Synthesis of novel benzimidazoles at room temperature, under solvent-free condition and their biological studies

Abstract

An efficient and facile synthesis of substituted novel benzimidazoles (3a–3h) mediated by fruit juices viz. Cocos nucifera L. juice, Citrus limetta juice and Citrus sinensis L. juice, via condensation of substituted aldehydes (1a–1h) and o-phenylenediammine (2a) under solvent-free condition at room temperature is presented in this paper. The purity of compounds was confirmed by melting point and thin layer chromatography. All synthesized compounds (3a–3h) were fully characterized via NMR and FTIR spectral data and evaluated for in vitro herbicidal activity against Raphanus sativus L. (Radish) seeds. The compounds (3a–3h) were also evaluated for their antibacterial activity against Erwinia cartovora and Xanthomonas citri by inhibition zone method. Antifungal activity was also determined against Rhizoctonia solani and Colletotrichum gloeosporioides by poisoned food techniques method. From activity data, it was found that compounds 3d and 3e were most active against R. sativus L. (root) and R. sativus L. (shoot), respectively. Compound 3g has shown maximum inhibition zone i.e. 8.00 mm against E. cartovora at 2000 µg/mL concentration. Maximum X. citrii growth was inhibited by compounds 3a showing inhibition zone 5.20 mm at highest concentration. Compound 3f was found most active against R. solani and C. gloeosporioides fungus at 2000 µg/mL concentration. In comparison with the conventional methods, the present method complies with several key requirements of green chemistry principles such as the utilization of renewable feedstock, auxiliary aqueous conditions and reduces waste with the use of nature-derived catalyst. Therefore, the present method offers an attractive option because of its ecological safety, environmental acceptance, cost effective and easy workup process.