Design, microwave-assisted synthesis, biological evaluation, molecular docking and ADME studies of pyrrole-based hydrazide-hydrazones as potential antioxidant agents

In this study, one novel N-pyrrolyl carboxylic acid (3), the corresponding N-pyrrolyl hydrazide (5), and four new hydrazide-hydrazones (5a-d) bearing electron donating moieties were designed, synthesized, and fully elucidated by 1H NMR, FT-IR, and HRMS. The hydrazide-hydrazones were produced in five steps, which were optimized by applying microwave heating. The microwave-assisted synthesis significantly decreased the reaction times and increased the yields of the title molecules. In addition, all novel compounds were assessed for their radical scavenging properties by employing DPPH and ABTS assays. The most promising agent was obtained after condensation of the title hydrazide (5) with a 3,5-dimetoxy-4-hydroxybenzaldehyde (5d). The latter compound showed better antioxidant properties than Trolox (6-hydroxy-2,5,7,8-tetramethylchroman-2-carboxylic acid) and could serve as a prominent lead structure for future optimization as an antioxidant agent. A possible binding conformation of 5d in the active site of NADPH oxidase was also identified through molecular docking simulations. Analysis of the major interactions showed the importance of the hydroxyl moiety for the antioxidant activity. Finally, the virtual calculations of the ADME properties of the synthesized compounds displayed good drug-like properties. Overall, an optimized synthetic protocol through MW irradiation was employed. The newly synthesized ethyl (E)-5-(4-bromophenyl)-1-(1-(2-(4-hydroxy-3,5-dimethoxybenzylidene)hydrazineyl)-3-(1H-indol-3-yl)-1-oxopropan-2-yl)-2-methyl-1H-pyrrole-3-carboxylate (5d) was found to possess the most prominent radical-scavenging capacity, which identifies it as a promising lead compound for the development of novel antioxidants.