Antioxidants in Natural Product Chemistry

In nature, plants do not have a lot of ways how to protect themselves from other living beings. As plants can not move, evolutionary they have developed numerous chemicals with various activities in order to protect themselves.

One of the main threats for them despite the necessity is the sun. Although the sun provides plants the energy necessary for photosynthesis, this energy has also a damaging effect in the form of UV radiation and promotes radical reactions. In order to protect from this, plants have several compounds that exhibit antioxidative activity.

Molecular structure – antioxidative activity relationship

Typically in order for the compound to exhibit antioxidative activity, it has to possess some structural motifs, that are able to neutralize threats.

Very common for anti-oxidative compounds like resveratrol, genistein, luteolin, and many more contain one or multiple hydroxyl groups connected to an aromatic, conjugated moiety.

On the one hand, the aromatic part can absorb UV radiation due to the accessible electron orbitals and peacefully neutralize it, on the other hand, the hydroxyl group can react with highly reactive radicals like reactive oxygen species. After the reaction, this radical is delocalized in an aromatic and/or conjugated system forming stable molecules, that do not react further in a harmful manner.

Testing of natural product antioxidant properties

There have been developed several methods to test antioxidative activity, but can be divided into three parts:

  • Spectrophotometric
  • Electrochemical
  • Chromatographic

The most commonly used are spectrophotometric variations due to the easy preparation and observation. A typical procedure would be a reaction between some sort of a radical and antioxidant and reaction is indicated with either loss of fluorescence from the indicator or discoloring of the organic radical.

One of the most popular tests are:

  • ORAC (oxygen radical absorbance capacity)
  • TRAP (total peroxy radical trapping antioxidant parameter)
  • CUPRAC (cupric reducing antioxidant power)
  • DPPH (2,2-di(4-tert-octylphenyl)-1-picrylhydrazyl test)
  • and others

Also, the electrochemical method is gaining popularity due to its cheapness and no use of toxic chemicals.

Mode of action of natural antioxidants

Natural antioxidants have been tested for various purposes, but essentially can boil down to three main directions of the protective effect:

  • UV absorption
  • Neutralization of reactive radicals
  • Mobilization of innate antioxidative mechanisms

UV absorption

A lot of natural antioxidants contain aromatic rings linked together with unsaturated carbon chains. Such a system is prone to UV radiation absorption to easily accessible lower unoccupied molecular orbitals. By UV excitation electron is transferred to this orbital and can just irradiate less energetic photons or react in a non-damaging way.

Neutralization of reactive radicals

The most commonly encountered reactive molecules around us are peroxides and nitric oxide radicals that are actively being formed in our bodies from biologically necessary oxygen and nitric oxide. A lot of natural oxidants exhibit reactivity towards their reactive oxygen and nitrogen species.

In order for the molecule to be a successful antioxidant, it has to react with reactive radicals rapidly and has to form much less reactive radicals that just end its life as non-toxic compounds.

Mobilization of innate antioxidative mechanisms

A lot of compounds exhibiting antioxidative properties directly interacting with radicals can also exhibit activation of several enzymatic pathways to activate your body’s natural response to oxidative molecules.

Furthermore, molecules, that structure possess almost no ability to delocalize radicals or absorb UV radiation like betulin and other triterpenoids, can significantly boost your body’s ability to fight reactive molecules.


Nature has provided us with a lot of various antioxidants for many purposes – cosmetics, weight regulation, cardioprotective effects, and many more. If you wish to expand your research on antioxidative compounds, visit our product page, to acquire high-quality natural antioxidants.