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Radical Chain-Growth Polymerization: Overview01:10

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Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
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In the presence of oxidizing agents, phenols are oxidized to quinones. Quinones can be easily reduced back to phenols using mild reducing agents. The electron-donating hydroxyl group enhances the reactivity of the aromatic ring, enabling oxidation of the ring even in the absence of an α hydrogen.
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Another method of radical formation is the elimination process. It is the opposite of the addition route and is driven by the instability of the radical. For example, as depicted in Figure 1, dibenzoyl peroxide yields a pair of unstable radicals upon homolysis. Given its instability, this radical spontaneously undergoes elimination via a C–C bond cleavage to form a relatively more stable phenyl radical. The mechanism involves cleavage of the bond between the α and β positions...
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The presence of electron-donating, electron-withdrawing, or conjugating groups adjacent to a radical center, imparts electronic stabilization to the radicals. Examples of such electronically-stabilized radicals are triphenylmethyl, tetramethylpiperidine‐N‐oxide, and 2,2‐diphenyl‐1‐picrylhydrazyl. These radicals are remarkably stable and are known as persistent radicals. Some of the persistent radicals can even be isolated and purified.
Along with electronic...
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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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Ideally, an unpaired electron shows a single peak in the EPR spectrum due to the transition between the two spin energy states. However, coupling interactions can occur between the spins of the unpaired electron and any neighboring spin-active nuclei. This hyperfine coupling results in hyperfine splitting, where the EPR signal is split into multiplets. The signals split into 2nI + 1 peaks, where n is the number of equivalent nuclei and I is the nuclear spin. These splitting patterns provide...
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An optimized pyrimidinol multifunctional radical quencher.

Omar M Khdour1, Pablo M Arce1, Basab Roy1

  • 1Center for BioEnergetics, Biodesign Institute, and Department of Chemistry and Biochemistry, Arizona State University , Tempe, Arizona 85287, United States.

ACS Medicinal Chemistry Letters
|June 6, 2014
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Summary

New aza analogues of idebenone show potent antioxidant and cytoprotective properties. These compounds may offer therapeutic potential for neurodegenerative diseases like Friedreich

Keywords:
Mitochondrial dysfunctionadenosine triphosphatecytoprotectionelectron transport chainlipid peroxidation

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Area of Science:

  • Medicinal Chemistry
  • Neuropharmacology
  • Mitochondrial Biology

Background:

  • Oxidative stress and mitochondrial dysfunction are implicated in neurodegenerative diseases.
  • Idebenone is an experimental neuroprotective drug with antioxidant properties.
  • Friedreich's ataxia (FRDA) is a neurodegenerative disease characterized by mitochondrial defects.

Purpose of the Study:

  • To synthesize and evaluate aza analogues of idebenone.
  • To assess the antioxidant and cytoprotective effects of these analogues in cellular models.
  • To identify potential therapeutic agents for FRDA and other neurodegenerative conditions.

Main Methods:

  • Synthesis of aza analogues (4-9) of idebenone.
  • Evaluation of antioxidant activity in glutathione-depleted cells.
  • Assessment of mitochondrial oxidative phosphorylation efficiency in FRDA and CoQ10-deficient lymphocytes.
  • Cytoprotective assays in cultured fibroblasts and lymphocytes.

Main Results:

  • Modification of the redox core improved antioxidant and cytoprotective properties.
  • Aza analogues with longer side chains (6, 7, 9) demonstrated potent antioxidant activity, superior to idebenone.
  • Optimized analogue 7 and its acetate (7a) effectively blocked oxidative stress and maintained mitochondrial function.

Conclusions:

  • Novel aza analogues of idebenone possess significant antioxidant and cytoprotective potential.
  • Compounds 6, 7, and 9 are promising candidates for further therapeutic development.
  • These analogues may be valuable in treating mitochondrial and neurodegenerative diseases, including FRDA and Alzheimer's disease.