Presentation Synthesis and Radical Scavenging Activity of C-Methylated Quercetin Analog

Imai, Kohei  ,  Nakanishi, Ikuo  ,  Ohba, Yusuke  ,  Matsumoto, Kenichiro  ,  Fukuhara, Kiyoshi

To feature the radical scavenging mechanism is of considerable importance in synthesis of novel antioxidant agent with strong radical scavenging activity. There are two mechanisms for the radical scavenging reactions of phenolic antioxidant agent. The radical scavenging mechanisms are either a one-step hydrogen atom transfer from the phenolic hydroxyl group or an electron transfer followed by a proton transfer. It is known that flavonoid such as catechin and quercetin scavenges free radicals by electron transfer reaction. The electron transfer reaction is performed via concomitant formation of the radical cation intermediate (ArOH•+). Thus, the radical scavenging activity is enhanced when the ArOH•+ is stabilized. Previously, we have developed antioxidant analogue that introduced an electron-donating group for stabilization of ArOH•+. Dimethyl catechin analogue, in which two methyl groups as electron-donor was introduced into (+)-catechin, exhibited 28-fold more potent radical scavenging activity than (+)-catechin. In this study, we developed quercetin analogue with methyl group at catechol. Synthesis of quercetin analogue was obtained by oxidizing the taxifolin that was synthetized by cyclization reaction of chalcone. The chalcone was obtained by the condensation of 2,4,6-tri-MOM phloracetophenone with aldehyde derivative which hydroxyl group of c-methylated catechol is protected with benzyl group. The radical scavenging activity of dimethyl quercetin 1, in which both positions ortho to the catechol hydroxyl groups was about 191-fold than quecetin.

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