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Radical Reactivity: Intramolecular vs Intermolecular01:33

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Radical reactions can occur either intermolecularly or intramolecularly. In an intermolecular radical reaction, a nucleophilic radical adds to an electrophilic alkene or vice versa. In such reactions, the radical and generally the alkene, which is also called the radical trap, are two different molecules. Additionally, for such intermolecular reactions to occur, the radical trap must be active, present in an excess concentration, and the radical starting material must have a weak...
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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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Radicals can be formed by adding a radical to a spin-paired molecule. This is typically observed with unsaturated species, where the addition of a radical across the π bond leads to the production of a new radical by dissolving the π bond. For example, the addition of a Br radical to an alkene yields a carbon-centered radical.
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Photogeneration of N-Heterocyclic Carbenes: Application in Photoinduced Ring-Opening Metathesis Polymerization
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Non-native Intramolecular Radical Cyclization Catalyzed by a B12 -Dependent Enzyme.

Jianbin Li1, Amardeep Kumar1, Jared C Lewis1

  • 1Department of Chemistry, Indiana University, Bloomington, IN 47405, USA.

Angewandte Chemie (International Ed. in English)
|October 24, 2023
PubMed
Summary
This summary is machine-generated.

Researchers repurposed a vitamin B12-dependent enzyme, CarH, for novel radical cyclization reactions. The engineered enzyme CarH* efficiently forms lactams and unique spirocycles, expanding biocatalysis applications.

Keywords:
DearomatizationLactamsNon-Native Enzyme CatalysisRadical CyclizationVitamin B12

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Area of Science:

  • Biocatalysis
  • Enzyme Engineering
  • Organic Synthesis

Background:

  • Vitamin B12 (cobalamin) and its derivatives possess unique reactivity.
  • B12-dependent enzymes are currently underutilized in biocatalysis.
  • Transcription factors offer potential protein scaffolds for enzyme engineering.

Purpose of the Study:

  • To repurpose the B12-dependent transcription factor CarH for non-native radical cyclization reactions.
  • To engineer a variant, CarH*, with enhanced reactivity and selectivity for B12-catalyzed transformations.
  • To explore the synthetic utility of engineered B12-dependent enzymes in forming complex cyclic structures.

Main Methods:

  • Engineering of the B12-dependent transcription factor CarH into CarH*.
  • Utilizing CarH* to catalyze radical cyclization reactions.
  • Mechanistic studies to elucidate reaction pathways and cofactor control.

Main Results:

  • CarH* successfully catalyzed the formation of gamma- and delta-lactams via redox-neutral or reductive ring closure.
  • Engineered enzyme demonstrated enhanced reactivity and selectivity compared to free B12 cofactor.
  • CarH* achieved unusual spirocyclization via dearomatization of pendant arenes, yielding bicyclic 1,3-dienes.
  • Demonstrated a novel synthetic route to 1,3-dienes, distinct from existing 1,4-diene methods.

Conclusions:

  • Protein scaffolds are crucial for controlling the reactivity of vitamin B12 cofactors.
  • Repurposed B12-dependent enzymes like CarH* significantly expand the synthetic toolbox for biocatalysis.
  • This work highlights the potential for engineering B12-dependent enzymes for novel chemical transformations.