Abstract
Eugenol is the major component of clove essential oil and has demonstrated relevant biological potential with well-known antimicrobial and antioxidant action. Therefore, this work carried out the synthesis, purification, characterization, and evaluation of the antioxidant and antibacterial potential of 19 eugenol derivatives. The derivatives were produced by esterification reactions in the hydroxyl group (−OH) of eugenol with different carboxylic acids and also by addition reactions in the double bond of the allyl group. The derivatives had a promising antibacterial potential, including a lower minimum inhibitory concentration of 500 μg/mL than eugenol (1000 μg/mL). In addition, the derivatives were active against bacterial strains (Escherichia coli, Staphylococcus aureus) that eugenol itself showed no activity, thus increasing the spectrum of antibacterial action. As for the antioxidant activity, it was observed that the derivatives that involved esterification reactions in the hydroxyl group (−OH) of the eugenol molecule’s phenol resulted in a significant reduction of the antioxidant action (IC50 > 100 μg/mL) when compared with the eugenol precursor molecule (IC50 = 4.38 μg/mL). On the other hand, the structural changes located in the double bond affected much more smoothly the capacity of capturing radicals than the starting molecule, also being obtained derivatives with proximal antioxidant capacity (IC50 = 19.30 μg/mL) to commercial standards such as Trolox (IC50 = 16.00 μg/mL).
Highlights
Molecular modification in structures of biologically active substances that occur naturally is one of the main strategies to enhance healthy biological effects, as well as to reduce eventual side effects [1,2,3]
The chemical modification in the double bond, in the case of the derivatives 12, 14, 16, 18, and 19, caused reduction in the antioxidant capacity against the radical DPPH, much lower than that caused by the esterification of the hydroxyl group
IC50 values higher than eugenol, the results reflect the behavior of the substances in vitro; in living biological systems, the antioxidant activity varies, among others, with factors such as the reduction potential in the medium, the displacement capacity of the radical structure formed, the ability to complex transition metals involved in the oxidative process, access to the site of action according to hydrophilicity or lipophilicity, and its partition coefficient [39, 40]
Summary
Molecular modification in structures of biologically active substances that occur naturally is one of the main strategies to enhance healthy biological effects, as well as to reduce eventual side effects [1,2,3]. Evaluation of the antibacterial activity of eugenol derivatives using the inhibition zone technique, measured in millimeter (mm), demonstrates the potential for inhibition of microbial growth by a given substance. Regarding derivatives 10–18 resulting from double bond addition, 10–14, 17, and 18 showed random and insufficient activities relative to eugenol.
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