Preparation and Biological Properties of Ring-Substituted Naphthalene-1-Carboxanilides

In this study, a series of twenty-two ring-substituted naphthalene-1-carboxanilides were prepared and characterized. Primary in vitro screening of the synthesized carboxanilides was performed against Mycobacterium avium subsp. paratuberculosis. N-(2-Methoxyphenyl)naphthalene-1-carboxamide, N-(3-methoxy-phenyl)naphthalene-1-carboxamide, N-(3-methylphenyl)naphthalene-1-carboxamide, N-(4-methylphenyl)naphthalene-1-carboxamide and N-(3-fluorophenyl)naphthalene-1-carboxamide showed against M. avium subsp. paratuberculosis two-fold higher activity than rifampicin and three-fold higher activity than ciprofloxacin. The most effective antimycobacterial compounds demonstrated insignificant toxicity against the human monocytic leukemia THP-1 cell line. The testing of biological activity of the compounds was completed with the study of photosynthetic electron transport (PET) inhibition in isolated spinach (Spinacia oleracea L.) chloroplasts. The PET-inhibiting activity expressed by IC50 value of the most active compound N-[4-(trifluoromethyl)phenyl]naphthalene-1-carboxamide was 59 μmol/L. The structure-activity relationships are discussed.


Chemistry
The studied compounds were prepared using two methods according to Scheme 1. The discussed compounds were synthesized by using two-step synthesis (Method A: a,b) via 1-naphthoyl chloride as intermediate [9] or by one-pot microwave-assisted synthesis (Method B: c) [10]. Both methods yielded a series of twenty-two N-substituted naphthalene-1-carboxanilides 1-8c. Scheme 1. Synthesis of ring-substituted naphthalene-1-carboxanilides 1-8c.
Lipophilicity is a property that has a major effect on bioavailability, biotransformation as well as pharmacological activity, because drugs cross biological membranes through passive transport, which strongly depends on their lipophilicity. Lipophilicity of the studied compounds was determined by RP-HPLC as capacity factor logarithm (log k). The procedure was performed under isocratic conditions with methanol as an organic modifier in the mobile phase using an end-capped non-polar C 18 stationary RP column. The results of ring-substituted naphthalene-1-carboxanilides 1-8c are shown in Table 1 and illustrated in Figure 1. The highest experimental lipophilicity was found for N- [4-(trifluoromethyl)-phenyl]naphthalene-1-carboxamide (7c), while N-(4-methoxyphenyl)naphthalene-1carboxamide (2c) showed the lowest log k value. Lipophilicity was also calculated as log P using ACD/Percepta ver. 2012 (Advanced Chemistry Development, Inc., Toronto, ON, Canada). Table 1. Structure of ring-substituted naphthalene-1-carboxanilides 1-8c, experimentally determined values of lipophilicity log k, calculated values of lipophilicity (log P), predicted hydrophobic distributive parameter π, predicted polar substituent constants σ*, in vitro antimycobacterial activity (MIC/IC 90 ) of compounds against clinical isolate of Mycobacterium avium subsp. paratuberculosis CIT03 (MAP) in comparison with isoniazid (INH), ciprofloxacin (CPX), and rifampicin (RIF) standards, in vitro cytotoxicity assay (LD 50   The results obtained with all the ring-substituted naphthalene-1-carboxanilides show that the experimentally-determined lipophilicity (log k) of the discussed compounds poorly correlates with the calculated values log P of compounds 1-8c as shown in Figure 1A,B. For the ortho-substituted derivatives no correlation was found. Similar poor correlation between experimentally and predicted lipophilicity values was described for ring-substituted 2-hydroxynaphthalene-1-carboxanilides and 1-hydroxynaphthalene-2-carboxanilides [11,12] and for hydroxyquinolinecarboxamides [24]; nevertheless, this poor correlation was attributed to the phenolic moiety in the position vicinal to the carboxamide group. As there is no any phenolic moiety in these structures, lipophilicity was additionally expressed as a hydrophobic distributive parameter π of the carboxamide moiety and ringsubstituted phenyl; it was also calculated using ACD/Percepta, see Table 1. Again, it can be stated that no match of log k to π of the ortho-substituted compounds was found ( Figure 1C), while the meta-and para-substituted derivatives showed better match, see Figure 1D. The most significant deviations within the dependence illustrated in Figure 1D can be observed for 4-CF 3 (7c) and 4-NO 2 (8c).
Based on these observations, some intramolecular interactions between the carboxamide moiety and the phenyl substituents could be supposed that influence the resulting lipophilicity of compounds. These interactions are characterized rather by using distributive parameter π of substituents in position 1 of naphthalene than by using log P parameter of the whole molecule. Differences between expected and found values were also observed during TLC, when the purity of the final compounds was checked. Ab initio/DFT calculations of charges in individual structures could provide more detailed information, nevertheless, such investigation was not the aim of this paper.
The influence of R substituents on lipophilicity (log k) is as follows within ortho-substituted derivatives: CH 3 < F = H < CF 3 < OCH 3 < Cl < Br < NO 2 and as follows within meta-and para-substituted derivatives: OCH 3 ≈ H < F < CH 3 < NO 2 < Cl < Br < CF 3 . Within the individual series the lipophilicity determined by log k values increases for halogens and methyl substituents as follows: ortho < para < meta; for OCH 3 and NO 2 as follows: para < meta < ortho. It can be assumed that log k values specify lipophilicity within individual series of the studied compounds.
Based on the above-mentioned observations, electronic properties of prepared compounds 1-8c were expressed as polar substituent constants σ* of the whole substituent in position 1 of naphthalene, i.e., influence of carboxamide moiety and ring-substituted phenyl was included. The individual σ* parameters were predicted using the ACD/Percepta software; they ranged from 0.26 (1, R = H) to 0.43 (8c, R = 4-NO 2 ).

In Vitro Antimycobacterial Evaluation
In vitro antimycobacterial screening of all the compounds against Mycobacterium avium subsp. paratuberculosis was performed, however most compounds did not show any activity (higher than 793 μmol/L). Only the eight compounds presented in Table 1 showed antimycobacterial effectivity. The antimycobacterial activity was expressed as minimum inhibitory concentration (MIC) that is defined for mycobacteria as a 90% or greater (IC 90 ) reduction of growth in comparison with the control. The MIC/IC 90 value is routinely and widely used in bacterial assays and is a standard detection limit according to the Clinical and Laboratory Standards Institute [47]. N-(2-Methoxyphenyl)naphthalene-1-carboxamide (2a), N-(3-methoxyphenyl)naphthalene-1-carboxamide (2b), N-(3methylphenyl)naphthalene-1-carboxamide (3b), N-(4-methylphenyl)-naphthalene-1-carboxamide (3c) and N-(3-fluorophenyl)naphthalene-1-carboxamide (4b) demonstrated two-fold higher activity than rifampicin and three-fold higher activity than ciprofloxacin. Figure 2 shows dependence of the antimycobacterial activities expressed as log(1/MIC [mol/L]) on lipophilicity expressed as log k (Figure 2A), distributive parameter π ( Figure 2B) and electronic properties expressed as polar substituent constants σ* ( Figure 2C). When inactive compound 1 (R = H) was eliminated (marked by cross), the dependences of log(1/MIC) on log k and of log(1/MIC) on σ* were biphasic: in the range of π from 0.6087 (2b) to 0.8013 (2a), as well as in the range of σ* from 0.29 (2a) to 0.38 (3c) the antimycobacterial activity remained practically constant while a further increase of log k or σ* resulted in a strong activity decrease. Consequently, it can be concluded that the lipophilicity of compounds higher than log k = 0.8013 is adverse in terms of antimycobacterial activity; increased electron-withdrawing properties of the whole substituent in position 1 of naphthalene (expressed as polar substituent constants σ*) exceeding value σ* = 0.38 are also unfavourable.
When antimycobacterial activities of both series of naphthalene-2-carboxanilides [9] and naphthalene-1-carboxanilides are compared, it can be stated that the discussed 1-carboxanilides demonstrated significantly higher activity. Comparison of 2-hydroxynaphthalene-1-carboxanilides [11] with naphthalene-1-carboxanilides is more complicated. It can be stated that 2-hydroxy derivatives showed wider spectrum of antimycobacterial effect; nevertheless when MICs of compounds and the standards are compared, it seems that compounds presented herein demonstrated more potent activity. In general it can be stated that in both series derivatives with lipophilicity log k > 0.6 can show antimycobacterial effect, and within both series rather meta-substituted derivatives demonstrated higher activity, which can be connected with the planarity of the structure [9,11,12], nevertheless in the series of 2-hydroxynaphthalene-1-carboxanilides substituents with significant electron-withdrawing effect are favoured [11], while among naphthalene-1-carboxanilides rather electron-neutral or slightly electron-withdrawing substituents are preferable, i.e., phenyl substituents with minimal effect on electronic density at the carboxamide moiety [10][11][12].

C
Of the eight compounds the three with the best efficacy were used to monitor their effect on the viability of M. avium subsp. paratuberculosis CIT03 over a period of five days, see Figure 3. A concentration range starting at 1,000 µg/mL to 15 µg/mL was used for compounds 2b, 3c, and 4b. The percent reduction of alamarBlue of these three compounds was compared to an untreated control of M. avium subsp. paratuberculosis and the standards rifampicin and ciprofloxacin. Figure 3A illustrates the dependence of the percent reduction of alamarBlue of compounds 2b, 3c, and 4b at their MICs (15 µg/mL, i.e., 54, 57, and 57 µmol/L) on time in comparison with ciprofloxacin (CPX) and rifampicin (RIF) standards at their MICs (60 and 90 µg/mL, i.e., 181 and 109 µmol/L) and the untreated control of M. avium subsp. paratuberculosis. Figure 3B-D show in detail individual dependences of the percent reduction of alamarBlue on time (in days) at various concentrations of the individual compounds (range from 1000 to 15 µg/mL) in comparison with the standards at their MICs. The percent reduction values for all treated M. avium subsp. paratuberculosis samples were less than 20% over the five-day period of testing. As previously outlined by Carroll et al. [48], percent reduction values less than 20% indicate insufficient cell metabolism and hence lack of cell viability.
Additionally, a standard MTT assay was performed on these same compounds. The MTT assay is a well-characterized method of assessing cell growth through measurement of respiration. As such, a low level of cell viability may suggest inhibition of cell growth through respiratory inhibition [49]. 3-Methoxy (2b) and 4-methyl (3c) derivatives showed more than 80% reduction in activity at the lowest tested concentration (8 µg/mL, i.e., ca. 30 µmol/L) after four hours of incubation, similar to the reduction observed in the rifampicin and ciprofloxacin standards. Compounds 2a and 4b achieved similar levels of inhibition at 16 µg/mL (ca. 60 µmol/L) concentration.   Janin mentioned that a similar type of carboxamides can interfere with the mycobacterial proton pump F 0 F 1 H + ATPase or inhibit biosynthesis of amino acids [50]. This hypothesis was confirmed in recently published papers [3,51,52], where the mechanism of action of bedaquiline (TMC-207, I) and its naphthalene analogues (II) as potent compounds inhibiting the respiratory chain of mycobacteria is discussed. Based on structure analogy, the discussed ring-substituted naphthalene-1-carboxanilides can be considered as simplified derivatives of bedaquiline and its naphthalene analogues, see Figure 4. Since the change in colour of alamarBlue is caused by a decrease of mycobacterial cell metabolism, it is possible that these compounds bind to the mycobacterial respiratory chain components. However, another possible site of action of the studied compounds in the mycobacteria cannot be excluded.  [3,50].

In Vitro Cytotoxicity Assay
The preliminary in vitro screening of cytotoxicity of the most effective antimycobacterial compounds 2a, 2b, 3b, 3c, and 4b was performed using the human monocytic leukemia THP-1 cell line. The cytotoxicity was evaluated as the LD 50 value (LD 50 -lethal dose to 50% of the cell population), see Table 1. The discussed anilides 2a, 2b, 3b, 3c and 4b were not soluble at concentrations above 30 μmol/L in testing medium containing 0.1% DMSO, therefore the highest available concentration 30.0 μmol/L was used for the toxicity assay. Treatment with 30 μmol/L of 2a, 2b, 3b, 3c, and 4b did not lead to significant lethal effect on THP-1 cells (e.g., LD 50 of oxaliplatin and of camptothecin assessed in this line formerly showed similar values: 1.7 ± 0.64 μmol/L and 0.16 ± 0.07 μmol/L, respectively). Based on these observations it can be concluded that the discussed anilides with antimycobacterial efficacy are nontoxic [53] and therefore they can be considered as promising agents for subsequent design of novel antimycobacterial agents.

Inhibition of Photosynthetic Electron Transport (PET) in Spinach Chloroplasts
The evaluated naphthanilide derivatives showed moderate or low inhibition of photosynthetic electron transport (PET) in isolated spinach (Spinacia oleracea L.) chloroplasts compared with the standard, see Table 1. The PET-inhibiting activity was expressed by IC 50 value, i.e., compound concentration in mol/L causing 50% inhibition of PET. Generally compounds showed poor aqueous solubility and IC 50 values of 1-3a, 4a, 4c, 5a, 6a, and 7a could not be determined due to precipitation of the compounds during the experiments. From rest twelve compounds compound 7c (R = 4-CF 3 ) expressed the highest PET-inhibiting activity (IC 50 = 59 µmol/L), while compound 8b (R = 3-NO 2 ) expressed the lowest PET-inhibiting activity (IC 50 = 492 µmol/L). However, it could be noted that limited solubility in tested medium at higher compound concentrations was observed also for 3c, 6b, 6c, 8a, and 8b.  4b, 5b, 5c, 7b, 7c, 8c) seems to be approximately linear. On the other hand, the dependence of PET-inhibiting activity on distributive parameter π of the whole substituents in position 1 of naphthalene showed bilinear dependence, the activity increased up to π = 1.41 (R = 4-CF 3 , compound 7c) and further lipophilicity increase resulted in activity decrease. The dependence of PET inhibition on the electronic properties σ* of the whole substituents in position 1 of naphthalene, showed also biphasic course with the optimum σ* = 0.41 (compound 7c).
When the PET-inhibiting activity is compared with that of 2-hydroxynaphthalene-1carboxanilides [11], it can be stated that 2-hydroxy derivatives showed higher solubility and higher activity, nevertheless similar relationships between PET inhibition and lipophilicity and electronic parameters of substituents were observed. Completely different dependences of PET inhibition on lipophilicity and electronic parameters of substituents were found within the series of naphthalene-2carboxanilides [9].

General
All reagents were purchased from Aldrich. TLC experiments were performed on alumina-backed silica gel 40 F254 plates (Merck, Darmstadt, Germany) using chloroform/acetone (2:1) as a mobile phase. The plates were illuminated under UV (254 nm) and evaluated in iodine vapor. The melting points were determined on Kofler hot-plate apparatus HMK (Franz Kustner Nacht KG, Dresden, Germany) and are uncorrected. Infrared (IR) spectra were recorded on a Smart MIRacle™ ATR ZnSe for Nicolet™ Impact 410 FT-IR spectrometer (Thermo Scientific, West Palm Beach, FL, USA). The spectra were obtained by accumulation of 256 scans with 2 cm −1 resolution in the region of 4,000-600 cm −1 . All 1 H and 13 C-NMR spectra were recorded on a Bruker Avance III 400 MHz FT-NMR spectrometer (400 MHz for 1 H and 100 MHz for 13 C, Bruker Comp., Karlsruhe, Germany). Chemical shifts are reported in ppm () using internal Si(CH 3 ) 4 as the reference with diffuse, easily exchangeable signals being omitted. Mass spectra were measured using a LTQ Orbitrap Hybrid Mass Spectrometer (Thermo Electron Corporation, USA) with direct injection into an APCI source (400 °C) in the positive mode.

Synthesis
General Procedure for Synthesis of Carboxamide Derivatives 1-8c Method A: Naphthalene-1-carboxylic acid (5.8 mmol) was dissolved in dry hot toluene (40 mL) and thionyl chloride (8.0 mmol) was added. After 2 h of refluxing, solvent and excessive thionyl chloride were evaporated under reduced pressure giving napthalene-1-carbonyl chloride as colourless liquid in quantitative yield. The product forms colourless needles after cooling. Mp. 18-19 °C (26 °C [54]). Naphthalene-1-carbonyl chloride (5.8 mmol), triethylamine (8.7 mmol) and corresponding substituted aniline (5.8 mmol) were dissolved in dry dichloromethane (30 mL) and the mixture was stirred for 12 h at ambient temperature. The solvent was evaporated under reduced pressure, the solid residue washed with 10% HCl, and the crude product was recrystallized from propan-2-ol with addition of active carbon.

Lipophilicity Determination Using HPLC (Capacity Factor k /Calculated log k)
A HPLC system Agilent 1200 equipped with DAD detector (Agilent, USA) was used. A chromatographic column Symmetry ® C 18 5 μm, 4.6  250 mm, Part No. WAT054275 (Waters Corp., Milford, MA, USA) was used. The HPLC separation process was monitored and evaluated by EZChrom Elite software ver. 3.3.2 (Agilent, USA). Isocratic elution by a mixture of MeOH p.a. (60%) and H 2 O-HPLC Mili-Q grade (40%) as a mobile phase was used. The total flow of the column was 1.0 mL/min, injection 20 μL, column temperature 40 °C, and sample temperature 10 °C. The detection wavelength 210 nm was chosen. The KI methanolic solution was used for the dead time (t D ) determination. Retention times (t R ) were measured in minutes. The capacity factors k were calculated according to formula k = (t R − t D )/t D , where t R is the retention time of the solute, whereas t D denotes the dead time obtained using an unretained analyte. Log k, calculated from the capacity factor k, is used as the lipophilicity index converted to log P scale. The log k values of individual compounds are shown in Table 1.

In Vitro Antimycobacterial Evaluation
A well-characterized clinical isolate of Mycobacterium avium subsp. paratuberculosis (CIT03) was grown in Middlebrook broth (MB), supplemented with Oleic-Albumin-Dextrose-Catalase supplement (OADC, Becton, Dickinson and Comp., Franklin Lakes, NJ, USA) and mycobactin J (2 µg/mL). Identification of this isolate was performed using biochemical and molecular protocols. At log phase growth, a culture sample (10 mL) was centrifuged at 15,000 rpm/20 min using a bench top centrifuge (Model CR 4-12, Jouan Inc., Winchester, VA, USA). Following removal of the supernatant, the pellet was washed in fresh Middlebrook 7H9GC broth and re-suspended in fresh supplemented MB (10 mL). The turbidity was adjusted to match McFarland standard No. 1 (3 × 10 8 cfu) with MB broth. A further 1:20 dilution of the culture was then performed in MB broth. The antimicrobial susceptibility of the mycobacterial species was investigated in a 96-well plate format. In these experiments, sterile deionized water (300 µL) was added to all outer-perimeter wells of the plates to minimize evaporation of the medium in the test wells during incubation. Each evaluated compound (100 µL) was incubated with the mycobacterial species (100 µL). Dilutions of each compound were prepared in duplicate. For all synthesized compounds, final concentrations ranged from 1,000 µg/mL to 8 µg/mL. All compounds were prepared in DMSO and subsequent dilutions were made in supplemented MB. The plates were sealed with parafilm and incubated at 37 °C for 11 days.
Following incubation, a 10% addition of alamarBlue (AbD Serotec, Kidlington, UK) was mixed into each well and readings at 570 nm and 600 nm were taken, initially for background subtraction and subsequently after 24 h re-incubation. The background subtraction is necessary for strongly coloured compounds, where the colour may interfere with the interpretation of any colour change. For non-interfering compounds, a blue colour in the well was interpreted as an absence of growth and a pink colour was scored as growth. Furthermore percent reduction of alamarBlue was calculated to generate quantitative data on cell viability during exposure to antimycobacterial compounds over a period of 5 days. The formula used to determine percent reduction of alamarBlue has been standardized for colorimetric analysis by Abd Serotec.
For the MTT assay, the same 96-well plate set up and incubation conditions listed above were used. After the incubation period, a 10% addition of MTT reagent was mixed into each well and incubated at 37 °C for 4 h. The reagent and media were then aspirated from the wells to which 50 µL DMSO was then added and plates were read at 550 nm.
The actimycobacterial activity was expressed as the minimum inhibitory concentration (MIC) that is defined for mycobacteria as a 90% or greater (IC 90 ) reduction of growth in comparison with the control. The MIC value is routinely and widely used in bacterial assays and is a standard detection limit according to the Clinical and Laboratory Standards Institute [47]. Isoniazid, rifampicin and ciprofloxacin (Sigma-Aldrich) were used as reference antimycobacterial drugs. The results are summarized in Table 1.

In Vitro Cytotoxicity Assay
Human monocytic leukemia THP-1 cells were obtained from the European Collection of Cell Cultures (ECACC, Salisbury, UK; Methods of characterization: DNA Fingerprinting (Multilocus probes) and isoenzyme analysis). These cells were routinely cultured in RPMI 1640 (Lonza, Verviers, Belgium) medium supplemented with 10% fetal bovine serum (FBS, Sigma-Aldrich, St. Louis, MO, USA), 2% L-glutamine, 1% penicillin and streptomycin (Lonza) at 37 °C with 5% CO 2 . Cells were passaged at approximately one-week intervals. Cells were routinely tested for the absence of mycoplasma (Hoechst 33258 staining method). The tested compounds were dissolved in DMSO (Sigma-Aldrich) and added in five increasing concentrations to the cell suspension in the culture medium. The maximum concentration of DMSO in the assays never exceeded 0.1%. Subsequently, the cells were incubated for 24 h at 37 °C with 5% CO 2 to various compound concentrations ranging from 0.37 to 20 μmol/L in RPMI 1640 medium. Cell toxicity was determined using a Cytotoxicity Detection Kit PLUS Lactate dehydrogenase (LDH) assay kit (Roche Diagnostics, Mannheim, Germany) according to the manufacturer's instructions, as described previously [10][11][12][13]. For LDH assays, cells were seeded into 96-well plates (5 × 10 4 cells/well in 100 μL culture medium) in triplicate in serum-free RPMI 1640 medium, and measurements at 492 nm wavelength (Synergy 2 Multi-Mode Microplate Reader, BioTek, Winooski, VT, USA) were taken 24 h after the treatment with tested compounds. The median lethal dose values, LD 50 , were deduced through the production of a dose-response curve. All data were evaluated using GraphPad Prism 5.00 software (GraphPad Software, San Diego, CA, USA). The results are summarized in Table 1.
LDH Test Principle: The LDH activity is determined by a coupled enzymatic reaction, whereby the tetrazolium salt INT is reduced to formazan. An increase in the amount of dead or plasma membrane damaged cells results in an increase of LDH enzyme activity in the culture supernatant. This increase in the amount of enzyme activity in the supernatant directly correlates to the amount of formazan formed during a limited time period. The formazan dye formed is water soluble and shows a broad absorption maximum at approximately 500 nm.

Study of Inhibition Photosynthetic Electron Transport (PET) in Spinach Chloroplasts
Chloroplasts were prepared from spinach (Spinacia oleracea L.) according to Masarovicova and Kralova [65]. The inhibition of photosynthetic electron transport (PET) in isolated spinach chloroplasts was determined spectrophotometrically (Genesys 6, Thermo Scientific, USA), using an artificial electron acceptor 2,6-dichlorophenol-indophenol (DCIPP) according to Kralova et al. [66], and the rate of photosynthetic electron transport was monitored as a photoreduction of DCPIP. The measurements were carried out in phosphate buffer (0.02 mol/L, pH 7.2) containing sucrose (0.4 mol/L), MgCl 2 (0.005 mol/L) and NaCl (0.015 mol/L). The chlorophyll content was 30 mg/L in these experiments and the samples were irradiated (~100 W/m 2 with 10 cm distance) with a halogen lamp (250 W) using a 4 cm water filter to prevent warming of the samples (suspension temperature 22 °C). The studied compounds were dissolved in DMSO due to their limited water solubility. The applied DMSO concentration (up to 4%) practically did not affect the photochemical activity in isolated spinach chloroplasts (observed differences in DCPIP photoreduction due DMSO addition were within experimental error). The inhibitory efficiency of the studied compounds was expressed by IC 50 values, i.e., by molar concentration of the compounds causing 50% decrease in the oxygen evolution rate relative to the untreated control. The comparable IC 50 value for a selective herbicide 3-(3,4dichlorophenyl)-1,1-dimethylurea, DCMU (Diuron ® ) was about 1.9 μmol/L. The results are summarized in Table 1.

Conclusions
A series of twenty-two substituted naphthalene-1-carboxanilides were prepared and characterized. The prepared compounds were tested for their antimycobacterial activity against clinical isolate of Mycobacterium avium subsp. paratuberculosis and for their ability to inhibit photosynthetic electron transport (PET) in isolated spinach chloroplasts (Spinacia oleracea L.). Generally compounds showed poor aqueous solubility, which significantly reduced their biological effect. Five compounds, N-(2-methoxyphenyl)naphthalene-1-carboxamide (2a), N-(3-methoxyphenyl)naphthalene-1-carboxamide (2b), N-(3-methylphenyl)naphthalene-1-carboxamide (3b), N-(4-methylphenyl)-naphthalene-1carboxamide (3c) and N-(3-fluorophenyl)naphthalene-1-carboxamide (4b) showed antimycobacterial activity two-fold higher than rifampicin and three-fold higher activity than ciprofloxacin. It was found that dependence of the antimycobacterial activities on lipophilicity and electronic properties were bilinear. Based on the results of the MTT assay of the most efficient compounds 2a, 2b, 3c, and 4b it seems that they could influence the mycobacterial respiratory chain. The most effective antimycobacterial compounds 2a, 2b, 3b, 3c and 4b were tested for their in vitro cytotoxicity against THP-1 cells and within this preliminary screening they demonstrated insignificant toxicity. Based on these facts, it can be concluded that the discussed anilides can be considered as promising agents for subsequent design of novel antimycobacterial agents. The PET-inhibiting activity was rather moderate or low, the most active compound N- [4-(trifluoromethyl)-phenyl]naphthalene-1-carboxamide (7c) expressed IC 50 = 59 μmol/L.