# The Synthesis and Biological Evaluation of 2-(1H-Indol-3-yl)quinazolin-4(3H)-One Derivatives
## 2 Results and Discussion
### In Vitro Biological Evaluation  
#### 2.2.1 Antibacterial Activity  
The 32 synthesized compounds were evaluated for their antimicrobial activity against _Staphylococcus aureus_, _Escherichia coli_, _Mycobacterium smgematis_, and _Candida albicans_. High activity against staphylococci was demonstrated by indolylquinazolininone **3k** (Table 1). Compound **3k** inhibited the growth of _S. aureus_ ATCC 25923, a standard reference strain for evaluating the activity of antimicrobial compounds, showing an MIC of 3.90 \(\upmu\)g/mL. At the same time, its MIC against the reference strain _S. aureus_ ATCC 43300 (MRSA) was even lower and did not exceed 1 \(\upmu\)g/mL. This is a very promising result, as MRSA is now widespread and a significant problem in human and veterinary medicine, because it is resistant to many antibacterial compounds. Additionally, we studied the activity of compound **3k** against another staphylococcus species, _S. epidermidis_ ATCC 12228. The MIC and MBC (minimum bactericidal concentration) in this case were 7.80 and 12.50 \(\upmu\)g/mL,respectively. All of the compounds were found to be inactive against the Gram-negative bacterium _E. coli_. In addition to their antibacterial properties, the antimycotic activity of the synthesized substances against _Candida albicans_ was studied (minimum fungicidal concentration--MFC). Compounds **3d**, **3p**, **3t**, **3u**, **5a**, and **6u** showed moderate activity against this microorganism, while substances **3k** and **3 ai** showed more pronounced activity (MIC 7.80, 62.50 ug/mL, respectively) (Table 1). Other quinazolinone derivatives **3** were found to be inactive (See Supplementary Materials). Mycobacteria are a special group of bacteria with unique structural and physiological features. This group includes both saprophytes and animal or human pathogens, in particular, the causative agent of tuberculosis, _Mycobacterium tuberculosis. Mycobacterium smegmatis_ is widely used as a model microorganism for studying antimycobacterial activity. Most of the compounds were found to be inactive against _M. smegmatis_. Although _M. smegmatis_ is used as a model organism for the study of _M. tuberculosis_, these bacteria are not identical and have their own individual characteristics. Particularly, there are significant differences in their growth rate and in the structure of their cell walls. Considering the high activity of compound **3k** against Gram-positive organisms (staphylococci), we studied its activity against _M. tuberculosis_ H\({}_{37}\)Rv using a BASTEC MGIT 960 growth system [49; 50]. This compound inhibited the growth of _M. tuberculosis_ H\({}_{37}\)Rv within 41 days at a concentration of 10 ug/mL. In the presence of 5 ug/mL of this substance, the growth of the mycobacteria was not observed for 18 days, and in the presence of 1 ug/mL, for 5 days (Table 2). Therefore, indolylquinazolinone **3k** is the leading compound that is promising for further studies in the field of anti-tubercular activity. \begin{table}
\begin{tabular}{c c c c c c c c c c c c} \hline \multirow{2}{*}{**Compounds**} & \multicolumn{2}{c}{_C. a._ 10231 b _} & _M. s._ 70084 c  & _E. c. 25922 d _ & _E. c. c._ 8739 e _ & _S. a._ 25923 f _ & **MRSA g**  \\ \cline{2-10}  & **MIC** & **MFC** & **MIC** & **MBC** & **MIC** & **MBC** & **MIC** & **MBC** & **MIC** & **MIC** & **MBC** \\ \hline
**3d** & 125 & 125 & - h & - & - & - & - & - & - & - & - & - \\
**3g** & - & - & - & - & - & - & - & - & -  
It is worth noting that several compounds studied in this work have previously been tested for their antibacterial activity. Compounds **3k**, **3t**, and **3z** are active against several species of _Leishmania_, which are intracellular parasites [8, 51]. Indolylquinazolinone **3k** has an antibacterial effect against _M. tuberculosis_, which is confirmed by our studies [7]. Compounds **3t**, **3u**, and **3x-z** have been tested against _E. coli_ and _S. aureus_, but did not show high activity [52], which is in agreement with our results.