Synthesis and antibacterial activity of N -substituted-[1,2,4]triazoles and 1,2,4-triazole[3,4-b][1,3,4]thiadiazines

New series of N-[3-(5-methyl-1-phenyl-1H-4-pyrazolyl)-5sulfanyl-4H-1,2,4-triazol-4-yl]-N'-arylthiourea derivatives 8a-e and 3-(5-methyl-1-phenyl-1H-4-pyrazolyl)-6-aryl-7H-[1,2,4] triazolo[3,4b][1,3,4]thiadiazines 9a-e have been prepared and screened for their antibacterial activity against four human pathogenic bacteria, Escherichia coli, Klebseilla pneumoniae, Shigella dysentriae and Shigella flexnei. Among the screened, compounds 8b, 8c and 8e, in which phenyl ring of isothiocyanate moiety bear 3-fluoro, 4-fluoro and 4-bromo substituents respectively, show high activity against all the micro-organisms employed. The compound 9c is highly active against all the test organisms employed. The zone of inhibition is more than what is found for the standard drug neomycin, and almost equal to the standard drug streptomycin.