Palladium–Catalyzed Sonogashira Synthesis of Mono- and Bis-Alkynylated Derivatives of Quinoline-5, 8-Dione and their Antimicrobial Activity
The synthesis of five mono- and five bis-alkynylated derivatives of quinoline-5,8-diones is reported. The intermediate 6,7-dibromoquinoline-5,8-dione was obtained by nitrosation of 8-hydroxyquinoline, followed by reduction and subsequent bromination and oxidation. The coupling reaction of 6,7-dibromoquinoline-5,8-dione via palladium-catalyzed Sonogashira cross-coupling gave the alkynylated products. The chemical structures of the products were confirmed using spectroscopic methods which include UV-visible spectrophotometry, Fourier Transform-Infrared (FT-IR) spectroscopy, 1H and 13C-NMR spectroscopy. The antimicrobial properties of the synthesized products were determined on Escherichia Coli 1, Escherichia Coli 12, Klebsiella Pneumonia, Pseudomonas aeruoginosa and Staphylococcus aureus using the agar-diffusion method. Results showed significant improvement in antibacterial activities compared with ampicillin and gentamycin.