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Milošević MD, Marinković AD, Petrović P, Klaus A, Nikolić MG, Prlainović NŽ, Cvijetić IN. Synthesis, characterization and SAR studies of bis(imino)pyridines as antioxidants, acetylcholinesterase inhibitors and antimicrobial agents. Bioorg Chem 2020; 102:104073. [PMID: 32693308 DOI: 10.1016/j.bioorg.2020.104073] [Citation(s) in RCA: 6] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/13/2020] [Revised: 05/02/2020] [Accepted: 06/30/2020] [Indexed: 12/17/2022]
Abstract
In this study we synthesized a series of sixteen bis(imino)pyridines (BIPs) starting from 2,6-diaminopyridine and various aromatic aldehydes, and evaluated their antioxidant, antibacterial, antifungal and acetylcholinesterase (AChE) inhibitory activity. The chemical structures were elucidated by FTIR, elemental analysis, ESR and HRMS. 1H and 13C NMR spectra couldn't be acquired due to the formation of stable, carbon-centered radical cations in a solution, as confirmed by ESR spectroscopy and DFT calculations. The in vitro antioxidant potency was evaluated using four assays: free radical scavenging activity (DPPH and ABTS), reducing power and total antioxidant capacity assay. BIPs demonstrated excellent antioxidant properties, and two derivatives proved to be more potent than reference antioxidants (ascorbic acid and Trolox) in all assays. DFT calculations on ωB97XD/6-311++g(d,p) level of theory provided valuable insights into the radical scavenging mechanism of BIPs. For hydroxyl-substituted BIPs, hydrogen atom transfer (HAT) is a predominant mechanism, while the single electron transfer coupled with proton transfer (SET-PT) governs the antioxidant activity of other derivatives. Intramolecular hydrogen bonding (IHB) plays an important role in the mechanism of antioxidant activity as revealed by noncovalent interaction analysis and rotational barrier calculations. The spin density of radical cations is localized on carbon atoms of a pyridine ring, which corroborates with g-factors and multiplicity obtained from ESR analysis. The most potent BIP exhibited moderate inhibitory activity toward AChE (IC50 = 20 ± 4 μM), while molecular docking suggested binding at the peripheral anionic site of AChE with the MMFF94 binding enthalpy of -43.4 kcal/mol. Moderate in vitro antimicrobial activity of BIPs have been determined against several pathogenic bacterial strains: Pseudomonas aeruginosa, Escherichia coli, Enterococcus faecalis, Staphylococcus aureus and clinical isolate of methicillin resistant S. aureus (MRSA). The antifungal activity of BIPs toward Candida albicans was also confirmed. The similarity ensemble approach combined with molecular docking suggested leucyl aminopeptidase as the probable antimicrobial target for the three most potent BIP derivatives.
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Affiliation(s)
- Milena D Milošević
- SI Institute of Chemistry, Technology and Metallurgy, National Institute, Department of Ecology and Techoeconomic, University of Belgrade, Njegoševa 12, 11000 Belgrade, Serbia
| | - Aleksandar D Marinković
- Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia
| | - Predrag Petrović
- Innovation Centre of Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia
| | - Anita Klaus
- Department for Industrial Microbiology, Institute for Food Technology and Biochemistry, University of Belgrade-Faculty of Agriculture, Nemanjina 6, 11080 Belgrade, Serbia
| | - Milica G Nikolić
- Faculty of Sciences and Mathematics, Department of Chemistry, University of Niš, Višegradska 33, 18000 Niš, Serbia
| | - Nevena Ž Prlainović
- Faculty of Technology and Metallurgy, University of Belgrade, Karnegijeva 4, 11000 Belgrade, Serbia
| | - Ilija N Cvijetić
- Innovation Center of the Faculty of Chemistry, University of Belgrade, Studentski trg 12-16, 11000 Belgrade, Serbia.
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