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相关概念视频

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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Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry01:29

Diels–Alder Reaction Forming Bridged Bicyclic Products: Stereochemistry

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Diels–Alder reactions between cyclic dienes locked in an s-cis configuration and dienophiles yield bridged bicyclic products.
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Photochemical Electrocyclic Reactions: Stereochemistry01:26

Photochemical Electrocyclic Reactions: Stereochemistry

2.0K
The absorption of UV–visible light by conjugated systems causes the promotion of an electron from the ground state to the excited state. Consequently, photochemical electrocyclic reactions proceed via the excited-state HOMO rather than the ground-state HOMO. Since the ground- and excited-state HOMOs have different symmetries, the stereochemical outcome of electrocyclic reactions depends on the mode of activation; i.e., thermal or photochemical.
Selection Rules: Photochemical Activation
2.0K
Thermal Electrocyclic Reactions: Stereochemistry01:17

Thermal Electrocyclic Reactions: Stereochemistry

2.3K
The stereochemistry of electrocyclic reactions is strongly influenced by the orbital symmetry of the polyene HOMO. Under thermal conditions, the reaction proceeds via the ground-state HOMO.
Selection Rules: Thermal Activation
Conjugated systems containing an even number of π-electron pairs undergo a conrotatory ring closure. For example, thermal electrocyclization of (2E,4E)-2,4-hexadiene, a conjugated diene containing two π-electron pairs, gives trans-3,4-dimethylcyclobutene.
2.3K
Diels–Alder Reaction Forming Cyclic Products: Stereochemistry01:28

Diels–Alder Reaction Forming Cyclic Products: Stereochemistry

4.4K
The Diels–Alder reaction is one of the robust methods for synthesizing unsaturated six-membered rings. The reaction involves a concerted cyclic movement of six π electrons: four π electrons from the diene and two π electrons from the dienophile.
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Thermal and Photochemical Electrocyclic Reactions: Overview01:26

Thermal and Photochemical Electrocyclic Reactions: Overview

2.7K
Electrocyclic reactions are reversible reactions. They involve an intramolecular cyclization or ring-opening of a conjugated polyene. Shown below are two examples of electrocyclic reactions. In the first reaction, the formation of the cyclic product is favored. In contrast, in the second reaction, ring-opening is favored due to the high ring strain associated with cyclobutene formation.
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一种形成中环乳的多基基基酶

De-Wei Gao, Cooper S Jamieson, Gaoqian Wang1

  • 1State Key Laboratory of Bio-organic and Natural Products Chemistry, Center for Excellence in Molecular Synthesis, Shanghai Institute of Organic Chemistry, University of Chinese Academy of Sciences, Shanghai, China.

Journal of the American Chemical Society
|December 22, 2020
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概括

研究人员发现了一种化酶,DcsB,有效催化中环乳化. 这种来自decarestrictine C1路径的酶具有广泛的基质范围,并具有挑战乳合成的生物催化剂的潜力.

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科学领域:

  • 生物化学
  • 有机化学
  • 酵素学

背景情况:

  • 由于不良的循环能量,中环乳很难合成.
  • 脱素C1生物合成途径涉及复杂的自然产物形成.

研究的目的:

  • 识别和描述参与中环乳形成的酶.
  • 探索DcsB作为乳化反应的生物催化剂的潜力.

主要方法:

  • 发现并从C1路径中分离酶.
  • 生物化学测定以评估DcsB活性和基质范围.
  • 进行X射线晶体学和计算建模以阐明催化机制.

主要成果:

  • 发现了硫酶DcsB,一种能有效催化中环乳化的酶.
  • DcsB与不同长度和替代物的线性前体具有广泛的基质混杂性.
  • 结构和计算分析揭示了DcsB的催化活性的分子基础.

结论:

  • DcsB是一种高效的中环乳化酶,克服了合成挑战.
  • 该酶的广泛基质范围使其成为各种乳合成应用的有希望的生物催化剂.
  • 了解DcsB的机制提供了对具有挑战性的循环的酶控制的见解.