Electrochemical transformations and evaluation of antioxidant activity of some Schiff bases containing ferrocenyl and (thio‐)phenol, catechol fragments

Electrochemical transformations and antioxidant activity of some Schiff bases 1–5 containing ferrocenyl group and (thio-)phenol, catechol fragments were investigated. Compounds under investigation are: 2-(ferrocenylmethylene)amino)phenol (1), 2-((ferrocenylmethylene)amino)-4,6-di-tert-butylphenol (2), 2-((ferrocenylmethylene)amino)-thiophenol (3), 3-((ferrocenylmethylene)hydrazonomethyl)-4,6-di-tert-butylcatechol (4) and 2-((3,5-di-tert-butyl-4-hydroxybenzylidene)amino)thiophenol (5). In a case of compounds 1–3 it has shown that the sequence of electrochemical transformations leads to the products of intramolecular cyclization – 2-ferrocenylbenzoxazole (benzothiazole). o-Quinone formation occurs during the electrochemical oxidation of catechol-ferrocene 4 at the first anode stage. Electrochemical oxidation of the redox-active fragments in Schiff bases 1–4 can be achieved indirectly at a lower potential corresponding to the oxidation of ferrocenyl moiety, consequently these substances can reveal more pronounced antioxidant properties. The antioxidant activities of the compounds were evaluated using 2,2′-diphenyl-1-picrylhydrazyl radical (DPPH) assay, the reaction of 2,2′-azobis(2-amidinopropane hydrochloride) (AAPH) induced glutathione depletion (GSH), the oxidative damage of the DNA, the process of lipid peroxidation of rat (Wistar) brain homogenates in vitro. The compounds 1–4 in the antioxidant assays show effectiveness comparable with standard antioxidants (vitamin E, Trolox) and in some parameters superior to them. In the reaction of AAPH with the glutathione compounds 2–5 have a more pronounced protective activity than Trolox. Compounds 1–5 inhibit AAPH induced oxidation damage of the DNA. The more effective inhibitors of the lipid peroxidation process in vitro are molecules containing the bulky tert-butyl groups: 2 and 4 and Schiff base 3.