Dr. Whitesell
Chem 151
16 February 2014
The Queen of Fruit
What makes mangosteen known as the queen of fruit? One major ingredient: xanthone.
“Xanthos” is Greek for “yellow” which gives xanthone its characteristic color. 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°C. 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 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 xanthones make
them the 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 because of its 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, thus contributing 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 C5. 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 other 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, ϒ-mangostin, gartanin,
mangostanol, and garcinone A through E5. Although xanthones are useful in combating
cancer, each xanthone has its own special functions. For example, α-mangostin 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 involves 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 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
1
ππ* 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
picosecond2. 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 are 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.? By blocking contact between free radicals and LDL
cholesterol, oxidation cannot occur and thus prevent 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.