- Oxidative chemistry of the natural antioxidant hydroxytyrosol: Hydrogen peroxide-dependent hydroxylation and hydroxyquinone/o-quinone coupling pathways
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Oxidation of the natural antioxidant hydroxytyrosol (1) with peroxidase/H2O2 in phosphate buffer at pH 7.4 led to the formation of two main ethyl acetate-extractable products. These could be isolated by preparative TLC after reduction and acetylation, and were identified as the tetraacetyl derivative of 2-(2,4,5-trihydroxyphenyl)ethanol (3) and the heptaacetyl derivative of the pentahydroxybiphenyl 4 by 2D NMR and MS analysis. Similar oxidation of 4-methylcatechol gave, after the same work-up, the acetylated derivatives of 1,2,4-trihydroxy-5-methylbenzene (5) and the pentahydroxybiphenyl 6. Mechanistic experiments suggested that hydrogen peroxide affects the course of the oxidation of 1 by adding to the first formed o-quinone to give a hydroxyquinone intermediate. This could bring nucleophilic attack to the o-quinone of 1 to give the dimer 4. These results disclose novel oxidative pathways of 4-alkylcatechols and provide an improved chemical basis to enquire into the mechanism of the antioxidant action of 1.
- De Lucia, Maria,Panzella, Lucia,Pezzella, Alessandro,Napolitano, Alessandra,D'Ischia, Marco
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p. 1273 - 1278
(2007/10/03)
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- Bi(OTf)3-catalyzed acylation of p-quinones: A facile synthesis of acylated hydroquinones
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p-Quinones undergo smooth acylation with acetic anhydride in the presence of 2mol% of bismuth triflate under mild conditions to afford the corresponding 1,4-diacylated-2-acetoxylated hydroquinones in excellent yields with high selectivity.
- Yadav,Reddy, B. V. Subba,Swamy,Rao, K. Raghavender
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p. 6037 - 6039
(2007/10/03)
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