Melatonin—A Highly Potent Endogenous Radical Scavenger and Electron Donor: New Aspects of the Oxidation Chemistry of this Indole Accessed in vitro a

@article{Poeggeler1994MelatoninAHP,
  title={Melatonin—A Highly Potent Endogenous Radical Scavenger and Electron Donor: New Aspects of the Oxidation Chemistry of this Indole Accessed in vitro a},
  author={Burkhard Poeggeler and Seppo Y O Saarela and Russel Joseph Reiter and Dun-Xian Tan and Li‐Dun Chen and Lucien C. Manchester and Lornell Barlow‐Walden},
  journal={Annals of the New York Academy of Sciences},
  year={1994},
  volume={738}
}
Endogenous indolamines derived from the essential aromatic amino acid tryptophan can act as substrates and mediators of electron transfer mechanisms and radical reactions.' The indoleamine melatonin is the most powerful and effective hydroxyl radical scavenger detected to date, which, due to its lipophilic nature, provides on-site protection against oxidative damage to biomolecules within every cell compartment.',* 
Actions of melatonin in the reduction of oxidative stress. A review.
Melatonin was discovered to be a direct free radical scavenger less than 10 years ago. Besides its ability to directly neutralize a number of free radicals and reactive oxygen and nitrogen species,
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The preliminary evaluation indicated that compound 4c showed improved scavenging activity compared with vitamin C and suggested that the cysteinyl‐conjugated derivative 4c may be a suitable lead to further optimize potent antioxidants for certain oxidative stress conditions.
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TLDR
This recently discovered function of melatonin establishes a role for this indole in every organism, and indeed in every cell, from the most primitive members of the animal kingdom up to and including the was shown to be a hormone produced in and secreted from the mammalian pineal gland.
Melatonin, hydroxyl radical‐mediated oxidative damage, and aging: A hypothesis
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Experiments investigating the effects of endogenous excitatory amino acid antagonists and stimulants of melatonin biosynthesis such as magnesium may finally lead to novel therapeutic approaches for the prevention of degeneration and dysdifferentiation associated with diseases related to premature aging.