Discovery of New Schiff Bases Tethered Pyrazole Moiety: Design, Synthesis, Biological Evaluation, and Molecular Docking Study as Dual Targeting DHFR/DNA Gyrase Inhibitors with Immunomodulatory Activity

A series of <i>Bis</i>-pyrazole Schiff bases (<b>6a</b>-<b>d</b> and <b>7a</b>-<b>d</b>) and mono-pyrazole Schiff bases (<b>8a</b>-<b>d</b> and <b>9a</b>-<b>d</b>) were designed and synthesized through the reaction of 5-aminopyrazoles <b>1a</b>-<b>d</b> with aldehydes <b>2</b>-<b>5</b> using mild reaction condition with a good yield percentage. The chemical structure of newly formed Schiff bases tethered pyrazole core was confirmed based on spectral and experimental data. All the newly formed pyrazole Schiff bases were evaluated against eight pathogens (Gram-positive, Gram-negative, and fungi). The result exhibited that, most of them have good and broad activities. Among those, only six Schiff bases (<b>6b</b>, <b>7b</b>, <b>7c</b>, <b>8a</b>, <b>8d</b>, and <b>9b</b>) displayed MIC values (0.97-62.5 µg/mL) compared to Tetracycline (15.62-62.5 µg/mL) and Amphotericin B (15.62-31.25 µg/mL), MBC values (1.94-87.5 µg/mL) and selectivity to tumor cell than normal cells. Immunomodulatory activities showed that the promising Schiff bases increase the immunomodulator effect of defense cell and the Schiff base <b>8a</b> is the highest one by (Intra. killing activity = 136.5 ± 0.3%) having a pyrazole moiety as well as amide function (O=C-NH₂) and piperidinyl core. Furthermore, the most potent one exhibited broad activity depending on both MIC and MBC values. Moreover, to study the mechanism of these pyrazole Schiff bases, two active Schiff bases <b>8a</b> and <b>9b</b> from six derivatives were introduced to study the enzyme assay as dihydrofolate reductase (DHFR) on <i>E. coli</i> organism and DNA gyrase with two different organisms, <i>S. aureus</i> and <i>B. subtilis</i>, to determine the inhibitory activities with lower values in the case of DNA gyrase (<b>8a</b> and <b>9b</b>) or nearly as DHFR compound <b>9b</b>, while pyrazole <b>8a</b> showed excellent inhibitory against all enzyme assay. The molecular docking study against dihydrofolate reductase and DNA gyrase were performed to study the binding between active site in the pocket with the two Schiff bases (<b>8a</b> and <b>9b</b>) that exhibited good binding affinity with different bond types as H-bonding, aren-aren, and arene-cation interaction as well as study the physicochemical and pharmacokinetic properties of the two active Schiff bases <b>8a</b> and <b>9b</b>.