## 3 Results and Discussion
### Chalcones and Flavonones Synthesis
The \({}^{1}\)H NMR spectra of compounds **1-3** and **6** present the signal characteristics of chalcone structures: (i) the resonance of the AB system assigned to the olefinic protons; (ii) doublets at \(\delta_{\rm H}\) 7.7-7.9 ppm with \(J\sim\) 15 Hz, which confirms the \(E\) configuration of the \(\alpha\),\(\beta\) double bond; (iii) the signal at \(\delta_{\rm C}\sim\)192 ppm assigned to the carbonyl group; (iv) the singlet at \(\delta_{\rm H}\) 14.4-13.7 ppm assigned to 2\({}^{\prime}\)-OH proton signal involvement in a hydrogen bond with the carbonyl oxygen atom; (v) two sets of doublets, with \(J=\) 6.8 Hz, at \(\delta_{\rm H}\) 6.9-7.8 ppm, assigned to the protons of the _para_-substituted aromatic ring B (Figure 1). The \({}^{1}\)H, \({}^{13}\)C and HSQC NMR spectra of chalcone **1** also display two sets of doublets at \(\delta_{\rm H}\) 5.9-6.1 ppm, with a _meta_-coupling constant (\(J=\) 2.4 Hz), that exhibit correlation with the signals at 93.8 and 91.2 ppm, which indicates the presence of a tetra-substituted aromatic ring (ring A, Figure 1). The three sets of singlets at \(\delta_{\rm H}\) 3.83-3.92 ppm, showing correlation with three signals at \(\delta_{\rm C}\) 55.4-55.8 ppm, are characteristic of three methoxyl groups. The MS spectrum of chalcone **1** showed a signal at \(m/z\) 315 correspondent to [M+H]\({}^{+}\), which agrees with the molecular formula C\({}_{18}\)H\({}_{18}\)O\({}_{5}\)All the spectroscopic data and the melting point are in agreement with previously published data [31], and additionally, the connectivities found in the HMBC NMR spectrum confirm compound **1** as 2'-hydroxy-4_4',6'_-trimethoxychalcone, also named flavokawain A. The \({}^{1}\)H and \({}^{13}\)C NMR spectra of chalcone **6** show three sets of signals in the range of \(\delta_{\rm C}\) 6.38-8.12 ppm, characteristic of the a trisubstituted aromatic ring (ring A, Figure 1). The MS spectrum showed a signal at _m/z_ 257 corresponding to [M+H]\({}^{+}\), which agrees with the molecular formula C\({}_{15}\)H\({}_{12}\)O\({}_{4}\). These data and the connectivities found in the HMBC spectrum confirm compound **6** as 2',_A',_A_-tri-hydroxychalcone, also known as isoliquiritigenin [48]. Compounds **4**, **5** and **7** are flavanones, and this fact is well confirmed by the presence of the signals characteristic of ring C (Scheme 1): two double doublets at \(\delta_{\rm H}\) 2.68-3.10 and \(\delta_{\rm H}\) 2.68-2.78 assigned to the protons H-3, and the double doublet at \(\delta_{\rm H}\) 5.34-5.46 ppm assigned to H-2 in coupling with H-3; the signal at \(\delta\) 196 ppm characteristic of the carbonyl group (C=O). Two sets of doublets at \(\delta_{\rm H}\) 7.29-7.42 (H-2' and H-6') and 6.86-6.95 ppm (H-3' and H-5'), with _orto_-coupling constant of \(J\) = 8.7 Hz, indicate the presence of a _para_-substituted aromatic ring (ring B). The presence of the methoxyl group in the ring B of compound **4** is deduced from the singlet at \(\delta\) 3.83, correlating with the signal at \(\delta_{\rm C}\) 55.4 ppm. The MS data showed a signal at _m/z_ 287 corresponding to the protonated molecule [M+H]\({}^{+}\) that is in accordance with the molecular formula C\({}_{16}\)H\({}_{14}\)O\({}_{5}\). The spectroscopic data and the melting point are consistent with the published data for isosakurametin [33; 49], and together with the connectivities found in HMBC spectrum, confirm that compound **4** is 5,7-dihydroxy-4'-methoxyflavanone. The signals found in the \({}^{1}\)H and \({}^{13}\)C NMR spectra of compound **5** are very similar to the ones found for compound **4**. The differences are the non-appearance of the signal at \(\delta_{\rm H}\) 12.05 ppm, which confirms the absence of a 5-OH group; and the appearance of two singlets at \(\delta_{\rm H}\) 3.86 and 3.81 ppm, which means that compound **5** has two methoxyl groups. The location of the two methoxyl groups and the hydroxyl group were confirmed by the connectivities found in the HMBC spectrum of compound **5**.