Design, synthesis, and pharmacological studies of some new Mannich bases and S-alkylated analogs of pyrazole integrated 1,3,4-oxadiazole

A facile and convenient synthesis of Mannich bases 5a–f and S-alkylated derivatives 6a–f and 7a–f has been carried out from the key intermediate 5-(5-methyl-1-phenyl-1H-pyrazol-4-yl)-1,3,4-oxadiazole-2(3H)-thione (4). Intermediate 4 was obtained from one-pot reaction of ethyl acetoacetate, phenylhydrazine, and N,N-dimethylformamide dimethyl acetal (DMF-DMA) followed by reaction with hydrazine hydrate and carbon disulfide. The structure of the newly synthesized compounds was established on the basis of elemental analysis, infrared (IR), 1H nuclear magnetic resonance (NMR), 13C NMR, and mass spectroscopic data. All synthesized compounds were screened for in vivo antiinflammatory, in vivo analgesic, and in vitro antimicrobial activity. From the activity studies, it was concluded that, among all the derivatives, compounds 5c, 5e, 5f, 6c, 7b, and 7c showed potent antiinflammatory activity, whereas 5b, 5c, 5e, 5f, 6c, 6f, 7b, 7c, and 7e exhibited good analgesic activity. Compounds 6a, 6c, 7b, 7c, and 7d showed maximum activity against the bacterial strains. Efforts were also made to establish structure–activity relationships among the tested compounds.