## 3 Results and Discussion
### Antioxidant Activity  
The antioxidant activity of _M. stylosa_ and _M. serrulata_ herb extracts and selected dominant compounds was estimated using well-known assays to explore the scavenging properties against 2,2-diphenyl-1-picrylhydrazyl radicals (DPPH\({}^{\bullet}\)), 2,2\({}^{\prime}\)-azino-bis(3-ethylbenzothazoline-6-sulfonic acid radicals (ABTS\({}^{\bullet+}\)), and \(N\),\(N\)-dimethyl-\(p\)-phenylenediamine radicals (DMPD\({}^{\bullet+}\)) (Table 4). The investigated herb extracts of _M. stylosa_ and _M. serrulata_ revealed good scavenging capacity against DPPH\({}^{\bullet}\), ABTS\({}^{\bullet+}\), and DMPD\({}^{\bullet+}\) radicals. _M. stylosa_ herb extract demonstrated the best values of half-maximal scavenging concentrations (IC\({}_{50}\)) of 21.17, 15.33 and 79.34 ug/mL for DPPH\({}^{\bullet}\), ABTS\({}^{\bullet+}\), and DMPD\({}^{\bullet+}\) radicals, respectively. The predominant phenolic compound, 5-O-caffeoylquinic acid, demonstrated superior scavenging activity against synthetic radicals while the alkaloid lycopsamine showed weak antiradical activity. Earlier antioxidant properties of _M. maritima_ shoots extracts were evaluated with DPPH\({}^{\bullet}\) and ABTS\({}^{\bullet+}\) assays (IC\({}_{50}\) 0.57 and 0.78 mg/mL, respectively) [24]. \begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Object**} & \multicolumn{2}{c}{**Assay 1 **} \\ \cline{2-3}  & **DPPH\({}^{\bullet}\)** & **ABTS\({}^{\bullet+}\)** & **DMPD\({}^{\bullet+}\)** \\ \hline _M. stylosa_ herb extract & 21.17 \(\pm\) 0.38 d & 15.33 \(\pm\) 0.31 d & 79.34 \(\pm\) 1.51 d \\ _M. serrulata_ herb extract & 37.95 \(\pm\) 0.65 e & 24.02 \(\pm\) 0.46 e & 96.11 \(\pm\) 1.92 e \\ Lycopsamine \(N\)-oxide & 397.45 \(\pm\) 7.95 f & 275.62 \(\pm\) 5.24 f & 57.286 \(\pm\) 10.88 f \\
5-O-caffeoylquinic acid & 8.14 \(\pm\) 0.15 b & 7.29 \(\pm\) 0.15 c & 21.14 \(\pm\) 0.40 a \\ Rutin & 9.54 \(\pm\) 0.19 e & 5.89 \(\pm\) 0.11 b & 38.19 \(\pm\) 0.73 b \\ Trolox c & 7.92 \(\pm\) 0.16 a & 3.41 \(\pm\) 0.06 a & 52.79 \(\pm\) 1.06 c \\ \hline \hline \end{tabular}  
* DPPH\({}^{\bullet}\)—2,2-diphenyl-1-picrylhydrazyl radical scavenging capacity; ABTS\({}^{\bullet+}\)—2,2-azino-bis(3-ethylbenzothazoline-6-sulfonic acid) cation radical scavenging capacity; DMPD\({}^{\bullet+}\)—\(N\)-dimethyl-\(p\)-phenylenediamine radical scavenging capacity. \({}^{\mathrm{b}}\) IC\({}_{50}\), ug/mL. \({}^{\mathrm{c}}\) Reference compound. Averages \(\pm\) standard deviation (S.D.) were obtained from five different experiments. Values with different letters (a–f) in each column indicate statistically significant differences among groups at \(p<0.05\) by Duncan test.[ENDFOOTNOTE]  
\end{table} 
Table 4: Antioxidant activity of _M. stylosa_, _M. serrulata_ herb extracts and selected compounds in three in vitro assays. Figure 5: Structures of phenolic compounds found in _M. stylosa_ and _M. serrulata_. Our studies have shown that two North mertensias, _M. stylosa_ and _M. serrulata_, are able to accumulate various phytochemicals, such as alkaloids and phenolics, involved in the antioxidant potential of plant extracts. Pyrrolizidine alkaloids are usually esters formed from a necine base and necic acids [27]. Depending on the structure of the necine base, such alkaloids can be divided into four types: retronecine, otonecine, platynecine, and heliotridine [28]. According to chemotaxonomic data on the distribution of alkaloids in the Boraginaceae family, the species of genus _Mertensia_ produce alkaloids of the retronecine type [29]. Pyrrolizidine alkaloids are known to have hepatotoxic and potentially carcinogenic properties [30; 31; 32; 33]. However, because pyrrolizidine alkaloids are mainly present in the form of \(N\)-oxides, such compounds are considered less toxic than free components owing to their high water solubility [34]. Lycoposamine is an unsaturated monoester, and the monoester and \(N\)-oxide are less toxic than the diester or macrocyclic ester [35]. Some useful properties of lycoposamine are also known.