Synthesis of new quinoline scaffolds via a solvent-free fusion method and their anti-microbial properties

Purpose: To develop a robust and simple fusion-based methodology for the synthesis of various 5-(-3nitrophenyl) pyrimido[5,4-c] quinoline-2,4(1H, 3H)-diones (5 - 9). Method: The synthesis involved formation of a Knoevenagel product using barbituric acid and 3-nitrobenzaldehyde which cyclized on fusing with various sulfanilamides in a sealed tube at 170 - 212 degrees C. This resulted in the synthesis of the target quinolines (5 - 9). To evaluate their antibacterial and antiviral properties, the synthesized quinolines were tested against four gram-negative bacterial strains and four poultry viruses. The MIC and IC50 of each active compound were calculated. Results: Data from NMR, mass spectrometry and elemental analysis confirmed the formation of quinoline scaffolds. Antibacterial screening revealed that all the compounds had antibacterial activities. However, the minimum inhibitory concentration (MIC) of compounds 6 - 8 and 9 against Proteus vulgaris and Klebsiella pneumoniae showed that these compounds were more active than the standard drug ampicillin. Antiviral studies and IC50 values showed that compounds 5 - 9 were effective against Newcastle disease virus (NDV) and infectious bursal disease virus (IBDV), while compounds 5, 6 and 8 were active against avian influenza virus subtype H9N2 (AIV); compounds 7 and 8 were active against infectious bronchitis virus (IBV). Conclusion: A simple strategy of fusion of Knoevenagel product with aromatic amines can be used to synthesize highly functionalized quinoline scaffolds which are potential drug candidates for development of new antibacterial and antiviral agents.