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，并 他们是诊断和治疗的目标。其中一个重要的子集 蛋白质是激活氧气(O2)或其还原类似物(如过氧化氢)的酶。这些酶利用 相同的铁辅助因子，可调节多种反应，包括有机物的单氧化和双氧化 底物、C-H活化、减饱和和C-C键断裂。大自然如何调谐金属中心和活力 这些酶的结合部位来调节如此广泛的功能是一个具有根本意义的问题 这将继续推动重大研究。这项建议集中在小分子的合成和反应活性上。 提出了关键中间体的分子模型络合物及其相关的成键/断键事件 在硫酸盐连接的血红素酶细胞色素P450(CYP)、氯过氧化物酶(CPO)和 芳香过氧酶(APO)和非硫氧连接的血红素双加氧酶色氨酸-2，3-双加氧酶 (TDO)和吲哚-2，3-双加氧酶(IDO)。硫酸盐连接的亚铁血红素酶能够氧化 碳氢碳氢键，所提出的机制涉及氢原子转移(HAT)(质子耦合电子-氢键)。 从R-H转移到称为化合物-I(Fe=O)的中间体，然后是羟基转移 (“反弹”)从质子化的化合物-II(Fe-OH)得到ROH产物。然而，反弹的步骤可以是 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，比如 控制HAT和反弹的基本结构、电子、热力学和动力学因素 台阶。相反，TDO/IDO被建议依赖Fe(O2)加合物和化合物II作为活性氧化剂， 尽管对这一机制仍有许多需要了解的地方。这项提案中的努力将解决这些问题 通过对仿生M=O、M-OH和M-O2物种的合成和研究，将其量身定做 设计用于稳定这些物种并允许对其进行直接研究的类卟啉配体。这些配体包括 环收缩腐蚀(CRL)和腐蚀氮化物(Cz)，它们具有修饰的卟啉核，呈现出 三阴离子(3-)带电给金属，类似于硫酸盐连接的血红素活性中心。我们之前的努力表明， CRL和Cz平台提供了在常规卟啉中未见的新物种的途径，包括 CPD-I类似物具有与在CYP和CPO中发现的相同的自旋基态，并且是质子化的第一个例子 CPD-II模型。通过建立这些小分子模型，可以对其进行系统的修正 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，在以下情况下可能具有挑战性或不可能获得 单独研究这些酶。拟议工作的长期目标是：1)解决根本问题 与血红素酶活性和机理有关的问题；2)建立知识库 关于合成的卟啉类化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.