Baschieri Andrea, Pulvirenti Luana, Muccilli Vera, Amorati Riccardo, Tringali Corrado
Department of Chemistry "G. Ciamician", University of Bologna, Via S. Giacomo 11, 40126 Bologna, Italy.
Department of Chemical Sciences, University of Catania, Viale A. Doria 6, I-95125 Catania, Italy.
Org Biomol Chem. 2017 Jul 26;15(29):6177-6184. doi: 10.1039/c7ob01195d.
Chemical modification of magnolol, an uncommon dimeric neolignan contained in Magnolia genus trees, provides a unique array of polyphenols having interesting biological activity potentially related to radical scavenging. The chain-breaking antioxidant activity of four new hydroxylated and methoxylated magnolol derivatives was explored by experimental and computational methods. The measurement of the rate constant of the reaction with ROO˙ radicals (k) in an apolar solvent showed that the introduction of hydroxyl groups ortho to the phenolic OH in magnolol increased the k value, being 2.4 × 10 M s and 3.3 × 10 M s for the mono and the dihydroxy derivatives respectively (k of magnolol is 6.1 × 10 M s). The di-methoxylated derivative is less reactive than magnolol (k = 1.1 × 10 M s), while the insertion of both hydroxyl and methoxyl groups showed no effect (6.0 × 10 M s). Infrared spectroscopy and theoretical calculations allowed a rationalization of these results and pointed out the crucial role of intramolecular H-bonds. We also show that a correct estimation of the rate constant of the reaction with ROO˙ radicals, by using BDE(OH) calculations, requires that the geometry of the radical is as close as possible to that of the parent phenol.
厚朴酚是木兰属树木中含有的一种罕见的二聚新木脂素，对其进行化学修饰可得到一系列独特的多酚，这些多酚具有与自由基清除潜在相关的有趣生物活性。通过实验和计算方法研究了四种新的羟基化和甲氧基化厚朴酚衍生物的断链抗氧化活性。在非极性溶剂中与ROO˙自由基反应的速率常数（k）的测定表明，在厚朴酚中酚羟基邻位引入羟基会增加k值，单羟基衍生物和二羟基衍生物的k值分别为2.4×10 M s和3.3×10 M s（厚朴酚的k值为6.1×10 M s）。二甲氧基化衍生物的反应活性低于厚朴酚（k = 1.1×10 M s），而同时引入羟基和甲氧基则没有影响（6.0×10 M s）。红外光谱和理论计算使这些结果得以合理化，并指出了分子内氢键的关键作用。我们还表明，通过使用BDE(OH)计算来正确估计与ROO˙自由基反应的速率常数，需要自由基的几何结构尽可能接近母体苯酚的几何结构。
