Microwave and Conventional Study of Coumarin-Oxadiazole Adducts and their Anti-Microbial Evaluation

Introduction: Nowadays, researchers are progressively concentrated to generate economical, affordable and also greener synthesis approach for the synthesis of various heterocycles. On look at the beauty of coumarin molecules and oxazoles, it seems to be lead molecules in the anti-microbial area. Aim: With the target to identify efficient molecules, we studied 2-oxo-2H-chromen-4-yl-2-((5-substituted aryl-1,3,4-oxadiazol-2-yl) thio)acetate derivatives using two synthetic protocol/methods, i.e. conventional synthesis and microwave-based synthesis.Materials and methods: Two simultaneous methods, i.e. conventional and microwave synthesis have been used for the synthe-sis of 2-oxo-2H-chromen-4-yl-2-((5-substituted aryl-1,3,4-oxadiazol-2-yl)thio)acetate (6a-l) derivatives. The desired molecules were synthesized by conventional and microwave synthesis and a comparative study was carried out to identify an easy route for industrial applications. The confirmations of the compounds were carried out by spectroscopic techniques such as IR, 1H NMR, 13C NMR, mass spectra and elemental analysis. Results: All synthesized compounds were evaluated for their in-vitro antibacterial activity against gram-positive bacteria (Staphylococcus aureus, Staphylococcus pyogenes), gram-negative bacteria (Escherichia coli, Pseudomonas aeruginosa), and antifungal activity (Candida albicans, Aspergillus niger). Conclusions: All conventional synthesis of final coumarin derivatives were completed within 4-6 h. While that of microwave-based reaction took comparatively more reaction time. Surprisingly, the compounds 6f and 6g could not be synthesized by microwave radiation even after 32 minutes of irradiation. As to the medicinal application part, microbial evaluation of synthesized analogues showed that the compounds 6b, 6e, 6d, and 6j were found more potent in comparison to the reference drug.