## 3 Results and Discussion
### Antioxidant Activity  
To determine antioxidant activities of 2-hydroxychalcones **2a-2k** and flavone analogs **3a-3k**, heat-induced oxidation in a \(\beta\)-carotene and linoleic acid system, DPPH radical scavenging activity and ABTS radical cation decolorization assay were evaluated. The EC\({}_{50}\) values of compounds, quercetin and \(\alpha\)-tocopherol obtained are shown in Table 1 and Figure 2.  
The results showed that most of the compounds exhibited high activity with DPPH and \(\beta\)-carotene assay and weak activity in ABTS; additionally, the flavone-type derivatives showed a better antiradical and antioxidant activity as compared to their chalcone precursors. Structure-antioxidant activity relationships of chalcones and flavones suggest this activity is related to a series of different mechanisms, like free radical neutralization, hydrogen donation, singlet oxygen quenching, and metal chelation [38]. The high double bond conjugation of chalcone and flavonoid systems, just as the presence of a C2-C3 double bond and a carbonyl in C-4 position, have been reported as structural characteristics for the antioxidant activity [39], being these incorporated in the basic skeleton of all the synthesized compounds. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Compound**} & \multicolumn{3}{c}{**B-Ring Substituent**} & \multicolumn{3}{c}{**Scavenging Activity (EC\({}_{\text{Sp}}\), ng/mL)**} \\ \cline{2-7}  & **R1** & **R2** & **R3** & **R4** & **ABTS (2-2\({}^{\prime}\)-azino-bis-(G-ethylbenzothazoline- & **DPPH** \\  & & & & & \(6\)-sulfonate))** & \\ \hline
**2a** & & & & & \(1.61\times 10^{4}\pm 5.5\times 10^{-3}\) & \(260\pm 1.17\times 10^{-2}\) \\
**2b** & OH & & & & \(21\pm 7.07\times 10^{-5}\) & \(8\pm 12.4\times 10^{-4}\) \\
**2c** & & OMe & OH & & \(164\pm 4.95\times 10^{-4}\) & \(19\pm 1.18\times 10^{-3}\) \\
**2d** & OH & & & NO\({}_{2}\) & \(564\pm 4.24\times 10^{-4}\) & \(23\pm 9.76\times 10^{-4}\) \\
**2e** & & & OMe & & \(341\pm 2.83\times 10^{-4}\) & \(100\pm 2.57\times 10^{-3}\) \\
**2f** & & OMe & & & \(487\pm 6.93\times 10^{-3}\) & \(170\pm 4.10\times 10^{-3}\) \\
**2g** & & OMe & OMe & & \(1.14\times 10^{-2}\pm 7.42\times 10^{-7}\) & \(5\times 10^{4}\pm 7.76\times 10^{-1}\) \\
**2h** & & & CI & & \(5.23\times 10^{3}\pm 9.90\times 10^{-4}\) & \(15\pm 7.43\times 10^{-4}\) \\
**2i** & & & N(CH\({}_{3}\))\({}_{2}\) & \(6.96\times 10^{-2}\pm 2.12\times 10^{-7}\) & \(9.3\pm 4.95\times 10^{-5}\) \\
**2j** & & Anthracene & & & \(548\pm 3.54\times 10^{-3}\) & \(1.7\pm 6.82\times 10^{-5}\) \\
**2k** & & & Furan & & \(79\pm 6.36\times 10^{-4}\) & \(5.4\times 10^{-3}\pm 6.50\times 10^{-8}\) \\
**3a** & & & & & \(2.53\times 10^{4}\pm 4.24\times 10^{-3}\) & \(170\pm 1.94\times 10^{-5}\) \\
**3b** & OH & & & & \(03\pm 3.54\times 10^{-5}\) & \(0.1\pm 1.39\times 10^{-6}\) \\
**3c** & OMe & OH & & & \(497\pm 1.98\times 10^{-4}\) & \(9\pm 4.60\times 10^{-5}\) \\
**3d** & OH & & NO\({}_{2}\) & \(155\pm 1.11\times 10^{-3}\) & \(6.2\pm 1.52\times 10^{-4}\) \\
**3e** & & & OMe & & \(3.00\times 10^{3}\pm 1.21\times 10^{-3}\) & \(30\pm 3.61\times 10^{-3}\) \\
**3f** & & OMe & & & \(112\pm 2.90\times 10^{-4}\) & \(39\pm 1.58\times 10^{-3}\) \\
**3g** & & OMe & OMe & & & \(861\pm 2.55\times 10^{-3}\) & \(410\pm 6.85\times 10^{-3}\) \\
**3h** & & & CI & & \(2.6\times 10^{3}\pm 1.06\times 10^{-3}\) & \(7.4\pm 1.09\times 10^{-5}\) \\
**3i** & & & & N(CH\({}_{3}\))\({}_{2}\) & \(1.9\times 10^{-3}\pm 6.51\times 10^{-8}\) & \(0.25\pm 2.14\times 10^{-5}\) \\
**3j** & & Anthracene & & & \(1.07\times 10^{5}\pm 3.99\times 10^{-4}\) & \(1\times 10^{-8}\pm 1.61\times 10^{-12}\) \\
**3k** & & Furan & & & \(1.26\times 10^{3}\pm 7.78\times 10^{-4}\) & \(0.1\pm 7.85\times 10^{-6}\) \\ \hline \multicolumn{7}{l}{*Quercetin} & \multicolumn{3}{c}{\(50\pm 4.1\times 10^{-4}\)} & \multicolumn{3}{c}{\(3\pm 2\times 10^{-4}\)} \\ \hline \hline \end{tabular}  
* * *Served as reference compound. Values are mean \(\pm\) SD, n = 2.  
\end{table}