## 2 Discussion  
According to [PERSON] [10], the main bioactive compounds found in plants can be classified in (a) glycosides, (b) flavonoids and proanthocyanidins, (c) tannins, (d) mono- and sesqui-terpenoids, and phenylpropanoids, (e) diterpenoids, (f) resins, (g) lignans, (h) alkaloids, (i) furocoumarins and naphtodianthrones, and (j) proteins and peptides. Glycosides  
The glycosides comprise a group of diverse compounds attached to mono- or oligosaccharides-charides or uronic acid (Figure 1). These bioactive compounds have been attributed to some beneficial activities in human health, such as anticancer, antimicrobial, antiviral, cardioprotective effects, amongst others. This group is formed by specific secondary metabolites, widely distributed in plants, with the most important being (i) cardiac glycosides, (ii) cyanogenic glycosides, (iii) glucosinolates, (iv) saponins, and (v) anthraquinone glycosides [10]. The identification of glycosides has been a common task due to the importance of these compounds. For this, spectroscopic and spectrometric methods have been applied to isolate, purify, identify, and quantify their presence in samples from diverse vegetal products. For example, the use of IR and UV-vis, nuclear magnetic resonance (NMR), MS, HPLC-UV-vis, and ultra-high-performance liquid chromatography (UPLC)-UV-vis methods have been applied for those purposes in recent years. Table 1 shows some examples of bioactive compounds, including a cardenolide glycoside, isolated from plant sources, their bioactive properties, and the methodologies used for their measuring. Flavonoids and proanthocyanidins  
Flavonoids comprise a group of bioactive substances with the presence of phenolic rings. These compounds contain molecules that are recognized for their beneficial effects on human health, associated with their high antioxidant anti-inflammatory, anticarcinogenic, antiviral, antimicrobial activities, amongst others. Several plants exhibit the presence of these bioactive molecules in different structures of their organisms--for example, in fruits, flowers, stems, grains, and barks. Flavonoids group commercially important compounds such as (i) flavones, (ii) isoflavunes, (iii) flavonoids, (iv)flavanols, (v)flavanones, (vi)flavanols, (vii) proanthocyanidins, (viii) chalcones, and (ix) anthocyanins (Figure 2). Due to the diverse biological activities of flavonoids and proanthocyanidins, they have received much attention. Nevertheless, their stability is a challenge for their application as nutraceuticals, cosmetics, pigments, and drugs. Table 1 shows examples of a flavonoid and a proanthocyanidin that have been studied very recently as well as the analytical methods used to isolate and characterize these molecules. \begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Group** & **Example** & **Source** & **Activity** & **References** & **Methods** \\ \hline Glycos & Cardenolide & _Narium olearned_ & Anti-inflammatory, anticancer & [11] & IR, UV-vis; HPLC-UV-vis \\  & & & & NMR \\ \hline Flavonoids & Silibinin & _Silbyum marianum_ & Anti-inflammatory, anticancer & [12; 13; 14; 15] & IR; HPLC-UV-vis; LC-MS \\ \hline Proanthocyanidins & A- and B-type & \begin{tabular}{c} Cranberry, bilberry, \\ curry, cinnamon, \\ tea \\ \end{tabular} & \begin{tabular}{c} Anti-inflammatory, \\ anticancer, \\ anti-micbial, \\ hypolipidemic \\ \end{tabular} & [16; 17] & IR; NMR; FT-ICR-ESI-MS-MS; \\ \hline Stilbenoids & Resveratrol & \begin{tabular}{c} Grape, apple, \\ berries, pistachios, \\ peanuts \\ \end{tabular} & \begin{tabular}{c} Anti-inflammatory, \\ anticancer; \\ anti-micbial, \\ anti-diabetic \\ \end{tabular} & [18; 19] & HPLC-UV-vis; UPLC-MS-MS; NMR \\ \hline Tannins & Ellagitannins & \begin{tabular}{c} Sorghum, apple, \\ grape \\ \end{tabular} & \
\begin{tabular}{c} Anti-inflammatory, \\ anticancer, antimicrobial, \\ antiviral \\ \end{tabular} & [20; 21] &
\begin{tabular}{c} HPLC-UV-vis; \\ NMR; HPLC-ESI-MS-MS \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}