@article{oai:repo.qst.go.jp:00048085,
 author = {Imai, Kohei and Nakanishi, Ikuo and Ohkubo, Kei and Ohba, Yusuke and Arai, Takuya and Mizuno, Mirei and Fukuzumi, Shunichi and Matsumoto, Kenichiro and Fukuhara, Kiyoshi and 今井 耕平 and 中西 郁夫 and 大久保 敬 and 荒井 卓也 and 松本 謙一郎},
 issue = {29},
 journal = {RSC Advances},
 month = {Mar},
 note = {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 stabiisation of the radical cation intermediate by the electron-donating effect of the methyl group as well as by the planar structure of the molecule.},
 pages = {17968--17979},
 title = {Synthesis of Methylated Quercetin Analogues for Enhancement of Radical-Scavenging Activity},
 volume = {7},
 year = {2017}
}