Bioinspired Copper-Promoted C-H Hydroxylations

项目摘要： 拟议研究的目标是开发合成无机铜配合物，以了解 铜依赖性单加氧酶结构和功能的基本方面。这些 金属酶在其活性中心含有1或2个Cu离子，它们将O2的还原与 通过形成瞬时Cun/O2反应性中间体氧化底物。我们特别感兴趣 在检查单核Cu/O2物种的反应性，因为它们已被提出作为活性氧化剂， C-H键的羟基化（肽基甘氨酸α-羟基化单加氧酶和溶解性多糖 单加氧酶）。关于活性Cu/O2物种的身份的许多问题仍然没有答案， 包括：i）Cu的氧化态（即CuI、CuII、CuIII）; ii）O2的还原/质子化态（O2-，（H）O22-， (H)O2−）以及与这些Cu/O2物质相关的pKa和氧化还原电位; iii） Cu/O2中间体进行C-H羟基化（例如O-O裂解机制，可能产生高- 在C-H氧化之前的价Cu-氧基物质）。在这个研究项目中，我们以一种 前所未有的方式：我们利用配体支架（L），其含有共价连接到其上的C-H底物， 结构（由酮和胺的缩合合成的含亚氨基吡啶底物的配体）。 这将使我们能够生成和表征LCu/O2物质，并评估它们对 底物-配体的分子内C-H羟基化。研究次级项目包括： (1)底物-配体支架修饰将允许我们：i）评估Cu/O2物质的能力， 氧化sp3 C-H键和sp2 C-H键; ii）通过以下方式控制Cu络合物的立体电子性质： 使用不同的配体供体（即N2、N3、N4），这将导致单核LCuO 2的产生， 双核L2 Cu 2 O2物种，并分析其对分子内C-H羟基化的反应性; iii）开发 生物启发的合成方案（胺/Cu/氧化剂）用于各种底物酮的羟基化。 (2)提出的铜配合物轴承基板配体支架提供了一个独特的机会，研究 LCuII（OOR）的化学性质，因为它们的结构可以通过三种方式进行修改：通过改变配体 密度（N2、N3和N4）、底物（sp3对sp2）和氧化剂（H2 O2、tBuOOH或CumOOH）。的产生 LCuII（OOR）物种（在低温下亚稳态）将导致：i）了解 LCuII（OOR）通过跟踪LCuII（OOR）的衰变和分子内的 羟基化产率; ii）分析LCuII（OOR）对H+和e−源的反应性，这可能导致 iii）研究LCuII（OOR）对生物学相关外部环境的反应性， 底物如C-H键、酚类和硫化物。 总的来说，这些研究将有助于更广泛地了解铜离子的生物化学作用， O2还原和生物相关氧化。

Project Summary: The goal of the proposed research is to develop synthetic inorganic copper complexes to understand the fundamental aspects of structure and function in Cu-dependent monooxygenase enzymes. These metalloenzymes contain 1 or 2 Cu ions in their active center and they couple the reduction of O2 with the oxidation of substrates via formation of transient Cun/O2 reactive intermediates. We are particularly interested in inspecting the reactivity of mononuclear Cu/O2 species since they have been proposed as active oxidants in the hydroxylation of C-H bonds (in peptidylglycine α-hydroxylating monooxygenase and lytic polysaccharide monooxygenase). Many questions concerning the identity of the active Cu/O2 species remain unanswered, including: i) oxidation state of Cu (i.e. CuI, CuII, CuIII); ii) reduction/protonation state of O2 (O2−,(H)O22−, (H)O2−) and the pKa and redox potentials associated with these Cu/O2 species; iii) mechanism by which the Cu/O2 intermediates carry out C-H hydroxylations (e.g. O-O cleavage mechanism, possible generation of high- valent Cu-oxyl species before C-H oxidation). In this research project, we tackle this problem in an unprecedented fashion: we utilize ligand scaffolds (L) that contain C-H substrates covalently attached to their structure (imino-pyridine substrate-containing ligands synthesized from condensation of ketones and amines). This will permit us to generate and characterize LCu/O2 species and evaluate their reactivity towards intramolecular C-H hydroxylation of the substrate-ligands. Research subprojects include: (1) Substrate-ligand scaffold modifications will permit us to: i) evaluate the ability of the Cu/O2 species to oxidize sp3 C-H bonds and sp2 C-H bonds; ii) control the stereo-electronic properties of the Cu complexes by the use of different ligand donors (i.e. N2, N3, N4) that will lead to the generation of mononuclear LCuO2 and dinuclear L2Cu2O2 species, and analyze their reactivity towards intramolecular C-H hydroxylation; iii) develop bioinspired synthetic protocols (amine/Cu/oxidant) for the hydroxylation of a wide variety of substrate-ketones. (2) The proposed Cu complexes bearing substrate-ligand scaffolds offer a unique opportunity to study the chemical properties of LCuII(OOR) since their structure can be modified in three ways: by changing the ligand denticity (N2, N3 and N4), substrate (sp3 vs. sp2) and oxidant (H2O2, tBuOOH or CumOOH). The generation of LCuII(OOR) species (metastable at low temperatures) will lead to: i) understanding the mechanism by which LCuII(OOR) oxidize C-H bonds by tracking the decay of LCuII(OOR) and the evolution of the intramolecular hydroxylation yields; ii) analyzing the reactivity of LCuII(OOR) towards H+ and e− sources that could lead to reductive O-O cleavage; iii) studying the reactivity of LCuII(OOR) towards biologically relevant external substrates such as C-H bonds, phenols, and sulfides. Overall, these studies will contribute to a broader understanding of the biochemical role of Cu ions involved in O2 reduction and biologically relevant oxidations.