## 3 Results and Discussion
### In Silico Evaluation of Synthesized Bases  
Regarding the analyses of prepared bases (**5a-g**), the PASS Online program [45,46] predicted the probability of their acting as general pump inhibitors (\(I_{\text{GPI}}\)) and membrane permeability inhibitors (\(I_{\text{MPI}}\)) as well as drugs for the treatment of cancer-associated diseases (\(I_{\text{CADT}}\)). In addition, the possible toxic effects of these bases on a cardiovascular system (i.e., probability of causing bradycardia (\(I_{\text{B}}\)), palpitation (\(I_{\text{P}}\)), and tachycardia (\(I_{\text{T}}\)) as well as prolongation of a QT interval in the heart (\(I_{\text{QTp}}\))) were also predicted (Table S3). The criteria for prediction of a specific activity are provided in the Supplementary Materials.  
**BDQ** inhibits the synthesis of ATP in mycobacteria. The substance interferes with the activity of an F\({}_{1}\)F\({}_{0}\) ATP synthase enzyme by inhibiting its proton pump, which is critical for the generation of membrane potential. This synthase is one of the enzymes considered essential for meeting the energy requirements of both the proliferating aerobic and hypoxic dormant stages of the life cycle for a variety of mycobacterial strains. ATP levels are highly reduced within bacterial cells upon the action of **BDQ**[82,83].  
The highest probability to act as general pump inhibitors was calculated for the compounds containing one or two phenyl rings substituted with hydrogens only (Table S3), i.e., **5g** (\(I_{\text{CSPI}}\) = 0.707) and **5a** (\(I_{\text{CSPI}}\) = 0.613). The presence of other substituents provided lower values regardless of their ED (**5b**) or EW (**5c-f**) properties.  
The pathogenic properties of _Mtb_ are based on thwarting the innate defense systems of a macrophage host cell. Virulence factors of _Mtb_ disrupt physiological host cell signaling. The destruction of macrophages starts when the pathogen enters a cell, affecting (destroying) a variety of host signal transduction pathways. Moreover, the surface of these cells is remodulated as a consequence of _Mtb_ action via altering the expression of the molecules, which are crucial for full activation of an adaptive immune response [84].  
Membrane permeability inhibitors could more or less block this process. The predicted \(I_{\text{MPI}}\) parameter for synthesized bases varied from 0.457 (**5g**) to 0.555 (**5d**). It seemed that the probability of their blocking activity was related to a precise selection of a substituent owning specific electronic and steric properties. The 4'-Cl substitution was the most favorable (**5d**), the lipophilicity of a given atom might be described by \(\pi_{\text{4'-Cl}}\) = 0.71 and the EW effect with a Hammett substituent constant \(\sigma\) (\(\sigma_{\text{4'-Cl}}\) = 0.23). The values set for hydrogen were as follows [68]: \(\pi_{\text{H}}\) = 0.00, \(\sigma_{\text{H}}\) = 0.00.  
Special attention should be paid to the molecule **5g** (as well as its antimycobacterially effective salt **6g**), as \(I_{\text{T}}\) = 0.605 and \(I_{\text{QTp}}\) = 0.640. The issue of polymorphic ventricular tachycardia and QT interval prolongation was also observed for **BDQ**. If the interval is prolonged, polymorphic ventricular tachycardia and/or \"torsades de pointes\" can occur. These dysfunctions may precipitate ventricular fibrillation resulting in sudden death. Fortunately, severe QT interval prolongation is an infrequent cause of **BDQ** interruption despite the frequent use of concomitant drugs that also prolong the QT interval [85,86].