Synthesis, characterization and antimicrobial activities of novel Ni (II) complex with methyl (E) 2-((3-amino-4-oxo-4H-thieno[3,4-c]chromen-1-yl)diazenyl)-4,5,6,7-tetrahydrobenzo[b]thio phene-3-carboxylate

Background: A coordination compound results from the association of a metal cation and anions or molecules in greater number than that fixed by the normal valence of the cation. Indeed, coordination compounds containing azo ligands are increasingly interesting because of their physical, chemical, photophysical, photochemical and catalytic properties (Amer and Zaniab, 2015). However, the resurgence of antimicrobial resistance encountered with conventional antibiotics vis-à-vis certain microorganisms has prompted the scientific community worldwide to intensify research for new biologically active molecules with new mechanisms of action. In this perspective, we investigate the synthesis of a new metal complex of nickel (II) with ligand methyl (E) 2-((3-amino-4-oxo-4H-thieno[3,4-c]chromen-1-yl)diazenyl)-4,5,6,7-tetrahydrobenzo[b]thio phene-3-carboxylate with the aim to discovering new coordination compounds with antimicrobial activities. Methodology: The required starting material was synthesized via the coupling of the hydrogen sulfate of 3-(methoxycarbonyl)-4,5,6,7-tetrahydrobenzo[b]thiophene-2-diazonium with 3-amino-4H-thieno[3,4-c][1]benzopyran-4-one at temperature between 0-5 °C. Metal chelate complex was obtained in good yield in ethanol by reacting ligand with nickel chloride hexahydrate salt NiCl2.6H2O in a molar ratio 1:2 (metal:ligand) at reflux for 6 hours. The in vitro antimicrobial activity of the synthesized compound have been evaluated against four bacterial strains (Pseudomonas aeruginosa 01, Staphylococcus aureus 56, Escherisha coli ATCC 8739, Staphylococcus aureus ATCC 25923) using Levofloxacine hemihydrate as a standard drug. The minimum inhibitory concentration (MIC) and minimum bactericidal concentration (MBC) values of the synthesized compounds were determined by broth micro-dilution method as described earlier (Newton et al., 2002). The synthesized compounds (ligand and complex) were characterized by Infrared spectroscopy, UV and Mass Spectrometry analysis. Results: Biological results showed that ligand with MIC value of 256 μg/mL had a moderate activity (CMI = 256 µg/ml) on Staphylococcus aureus ATCC 25923, while complex with CMI values between 8 and 256 µg/ml was more active with a CMI = 8 µg/ml on Staphylococcus aureus ATCC 25923. However we found that, the metal complex displayed significant antimicrobial activity compared to the free ligand. Conclusion: The main objective of this study was to evaluate the impact of complexation on antimicrobial activities of an organic ligand. However, it emerges from this study that the metal complex displayed significant antimicrobial activity (MIC = 8–256 μg/mL) compared to the free ligand (MIC = 256 μg/mL). Based on these results, we can say that our findings are promising.

Keywords: Synthesis; Antimicrobial Activities; 2-aminothiophene; Coordination Compounds