## 3 Results and Discussion
### Acetylcholinesterase Inhibitors Assay  
In this assay, galantamine was more active than the products evaluated. Nevertheless, as an initial screening a structure activity relationship is attempted to obtain valuable information for future research.  
Among the synthesized products, compound **1** showed the best activity with 25.8% of inhibition (Figure 1). AChE inhibitors bond with the enzyme in a well-known gorge, which in its bottom presents a Trp residue (Trp84 for _Tetronarce californica_ AChE, the enzyme used for the in vitro assay). This residue is of crucial importance for ligand interaction by means of a \(\pi\)-cation interaction [34; 35]; however, it can also have purely hydrophobic interactions. In the case of galantamine and doneezil [34; 36] this residue presents classical \(\pi\)-\(\pi\) stacking with a galantamine double bond, and with the benzyl ring in donepezil. In a similar way, compound **1** could adopt a similar position against AChE, presenting a \(\pi\)-\(\pi\) interaction with Trp84 through its A ring, which has no substitutions that could affect the \(\pi\) electron cloud in the ring, thus explaining the result shown. Hydrophobic and \(\pi\)-\(\pi\) interactions tend to be the most observed ones between AChE and the scaffolds of different inhibitors [37; 38; 39].  
The next compounds with high inhibition percentages were compounds **11** and **12**, which presented a nitro functionality in their \(p\)- and \(o\)- positions. The nitrogen atom in this group is positively charged; in this manner, these compounds could have \(\pi\)-cation interactions with Trp84, or even with Phe330, which is another residue that commonly has this interaction. This could explain why **11** and **12** followed compound **1** with the best results.  
Some tendencies seen in the results when comparing **2** (which has an \(o\)-OH substitution) against **6** (which presents an \(o\)-OMe one), we can see that the inhibition activity diminishes; the same pattern was observed with **7** and its methoxy version **8**, although the comparison between **3** and **4** appeared as the exception of this behavior. Compound **9** had only 5.9% inhibition activity; as \(\pi\)-\(\pi\) interactions with AChE are important, the chloride presence in **9** could alter the electron cloud from the A ring, disturbing the \(\pi\)-\(\pi\) interactions that can be made.  
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Compounds**} & \multicolumn{2}{c}{**Antioxidant Activity (EC\({}_{\text{50}}\), mg/mL)**} \\ \cline{2-3}  & **DPPH** & **ABTS** \\ \hline
**1** & \(3.25\pm 0.137\) & \(34.312\pm 0.245\) \\
**2** & \(1.389\pm 0.631\) & \(0.188\pm 0.011\) \\
**3** & \(0.141\pm 0.094\) & \(0.168\pm 0.046\) \\
**4** & \(16.74\pm 0.003\) & \(1.644\pm 0.584\) \\
**5** & \(16.89\pm 0.636\) & \(37.223\pm 2.629\) \\
**6** & \(7.12\pm 1.916\) & \(15.643\pm 0.324\) \\
**7** & \(0.341\pm 0.101\) & \(0.199\pm 0.001\) \\
**8** & \(12.23\pm 3.042\) & \(1.964\pm 0.37\) \\
**9** & \(5.62\pm 1.752\) & ND \\
**10** & \(0.174\pm 0.041\) & \(0.162\pm 0.006\) \\
**11** & ND & \(8.025\pm 0.771\) \\
**12** & ND & \(42.158\pm 2.697\) \\
**13** & \(4.00\pm 0.135\) & \(0.449\pm 0.03\) \\ \hline Imidazole & \(>\)15 & \(>\)10 \\
* Quercetin & \(0.052\pm 0.037\) & \(0.075\pm 0.002\) \\ \hline \hline \end{tabular}  
* *