Abstract
Purpose: To develop a robust and simple fusion-based methodology for the synthesis of various 5-(-3- nitrophenyl) 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°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 IC 50 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 IC 50 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. Keywords: Quinoline scaffolds, Barbituric acid, Knoevenagel condensation, Antiviral, Antibacterial
Highlights
INTRODUCTIONTheir heterocyclic scaffold is a fused product of benzene and pyridine (benzopyridine)
All selected viruses i.e. Newcastle disease virus (NDV), infectious bronchitis virus (IBV), BDV and avian influenza virus subtype H9N2 (AIV) H9N2 strains were subjected to propagation in chicken embryonated (CE) eggs (9 -11 day-old) and incubated in egg incubator at 37 °C
After 48 h of incubation, the allantoic fluids of the eggs were tested for HA, and subjected to indirect hemagglutination (IHA) test [26]
Summary
Their heterocyclic scaffold is a fused product of benzene and pyridine (benzopyridine). The quinoline scaffold is considered a privileged medicinal motif, based on the fact that it is abundant in a number of natural products like alkaloids such as quinine, camptothecin and cinchonidine [6,7,8]. Quinolines have been used as basic ingredients for the production of different biocides, vermicides, alkaloids, fungicides, rubber chemicals and flavoring agents [22]. Starting with the Knoevenagel product of barbituric acid and aryl aldehydes, further cyclization with various sulfanilamides resulted in the formation of quinoline derivatives. In these reactions, fusion played a vital role. Four different viruses were propagated in chicken embryonated eggs at Islamia University of Bahawalpur, Bahawalpur, Pakistan
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