## 3 Results and Discussion
### Structure-Activity Relationship Analysis  
The influence of substitution patterns of the phenolic nor-triterpenes on their antimicrobial activity was analyzed, taking into account three regions of the triterpene skeleton, the phenolic moiety, the extended B-ring conjugation, and the triterpene scaffold (pristimerin, tingenone, or giuesterin). This analysis revealed the following trends in the structure-activity relationship (SAR) (Figure 4). Regarding the results obtained against _Bacillus_ spp., the SAR studies suggest that: (a) A substituent at C-4 seems essential for the activity. Thus, comparison of the activities (MICs against _B. subtilis_) of **14**, **10**, **12**, and **1**, whose only structural difference is the substituent at C4, showed that the most effective \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \hline
**Compound** & \(\boldsymbol{S.\,a.}\) & \(\boldsymbol{S.\,e.}\) & \(\boldsymbol{S.\,s.}\) & \(\boldsymbol{E.\,f.}\) & \(\boldsymbol{B.\,s.}\) & \(\boldsymbol{B.\,a.}\) & \(\boldsymbol{B.\,c.}\) & \(\boldsymbol{B.\,m.}\) & \(\boldsymbol{B.\,p.}\) & \(\mathbf{dog\,P}\) & **Reference** \\ \hline
**2** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 40–20 & \(>\)40 & 40–20 & 40 & \(>\)40 & 5.43 & \\
**3** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 40–20 & \(>\)40 & 40 & \(>\)40 & \(>\)40 & 6.41 & \\
**5** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 40–20 & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 5.26 & \\
**6** & \(>\)40 & \(>\)40 & \(>\)40 & 20–10 & 1 & 20–10 & 2.5 & 10–5 & 10–5 & 5.95 & \\
**10** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 8–4 & - & \(>\)40 & - & - & 5.42 & [21] \\
**12** & 40 & 20 & \(>\)40 & \(>\)40 & 10 & 7 & 12 & 20 & 25 & 5.67 & [22] \\
**13** & 25 & 20 & 40 & \(>\)40 & 13 & \(>\)40 & 20 & \(>\)40 & 10 & 5.04 & [22] \\
**14** & 6 & \(>\)40 & \(>\)40 & \(>\)40 & 3 & 4 & 5 & 4 & 6 & 5.21 & [23] \\
**15** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 13 & \(>\)40 & 30 & \(>\)40 & \(>\)40 & 4.67 & [23] \\
**16** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 14–12 & - & \(>\)40 & \(>\)40 & \(>\)40 & 5.58 & [20] \\
**17** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 39–35 & - & \(>\)40 & \(>\)40 & \(>\)40 & 6.20 & [20] \\
**20** & \(>\)40 & \(>\)40 & \(>\)40 & \(>\)40 & 25 & - & 40 & \(>\)40 & \(>\)40 & 6.86 & [20] \\
**22** & 30 & \(>\)40 & \(>\)40 & \(>\)40 & - & 8–4 & - & 10 & - & - & 5.79 & [21] \\
**24** & \(>\)40 & 0.625 & 10–5 & \(>\)40 & 1–0.5 & 5–2.5 & 2.5 & 20–10 & 5–2.5 & 7.09 & [21] \\
**25** & \(>\)40 & 20–10 & \(>\)40 & \(>\)40 & 10–5 & 40–20 & 20–10 & \(>\)40 & 20–10 & 6.41 & [21] \\
**26** & \(>\)40 & 2 & 20–10 & \(>\)40 & 5–2.5 & 10–5 & 10–5 & 40–20 & \(>\)40 & 6.41 & [21] \\
**Control \({}^{3}\)** & 25 & 25 & 0.6 & \(>\)20 & 8– & 10 & - & \(>\)20 & 0.14 & \\ \hline \hline \end{tabular} _S. a.: Staphylococcus aureus, S. e.: S. epidermidis, S. s.: S. saprophysics, E. f.: Enterococcus faecalis, B. s.: Bacillus subtilis, B. a.: B. alvei, B. c.: B. cereus, B. m.: B. megaterium, B. p.: B. pumilus.—not_ assayed. \({}^{1}\) The experiments were carried out in triplicate, and values represent average of MIC values. \({}^{2}\) All compounds were inactive against Gram-negative bacteria (MIC \(>\) 40 \(\upmu\)g/mL). Compounds (_clog P_) **1** (6.15), **4** (6.07), **7-9** (7.18, 6.90 and 6.90), **11** (6.38), **18** (6.47), **19** (5.44), **21** (7.17), and **23** (5.72) were inactive against all microorganisms assayed. \({}^{3}\) Cephotaxime was used as a positive control.  
\end{table} 
Table 1: Minimal inhibitory concentration (MIC, \(\upmu\)g/mL) \({}^{1}\) against Gram-positive bacteria of phenolic nor-triterpenes \({}^{2}\) and lipophilicity (clog _P_). group at this position was a carboxylic acid (**14**), followed by hydroxyl (**10**) and aldehyde (**12**) groups, while a methyl group, as in **1**, led to a loss of activity. _B. cereus_, _B. alvei_, _B. megaterium_, and _B. pumilus_ showed similar behavior to _B.