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Molecules 2010, 15(7), 4722-4736; doi:10.3390/molecules15074722
Article

Regioselective O-Derivatization of Quercetin via Ester Intermediates. An Improved Synthesis of Rhamnetin and Development of a New Mitochondriotropic Derivative

1, 2, 1, 2, 1, 2,3 and 1,*
1 Department of Chemical Sciences, Università di Padova, via Marzolo 1, 35131 Padova, Italy 2 Department of Biomedical Sciences, Università di Padova, viale G. Colombo 3, 35121 Padova, Italy 3 CNR Institute of Neuroscience, viale G. Colombo 3, 35121 Padova, Italy
* Author to whom correspondence should be addressed.
Received: 10 June 2010 / Revised: 22 June 2010 / Accepted: 2 July 2010 / Published: 6 July 2010
(This article belongs to the Special Issue Phenolics and Polyphenolics)
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Abstract

The regioselective synthesis of several quercetin (3,3’,4’,5,7-pentahydroxy flavone) tetraesters bearing a single free OH on 5-C was achieved in good yield by proper choice of reaction conditions using common esterification procedures. Tetracetylated quercetin with the free OH on 7-C was selectively obtained instead via imidazole-promoted deacylation of the corresponding pentaester. Unambiguous structural characterization of the two isomeric tetraacetyl quercetin derivatives was obtained by combined HSQC and HMBC 2D-NMR analysis. These molecules can be used as starting materials for the regioselective synthesis of other derivatives. High yield syntheses of the natural polyphenol rhamnetin (7-O-methylquercetin) and of the new mitochondriotropic compound 7-(4-triphenylphosphoniumbutyl) quercetin iodide are reported as examples.
Keywords: regioselective alkylation; mitochondrial targeting; quercetin; rhamnetin; polyphenols regioselective alkylation; mitochondrial targeting; quercetin; rhamnetin; polyphenols
This is an open access article distributed under the Creative Commons Attribution License (CC BY 3.0).
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Mattarei, A.; Biasutto, L.; Rastrelli, F.; Garbisa, S.; Marotta, E.; Zoratti, M.; Paradisi, C. Regioselective O-Derivatization of Quercetin via Ester Intermediates. An Improved Synthesis of Rhamnetin and Development of a New Mitochondriotropic Derivative. Molecules 2010, 15, 4722-4736.

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