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

机译：合成甲基化槲皮素类似物以增强自由基清除活性

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摘要

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.
机译：设计并合成了三种具有增强的自由基清除活性的槲皮素衍生物。因为已知槲皮素的自由基清除反应是通过电子从槲皮素转移至自由基进行的，从而产生相应的槲皮素自由基阳离子中间体，所以预期将供电子基团引入槲皮素分子中会增强其清除自由基的活性。因此，甲基被引入到槲皮素分子中2'-或5'-位置或两者的邻苯二酚部分中。发现所有三种槲皮素类似物均比亲本槲皮素具有更高的自由基清除活性。在这三个类似物中，5'-甲基槲皮素的活性最高。通过密度泛函理论计算得到的5'-甲基槲皮素的优化结构表明4'H'-curmomen（AC环）和邻苯二酚（B环）部分是共面结构，而二甲基槲皮素和2'-甲基槲皮素具有AC和B环之间的扭曲结构。这些结果证明5'-甲基槲皮素的最高自由基清除活性是由于通过甲基的供电子作用以及分子的平面结构使自由基阳离子中间体稳定。

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