Department of Material and Life Science, Division of Advanced Science and Biotechnology, Graduate School of Engineering, Osaka University, 2-1 Yamada-oka, Suita, Osaka 565-0871, Japan.
Inorg Chem. 2011 Mar 7;50(5):1633-47. doi: 10.1021/ic101832c. Epub 2011 Feb 1.
Copper(II) complexes supported by a series of phenol-containing bis(pyridin-2-ylmethyl)amine N(3) ligands (denoted as L(o)H, L(m)H, and L(p)H) have been synthesized, and their O(2) reactivity has been examined in detail to gain mechanistic insights into the biosynthesis of the TPQ cofactor (2,4,5-trihydroxyphenylalaninequinone, TOPA quinone) in copper-containing amine oxidases. The copper(II) complex of L(o)H (ortho-phenol derivative) involves a direct phenolate to copper(II) coordination and exhibits almost no reactivity toward O(2) at 60 °C in CH(3)OH. On the other hand, the copper(II) complex of L(m)H (meta-phenol derivative), which does not involve direct coordinative interaction between the phenol moiety and the copper(II) ion, reacts with O(2) in the presence of triethylamine as a base to give a methoxy-substituted para-quinone derivative under the same conditions. The product structure has been established by detailed nuclear magnetic resonance (NMR), infrared (IR) spectroscopy, and electrospray ionization-mass spectroscopy (ESI-MS) (including (18)O-labeling experiment) analyses. Density functional theory predicts that the reaction involves (i) intramolecular electron transfer from the deprotonated phenol (phenolate) to copper(II) to generate a copper(I)-phenoxyl radical; (ii) the addition of O(2) to this intermediate, resulting in an end-on copper(II) superoxide; (iii) electrophilic substitution of the phenolic radical to give a copper(II)-alkylperoxo intermediate; (iv) O-O bond cleavage concomitant with a proton migration, giving a para-quinone derivative; and (v) Michael addition of methoxide from copper(II) to the para-quinone ring and subsequent O(2) oxidation. This reaction sequence is similar to that proposed for the biosynthetic pathway leading to the TPQ cofactor in the enzymatic system. The generated para-quinone derivative can act as a turnover catalyst for aerobic oxidation of benzylamine to N-benzylidene benzylamine. Another type of copper(II)-phenol complex with an L(p)H ligand (para-phenol derivative) also reacts with O(2) under the same experimental conditions. However, the product of this reaction is a keto-alcohol derivative, the structure of which is qualitatively different from that of the cofactor. These results unambiguously demonstrate that the steric relationship between the phenol moiety and the supported copper(II) ion is decisive in the conversion of active-site tyrosine residues to the TPQ cofactor.
已经合成了一系列含有酚基的双（吡啶-2-基甲基）胺 N(3)配体（表示为 L(o)H、L(m)H 和 L(p)H）的铜(II)配合物，并详细研究了它们与 O(2)的反应性，以深入了解含铜胺氧化酶中 TPQ 辅因子（2,4,5-三羟基苯丙氨酸醌，TOPA 醌）的生物合成机制。邻位酚衍生物 L(o)H 的铜(II)配合物涉及直接的酚盐与铜(II)配位，并且在 60°C 的 CH(3)OH 中几乎没有对 O(2)的反应性。另一方面，不涉及酚部分与铜(II)离子之间直接配位相互作用的 L(m)H（间位酚衍生物）的铜(II)配合物，在三乙胺作为碱的存在下与 O(2)反应，在相同条件下生成甲氧基取代的对醌衍生物。通过详细的核磁共振（NMR）、红外（IR）光谱和电喷雾电离质谱（ESI-MS）（包括（18）O 标记实验）分析确定了产物结构。密度泛函理论预测该反应涉及：（i）来自去质子化酚（酚盐）的分子内电子转移到铜(II)以生成铜(I)-苯氧自由基；（ii）该中间体与 O(2)加成，生成末端铜(II)过氧化物；（iii）酚自由基的亲电取代，生成铜(II)-烷过氧化物中间体；（iv）O-O 键断裂伴随着质子迁移，生成对醌衍生物；（v）铜(II)上的甲氧基对间醌环进行迈克尔加成，随后进行 O(2)氧化。此反应序列类似于酶系统中导致 TPQ 辅因子生物合成途径的建议。生成的对醌衍生物可以作为有氧氧化苄胺生成 N-苄基亚苄基胺的周转催化剂。具有 L(p)H 配体（对位酚衍生物）的另一种类型的铜(II)-酚配合物也在相同的实验条件下与 O(2)反应。然而，该反应的产物是酮醇衍生物，其结构与辅因子明显不同。这些结果明确表明，酚部分与支撑的铜(II)离子之间的空间关系决定了活性位点酪氨酸残基向 TPQ 辅因子的转化。
