Design and synthesis of 3,5-disubstituted-1,2,4-oxadiazoles as potent inhibitors of phosphodiesterase4b2.

A series of 3,5-disubstituted-1,2,4-oxadiazoles has been prepared and evaluated for phosphodiesterase inhibition (PDE4B2). Among the prepared 3,5-disubstituted-1,2,4-oxadiazoles, compound 9a is the most potent inhibitor (PDE4B2 IC(50)  = 5.28 μm). Structure-activity relationship studies of 3,5-disubstituted-1,2,4-oxadiazoles revealed that substituents 3-cyclopentyloxy-4-methoxyphenyl group at 3-position and cyclic ring bearing heteroatoms at 5-position are important for activity. Molecular modeling study of the 3,5-disubstituted-1,2,4-oxadiazoles with PDE4B has shown similar interactions of 3-cyclopentyloxy-4-methoxyphenyl group; however, heteroatom ring is slightly deviating when compared to Piclamilast. 3-(3-Cyclopentyloxy-4-methoxyphenyl)-5-(piperidin-4-yl)-1,2,4-oxadiazole (9a) exhibited good analgesic and antiinflammatory activities in formalin-induced pain in mice and carrageenan-induced paw edema model in rat.