Synthesis of Some Novel Quinolinols with In-vitro Antimicrobial, and Antioxidant Activity

Background: Amongst the quinolone core structures, 8-hydroxyquinoline (8-HQ or quinolinol) stands out as the greatest frequently used therapeutic moietiy. This includes the most critical molecules in medicinal chemistry. Quinolinol remains a broad-spectrum ligand capable of chelating to a large number of metal ions. Methods: The synthesized quinolinols Mannich bases were screened for their in vitro antimicrobial activity against Staphylococcus aureus (ATTCC 6538), Escherichia coli (ATTCC 7839), Klebsiella pneumonia (ATCC10131). The antifungal activity of the prepared compounds was assessed against Candida albicans (10231), Aspergillus niger and Penicillium sp. The antioxidant activity of the established compounds was assessed by means of α, α-diphenyl-β-picrylhydrazyl (DPPH) free radical scavenging method. Results: The antimicrobial outcomes indicated that all the synthesized compounds excluding 5 and 9b displayed reasonable antibacterial activity against Staphylococcus aureus (ATTCC 6538) and Escherichia coli (ATTCC 7839) with an inhibition zones ranging from 13 to 23 mm. However, in the case of Klebsiella pneumonia (ATCC10131) only compound 6 did not show any activity. The results also indicated that compounds 2b and 3 were the most potent antibacterial compounds against the verified strains with minimum inhibitory concentration (MIC) values ranging from 0.05 to 0.5mg/ml. In the antifungal assay, all compounds showed good activity against Candida albicans (10231) except compounds 5 and 9b. However, in the case of Aspergillus niger and Penicillium sp. only compounds 2b and 3 showed good activity. In the antifungal assay, MIC values for compounds 2b and 3 ranged from 0.25 to 2.5 mg/ml against the specified fungal strains. The antioxidant activity was assessed using the DPPH scavenging activity method. The results indicated that 2b was the most active among all tested compounds, with almost double the antioxidant activity as compared with that of trolox (positive control). Conclusion: In this work, we describe the synthesis of new Mannich bases comprising 8-HQ (1) and its derivative (8). The resulted Mannich bases of type 2 were used in transamination reactions with hydrazine and hydrazine derivatives. The structures of the newly synthesized Mannich bases were confirmed based on the NMR spectroscopic data and elemental analysis. Antimicrobial and antioxidant activities were also assessed.