Modular and Computational Access to Innocuous Multistep MetalFree Synthesis of 1,3,4-Oxadiazoles as Enzyme Inhibitors

An array of 1,3,4-oxadiazole hybrids, 7a-s, structurally intriguing cores with potential in natural product synthesis and drug discovery, have been synthesized using innovative comparable conventional and microwave-assisted protocols. The synthesis was performed by the reaction of secondary amine-based acetamides, 6a-s, as the electrophile and piperidine-based oxadiazoles as the nucleophile, 3, under the metalfree reaction conditions. High yield in minimum time with highest purity was obtained by the microwave-irradiated method instead of the conventional one. The structural elucidations were made through infrared, H-1 NMR, C-13 NMR, and elemental analysis studies. The whole array of synthesized compounds, 7a-s, was evaluated for their potential against a-glucosidase and butyryl cholinesterase (BChE) enzymes. Natural bond orbital and structural optimizations were made by using the B3LYP method and the basis set of 6-311++G(d,p). Frontier molecular orbitals and molecular electrostatic potential were calculated at the same level of selected compounds as potential candidates against BChE and alpha-glucosidase enzymes utilizing the time-dependent density functional theory. Fifteen compounds out of 19 were observed to be active against a-glucosidase enzyme in comparison with acarbose as the reference standard and 7 against the BChE enzyme compared to eserine as the reference standard. The highest potential of compound 7j against BChE is well correlated by the higher binding interaction with target protein as -10.2, calculated by docking studies. The recruited compounds against both enzymes could be the best anti-enzymatic drugs and part of drugs discovery programs after further analysis.