Synthesis , Characterization and Biological Evaluation of 1 , 2-Disubstituted Benzimidazole Derivatives using Mannich Bases

The ring system in which a benzene ring is fused to the 4,5-positions of imidazole is designated as benzimidazole. Condensations of 2-substituted benzimidazole derivatives were synthesized by different carboxylic acids using Mannich base and anti-inflammatory activity. The various positions on the benzimidazole ring are numbered in the manner indicated with the imino function as number one. The formations of the product were conformed by the analytical and spectral data.


Introduction
The ring system in which a benzene ring is fused to the 4,5-positions of imidazole is designated as benzimidazole 1 .The various positions on the benzimidazole ring are numbered in the manner indicated with the imino function as number one [2][3][4] .The benzimidazoles possessing free imino hydrogen are tautomeric systems.The two possible tautomeric forms of benzimidazole (and of those of its derivatives possessing a plane of symmetry) are identical and a definite assignment of structure is possible [5][6][7] .
The formations of the product were confirmed by the analytical and spectral data.Antiinflammatory activity of the synthesized compound was confirmed by significant effect over carrageenan induced paw edema.

Experimental
o-Phenylene diamine was condensed with different aromatic carboxylic acids to give 2-substituted benzimidazole 1,3,5 .The procedure for conventional benzimidazole synthesis is depicted below.Benzimidazole was synthesized by o-phenylene diamine (12 mmol) and phenyl glycine (36 mmol) were stirred in 4N HCl (40 mL) and refluxed for 4 h, then cooled at room temperature.The completion of this reaction was monitored by thin layer chromatography 3,[8][9][10] .The pH was adjusted to 7.2 using sodium hydroxide pellets.The resulting brown solid was filtered and washed with water dried in vacuum and recrystallized from acetone.
The yield of 2-(1-amino benzyl) benzimidazole was found to be 78.5% and the m.p is 280 °C.The completion of the reaction was monitored by thin layer chromatography using solvent system ethyl acetate: N-hexane: methanol.The Mannich base used in the above procedure was synthesized by following procedure.2-(1-Amino benzyl) benzimidazole (10 mmol) was dissolved in dimethyl sulfoxide corresponding to secondary amine (10 mmol) and formaldehyde (37% W/V (15 mmol)).The reactants were refluxed with stirring at 70-75 °C (The condensation time varied between 5-8.5 h).The completion of this reaction was monitored by thin layer chromatography.The reaction mixture was kept in a refrigerator for overnight; the solvent removed under reduced pressure and the product was recrystallized from acetone.

Description
The yield of 1-dimethyl amino-2-(2-benzyl amine) benzimidazole was found to be 65% and m.p was found to be 185 °C.The completion of the reaction was monitored by the thin layer chromatography using solvent system ethyl acetate: N-hexane: methanol.

Results and Discussion
In the present work, ortho phenylene diamine was condensed with different acids such as phenyl glycine and phenyl acetic acid.The completion of the reaction was confirmed by TLC and was characterized by IR.The melting point of the synthesized compound was measured by open capillary tube method.IR, 1 H NMR and mass spectrum confirmed the chemical structure of the synthesized compound, which is showed in Figure 3-5.In the mass spectrum of the synthesized compound produced (M + ) molecular ion peak such as 223 for compound-I, which corresponds with their molecular weights.

Pharmacological studies Acute oral toxicity-acute toxic class method
Acute oral toxicity studies were performed based on Organization of Economical Cooperation and Development (OECD) guidelines, for the synthesized compound.No toxicity or death was observed for synthesized compound on administration of a dose of 2000 mg/kg.Hence the synthesized compound was considered as safe (x-unclassified).Based on this observation, a dose of 200 mg/kg was selected for the anti-inflammatory studies.

Figure 1 .
Figure 1.Preparation of benzimidazole derivatives.Benzimidazole was synthesized by o-phenylene diamine (12 mmol) and phenyl glycine (36 mmol) were stirred in 4N HCl (40 mL) and refluxed for 4 h, then cooled at room temperature.The completion of this reaction was monitored by thin layer chromatography3,[8][9][10] .The pH was adjusted to 7.2 using sodium hydroxide pellets.The resulting brown solid was filtered and washed with water dried in vacuum and recrystallized from acetone.The yield of 2-(1-amino benzyl) benzimidazole was found to be 78.5% and the m.p is 280 °C.The completion of the reaction was monitored by thin layer chromatography using solvent system ethyl acetate: N-hexane: methanol.
Ethylacetate: N-Hexane: Methanol (3: 2: 1) The above mentioned procedure for the synthesis of benzimidazole derivative using conventional various carboxylic acids in presence of conc.HCl[11][12][13] , but in present work we have used Mannich bases, which give advantage for various substitutions in benzimidazole nucleus.Benzimidazoles were synthesized by Mannich base by following procedure.