## 3 Results and Discussion
### Biological Evaluations
#### 3.2.4 Antitumor Activity  
Considering the antitumor activity of the studied compounds, it can be noticed that compounds **5** and **8** were the most active, presenting very similar IC\({}_{50}\) values. Compounds **1** and **4** showed some activity, although lower than the ones mentioned above (Table 3). However, none of the compounds tested were as active as colchicine or paclitaxel, the reference compounds used (Table 3). It was also observed that the inhibition of tumor cell growth is dose-dependent for all the compounds tested (Figure S15, supplementary material).  
\begin{table}
\begin{tabular}{c c c c} \hline \hline \multirow{2}{*}{**Compounds and** **References**} & \multicolumn{3}{c}{**IC\({}_{50}\) \(\upmu\)g/mL (\(\upmu\) SD)**} \\ \cline{2-3}  & _M. luteus_ & _B. subtilis_ & _E. coli_ \\ \hline
**1** & \(>\)200 & \(>\)200 & \(>\)200 \\
**4** & 164.89 (\(\pm\)2.97) \({}^{\mathrm{a}}\) & 76.46 (\(\pm\)4.27) \({}^{\mathrm{a}}\) & \(>\)200 \\
**5** & \(>\)200 & \(>\)200 & \(>\)200 \\
**6** & 23.78 (\(\pm\)2.04) \({}^{\mathrm{b}}\) & 9.33 (\(\pm\)0.25) \({}^{\mathrm{b}}\) & \(>\)200 \\
**7** & 23.64 (\(\pm\)2.24) \({}^{\mathrm{b}}\) & 20.48 (\(\pm\)3.13) \({}^{\mathrm{c}}\) & \(>\)200 \\
**8** & \(>\)200 & 74.64 (\(\pm\)3.92) \({}^{\mathrm{a}}\) & \(>\)200 \\ Penicillin & 8.47 (\(\pm\)0.55) \({}^{\mathrm{c}}\) & 0.28 (\(\pm\)0.02) \({}^{\mathrm{d}}\) & \(>\)40 \\ Streptomycin & 0.59 (\(\pm\)0.02) \({}^{\mathrm{d}}\) & 15.86 (\(\pm\)0.21) \({}^{\mathrm{e}}\) & 14.45 (\(\pm\)1.73) \\ \hline \hline \end{tabular} In each column, the letters a, b, c, d, and e indicate significant differences (\(p<\) 0.05).  
\end{table}
Table 2: Antimicrobial activity of synthesized compounds **1, 4–8**.  
Figure 5: Structure/activity relationships established for antibacterial effect against _M. luteus_.  
Figure 6: Structure/activity relationships established for antibacterial effect against _B. subtilis_.  
Results for the activity of compounds **6** and **7** against the A549 cell line have already been reported in the literature [7; 59; 60; 61]; however, their activity was tested in order to facilitate the comparison of the results, since all the compounds were tested in the same conditions. The results for compound **7** are concordant with the literature, since it is reported that the effects of this compound in A549 cells is limited to the inhibition of cell migration, without any effects on growth or cytotoxicity level [7; 60]. Compound **6** did not present any activity, which was unexpected, since it is reported to possess antitumor activity against several cell lines, including A549, by inhibiting proliferation and inducing tumor cell apoptosis [59; 61]. This can be explained by the fact that the authors used a much lower cell concentration than the one used in the present work, and it has been proved that lower cell concentrations are correlated with higher activities of the compounds tested [62].  
From the results obtained, the only conclusions that can be drawn regarding structure/activity relationships are that neither the \(\alpha\),\(\beta\) unsaturated carbonyl bridge nor the cyclization of chalcone into flavanone have an influence in the inhibition of tumor-cell growth, since both chalcones and flavanones presented interesting activities (Figure 7). Also, the presence of methoxyl groups has some importance in the antitumor effect of the compounds, since compounds **6** and **7**, which do not have methoxyl groups, did not present any activity against the A549 cell line (Table 3). The influence of a methoxyl group in synthetic polyphenic compounds' antitumor activity was not a surprise because it was previously detected in our group [63].