Synthesis and Antimicrobial Evaluation of Benzimidazolyl Pyrimido [4, 5- b] Quinolinones

As infectious diseases causing bacteria and fungi are developing resistance to existing antimicrobial drugs, it is necessary to search for new drug targets with different structures and modes of action. Hence, it is essential to screen for new antimicrobial drugs with good efficacy and less toxicity. The reaction of 2-amino benzimidazoles 1 with ethyl cyanoacetate 2 afforded N-(1H-benzo[d]imidazol-2-yl)-2- cyanoacetamides 3. Compounds 3 on Knoevenagel condensation with o-nitro benzaldehydes 4 produced (E)-N-(1H-benzo[d]imidazol-2-yl)-2-cyano-3-(2-nitrophenol) acylamides 5. Compounds 5 were converted to 2-amino -N-(1H-benzo[d]imidazol-2-yl) quinoline-3-carboxamides 6 on treatment with stannous chloride by reductive cyclization. The target compounds viz., 3-(1H-benzo[d]imidazol-2-yl)-2- methylpyrimido [4, 5-b] quinolin-4(3H)-ones 7 were obtained by N-acetylation followed by cyclodehydration of compounds 6 in situ by treatment with acetic anhydride. 3-(1H-Benzo[d]imidazol-2-yl)-2- methylpyrimido [4, 5-b] quinolin-4(3H)-ones 7 have been synthesized from commercially available materials in excellent yields. The title compounds 7a-h are evaluated for in vitro antimicrobial activity. Compounds 7e, 7f and 7h have shown more antimicrobial activity than that of standard drugs. The structures of all the newly synthesized compounds 3, 5, 6 & 7 are confirmed on the basis of spectral data. Antimicrobial studies of compounds 7a-h have revealed that compounds 7e and 7f have more efficient activity when compared to the standard drugs.