Regioselective O-derivatization of quercetin via ester intermediates. An improved synthesis of rhamnetin and development of a new mitochondriotropic derivative.
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.
Mattarei
Andrea
A
Department of Chemical Sciences, Università di Padova, via Marzolo 1, 35131 Padova, Italy.
Biasutto
Lucia
L
Rastrelli
Federico
F
Garbisa
Spiridione
S
Marotta
Ester
E
Zoratti
Mario
M
Paradisi
Cristina
C
D000818:Animals; D004952:Esters / Q000737:chemistry; D006801:Humans; D008928:Mitochondria / Q000378:metabolism*; D015394:Molecular Structure; D011794:Quercetin / Q000031:analogs & derivatives* / Q000138:chemical synthesis / Q000737:chemistry
D004952:Esters; C063423:rhamnetin; D011794:Quercetin