A heterogeneous catalyst, SiO2-ZnBr2: An efficient neat access for α-aminophosphonates and antimicrobial activity evaluation

An efficient, environmentally benign and green method was developed for the synthesis of alpha-aminophosphonates by one-pot three-component reaction (Kabachnik-Fields reaction) of amine (4-(4-chlorophenoxy)aniline), aldehydes and diethyl phosphite using catalyst, SiO2-ZnBr (2) under solvent-free conditions. The developed method under conventional conditions was further optimized in microwave and ultrasonication methods. A series of alpha-aminophosphonates, diethyl (4-(4-chlorophenoxy)phenylamino)(aryl/ heteroaryl)methylphosphonates was synthesized to check the generality. The catalyst, SiO2-ZnBr2 afforded good yields of products in all the methods in the range of 85-97% but variation was observed in reaction time. Microwave irradiation method took very less time (4-8 min) as compared with ultrasonication (35-52 min) and conventional (2-3 h) conditions. The major advantages are simple and mild conditions, short reaction times, high yield of the product with purity, use of cheap catalyst and reusability of the catalyst until to three times without significant loss of activity. Antibacterial and antifungal activities were evaluated for the title compounds (50 and 100 mu g/mL) including minimum inhibitory concentrations. A few of the newly synthesized alpha-aminophosphonates exhibited promising antimicrobial activity at lower MIC values in the range of 15.0-25.0 mu g/mL and closer to the standards (5-12 mu g/mL).