和非硫醇盐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)。硫醇盐连接的血红素酶能够氧化 碳氢化合物 C-H 键，所提出的机制涉及氢原子转移 (HAT)（质子耦合电子- PCET）从 R-H 转移到称为化合物-I (Fe=O) 的中间体，然后进行羟基转移 （“反弹”）从质子化的化合物-II (Fe-OH) 得到 ROH 产物。然而，反弹步骤可以是 转移到其他途径，导致截然不同的反应结果。许多问题仍然存在 控制 HAT 和回弹的基本结构、电子、热力学和动力学因素 步骤。相比之下，TDO/IDO 被认为依赖 Fe(O2) 加合物和化合物-II 作为活性氧化剂， 尽管关于这一机制还有很多东西需要了解。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，这些物种将通过定制方法制备 类卟啉配体旨在稳定这些物种并允许对其进行直接研究。这些配体包括 缩环咔咯（Crl）和咔咯嗪（Cz），它们具有修饰的卟啉核，呈现出 金属上带有三阴离子 (3-) 电荷，类似于硫醇盐连接的血红素活性位点。我们之前的努力表明 Crl 和 Cz 平台提供了传统卟啉所未见的新物种，包括 Cpd-I 类似物具有与 CYP 和 CPO 中相同的自旋基态，并且是质子化的第一个例子 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）解决根本问题 与血红素酶反应性和机制相关的问题，以及 2) 建立知识库 关于合成卟啉复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.