Evaluation of the antioxidant activity of semi-synthetic derivatives of eugenol.

Eugenol, obtained from clove oil (Eugenia caryophyllata), possess several biological activities. It is anti-inflammatory, analgesic, anesthesic, antipyretic, anti-platelet, anticonvulsant, antioxidant, antibacterial, antidepressant, antifungal and antiviral. Phenolic derivatives, as eugenol, are a major class of natural compounds with antioxidant activity, and they have the ability to neutralize free radicals by transfer of a single electron. The antioxidant activities of eugenol have already been proven. From this perspective testing a series of planned structural derivatives of eugenol helped advance the search for optimization and consequent increase of the potency of these biological activities. In an attempt to increase structural variability, sixteen compounds were synthesized by O-acylation and O-alkylation of the phenolic hydroxyl group. Antioxidant activity capacity was based on the capture of DPPH radical (2,2-diphenyl-1-picryl-hydrazyl), ABTS radical 2,2'-azino-bis(3- ethylbenzothiazoline-6-sulphonic acid), besides evaluated the antioxidant capacity of these compounds in biological systems using of TBARS (thiobarbituric acid-reactive species), total sulfhydryl and carbonyl content. Changes at position 1 of the eugenol are important, differences in size and features of the carbon chain (aliphatic or aromatic) could provide information on the required characteristics to increase activity. Four derivatives presented an efficient concentration able to decrease 50% of the DPPH radical (EC50)<100 μM, which has a good potential antioxidant as a free radical scavenger. Three of these compounds also showed reduction of ABTS radical. Eugenol derivatives reduce lipid peroxidation, protein oxidative damage by carbonyl formation and preserves total thiol content in cerebral cortex. But in liver, they were less effective. Our results suggest that these molecules are promising antioxidants agents.Sem bolsaO eugenol, obtido a partir de óleo de cravo (Eugenia caryophyllata), apresenta várias atividades biológicas comprovadas, tais como anti-inflamatória, analgésica, anestésica, antipirética, antiplaquetária, anticonvulsivante, antioxidante, antibacteriana, antidepressiva, antifúngica e antiviral. O eugenol é um derivado fenólico, que apresenta capacidade de neutralizar radicais livres pela transferência de um único elétron. A atividade antioxidante do eugenol já foi comprovada, nesse panorama, o teste de uma série de derivados estruturais planejados do eugenol pode favorecer o avanço na busca da otimização e consequente aumento da potência desta atividade. Na procura por aumentar a variabilidade estrutural, dezesseis compostos foram sintetizados por O-acilação e O-alquilação de hidroxila fenólica. A avaliação da atividade antioxidante baseou-se na capacidade de captura dos radicais DPPH (2,2-difenil-1-picril-hidrazil) e ABTS (2,2'-azino-bis (ácido 3- etilbenzotiazolino-6-sulfónico)). Além disso, avaliou-se a capacidade antioxidante desses compostos em sistemas biológicos, utilizando a medida de espécies reativas do ácido tiobarbitúrico (TBARS), conteúdo de tióis totais e conteúdo de carbonilas. Observou-se que mudanças na posição 1 do eugenol são importantes, as diferenças no tamanho e as características da cadeia de carbono (alifático ou aromático) pode permitir conhecer as características requeridas para aumentar a atividade. Quatro derivados apresentaram uma concentração eficiente para diminuir 50% do radical DPPH (EC50)