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Acid-Catalyzed Ring-Opening of Epoxides02:24

Acid-Catalyzed Ring-Opening of Epoxides

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Epoxides that are three-membered ring systems are more reactive than other cyclic and acyclic ethers. The high reactivity of epoxides originates from the strain present in the ring. This ring strain acts as a driving force for epoxides to undergo ring-opening reactions either with halogen acids or weak nucleophiles in the presence of mild acid. The acid catalyst converts the epoxide oxygen, a poor leaving group, into an oxonium ion, a better leaving group, making the reaction feasible. The...
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Base-Catalyzed Ring-Opening of Epoxides02:26

Base-Catalyzed Ring-Opening of Epoxides

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Due to their highly strained structures, epoxides can readily undergo ring-opening reactions through nucleophilic substitution, either in the presence of an acid or a base. The nucleophilic substitution reactions in the presence of acid are called acid-catalyzed ring-opening reactions, and nucleophilic substitution reactions in the presence of a base are called base-catalyzed ring-opening reactions. Epoxides undergo base-catalyzed ring-opening reactions in the presence of a strong nucleophile...
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Preparation of Epoxides03:00

Preparation of Epoxides

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Overview
Epoxides result from alkene oxidation, which can be achieved by a) air, b) peroxy acids, c) hypochlorous acids, and d) halohydrin cyclization.
Epoxidation with Peroxy Acids
Epoxidation of alkenes via oxidation with peroxy acids involves the conversion of a carbon–carbon double bond to an epoxide using the oxidizing agent meta-chloroperoxybenzoic acid, commonly known as MCPBA. Since the O–O bond of peroxy acids is very weak, the addition of electrophilic oxygen of peroxy...
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Regioselectivity of Electrophilic Additions-Peroxide Effect02:35

Regioselectivity of Electrophilic Additions-Peroxide Effect

12.0K
In the presence of organic peroxides, the addition of hydrogen bromide to an alkene yields the isomer that is not predicted by Markovnikov’s rule. For example, the addition of hydrogen bromide to 2-methylpropene in the presence of peroxides gives 1-bromo-2-methylpropane. This addition reaction proceeds via a free radical mechanism, which reverses the regioselectivity. The free radical reaction mechanism involves three stages: initiation, propagation, and termination.
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E2 Reaction: Stereochemistry and Regiochemistry02:43

E2 Reaction: Stereochemistry and Regiochemistry

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Elimination reactions of alkyl halides can yield one or more alkenes depending on the specific regiochemical and stereochemical considerations. While the regiochemistry of the reaction governs the location of the double bond in the product, the stereochemical requirements often influence the geometry.
When a substrate with two different β hydrogens undergoes an E2 elimination, the presence of a strong base can yield two regioisomeric alkenes. The more-substituted alkene is the major...
15.0K
Regioselective Formation of Enolates01:33

Regioselective Formation of Enolates

3.8K
As depicted in the figure below, the unsymmetrical ketones can form two possible enolates: less substituted or more substituted enolates. Usually, the thermodynamic enolates are formed from the more substituted α-carbon atom, while the kinetic enolates are formed faster by deprotonation from the less substituted position. The thermodynamic enolates have lower energy, so they are more stable. But the energy required to form kinetic enolates is less.
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Preparation of Enantiopure Non-Activated Aziridines and Synthesis of Biemamide B, D, and epiallo-Isomuscarine
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Mechanistically Defined Epoxide- and Aziridine-2-carboxamide Electrophiles Enable Stereoselective Covalent

Chungen Li1,2, Xueyi Yang1,3, Jingsong Shan1,3

  • 1Department of Chemistry, The Herbert Wertheim UF Scripps Institute for Biomedical Innovation & Technology, 130 Scripps Way, Jupiter, Florida 33458, United States.

Journal of the American Chemical Society
|April 16, 2026
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Summary

Researchers developed novel epoxide and aziridine small molecules for covalent RNA targeting. These compounds selectively modify RNA, offering a versatile platform for drug discovery and understanding RNA function.

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Area of Science:

  • Medicinal Chemistry
  • Molecular Biology
  • Chemical Biology

Background:

  • RNA is an underutilized therapeutic target due to challenges in developing stable, reactive small molecules.
  • Existing methods lack predictable reactivity and stability for covalent RNA modification.

Purpose of the Study:

  • To develop a novel class of electrophilic small molecules for targeted covalent modification of RNA.
  • To demonstrate the versatility and applicability of these molecules against pathogenic RNA and riboswitches.

Main Methods:

  • Synthesis and characterization of epoxide- and aziridine-2-carboxamide electrophiles.
  • Mechanistic studies on reactivity and stability under physiological conditions.
  • Application in structure-guided covalent modification of r(CUG)exp repeat RNA and flavin mononucleotide riboswitch.

Main Results:

  • A new class of tunable epoxide and aziridine electrophiles was identified, derived from 3-chloropivalamide precursors.
  • These electrophiles selectively react with guanine N7, with reactivity modulated by chemical and stereochemical factors.
  • Demonstrated covalent modification of pathogenic RNA and disruption of RNA-protein interactions, as well as stereoselective modulation of a riboswitch in vitro and in cells.

Conclusions:

  • Epoxide- and aziridine-2-carboxamides represent a versatile platform for covalent RNA targeting.
  • This work provides a framework for rational design of stereochemically controlled, RNA-reactive small molecules.
  • Enables new strategies for RNA-targeted drug discovery and chemical biology research.