Synthesis and antibacterial activity of N1-(carbazol-3-yl)amidrazones incorporating piperazines and related congeners

A selected set of N1-(4-chloro-9-ethylcarbazol-3-yl)amidrazones (7a-n) has been synthesized by reacting the respective hydrazonoyl chloride 5 derived from 3-amino-9-ethylcarbazole (3), with an appropriate sec-cyclic amine (6a-n) in ethanol in the presence of triethylamine. Unexpectedly, aromatic ring chlorination occurred at C-4 of 3 during its conversion to 6 as evidenced by analytical and spectral data and further confirmed by single crystal X-ray structure determination of the amidrazone 7n. Compounds 7a-n were tested for their in vitro antibacterial activity. Among the tested bacterial strains, methicillin-resistant Staphylococcus aureus was the most susceptible to 7f and Bacillus cereus to 7b both with a minimum inhibitory concentration value of 1.56 mu g mL(-1). Compounds 7c, 7f, and 7h could be useful as lead structures for further development of new antibacterial agents against Gram-positive and Gram-negative pathogens.