## 3 Results and Discussion
### Antioxidant Activity

Table 1: Antioxidant activity of synthesized compounds **2a-2k** and **3a–3k**. Figure 2: Percentage of antioxidant activity in \(\beta\)-carotene/linoleic acid bleaching assay of chalcone (**2a–2k**) and flavone analogs (**3a–3k**). \(\alpha\)-tocopherol served as reference compound. Bars are mean \(\pm\) SD, n = 2. Bearing this in mind, molecules **2a** and **3a** have no substituents in their structures, having the lowest activity of all the generated analogs, therefore it is possible to infer that the addition of at least one substitution favors the antioxidant potential. In chalcone type molecules, the antioxidant properties are vastly influenced by the two aryl groups and their substitution patterns. The presence of hydroxyl groups to improve the antioxidant activity due to its easy conversion to phenoxy radicals by the hydrogen transfer mechanism is considered to be indispensable [40]. Hydroxyl group presence was evaluated in the **2b** (_o_-OH), **2c** (_p_-OH, _m_-OMe), and **2d** (_o_-OH, _m_-NO\({}_{2}\)) analogs; despite that the three had great activity in the tested techniques (see Table 1), **2b** showed better results when compared to the other analogs in the antiradical techniques DPPH and ABTS, with an EC\({}_{50}\) of 8 ug/mL and 21 ug/mL respectively, surpassing quercetin as the control used in ABTS (EC\({}_{50}\) of 50 ug/mL). This indicates that in the radical reduction mechanism by hydrogen donation (like DPPH and ABTS), the addition of other substitutions different from hydroxyl groups diminishes activity, especially using electron-attractor groups as NO\({}_{2}\)[41]. A similar behavior is appreciated in the results of flavones **3b**, **3c**, and **3d**, with **3b** showing good activity with an EC\({}_{50}\) of 0.1 ug/mL in DPPH and 0.3 ug/mL in ABTS, in both situations surpassing the positive control; again, it was observed that the presence of electron-attractor groups lowers the activity. Analogs **2h** and **3h** with _p_-Cl substitutions did not show considerable activity when compared to the controls. The influence of electron-donor groups, like methoxyl, can be analyzed with the **2e** (_p_-OMe), **2f** (_m_-OMe), and **2g** (_p_,_m_-OMe) analogs; the presence of these groups did not favor the activity, getting concentrations of 100, 170, and 5 \(\times\) 10\({}^{4}\) ug/mL, respectively, in DPPH assay, having a similar behavior of the flavones **3e-g**, with EC\({}_{50}\) of 30, 39, and 410 ug/mL. These results may appear to contrast with the reported by many authors where methoxyl groups are considered an important factor for the antioxidant activity [42; 43], however, this is the case where methoxyl groups help with the lipophilicity of the molecule, for example, when the antioxidant activity is measured by the lipid peroxidation activity assay [39]. When employing DPPH test, the transfer of acid protons is required; this implies that just as in the case of the chalcones, we consider indispensable the presence of at least one hydroxyl group, explaining the lack of scavenging activity for the synthesized compounds with only methoxyl groups (**3e-g**). Molecules **2i-3i**, both with _p_-dimethylamino substituent showed excellent results with an EC\({}_{50}\) of 9.3 and 0.25 ug/mL, respectively, in the DPPH assay, having an EC\({}_{50}\) of 6.9 \(\times\) 10\({}^{-2}\) and 1.9 \(\times\) 10\({}^{-3}\) ug/mL in ABTS; substituents that increase the electronic density, like dimethylamine groups, show potent antioxidant activity that is attributed to the resonance effect involving the pair of electrons of the heteroatom [44]. The \(\beta\)-carotene decolorization assay brings an outlook to the capacity of an antioxidant to inhibit the lipid peroxidation initiated by the hydrogen abstraction or addition of oxygen radical [45]. The chalcones **2c** and **2d** with hydroxyl substitution showed good activity in this technique with percentages of activity between 76-84%, while the flavones with the same substitution showed results between 67-77%.