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Eco-Friendly Methodology to Prepare N-Heterocycles Related to Dihydropyridines: Microwave-Assisted Synthesis of Alkyl 4-Arylsubstituted-6-chloro-5-formyl-2-methyl-1,4-dihydropyridine-3-carboxylate and 4-Arylsubstituted-4,7-dihydrofuro[3,4-b]pyridine-2,5(1H,3H)-dione
Molecules 2011, 16(11), 9636-9650; doi:10.3390/molecules16119636

A Planar Conformation and the Hydroxyl Groups in the B and C Rings Play a Pivotal Role in the Antioxidant Capacity of Quercetin and Quercetin Derivatives

1,2,* , 2, 2, 1, 2, 1 and 1
1 Department of Toxicology, Maastricht University, 6200 MD Maastricht, The Netherlands 2 Zuydlab, Hogeschool Zuyd, 6400 AN Heerlen, The Netherlands
* Author to whom correspondence should be addressed.
Received: 29 September 2011 / Revised: 11 November 2011 / Accepted: 14 November 2011 / Published: 21 November 2011
(This article belongs to the Section Medicinal Chemistry)
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The polyphenol quercetin (Q) that has a high antioxidant capacity is a lead compound in the design of antioxidants. We investigated the possibility of modifying quercetin while retaining its antioxidant capacity as much as possible. To this end, the antioxidant capacities of Q, rutin, monohydroxyethyl rutinoside (monoHER) and a series of synthesized methylated Q derivatives were determined. The results confirm that the electron donating effect of the hydroxyl groups is essential. It was also found that the relatively planar structure of Q needs to be conserved. This planar conformation enables the distribution of the electron donating effect through the large conjugated π-system over the entire molecule. This is essential for the cooperation between the electron donating groups. Based on the activity of the compounds tested, it was concluded that structural modification at the 5 or 7 position is the most optimal to retain most of the antioxidant capacity of Q. This was confirmed by synthesizing and testing Q5OMe (Q6) and Q7OMe (Q7) that indeed displayed antioxidant capacities closest to Q.
Keywords: antioxidant capacity; flavonoids; methylation; quercetin; rutin antioxidant capacity; flavonoids; methylation; quercetin; rutin
This is an open access article distributed under the Creative Commons Attribution License (CC BY) which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited.

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Moalin, M.; Strijdonck, G.P.F.; Beckers, M.; Hagemen, G.J.; Borm, P.J.; Bast, A.; Haenen, G.R.M.M. A Planar Conformation and the Hydroxyl Groups in the B and C Rings Play a Pivotal Role in the Antioxidant Capacity of Quercetin and Quercetin Derivatives. Molecules 2011, 16, 9636-9650.

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