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Radical Reactivity: Nucleophilic Radicals01:16

Radical Reactivity: Nucleophilic Radicals

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Radicals adjacent to electron-donating groups are called nucleophilic radicals. These radicals readily react with electrophilic alkenes. The SOMO–LUMO interactions are the driving force for the reaction, where the high-energy SOMO of the electron-rich, nucleophilic radicals interacts with the low-energy LUMO of the electron-deficient, electrophilic alkenes. Such SOMO–LUMO interactions are the basis of reactive radical traps, affecting the selectivity in radical reactions. For...
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Radical Reactivity: Electrophilic Radicals01:02

Radical Reactivity: Electrophilic Radicals

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Radicals adjacent to electron‐withdrawing groups are called electrophilic radicals. These radicals readily react with nucleophilic alkenes. For example, the malonate radical, in which the radical center is flanked by two electron‐withdrawing groups, reacts readily with butyl vinyl ether, which consists of an electron‐donating oxygen substituent. The reaction between electrophilic malonate radical and nucleophilic vinyl ether is favored because the radical has a...
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Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization01:13

Intramolecular Claisen Condensation of Dicarboxylic Esters: Dieckmann Cyclization

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Dieckmann cyclization is an intramolecular Claisen condensation of diesters. The reaction occurs in the presence of a base and generates a cyclic β-ketoester as the final product. Commonly, 1, 6 and 1, 7-diesters are preferred substrates for the reaction since the generated five, and six-membered cyclic β-keto esters are particularly more stable.
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Radical Autoxidation01:20

Radical Autoxidation

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The oxidation of an organic compound in the presence of air or oxygen is called autoxidation. For example, cumene reacts with oxygen to form hydroperoxide. Autoxidation involves initiation, propagation, and termination steps. Many organic compounds are susceptible to autoxidation—especially ethers in the presence of oxygen, which form hydroperoxides. Even though this reaction is slow, old ether bottles contain small amounts of peroxide, which leads to laboratory explosions during ether...
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Radical Formation: Overview01:03

Radical Formation: Overview

2.6K
A bond can be broken either by heterolytic bond cleavage to form ions or homolytic bond cleavage to yield radicals. A fishhook arrow is used to represent the motion of a single electron in homolytic bond cleavage. There are two main sources from which radicals can be formed:
Radicals from spin-paired molecules:
Radicals can be obtained from spin-paired molecules either by homolysis or electron transfer. While two radicals are formed in the former, an electron is added in the...
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Radical Formation: Homolysis00:54

Radical Formation: Homolysis

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A bond is formed between two atoms by sharing two electrons. When this bond is broken by supplying sufficient energy, either two electrons can be taken up by one atom forming ions by the cleavage called heterolysis, or the two electrons are shared by two atoms, with one each creating radicals by the cleavage called homolysis.
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Free Radicals in Chemical Biology: from Chemical Behavior to Biomarker Development
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酶的光激发可以实现立体选择性的基质循环

Kyle F Biegasiewicz1, Simon J Cooper1, Xin Gao1

  • 1Department of Chemistry, Princeton University, Princeton, NJ 08544, USA.

Science (New York, N.Y.)
|June 22, 2019
PubMed
概括

称为黄素依赖的"乙烯"减少酶可以被光激发以启动不对称的激素循环反应. 这种新的生物催化方法可使各种乳在高度立体化学控制下得到合成.

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科学领域:

  • 生物催化和合成化学
  • 酶学和基因反应机制

背景情况:

  • 光刺激是化学合成中激进反应的关键策略.
  • 黄素依赖的酶,特别是"缩酶",是重要的生物催化剂.
  • 控制激素反应中的立体化学仍然是一个重要的合成挑战.

研究的目的:

  • 调查光刺激对黄素依赖的""还原酶的催化功能的影响.
  • 探索这些酶在促进不对称的激素循环反应中的潜力.
  • 开发一种用于合成乳结构的新生物催化方法.

主要方法:

  • 黄素依赖的""还原酶的光激发.
  • 酶催化不对称基循环的分析.
  • 基质-酶相互作用和电子转移机制的表征.
  • 合成乳产品的立体化学分析.

主要成果:

  • 光刺激改变了依赖于黄素的""减少酶的催化功能.
  • 酶成功促进了不对称的基因循环,形成了五到八个成员的乳酸酶.
  • 观察到高立体化学偏好,由酶的活性部位决定.
  • 发现了一种涉及直接激发电子捐赠-接受复合物的新机制.
  • 从黄素中获得酶的原子输送,以获得前性基.

结论:

  • 黄素依赖的"乙烯"降解酶的光激发为不对称的基因循环提供了一种新的生物催化途径.
  • 这种方法使不同乳酸的立体选择合成成为可能.
  • 这些发现为合成化学中利用黄酶引入了一个新范式.