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. 2011 Nov 21;16(11):9636-50.
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

Mohamed Moalin  1 , Gino P F van Strijdonck, Maud Beckers, Geja Hagemen, Paul Borm, Aalt Bast, Guido R M M Haenen
Affiliations

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

Mohamed Moalin et al. Molecules. .

Abstract

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.

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Figures

Scheme 1
Scheme 1
Synthesis of the methylated derivatives of quercetin.
Figure 1
Figure 1
Three dimensional structure of rutin (R1), illustrating the dihedral angle (φ) of 38° between the plane of the AC-ring and that of the B-ring.
See this image and copyright information in PMC

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