Synthesis, antibacterial and antioxidant activities of new 1-alkyl-4-(1-alkyl-4-oxo-1,4-dihydroquinolin-2-yl)pyridinium bromides

New 1-alkyl-4-(1-alkyl-4-oxo-1,4-dihydroquinolin-2-yl)pyridinium bromides (3a–k) were synthesized from 1,4′-diazaflavone [2-pyridin-4-ylquinolin-4(1H)-one] and evaluated for antibacterial and antioxidant activities. A rapid one-pot preparation of 1,4′-diazaflavone (2) was done from 2′-amino substituted chalcone (1) by intramolecular Michael addition using solvent-free microwave heating. New N,N′-dialkyl substituted (C5–C15) 1,4′-diazaflavonium bromides were synthesized from compound 2 with corresponding alkyl halides. Compounds 3a–k were active against six bacteria (MIC: 7.8–500.0 μg/mL). They also showed good antioxidant activities in DPPH scavenging (SC50: 45–133 μg/mL) and ferric reducing/antioxidant power (14–141 μM TEAC) tests. The biological activities decreased as alkyl chain length increased. The reason behind the obvious negative effect of alkyl chain elongation is unclear and requires investigations about the intermolecular interactions of these pyridinium salts with bioassay components. New N,N′-dialkyl substituted 1,4′-diazaflavonium bromides active in antibacterial and antioxidant tests were synthesized. The biological activities decreased as the alkyl chain length increased. [Display omitted] •New N,N′-dialkyl substituted 1,4′-diazaflavonium bromides were synthesized.•All the compounds were active in antibacterial and antioxidant activity tests.•The elongation of alkyl chain has a detrimental effect on the biological activities.