One of the geographical areas where nutritional habits have drawn attention as a prototype of nutrit — Organic Chemistry Chemistry Question
Oleuropein Hydrolysis
One of the geographical areas where nutritional habits have drawn attention as a prototype of nutrition is the island of Crete in Greece. In a five countries study, Cretan diet has been associated with low rates of coronary heart disease (CHD). The mortality rate from CHD was 7 in 10000 subjects, while it was 566, 424, 317 and 200 in Finland, USA, the Netherlands and Italy, respectively. This has been attributed to the high olive oil consumption, which is rich in oleuropein (A), a powerful antioxidant. (R represents an alkylpolyphenolic group)
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The acid–catalyzed hydrolysis of oleuropein gives apart from glucose, two other compounds, one alkylpolyphenolic (A1) and one monoterpenoid (A2).
Indicate with an arrow in the formula of oleuropein:
a) The oxygen atom that will be protonated in the acid hydrolysis leading to polyphenolic compound A1.
b) The most likely carbon–oxygen bond to be cleaved in order to form glucose.
Model Answer
29.1
a) The oxygen atom that will be protonated in the acid hydrolysis is the ester oxygen connecting the monoterpenoid part to the polyphenolic group R (the phenolic ester oxygen of the oleuropein structure).
b) The most likely carbon-oxygen bond to be cleaved is the glycosidic C-O bond (the bond between the glucose unit and the monoterpenoid core).
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In the mass spectrum of A1, the peak corresponding to the molecular ion is situated at 154 mass units. The 400 MHz 1 H–NMR spectrum of compound A1 in DMSO/D2O is shown below. The hydroxylic protons are exchangeable and therefore do not appear in the spectrum:
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Choose the correct structure of A1 that can be deduced on the basis of the 1 H-NMR and mass spectrum information given.
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Candidate structures:
- A
- B
- C
Model Answer
29.2 The correct structure is C (hydroxytyrosol, 2-(3,4-dihydroxyphenyl)ethanol).
Draw the structure of A1 and use the letters a, b, c, d and e to designate the protons that correspond to the respective peaks in the 1 H-NMR spectrum.
Model Answer
29.3 The structure of A1 (hydroxytyrosol) and the corresponding proton designations for the 1H-NMR peaks are:
- a: CH2 protons adjacent to the aromatic ring (~2.7 ppm)
- b: CH2 protons adjacent to the terminal hydroxyl group (~3.6 ppm)
- c: aromatic proton H6 (~6.5 ppm)
- d: aromatic proton H2 (~6.7 ppm)
- e: aromatic proton H5 (~6.6 ppm)
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