Novel Microwave Assisted Synthesis and Antimicrobial Activity of New Quinolone-Hybrids

Background: Carbo(thio)amid derivatives 4a, 4b were obtained starting from nalidixic acid in three steps. The acidic treatment of compound 4a generated the corresponding 1,3,4-oxadiazole (5), while the compound 4a gave 1,2,4-triazole derivatives 8a, 8b in basic media. The condensation of 4a with ethyl bromoacetate and 4-chlorophenacyl bromide afforded 1,3-oxazolidine, 6 and 1,3-thiazolidine, 7 derivatives. The synthesis of Mannich bases of 9-15 and 17-19 were achieved from the reaction of 1,2,4- triazoles, 8a, 8b and 1,3,4-oxadiazole, 16, with several heterocyclic amines that has biological activity. Methods: In this article, a series of triazole or 1,3,4-oxadiazole rings containing some novel biologically active quinolone derivatives. Conventional and microwave assisted methods were used for all syntheses. Moreover, the effect of acid catalyst on Mannich reactions was investigated. The structures of newly synthesized compounds were elucidated on the basis of 1H NMR, 13C NMR, FT IR, EI MS techniques and elemental analysis. All these compounds were screened in vitro for their antimicrobial activity against various gram-positive and gram-negative bacterial and fungal strains. Results: This study reports the successful synthesis of some new hybrid compounds starting from nalidixic acid. Two methods containing conventional and microwave assistance with/without catalyst were used to obtain the target compounds. Microwave assistance supplied more efficient way leading the formation of target compounds. Moreover, the effect of acid catalyst on Mannich reactions was investigated. The antimicrobial activity screening studies were also performed in the study. Conclusion: The antimicrobial screening suggests that the compounds containing norfloxacin (9a,b and 17), ciprofloxacin (10a,b and 18) or 7-aminocephalosporanic (12) acid nucleus displayed excellent antimicrobial activity. Moreover, some of them (5-7, 8-13, 15-18) displayed inhibition properties on Escherichia coli (Ec) and Mycobacterium smegmatis (Ms) better from ampicillin or streptomycin with the mic value 0.24 μg/mL.