## 4 Discussion  
5-HT is a key neurotransmitter in the CNS, gastrointestinal tract, and platelets. It performs many important functions in the human body, such as the following: it regulates intestinal peristalsis; it is a vasoconstritor and helps maintain homeostasis balance and contributes to proper blood clotting. The function of 5-HT in the CNS is not fully understood. So far, it is known that it is responsible for cognitive functions and regulates mood and appetite. Although there is only 10% of serotonin in the CNS, its reduction affects the occurrence of depression, obsessive-compulsive disorders, and anxiety states. Reduced 5-HT levels also contribute to developing heart disease and inflammation [34; 35; 36]. Therefore, proposing new, non-toxic compounds that inhibit MAO-A is essential. The studies documented that compounds such as diols and hydroxy ketones obtained using chemo-enzymatic methods from propenylbenzene bind to MAO-A in the active site. This means that they increase serotonin transport by inhibiting MAO-A. Additionally, by inhibiting deamination, the inactivation of MAO-A prevents the formation of intermediate products such as hydrogen peroxide and aldehydes, which contribute to inflammation through the formation of amyloid plaques and accompanying the degradation of neuronal membranes [34; 37]. An ITC experiment was carried out to verify the possibility of \begin{table}
\begin{tabular}{c c c c c c c c} \hline \hline
**Compound** & **1b** & **2b** & **2c** & **3b** & **3c** & **4b** & **5b** \\ \hline AD Docking & \(-\)31.18 & \(-\)25.71 & \(-\)26.63 & \(-\)26.58 & \(-\)27.25 & \(-\)26.71 & \(-\)27.21 \\ Score (k/mol) & & & & & & & \\ LF Docking & \(-\)30.64 & \(-\)26.28 & \(-\)23.28 & \(-\)26.96 & \(-\)25.33 & \(-\)29.72 & \(-\)32.94 \\ Score (k/mol) & & & & & & & \\ ILE23 & AD and LF & AD and LF & No & No & AD and LF & LF & AD \\ SER24 & AD and LF & No & No & LF & AD and LF & LF & AD and LF \\ GLY49 & No & LF & No & No & No & No & No \\ ARG51 & No & AD and LF & AD and LF & LF & AD and LF & LF & AD and LF \\ THR52 & No & AD and LF & LF & LF & AD and LF & LF & LF \\ GLY67 & No & No & No & LF & AD and LF & LF & No \\ ALA68 & No & No & No & AD & No & AD & No \\ TYR69 & No & No & No & AD & No & AD & No \\ ALA272 & No & No & LF & No & No & No & No \\ VAL303 & No & No & No & No & No & No & No \\ LYS305 & No & No & No & No & No & No & No \\ PHE352 & No & No & No & AD & No & AD & No \\ TYR407 & AD and LF & AD & AD & AD and LF & LF & AD and LF & AD and LF \\ THR435 & AD and LF & AD and LF & LF & LF & AD and LF & LF & AD and LF \\ GLY443 & AD and LF & No & AD & No & No & No & LF \\ TYR444 & No & No & AD & Ad & No & AD & AD \\ MET445 & No & AD & AD & No & No & No & No \\ ALA448 & AD and LF & AD and LF & LF & LF & AD and LF & LF & No \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Propenylbenzene derivative (diol and hydroxy ketone) interactions with identical amino acid residues on MAO-A. binding the studied diols and hydroxy ketones in the active site of the enzyme under the physiological concentrations. It was observed that compounds **1a**, **1c**, **2a**, **3a**, **4a**, **4c**, and **5a** did not inhibit MAO-A. The experiment was repeated at different larger concentrations to determine the relationship between concentration and inhibition activity. Interestingly, diols and hydroxy ketones were already bound in the active site of MAO-A, protecting serotonin against deamination. Such a relationship was observed for compounds **1b**, **2b**, **2c**, **3b**, **3c**, **4b**, and **5b**. The most stable bonds with MAO-A were formed by compounds **5b** (\(\Delta\)H = \(-\)40.53 kJ/mol; \(\Delta\)G = \(-\)24.24 kJ/mol; IC50 = 2.38 umol/L) and **3b** (\(\Delta\)H = \(-\)38.44 kJ/mol; \(\Delta\)G = \(-\)34.12 kJ/mol; IC50 = 3.02 umol/L). Our research found isoeigenenol (**5a**) as an efficient MAO-A inhibitor. Eugenol did not show any inhibitory effect; however, the already synthesized diol **5b** was the best MAO-A inhibitor (K\({}_{i}\) < 0.001).