## 2 Results and Discussion
### In Vitro Biological Evaluation
#### 2.2.1 Antimicrobial Activity
However, bacteria do not contain tubulin, and the target for these substances in prokaryotic cells is obviously different. It is even more interesting that the synthesized library contains some substances **3j**, **3y**, and **3 al** with selective activity against staphylococci, which do not have an inhibitory effect against fungi, Gram-negative bacteria, or mycobacteria. Previously, the antistaphylococcal activity of benzimidazoles was registered in some studies; however, MIC values were 10s and 100s of \(\mathrm{\SIUnitSymbolMicro}\)/mL [26; 30; 37]. There are data on the activity of these compounds with MICs of 4 \(\mathrm{\SIUnitSymbolMicro}\)/mL [38], 3.12 \(\mathrm{\SIUnitSymbolMicro}\)/mL [39], and 6 \(\mathrm{\SIUnitSymbolMicro}\)/mL [40]. In our studies, nine compounds showed the high activity against staphylococci: **3j**, **3n**, **3 aa**, **3 ab**, **3 ad**, **3 ag**, **3 ao**, and **3 az**, and two of them (**3 ao** and **3 aq**) demonstrated an MIC \(<\) 1 \(\mathrm{\SIUnitSymbolMicro}\)/mL. A special group of microorganisms are mycobacteria. They include the causative agents of dangerous diseases, primarily tuberculosis. Bacteria in this group have a unique cell wall structure and some metabolic features that provide them with reduced sensitivity to many antibiotics. To test the antimycobacterial activity of the compounds, we used the model object _M. smegmatis_ mc2155, which has a high growth rate and is not pathogenic. Seventeen compounds demonstrated moderate antimicrobial activity against _M. smegmatis_ (MIC 17-125 \(\mathrm{\SIUnitSymbolMicro}\)/mL). Two of the tested substances **3i** and **3 ag** showed a high ability to inhibit the growth of mycobacteria (MIC 7.8 and 3.9 \(\mathrm{\SIUnitSymbolMicro}\)/mL, respectively). Since mycobacteria have probably been the most \"problematic\" group of bacteria in terms of antibiotic therapy for decades, the discovery of a sufficiently high antimycobacterial activity in synthesized compounds seems promising. A comparative evaluation of the activity of compounds **3o** and **3 ao** showed that the introduction of the bromine atom into the core of benzimidazole leads to a significant increase in antimicrobial activity. In this case, the MIC against _S. aureus_ decreased from 31.1 \begin{table}
\begin{tabular}{c c c c c c c c c c c c c} \hline \multirow{2}{*}{**Compounds**} & \multicolumn{2}{c}{_C.a._ **10231 b**} & \multicolumn{2}{c}{_M. s._ **70084 c**} & \multicolumn{2}{c}{_E. c. c._ **25922 d**} & \multicolumn{2}{c}{_E. c. c._ **8739 e**} & \multicolumn{2}{c}{_S. a._ **25923 f**} & \multicolumn{2}{c}{**MRSA 8**} \\ \cline{2-13}  & **MIC** & **MFC** & **MIC** & **MBC** & **MIC** & **MBC** & **MIC** & **MBC** & **MIC** & **MIC** & **MIC** & **MBC** \\ \hline Isoniazid & n.d. & n.d. & n.d. & 4.58 & 9.16 & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. \\ Rifampicin & n.d. & n.d. & 1.22 & 19.53 & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. & n.d. \\ \hline \end{tabular}  
* In the table, the Mode values from 3–6 independent experiments are presented. MIC—minimum inhibitory concentration; MBC—minimum bactericidal concentration; MFC—minimum fungicidal concentration; b _Candidia albicans_ ATCC 10231; c _Mycobacterium smegmatis_ ATCC 70084; d _Escherichia coli_ ATCC 25922; e _Escherichia coli_ ATCC 8739; f _Staphylococcus aureus_ ATCC 25923; g _Staphylococcus aureus_ ATCC 43300 (MRSA); h (-) \(>\)1000 \(\mathrm{\SIUnitSymbolMicro}\)/mL; i n.d.—not determined.  
\end{table} 
Table 1: _Cont._to 0.98 \(\upmu\)g/mL, and against _C. albicans_ from 62.5 to 15.6 \(\upmu\)g/mL. It should be noted that 2-(1\(H\)-indol-3-yl)-6,7-dimethyl-1\(H\)-benzo[\(d\)]imidazole (**3 ae**) showed moderate activity against _C. albicans_; _S. aureus_, including MRSA; and _M. smegmatis_. The introduction of a bromine atom into the imidazole fragment (for **3 aq**) significantly improved the antimicrobial activity: it increased by 32 times against _S. aureus_, by 16 times against MRSA, and by 8 times against _C. albicans_.