Synthesis of methylated quercetin analogues for enhancement of radical-scavenging activity

Kohei Imai, Ikuo Nakanishi, Kei Ohkubo, Yusuke Ohba, Takuya Arai, Mirei Mizuno, Shunichi Fukuzumi, Ken ichiro Matsumoto, Kiyoshi Fukuhara

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19 Scopus citations


Three quercetin derivatives with enhanced radical-scavenging activity were designed and synthesised. Because the radical-scavenging reaction of quercetin is known to proceed via an electron transfer from quercetin to radicals, producing the corresponding quercetin radical cation intermediate, the introduction of electron-donating groups into the quercetin molecule is expected to enhance its radical-scavenging activity. Thus, methyl groups were introduced into the catechol moiety in the quercetin molecule at either the 2′- or 5′-position, or both. All three quercetin analogues were found to exhibit higher radical-scavenging activity than the parent quercetin. The activity of 5′-methylquercetin is the highest among the three analogues. The optimised structure of 5′-methylquercetin calculated by density functional theory demonstrated a coplanar structure between the 4H-curomen (AC rings) and catechol (B ring) moieties, while dimethylquercetin and 2′-methylquercetin have a twisted structure between the AC and B rings. These results demonstrate that the highest radical-scavenging activity of 5′-methylquercetin is due to the stabilisation of the radical cation intermediate by the electron-donating effect of the methyl group as well as by the planar structure of the molecule.

Original languageEnglish
Pages (from-to)17968-17979
Number of pages12
JournalRSC Advances
Issue number29
StatePublished - 2017

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