Quercetin (=2-(3,4-Dihydroxyphenyl)-3,5,7-trihydroxy-4H-1- benzopyran-4-one) Glycosides and Sulfates: Chemical Synthesis, Complexation, and Antioxidant Properties

Glycosides, acylated glycosides, and sulfates of quercetin (=3,3′,4′,5,7-pentahydroxyflavone; 1), which is, together with its derivatives, among the most common polyphenols found in plants and in the human diet, were prepared and quantitatively investigated for their ability to bind metal ions (AlIII, FeII, FeIII), enhance and vary natural colours (anthocyanin copigmentation), and trap potentially damaging radicals (antioxidant activity).