Influence of the Environment on the Protective Effects of Guaiacol Derivatives against Oxidative Stress: Mechanisms, Kinetics, and Relative Antioxidant Activity

Abstract

The peroxyl radical scavenging activity of five guaiacol derivatives (GD) has been studied in nonpolar and aqueous solutions, using the density functional theory. The studied GD are guaiacol, vanillin, vanillic alcohol, vanillic acid, and eugenol. It was found that the environment plays an important role in the peroxyl scavenging activity of these compounds. They were all found to react faster in aqueous solution than in nonpolar media. The order of reactivity in nonpolar environments was found to be vanillic alcohol > eugenol > guaiacol > vanillin > vanillic acid, while, in aqueous solution, at physiological pH, it becomes vanillic acid > vanillic alcohol > guaiacol ≈ eugenol > vanillin. It was also found that in aqueous solution as the pH increases so does the reactivity of GD toward peroxyl radicals. The environment also has important effects on the relative importance of the hydrogen transfer (HT) and the sequential proton electron transfer (SPET) mechanisms, which are the ones relevant to the peroxyl radical scavenging activity of GD. The HT from the phenolic OH was identified as the main scavenging process in nonpolar media, and in aqueous solution at pH ≤ 4. On the other hand, SPET is proposed to be the one contributing the most to the overall peroxyl scavenging activity of GD in aqueous solution at pH ≥ 6.

Kinetic Study of the Radical Scavenging of Capsaicin in Homogeneous Solutions and Aqueous Triton X‐100 Micellar Suspensions

“…Then, we investigated the rate constant of the phenolate anion form of CAP with radicals using the p K a value and molar fraction of CAP, indicating that the phenolate anion form of CAP reacts with radicals about 6 times as fast as the undeprotonated form of CAP. Furthermore, the effects observed from these results are general evidence for the proposal that SPLET from phenolic hydrogen of CAP is proposed to be the mechanism contributing to the scavenging of radicals in aqueous micellar suspensions at pH > 9.0 (Galano and others ). We propose that CAP could be useful substances with high antioxidant activity in alkali solutions.…”

The Molecular Basis for the Pharmacokinetics and Pharmacodynamics of Curcumin and Its Metabolites in Relation to Cancer

“…Several of the characterized curcumin catabolites are antioxidants, including vanillin (Sawa et al, 1999;Maurya et al, 2007;Shyamala et al, 2007;Chou et al, 2010;Makni et al, 2011;Tai et al, 2011;Galano et al, 2012), vanillic acid (Sawa et al, 1999;Shyamala et al, 2007;Chou et al, 2010;Kumar et al, 2011;Prince et al, 2011;Stanely Mainzen Prince et al, 2011;Galano et al, 2012), ferulic acid (Scott et al, 1993;Kaul and Khanduja, 1998;Kanski et al, 2002;Kikuzaki et al, 2002;Hirata et al, 2005;Srinivasan et al, 2007;Jung et al, 2009), and 4-vinylguaiacol (Tressl et al, 1976). These catabolites may therefore elicit anticancer effects in various phases of cancer biology.…”

Regioselektive o‐Hydroxylierung monosubstituierter Benzole mit P450 BM3

“…[1b,c] Isomerenreine Verbindungen für die Arzneimittelsynthese werden zumeist aufwendig aufgereinigt. [5] Guaiacol kann aus Pflanzen isoliert oder synthetisch aus Catechol mit NaOH und weiteren korrosiven Reagentien hergestellt werden. [5] Guaiacol kann aus Pflanzen isoliert oder synthetisch aus Catechol mit NaOH und weiteren korrosiven Reagentien hergestellt werden.…”

“…[1e, 4] Guaiacol und dessen Derivate Vanillin und Eugenol werden als Duft-und Geschmacksstoffe sowie als Antioxidantien in der Krebstherapie verwendet, darüber hinaus auch in der Behandlung kardiovaskulärer Erkrankungen sowie von Parkinson und Alzheimer. [5] Guaiacol kann aus Pflanzen isoliert oder synthetisch aus Catechol mit NaOH und weiteren korrosiven Reagentien hergestellt werden. [6] Die direkte chemische Hydroxylierung von substituierten Benzolen ist synthetisch unattraktiv, da Reaktionen an nicht-aktivierten C-Atomen zumeist unselektiv sind [7] und nicht am aromatischen Ring stattfinden.…”