An efficient microwave-promoted three-component synthesis of thiazolo[3,2-a]pyrimidines catalyzed by SiO2-ZnBr2 and antimicrobial activity evaluation

One-pot three-component Biginelli-type reaction of substituted thiazol-2-amines, 2-( 4-nitrophenyl) acetonitrile, and aromatic aldehydes, promoted by heterogeneous catalyst SiO2-ZnBr2 and diisopropylethylamine as base, has been developed for the synthesis of 2,5-substituted-6-(4-nitrophenyl)-5H-thiazolo[3,2-a]pyrimidin-7-amines. This method, optimized under microwave conditions, was highly efficient and environmentally benign and delivered the desired products in good yields (89-96%) in short reaction time (<6 min). The method has many additional advantages such as wide substrate tolerance, high atom economy, operational simplicity, reusability of the catalyst, and inexpensive solvent. In screening tests of antimicrobial activity against four bacteria and three fungi species, few of the synthesized compounds showed activity in the MIC range 6.25-25.0 g/ml, which was close to the standard drugs, tetracycline and amphotericin B (MIC 3.125-6.25 mu g/ml).