The medicinal chemistry is devoted to the discovery and development of new agents for cure and prevention of diseases. A new drug discovery is exceeding complex and involves selection of moiety, establishing their synthesis and recogination of biological activity. Benzimidazole is a bicyclic ring system in which benzene ring fused with 4- and 5- position of the imidazole ring, imidazole ring contain two nitrogen atoms at nonadjacent position. Benzimidazole is a very important pharmacophore in drug discovery, and its derivatives are used as an important class of bioactive molecules in the field of new drug development. The structures of the newly synthesized benzimidazole derivatives were accomplished through IR, 1H NMR and mass spectral data. All derivatives showed moderate to good anthelmintic activity against Phaeritima posthuma species of earthworm at the concentration of 75.0 mg/ml, when compared with piperazine citrate as reference compound. Among all the synthesized compounds, the compound N-{(2’-Methyl-1H-benzo[d]imidazol-1-yl)methyl}-4-nitrobenzenamine (1a), 4-Chloro-N-{(2’-methyl- 1H-benzo[d]imidazol-1-yl) methyl} benzenamine (1c), N-{(4'-Fluorophenyl)(2’’-methyl-1H-benzo[d]imidazol-1- yl)methyl}-4-nitrobenzenamine (2b), N-{(3’-Nitrophenyl)(2’’-methyl-1H-benzo[d]imidazol-1-yl)methyl}-4-chloro benzenamine (2d), 1-{(4’-Nitrophenylamino) methyl}-1H-benzo[d]imidazole-2-thiol (3a), 1-{(4’-Chloro phenylamino) methyl}-1H-benzo[d]imidazole-2-thiol (3c), 1-{(4’-Nitrophenylamino)(4’’-fluorophenyl)methyl}-1Hbenzo[ d]imidazole-2-thiol (4b), 1-{(4’-Chlorophenylamino)(3’’-nitrophenyl)methyl}-1H-benzo[d]imidazole-2-thiol (4d) were found to be most potent towards anthelmintic activity.
