Synthesis and antimicrobial activity of methoxy azachalcones and N-alkyl substituted methoxy azachalconium bromides

In this study, 18 new N-octyl, N-decyl, and N-dodecyl substituted o-, m-, and p-methoxy (E)-3- and 4-azachalcones, {4- or 3-[(1E)-3-(4-, 3-, or 2-methoxyphenyl)-3-oxoprop-1-en-1-yl]-1-alkyl (C8,10,12) pyridinium bromides} (1a-6a, 1b-1b, and 1c-6c), and 4 new o-, and m-methoxy (E)-3- and 4-azachalcones (2, 3, 5, and 6) were synthesized and tested for antimicrobial activities against Escherichia coli, Yersinia pseudotuberculosis, Enterobacter aerogenes, Pseudomonas aeruginosa, Staphylococcus aureus, Enterococcus faecalis, Bacillus cereus, and Candida albicans. N-Alkyl substituted azachalconium bromides showed good antimicrobial activity against all tested microorganisms with minimal inhibitory concentration (MIC) values in the range of 0.42-58.7 m g/mL in most cases. Nonalkylated compounds 1-9 were not as effective as the alkylated compounds. They showed only antimicrobial activity against gram-positive bacteria and yeast in the range of 1.77-123.7 m g/mL. The optimum length of the alkyl chain for better activity is situated with 12 carbon atoms in the series of compounds 1a-c, 2a-c, 3a-c, 4a-c, 5a-c, and 6a-c. N-Alkyl derivatives of m-methoxy (E)-3-azachalcone (4a-c, 5a-c, and 6a-c) showed better activity in comparison to those of o- and p-methoxy (E)-4-azachalcones (1a-c, 2a-c, and 3a-c).