## 3 Results and Discussion  
Desired 4,5-dihydro-1\(H\)-pyrazole derivatives were synthesized from corresponding chalcones. Chalcones were obtained in the typical aldol condensation reaction of aldehydes and acetophenones, while pyrazoles were synthesized from corresponding chalcones in the presence of hydrazine hydrate and formic acid (Figure 2). Their structures were confirmed by \({}^{1}\)H NMR, \({}^{13}\)C NMR, and mass spectra. All compounds show characteristic peaks for -CHO proton around 8.67 ppm, pyrazole C-5 proton peak around 5.58 ppm and pyrazole C-4 proton peaks around 3.24 ppm and 3.90 ppm. Other peaks correspond to aromatic protons (6.90-7.90 ppm) and specific substituents on the phenyl ring. Mass spectra for each compound corresponds to its molar mass. All compounds were further characterized by their melting points and \(R_{\text{f}}\) values as indicated in the Materials and Methods Section. After synthesis, purification, and full characterization, all compounds were investigated for their antibacterial activity against two Gram-positive and two Gram-negative bacteria (Table 1) and tyrosinase inhibiting activity (Table 2). \begin{table}
\begin{tabular}{c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multicolumn{3}{c}{**Minimum Inhibitory Concentration (\(\mu\)g mL\({}^{-1}\))**} \\ \cline{2-5}  & _E. coli_ & _P. aeruginosa_ & _B. subtilis_ & _S. aureus_ \\ \hline
**3a** & 62.5 & 62.5 & 62.5 & 62.5 \\
**3b** & 62.5 & 62.5 & 62.5 & 62.5 \\
**3c** & 62.5 & 62.5 & 62.5 & 62.5 \\
**3d** & 62.5 & 62.5 & 62.5 & 62.5 \\
**3e** & 62.5 & 62.5 & 62.5 & 62.5 \\
**3f** & 62.5 & 62.5 & 125 & 125 \\
**3h** & 62.5 & 62.5 & 250 & 250 \\
**3i** & 62.5 & 62.5 & 250 & 250 \\
**3j** & 62.5 & 62.5 & 250 & 250 \\ amikacin & 1.95 & 0.49 & 0.24 & 1.95 \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Antibacterial activity of synthesized compounds in terms of minimum inhibitory concentration (MIC) against _Escherichia coli_, _Pseudomonas aeruginosa_, _Bacillus subtilis_ and _Staphylococcus aureus_ (\(\mu\)g mL\({}^{-1}\)). \begin{table}
\begin{tabular}{c c c} \hline \hline \multicolumn{1}{c}{**Compound**} & **Monophenolase Inhibition Rate (\%)** & **Diphenolase Inhibition Rate (\%)** \\ \hline
**3a** & \(10.84\pm 1.20\) & \(21.08\pm 1.86\) \\
**3b** & \(5.22\pm 1.84\) & \(15.98\pm 3.25\) \\
**3c** & \(0.21\pm 1.39\) & \(10.11\pm 3.92\) \\
**3d** & \(28.80\pm 4.10\) & \(22.81\pm 0.33\) \\
**3e** & \(21.74\pm 2.82\) & \(16.55\pm 0.29\) \\
**3f** & \(20.11\pm 1.63\) & \(13.67\pm 0.50\) \\
**3g** & \(25.54\pm 2.49\) & \(14.34\pm 0.88\) \\
**3h** & \(24.46\pm 3.77\) & \(20.79\pm 0.17\) \\
**3i** & \(32.07\pm 3.39\) & \(15.11\pm 0.50\) \\
**3j** & \(25.54\pm 4.10\) & \(18.38\pm 1.01\) \\ Kojic acid & \(100\pm 0.00\) & \(88.45\pm 0.83\) \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Tyrosine inhibiting activity of synthesized compounds *. Figure 2: Synthetic pathway for fluorinated pyrazole aldehydes. The antibacterial assay revealed that Gram-negative bacteria were more susceptible to the tested compounds than Gram-positive ones. The cell wall of Gram-positive bacteria ranges from 20 to 80 nm, while for Gram-negative bacteria it ranges from 1.5 to 10 nm [24; 25]. Of the four tested bacteria, the Gram-positive had higher resistance against tested compounds, with up to threefold higher MIC values (62.5-250 \(\upmu\)g mL\({}^{-1}\) for _B. subtilis_ and _S. aureus_) than for Gram-negative bacteria (62.5 \(\upmu\)g mL\({}^{-1}\) for _E. coli_ and _P. aeruginosa_ for all tested compounds). Electrostatic interactions can regulate the interaction of the bacterial surface with acidic and basic functional groups and various agents, which can lead to changed cell surface permeability and thus lead to the death of the cell. The target protein often tolerates the replacement of a hydrogen atom with fluorine, since it has a small atom volume. In order to increase the half-life of the drug and human exposure, many drugs on the market contain introduced fluorine atoms [26].