Selenium-containing polyphenols: antioxidant properties

• Autor(a) principal: Farinha, David Fernandes
• Data de Publicação: 2016
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10362/21502
• topic: Selenium; Organoselenium; Selenation; Antioxidant; Domínio/Área Científica::Engenharia e Tecnologia::Engenharia Química

Interest in organic compounds containing selenium in its composition has grown, mainly due to its antioxidant and anti-carcinogenic potential. For that reason, introducing a selenium atom in molecules where it is not present initially is viewed as a promising technique in order to attain more powerful and versatile antioxidants with possible biomedical purposes. The present work was aimed at introducing a selenium atom in different molecular structures, in order to obtain several compounds able to be tested for their potential antioxidant activity. As such, a methodology based on microwave synthesis was initially considered for the preparation of selenated purines. However, reaction conditions did not allowed to obtain products able to be analysed. A new synthetic methodology was then selected, based on the direct selenation of stilbenes using selenium powder, which afforded the desired benzoselenohene compounds in low yields, for most cases. These were structurally completely characterized, namely by the Nuclear Magnetic Resonance and Mass Spectrometry techniques. In order to confirm the desired increase of antioxidant activity, synthesized compounds were tested for their free radical scavenging and GPx-like activities. For the first test, of the three tested compounds, 31a and 36 presented improvements regarding the H-atom transfer activity, when compared to their respective starting materials. O-H bond dissociation energy (BDE) was computationally calculated. Results show that selenation for both compounds 35 and 36 leads to a decrease in O-H bond energy for all the OH groups present in those compounds. Compound 31a presents a reduction of the O-H bond energy for the OH group at position R1, structurally closer to the new selenium atom, and an O-H bond energy increase for the OH groups at positions R3 and R4’. For the second test, all four synthesized compounds showed a significant increase in the reduction of hydrogen peroxide, when compared with the parent stilbene. Results presented in this work are promising, and indicate that the antioxidant activity of stilbenes is boosted upon selenation, making this a technique to consider when developing new drugs for therapeutic purposes.