Dr. Whitesell
Chem 151
16 February 2014
The Queen of Fruit
Ever since I was a child, my mother would always make tea infused with mangosteen for
me to drink. I always reached for the mug of hot tea with a sigh of happiness as I inhaled
the fruity scent of mangosteen through my tiny nose. After every mug of tea, my mother
would say, “Drink this every day even when I am not around for mangosteen is the
‘queen of fruit.’” I would always crinkle my nose and giggle at the thought that one fruit
could be the queen of anything and did not think much of it. As I grew up and moved out
of the house, due to my mother’s wishes, I continue to drink mangosteen tea. Even after
many years of my mother talking about mangosteen, I never was curious about
mangosteen’s benefits until one day I decided to research mangosteen and its various
mechanisms of a certain molecule prevalent in the fruit called xanthone.
What makes mangosteen known as the queen of fruit? One major ingredient: xanthone.
The term “xanthos” is Greek for “yellow” which deems true since xanthone’s
characteristic color is yellow. Xanthone is a heterocyclic organic compound found in the
pericarp, or the rind, of the mangosteen fruit. Xanthone, a crystalline solid, has the
molecular formula C13H8O2 and a melting point range from 170°C to 172°C4. In contrast
to the melting point of water at 0°C, organic compounds tend to have a higher melting
point and are less likely to be denatured at a high temperature. A high melting point
indicates strong intermolecular forces since more heat is required to break the bonds. The
chemical and physical properties of xanthone make them prime examples of heat stable
compounds with powerful antioxidant features.
Figure 1. Ball-and-stick Model of Xanthone6. The stick illustrates the bond between
two atoms and the ball represents the atom; black is carbon, red is oxygen, and white is
hydrogen.
Xanthone’s IUPAC name is 9H-xanthene-9-one, which consists of conjugated aromatic
rings, several double carbon bonds, and an aromatic ketone at carbon 9. Xanthone
contains two different atoms, carbon and oxygen, in a closed ring and thus contributes to
its heterocyclic properties. The carbon-oxygen bond of the carbonyl group is polarized
because the oxygen atom, which is more electronegative than carbon, pulls the electrons
towards itself and thus results in a higher electron density and a more electronegative
charge. The electrons are moving away from the carbon atom, giving carbon a more
positive charge. The polar vector points toward the direction of the more electronegative
atom, which in this case is the oxygen atom.
Figure 2. Components of Mangosteen. The mangosteen super fruit (Garcinia
Mangostana) is primarily found in several tropical plants in Southeast Asia.
The mangosteen fruit7, or the pulp, contains essential minerals and vitamins, such as
calcium and Vitamin C, respectively5. The pericarp, or the rind, is a major and natural
source of xanthones. There are over 120 classifications of xanthones and out of the 120
different xanthones, approximately 43 types are in the mangosteen fruit which is more
than the amount of xanthones in any plant. Xanthones share a common backbone, but the
functional side chains give rise to unique xanthone derivatives, which are key
components in polyester production in textiles1. Among the plethora of xanthones found
in mangosteen, a few essential xanthones include α-mangostin, β-mangostin, ϒmangostin, gartanin, mangostanol, and garcinone A through E5. Although xanthones are
useful in combating cancer, each xanthone has a special function. For example, αmangostin helps suppress tumor cells that cause cancer while garcinone E targets cancer
cells in the lungs, liver, and gastrointestinal (G.I.) tract. ϒ-mangostin is effective in
inhibiting the cyclooxygenase (COX) 2 enzyme which induces inflammation, a major
cause in arthritis and other diseases such as Alzheimer’s, cancer, and Parkinson’s.
Inhibition by the xanthone ϒ-mangostin allows it to decelerate the natural production of
the COX 2 enzyme in the body. Garcinone B, α-mangostin, and β-mangostin are capable
of inhibiting tuberculosis6.
Synthesis of Xanthones
Xanthones were first synthesized in 1939 by heating phenyl salicylate but another method
is to oxidize xanthene in presence of chromic acid1. Phenyl salicylate is an important
precursor in the production of xanthone. Thus, the question is, how is it synthesized?
Phenyl salicylate is produced by reacting salicylic acid and phenol in the presence of an
acid catalyst and heat. The reaction of a carboxylic acid and an alcohol leads to the
formation of an ester.
[MECHANISM]
The oxygen atom of the carbonyl group becomes slightly negative and acts as the
nucleophile, which attacks the proton. Then the oxygen atom of the alcohol attacks the
electrophilic carbon in the carbonyl group. The oxygen of the alcohol undergoes
deprotonation with the addition of a base. The hydroxyl group becomes a good leaving
group via protonation. Pushing an electron pair from the oxygen atom forms a double
bond with the carbonyl carbon and gives the oxygen a more positive charge. The release
of a water molecule results from pushing electrons. In solution, the oxygen atom of a
water molecule attacks the hydrogen and releases an oxonium ion H3O+. Since the water
molecule removes the hydrogen atom, the electrophilic oxygen atom of the carbonyl
group pulls the electron pair towards itself and thus eliminates the positive charge of the
oxygen. In the presence of an acid catalyst and the addition of heat, salicylic acid and
phenol undergoes Fischer esterification to produce phenyl salicylate which is used to
synthesize xanthones.
Detection of Xanthones
The identification of xanthones involves using fluorescence markers or dyes to label the
compounds and a fluorescent spectrometer for analysis. There are other methods to detect
these organic compounds, such as absorption, but fluorescent spectroscopy has greater
sensitivity and thus can help provide a more efficient way to detect the xanthones.
Figure 3. Fluorescence of Xanthones. An incoming photon (hυ) of energy bombards
and excites the xanthone compound via intersystem crossing (ISC)2. The photo-excited
state 1ππ* is lower in energy than the triplet excited state 3nπ*.
Upon the absorption of a photon, the electrons transition from the ground to the excited
state. The emission of the photon, or non-radiative vibrational relaxation, leads to
fluorescence. The fluorescence quantum yield of xanthone in water is 100 fold larger than
in other solvents, which is around 10-4. Both processes yield an ultrafast time of 1
picoseconds2. The quantum yield determines the efficiency of fluorescent processes;
quantum yield is equal to the number of photons emitted over the number of photons
absorbed. A high fluorescent quantum yield results in a high fluorescent sensitivity.
The VEMMA Solution: Elimination of Free Radicals
The xanthones in mangosteen are powerful antioxidants, anti-inflammatories, and contain
multiple health benefits such as eliminating and preventing free radicals from coming
into contact with harmful enzymes in the body. Since ketones lack a hydrogen atom on
the carbonyl group, ketones will not undergo oxidation and therefore is the reason why
xanthone is a potent antioxidant and contains medicinal and nutritional properties.
Xanthones can help lower LDL (low-density lipoprotein) cholesterol, also known as the
harmful type of cholesterol. How do xanthones do this? By blocking contact between free
radicals and LDL cholesterol, oxidation cannot occur and thus it prevents LDL
cholesterol from clinging to the arteries, which can lead to blood clots and heart diseases,
such as atherosclerosis. In addition, xanthones can inhibit oxidative processes in the body
by accepting or donating electrons to trap reactive oxygen species, such oxygen free
radicals and hydrogen peroxide, or other radicals, such as hydroxyl and lipid radicals. An
abundance of molecular oxygen can generate oxygen free radicals, which are unstable
oxygen molecules and lipid radicals can result in lipid peroxidation. These oxidative
processes will cause DNA degradation, cellular damage and dysfunction. Although
xanthones cannot cure cancer, they can suppress tumor production, which leads to cancer.
A clinically studied formula from Vemma, a company specializing in healthy energy and
liquid nutrition, and vitamins, essential minerals, aloe vera, and xanthone-rich
mangosteen juice all serve as antioxidants and nutrients to help fight cancer, neutralize
free radicals, and enhancing the body’s defense and overall health.
References
1. eHow. “What is Xanthone?” Web. Jan 18, 2014.
2. Heinz, B, et al. “On the Unusual Fluorescence Properties of Xanthones in Water.”
Physical Chemistry Chemical Physics. Journal. Feb 15, 2014.
3. Maui Farmers United Union. “Adding Value to Locally Grown Crops.” Web. Feb 7,
2014.
4. Organic Syntheses. Xanthones. Web. Feb 1, 2014.
5. VemmaNews. “Mangosteen 101: Part Three.” Jun 12, 2012. Web. Jan 18, 2014.
6. VemmaSolution. All About Xanthones. Web. Jan 18, 2014.
7. Wikipedia. Xanthones. Web. Jan 18, 2014.