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Design, Synthesis and Antimycobacterial Activity of Some New Azaheterocycles: Phenanthroline with p-halo-benzoyl Skeleton. Part V Ramona Danac1, Teofil Daniloaia1, Vasilichia Antoci2, Violeta Vasilache3 and Ionel I. Mangalagiu1,* 1“

Al. I. Cuza” University of Iasi, Faculty of Chemistry, Bd. Carol 11, 700506 Iasi, Romania

2“

Al. I. Cuza” University of Iasi, Faculty of Chemistry, Research Department, Bd. Carol 11, 700506 Iasi, Romania

3”

tefan cel Mare” University, 13 Universitatii Street, RO-720229, Suceava, Romania Abstract: We report herein a feasible study concerning the design, synthesis, structure and in vitro antimycobacterial activity of new phenanthroline derivatives with p-halo-benzoyl skeleton. The preparation is straight and efficient, involving an N-alkylation reaction of 1,7- phenanthroline. The antimycobacterial agents have been prepared in good yields and purity. The antimycobacterial activity of the synthesized compounds was investigated against Mycobacterium tuberculosis H37Rv. Five from the eight tested compounds had activity against M. tuberculosis H37Rv under aerobic conditions. A certain influence of substituents from the para position of the benzoyl moiety was observed; thus, the 1,7phenanthrolinium salts substituted with p-halo (Br, Cl)- benzoyl have shown the most pronounced antimycobacterial activity. SAR correlations have been done.

Keywords: Antimycobacterial, design, synthesis, N-alkylation, 1,7-Phenanthroline, p-Halo-benzoyl, SAR. INTRODUCTION

MATERIALS AND METHODS

Human tuberculosis (TB), a contagious disease caused by Mycobacterium tuberculosis (Mtb), remains the leading infectious disease among humans, claiming approximately 1.8 million life’s every year worldwide [1]. The association with HIV infection and the emergence of multi-drugresistant (MDR) and extensively drug-resistant (XDR) to Mtb, is known to be a deadly synergistic factor for TB [2-4]. Usually, TB is currently treated with a cocktail of drugs, for a long period of time (at least six months). Therefore, the search for new antituberculous drugs active against Mtb remains one of the priority tasks of medicinal chemistry [5-9]. One of the approaches for developing new drugs against TB consists of searching for novel structures which the TB organism has never encountered with before, especially for the MDR- and XDR-TB treatment [10]. In our previous research work we showed that some six member ring azaheterocycles have a significant anti-TB activity [11-14].

Chemistry All the reagents and solvents employed were of the best grade available and were used without further purification. Melting points were determined using an electrothermal apparatus (MELTEMP II) and are uncorrected. The IR spectra were recorded on an FTIR Shimadzu Prestige 8400s spectrophotometer. The NMR spectra were recorded on a Bruker Avance 400 DRX or 500 DRX spectrometer (operating at 400/500 MHz for 1H and 100/125 MHz for 13C). The following abbreviations were used to designate chemical shift multiplicities: s = singlet, d = doublet, t = triplet, m = multiplet, br = broad. Chemical shifts are given in ppm (-scale), coupling constants (J) in Hz. General Procedure for Synthesis of Phenanthroline Salts (1–8).

As part of our ongoing research aiming the synthesis of novel anti-TB compounds with azaheterocycles skeleton, we report here the design, synthesis, structure and in vitro antimycobacterial activity of new phenanthroline derivatives with p-halo-benzoyl skeleton.

1 mmol of 1,7-phenanthroline was dissolved in 7 mL solvent (acetone for compounds 1-7 and acetonitrile for 8). Then 1.1 mmol of reactive halide was added and the resulted mixture was stirred at room temperature (for compounds 16) or reflux (for compounds 7-8) for 24 hours. The formed precipitate was filtered and washed with diethyl ether to give the desired product.

*Address correspondence to this author at the “Al. I. Cuza” University of Iasi, Faculty of Chemistry, 11 Carol I, 700506 Iasi, Romania. Tel. +40 232201343; Fax: +40 232 201313; E-mail: [email protected]

7-(2-Oxo-2-(p-tolyl)ethyl)-1,7-phenanthrolin-7-ium bromide (1). Cream powder, mp: = 216-218 oC, Yield: 65%. IR (KBr), /cm-1: 3040 (C–H arom.), 2980, 2850 (C–H aliph.), 1684 (CO). 1H NMR (400 MHz, DMSO-d6): ppm: 2.49 (s, 3H: CH3), 7.12 (s, 2H: H15), 7.53 (d, J = 8.4 Hz, 2H:

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Design, Synthesis and Antimycobacterial Activity

phenyl-H,), 8.03 (dd, J = 8.0, 4.4 Hz, 1H: H3), 8.08 (d, J = 8.4 Hz, 2H: phenyl-H), 8.46 (d, J = 9.6 Hz, 1H: H6), 8.53 (dd, J = 8.0, 5.6 Hz, 1H: H9), 8.70 (d, J = 9.6 Hz, 1H: H5), 8.77 (dd, J = 8.0, 1.2 Hz, 1H: H4), 9.33 (dd, J = 4.4, 1.2 Hz, 1H: H2), 9.63 (ad, J = 5.6 Hz, 1H: H8), 10.4 (ad, J = 8.0 Hz, 1H, H10). 13C-NMR, (100 MHz, DMSO-d6): ppm: 21.3 (CH3), 63.7 (C15), 117.2 (C6), 123.5 (C9), 125.2 (C3), 125.9 (C11), 128.6 (C13), 128.7 (2xCH-Ph), 129.5 (2xCH-Ph), 131.0 (Cq-Ph), 136.6 (C5), 137.3 (C4), 141.2 (C12), 143.0 (C10, C14), 145.6 (Cq-Ph), 149.9 (C8), 152.5 (C2), 190.1 (C16). Anal. Calcd. for C21H17BrN2O: C-64.13, H-4.36, N-7.12; Found: C-64.25, H-4.28, N-7.31 %. 7-(2-(4-methoxyphenyl)-2-oxoethyl)-1,7-phenanthrolin-7-ium bromide (2). Cream powder, mp: 220-222 oC, Yield: 68%. IR (KBr), /cm-1: 3040 (C–H arom.), 2997, 2850 (C–H aliph.), 1680 (CO). 1H NMR (400 MHz, DMSO-d6): ppm: 3.94 (s, 3H: OCH3), 7.10 (s, 2H: H15), 7.24 (d, J = 8.8 Hz, 2H: phenyl-H), 8.03 (dd, J = 8.0, 4.0 Hz, 1H: H3), 8.16 (d, J = 8.8 Hz, 2H: phenyl-H), 8.44 (d, J = 9.6 Hz, 1H: H6), 8.53 (dd, J = 8.4, 6.0 Hz, 1H: H9), 8.70 (d, J = 9.6 Hz, 1H: H5), 8.76 (dd, J = 8.0, 1.6 Hz, 1H: H4), 9.32 (dd, J = 4.0, 1.6 Hz, 1H: H2), 9.62 (dd, J = 6.0, 1.2 Hz, 1H: H8), 10.39 (dd, J = 8.4, 1.2 Hz, 1H: H10). 13C-NMR, (100 MHz, DMSO-d6): ppm: 55.8 (OCH3), 63.5 (C15), 114.3 (2xCHPh), 117.2 (C6), 123.5 (C9), 125.2 (C3), 125.9 (C11), 126.3 (Cq-Ph), 128.6 (C13), 131.6 (2xCH-Ph), 136.6 (C5), 137.3 (C4), 141.1 (C12), 142.9 (C10), 143.0 (C14), 149.9 (C8), 152.5 (C2), 164.4 (Cq-Ph), 188.8 (C16). Anal. Calcd. for C21H17BrN2O2: C, 61.63; H, 4.19; N, 6.84. Found: C, 61.65; H, 4.08; N, 6.98. 7-(2-(4-nitrophenyl)-2-oxoethyl)-1,7-phenanthrolin-7ium bromide (3). Beige powder, mp: 219-220 oC, Yield: 70%. IR (KBr), /cm-1 : 3051, 3020 (C–H arom.), 2998 (C–H aliph.), 1699 (CO), 1520, 1347 (NO2). 1H NMR (400 MHz, DMSO-d6): ppm: 7.25 (s, 2H: H15), 8.04 (dd, J = 8.4, 4.4 Hz, 1H: H3), 8.43 (d, J = 8.8 Hz, 2H: phenyl-H), 8.53 (d, J = 8.8 Hz, 2H: phenyl-H), 8.59 (H6, overlapped signals, 2H: H9), 8.73 (d, J = 9.6 Hz, 1H: H5), 8.78 (dd, J = 8.4, 1.6 Hz, 1H: H4), 9.33 (dd, J = 4.4, 1.6 Hz, 1H: H2), 9.67 (ad, J = 4.8 Hz, 1H: H8), 10.41 (ad, J = 8.4 Hz, 1H: H10). 13C-NMR, (100 MHz, DMSO-d6): ppm: 64.1 (C15), 117.4 (C6), 123.6 (C9), 123.9 (2xCH-Ph, Cq-Ph), 125.2 (C3), 126.0 (C11), 128.6 (C13), 130.2 (2xCH-Ph), 136.7 (C5), 137.3 (C4), 138.3 (CqPh), 141.2 (C12), 143.0 (C10), 143.2 (C14), 150.0 (C8), 152.5 (C2), 190.0 (C16). Anal. Calcd. for C20H14BrN3O3: C, 56.62; H, 3.33; N, 9.90. Found: C, 56.75; H, 3.19; N, 10.01. 7-(2-oxo-2-phenylethyl)-1,7-phenanthrolin-7-ium bromide (4). Cream powder, mp: 217-219 oC, Yield: 60%. IR (KBr), /cm-1: 3037 (C–H arom.), 2927, 2832 (C–H aliph.), 1684 (CO). 1H NMR (400 MHz, DMSO-d6): ppm: 7.21 (s, 2H: H15), 7.72 (t, J = 7.6 Hz, 2H: phenyl-H), 7.85 (t, J = 7.2 Hz, 1H: phenyl-H), 8.02 (dd, J = 8.0, 4.4 Hz, 1H: H3), 8.21 (d, J = 7.6 Hz, 2H: phenyl-H), 8.51 (d, J = 9.6 Hz, 1H: H6), 8.55 (dd, J = 8.4, 5.6 Hz, 1H: H9), 8.71 (d, J = 9.6 Hz, 1H: H5), 8.77 (dd, J = 8.0, 1.6 Hz, 1H: H4), 9.31 (dd, J = 4.4, 1.6 Hz, 1H: H2), 9.69 (d, J = 5.6 Hz, 1H: H8), 10.38 (ad, J = 8.0 Hz, 1H: H10). 13C-NMR, (100 MHz, DMSO-d6): ppm: 63.4 (C15), 117.3 (C6), 123.5 (C9), 125.2 (C3), 125.9 (C11), 128.6 (C13), 128.6 (2xCH-Ph), 129.0 (2xCH-Ph), 133.5 (Cq-Ph), 134.8 (Cq-Ph), 136.6 (C5) 137.2 (C4), 141.1

Letters in Drug Design & Discovery, 2015, Vol. 12, No. 1

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(C12), 143.0 (C10), 143.0 (C14), 149.9 (C8), 152.4 (C2), 190.6 (C16). Anal. Calcd. for C20H15BrN2O: C, 63.34; H, 3.99; N, 7.39. Found: C, 63.50; H, 3.79; N, 7.51. 7-(2-(4-chlorophenyl)-2-oxoethyl)-1,7-phenanthrolin7-ium bromide (5). Cream powder, mp: 218-220 oC, Yield: 75%. IR (KBr), /cm-1 : 3015 (C–H arom.), 2923, 2834 (C–H aliph.), 1694 (CO). 1H NMR (500 MHz, DMSO-d6): ppm: 7.10 (s, 2H: H15), 7.80 (d, J = 8.5 Hz, 2H: phenyl-H), 8.03 (dd, J= 8.0, 4.5 Hz, 1H: H3), 8.18 (d, J = 8.5 Hz, 2H: phenylH), 8.53 (m, 2H: H6, H9), 8.70 (d, J = 9.5 Hz, 1H: H5), 8.76 (d, J = 7.5 Hz, 1H: H4), 9.33 (d, J = 4.5 Hz, 1H: H2), 9.57 (dd, J = 6.0 Hz, 1H: H8), 10.41 (d, J = 8.5 Hz, 1H: H10). 13CNMR, (125 MHz, DMSO-d6): ppm: 63.8 (C15), 117.4 (C6), 123.6 (C9), 125.3 (C3), 126.0 (C11), 128.7 (C13), 129.2 (2xCH-Ph), 130.6 (2xCH-Ph), 132.4 (Cq-Ph), 136.8 (C5), 137.4 (C4), 139.7 (Cq-Ph), 141.2 (C12), 143.1 (C10), 143.2 (C14), 150.0 (C8), 152.6 (C2), 189.9 (C16). Anal. Calcd. for C20H14BrClN2O: C, 58.07; H, 3.41; N, 6.77. Found: C, 58.10; H, 3.29; N, 6.87. 7-(2-(4-bromophenyl)-2-oxoethyl)-1,7-phenanthrolin7-ium bromide (6). Cream powder, mp: 224-226 oC, Yield: 70%. IR (KBr), /cm-1: 3010 (C–H arom.), 2923 (C–H aliph.), 1690 (CO). 1H NMR (500 MHz, DMSO-d6): ppm: 7.10 (s, 2H: H15), 7.95 (d, J = 8.5 Hz, 2H: phenyl-H), 8.03 (dd, J = 8.0, 4.0 Hz, 1H: H3), 8.10 (d, J = 8.5 Hz, 2H: phenyl-H), 8.52 (m, 2H: H9, H6), 8.70 (d, J = 9.5 Hz, 1H: H5), 8.76 (ad, J = 8.0 Hz, 1H: H4), 9.32 (ad, J = 4.0 Hz, 1H: H2), 9.58 (d, J = 5.5 Hz, 1H: H8), 10.40 (d, J = 8.5 Hz, 1H: H10). 13C-NMR, (125 MHz, DMSO-d6): ppm: 63.8 (C15), 117.4 (C6), 123.6 (C9), 125.3 (C3), 126.4 (C11), 128.7 (C-Br), 130.0 (C13), 130.6 (2xCH-Ph), 132.2 (2xCH-Ph), 132.7 (CqPh), 136.7 (C5), 137.4 (C4), 141.2 (C12), 143.1 (C10), 143.2 (C14), 150.0 (C8), 152.6 (C2), 190.1 (C16). Anal. Calcd. for C20H14Br2N2O: C, 52.43; H, 3.08; N, 6.11. Found: C, 52.59; H, 3.00; N, 6.20. 7-(2-amino-2-oxoethyl)-1,7-phenanthrolin-7-ium iodide (7). Yellow powder, mp: 264-266 oC, Yield: 81%. IR (KBr), /cm-1: 3357, 3169 (N-H), 1673 (CO). 1H NMR (500 MHz, DMSO-d6): ppm: 5.95 (s, 2H: H15), 7.87 (s, 1H: NH), 7.99 (dd, J = 8.0, 4.5 Hz, 1H: H3), 8.19 (s, 1H: NH), 8.30 (d, J = 10.0 Hz, 1H: H6), 8.46 (dd, J = 8.5, 6.0 Hz, 1H: H9), 8.74 (ad, J = 9.0 Hz, 2H: H4, H5), 9.28 (dd, J = 4.0, 1.0 Hz, 1H: H2), 9.60 (d, J = 5.5 Hz, 1H: H8), 10.31 (d, J = 8.5 Hz, 1H: H10). 13C-NMR, (125 MHz, DMSO-d6): ppm: 59.3 (C15), 116.6 (C6), 125.2 (C3), 123.3 (C9), 125.9 (C11), 128.6 (C13), 136.7 (C5), 137.3 (C4), 140.7 (C12), 142.7 (C10), 143.1 (C14), 150.2 (C8), 152.5 (C2), 165.8 (C16). Anal. Calcd. for C14H12IN3O: C-46.05, H-3.31, N-11.51. Found: C, 46.09; H, 3.26; N, 11.59. 7-(2-methoxy-2-oxoethyl)-1,7-phenanthrolin-7-ium bromide (8). Faint/pale pink powder, mp: 229-231 oC, Yield: 50%. IR (KBr), /cm-1: 3088 (C–Harom), 2936 (C– Haliph), 1748 (CO), 1222 (C-O). 1H NMR (500 MHz, DMSO-d6): ppm: 3.81 (s, 3H: OCH3), 6.31 (s, 2H: H15), 8.03 (dd, J = 8.0, 4.0 Hz, 1H: H3), 8.51 (m, 2H: H9, H6), 8.78 (m, 2H: H4, H5), 9.31 (dd, J = 4.5, 1.5 Hz, 1H: H2), 9.66 (d, J = 5.5 Hz, 1H: H8), 10.37 (d, J = 8.0 Hz, 1H: H10). 13C-NMR, (125 MHz, DMSO-d6): ppm: 53.3 (OCH3), 57.9 (C15), 117.1 (C6), 125.4 (C3), 123.6 (C9), 126.0 (C11), 128.7 (C13), 137.0

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A

B

100

% Growth

% Growth

100

50

50

IC50

MIC

10 1 Compound concentration ( M)

100

10 1 Compound concentration ( M)

IC90

100

Fig. (1). Dose response curves used to calculate MIC, IC50 and IC90.

(C5), 137.4 (C4), 140.8 (C12), 143.6 (C10), 143.0 (C14), 150.2 (C8), 152.6 (C2), 166.6 (C16). Anal. Calcd. for C15H13BrN2O2: C, 54.07; H,3.93; N, 8.41. Found: C, 54.00; H, 3.81; N, 8.51.

dose response curves were generated using the LevenbergMarquardt algorithm and the concentrations that resulted in 50% and 90% inhibition of growth were determined (IC50 and IC90 respectively) (Fig. 1B).

Microbiology

Data points obtained from a dose response growth inhibition assay are curve-fitted using (A) the Gompertz model to calculate MIC and (B) the Levenberg-Marquardt algorithm to calculate IC50 and IC90. (A) The MIC is the concentration at which complete inhibition growth is seen and is derived from the point of inflection at which the curve meets the lower asymptote (zero growth). (B) IC50 and IC90 are points at which growth is inhibited by 50% and 90% respectively. Orange line = MIC; Green line = IC50; Blue line = IC90.

Compounds were evaluated for antimycobacterial activity against Mycobacterium tuberculosis, as a part of the TAACF TB screening program under direction of the US National Institute of Health, the NIAID division. Antimycobacterial activities of the compounds were performed by Center of Tuberculosis Antimicrobial Acquisition and Coordinating Facility (TAACF) at Southern Research Institute. The Primary Cycle High Throughput Screening (HTS). Determination of 90% inhibitory concentration (IC90), 50% inhibitory concentration (IC50) and Minimum Inhibitory Concentration (MIC) The MIC of compound was determined by measuring bacterial growth after 5 days in the presence of test compounds [18-21]. Compounds were prepared as 10-point twofold serial dilutions in DMSO and diluted into 7H9-TwOADC medium in 96-well plates with a final DMSO concentration of 2%. The highest concentration of compound was 200 M where compounds were soluble in DMSO at 10 mM. For compounds with limited solubility, the highest concentration was 50X less than the stock concentration e.g. 100 M for 5 mM DMSO stock, 20 M for 1 mM DMSO stock. For potent compounds, assays were repeated at lower starting concentrations. Each plate included assay controls for background (medium/DMSO only, no bacterial cells), zero growth (100 M Rifampicin) and maximum growth (DMSO only), as well as a rifampicin dose response curve. Plates were inoculated with M. tuberculosis and incubated for 5 days: growth was measured by OD590 and fluorescence (Ex 560/Em 590) using a BioTek™ Synergy 4 plate reader. Growth was calculated separately for OD590 and RFU. To calculate the MIC, the 10-point dose response curve was plotted as % growth and fitted to the Gompertz model using GraphPad Prism 5. The MIC was defined as the minimum concentration at which growth was completely inhibited and was calculated from the inflection point of the fitted curve to the lower asymptote (zero growth) (Fig. 1A). In addition

MIC values were reported when the following quality control criteria were satisfied: •

•

For each plate o

No growth in the background (un-inoculated) control wells

o

OD590 >0.3 in maximum growth wells

o

Rifampicin MIC within 3-fold of the expected value

For each compound curve. MICs were reported if o

There were 2 points with growth >75%

o

There were 2 points with growth 75% inhibition then the MIC value was reported as the maximum concentration tested

•

If no point reached 75% inhibition, the MIC was reported as > maximum concentration tested

RESULTS AND DISCUSSION In order to reach our goal we initially synthetize the phenanthrolinium monoquaternary salts 1- 8. The reaction pathway adopted for synthesis of phenanthroline derivatives is straightforward and efficient, involving an N-alkylation reaction of 1,7-phenanthroline, Scheme (1).



R 16

O 5 N

X

O

15 X 12 7 N

1:1.1

+ N

6

4 11 3

R

2 1:2.2 1:5 1:7

N 1

8

13

14

10

9

1. R =C6H4Me(p), X=Br 2. R = C6H4OMe(p), X=Br 3. R = C6H4NO2(p), X=Br 4. R = C6H5, X=Br 5. R = C6H4Cl(p), X=Br 6. R =C6H4Br(p), X=Br 7. R=NH2, X=I 8. R=OMe, X=Br O

R

R

O

N N N

17

X

X

N X O

9-16 R

Scheme (1). Reaction pathway to obtain phenanthrolinium salts.

The salts have been prepared in moderate to good yields (50-80%), using a minimum volume of solvent (acetone or acetonitrile), at room temperature or reflux. Our initial target was to obtain both the phenanthrolinium monoquaternary salts (1- 8) and diquaternary salts (9-16). No matter the conditions we employed in terms of molar ratio (1:2.2; 1:5; 1:7) and reaction conditions (solvents, temperature), only phenanthrolinium mono salts, 1- 8, have been obtained. A reasonable explanation for this behaviour could be related to the basicity of N1-nitrogen atom: after the N7-alkylation of 1,7phenanthroline, in the obtained phenanthrolinium mono salts the basicity of N1-nitrogen decreases so much that a second alkylation could not take place. The structure of compounds was assigned by elemental and spectroscopic analysis: IR, 1H NMR, 13C NMR, COSY, HMQC and HMBC. Thus, the most important data furnished by 1H NMR spectra are the following: the signals for methylene protons H15 from compounds 1- 6 appear at low field (7.10 – 7.25 ppm, singlet), according with the substituent from the para position of the benzoyl ring. The same protons appear more shielded (5.95 ppm respectively 6.31 ppm) for compounds 7 and 8, due to the weaker withdrawing effect of the adjacent carbonyl amide and ester groups. In the aromatic region, the most unshielded protons are H10 (10.3110.41 ppm), which are involved in an intramolecular hydrogen bond with atom N1, followed by H8 (9.57-9.69 ppm) situated in the proximity of the positive nitrogen N7. In the 1 H NMR spectra of compound 7, the two amide protons (NH2) furnished two singlet signals at 7.87 and 8.19 ppm, respectively, while in the spectrum of compound 8, the methyl ester protons appear as a singlet at 3.81 ppm. In the 13 C NMR spectra, the most important data are furnished by the signals corresponding to the C16 (carbonyl) and C15 (methylene) atoms. Thus, for compounds 1-6 possessing C=O ketone groups, the signals for C16 appear at 190.6-188.8 ppm, while for compound 7 having an amide group, respectively for compound 8 with an ester group appear at 165.8 ppm, respectively 166.6 ppm. Methylene C15 atoms give signals at 63.4 -64.1 ppm for compounds 1-6 and at 57.9 59.3 ppm for compounds 7-8. All the remaining signals from NMR spectra are in accordance with the proposed structures.

See also Supporting Information for the 1H and spectra for compounds (5) and (6).

13

C NMR

DESIGN AND BIOLOGICAL ACTIVITY Recently, a successful result on the identification of new antimycobacterial derivatives which contain 1,10phenanthroline skeleton as pharmacophoric moiety was reported [15]. On the other hand, in case of some diazoles derivatives, it was found that the p-halo-benzoyl moiety is crucial for the antimycobacterial activity [16]. Encouraged by our previous promising results in the field of anti-TB derivatives with nitrogen heterocycle skeleton [11-14] as well as by the good antimicrobial activity of the phenanthrolinium salts 1- 8 [17], we decided to combine the biological potentials of phenanthrolines and p-halo-benzoyl moiety, intending to obtain compounds with better activity and better pharmaceutical properties (i.e., increasing the water solubility, being salts), Scheme (2). In equal measure we were interested to see if changing of the nitrogen position of phenanthroline from 1,10-, to more sterically released 1,7-, will affect somehow the activity. We have had also in view some related salts, 1,7phenanthrolinium salts with p-substituted-benzoyl / carbalkoxy / acetamide moiety, in order to allow SAR comparisons. The phenanthrolinium monoquaternary salts 1- 8, were evaluated for in vitro antimycobacterial activity against Mycobacterium tuberculosis H37Rv, grown under aerobic conditions (see Microbiology part). The obtained results are listed in Table 1. The data from Table 1 illustrate that five from the eight tested compounds had activity against M. tuberculosis H37Rv under aerobic conditions. We may also notice that 1,7-phenanthrolinium salts substituted with p-halo-benzoyl moiety have shown the most pronounced antimycobacterial activity. In the series of 1,7-phenanthrolinium salts, we may notice that salts containing a p-substituted-benzoyl skeleton are more active comparative as those one with carbalkoxy or acetamide moiety.

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(p-halogeno-benzoyl) Hlg Y O O N

Z= -OAlkyl; -NH2 N X

Pharmacophoric moieties with anti-TB potential

N

O

Z

N

N

(1,10-phenanthroline)

Scheme (2). Design in the class of 1,7-phenanthrolinium derivatives with p-halo-benzoyl moiety. Table 1. Antimycobacterial activity of phenanthrolinium salts 1- 8 against M. tuberculosis H37Rv. Compound

IC50 (g/mL)

IC90 (g/mL)

MIC (M)

1 (R=C6H4-Mep)

100

>200

>200

3 (R=C6H4-NO 2p)

180

>200

>200

4(R=C6H 5)

120

>200

>200

5 (R=C6H4-Clp)

88

>200

>200

6 (R=C6H4-Brp)

88

>200

>200

2 (R=C6H4-OMep)

>200

>200

>200

7 (R=OCH3)

>200

>200

>200

8 (R=NH2)

>200

>200

>200

Rifampicin

0.0036

0.0061

0.0055

CONCLUSION

ACKNOWLEDGEMENTS

In conclusion, the design, synthesis, structure and in vitro antimycobacterial activity of a new class of antimycobacterial of new phenanthroline derivatives with p-halo-benzoyl skeleton is presented. Compounds were prepared by using a straight and efficient method of synthesis. The in vitro antimycobacterial activity of the synthesized compounds was investigated against Mycobacterium tuberculosis H37Rv. Five of the eight tested compounds had activity against M. tuberculosis H37Rv under aerobic conditions, the 1,7phenanthrolinium derivatives substituted with p-halobenzoyl moiety having the best activity. A certain influence of the para position of the benzoyl moiety substituents was observed, the 1,10-phenanthrolinium salts substituted with phalo (Br, Cl)- benzoyl moiety showing the most pronounced antimycobacterial activity (further studies remain to be done in this respect).

Authors are thankful to CNCS Bucharest, Romania, project PN-II-DE-PCE-2011-3-0038, no. 268/05.10.2011, for financial support. Part of this work (biological tests) was supported by National Institutes of Health and the National Institute of Allergy and Infectious Diseases, Contract No. HHSN272201100012I. We also thanks to the POSCCE-O 2.2.1, SMIS-CSNR 13984-901, No. 257/28.09.2010 Project, CERNESIM, for the NMR.

CONFLICT OF INTEREST The authors declare that this article content has no conflict of interest.

SUPPLEMENTARY MATERIAL The NMR spectra (1H NMR, (5) and (6).

13

C NMR) for compounds

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Revised: August 16, 2014

Accepted: August 19, 2014