Abstract
A series of heterocyclic compounds bearing the well-known free radical scavenging 3,4,5-trimethoxybenzyloxy group, was synthesized. The key compound 4-(3,4,5-trimethoxybenzyl-oxy)benzohydrazide was converted into thiosemicarbazide derivatives, which were subsequently cyclized with NaOH to provide 1,2,4-triazole derivatives. Alternative treatment of the acid hydrazide with carbon disulfide in the presence of KOH led to the corresponding 1,3,4-oxadiazole and various alkylated derivatives. The newly synthesized compounds were purified and the structures of the products were elucidated and confirmed on the basis of their analytical and spectral data. Their antioxidant activities were evaluated using 2,2-diphenyl-1-picrylhydrazyl (DPPH•) and Ferric Reducing Antioxidant Power (FRAP) assays. The thiosemicarbazide derivatives were highly active in both antioxidant assays with the lowest IC50 value for DPPH radical scavenging. Theoretical calculations based on density functional theory (DFT) were performed to understand the relative importance of NH, SH and CH hydrogens on the radical scavenging activities of these compounds.
Highlights
Reactive oxygen species (ROS) is a collective term for different reactive molecules and free radicals derived from molecular oxygen, which are continuously produced as byproducts of mitochondrial electron transport of cellular respiration in the body
This study reports the preparation of new heterocyclic compounds and their analogs bearing the 3,4,5-trimethoxybenzyl moiety and evaluates the differences between their antioxidant activities
Electron withdrawing substituents enhanced the antioxidant activities in thiosemicarbazides and para-substituted derivatives were more active than ortho ones
Summary
Reactive oxygen species (ROS) is a collective term for different reactive molecules and free radicals derived from molecular oxygen, which are continuously produced as byproducts of mitochondrial electron transport of cellular respiration in the body. The most common ROS include superoxide anion (O2 ́ ), hydrogen peroxide (H2 O2 ), hydroxyl radical (HO‚ ) and singlet oxygen (1 O2 ) [1]. These species are unstable and react with other molecules to achieve stability. The pro-oxidative state when ROS level exceeds the capability of defense mechanisms is often referred to as “oxidative stress” This poses a threat to cells, causing damage to DNA, lipids and proteins, potentially leading to disease conditions such as cell ageing, cardiovascular diseases and cancerous tumor growth [2,3]. Synthetic compounds are widely studied for their antioxidant activities using different methodologies [5,6]
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