DOI:
10.1039/C5RA00388A
(Communication)
RSC Adv., 2015,
5, 16000-16009
Green synthesis and pharmacological screening of polyhydroquinoline derivatives bearing a fluorinated 5-aryloxypyrazole nucleus†
Received
8th January 2015
, Accepted 28th January 2015
First published on 28th January 2015
Abstract
A novel series of polyhydroquinoline scaffolds 8a–p has been designed and synthesized under ultrasonic irradiation by a one-pot three-component cyclocondensation reaction of 3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes 3a–d with malononitrile 7 and various enhydrazinoketones 6a–e in the presence of piperidine as basic catalyst. All the synthesized compounds have been characterized by various spectroscopic techniques and elemental analysis. All the synthesized compounds were evaluated for their in vitro antibacterial activity against a panel of pathogenic strains of bacteria and fungi, in vitro antitubercular activity against Mycobacterium tuberculosis H37Rv strain and also for their in vitro antimalarial activity against Plasmodium falciparum. Compounds 8c, 8i, 8j, 8l and 8m exhibited excellent antimalarial potency. The cytotoxicity of the synthesized compounds was tested using a bioassay of S. pombe cells at the cellular level. Compounds 8i, 8j, 8k and 8l were found to have maximum toxicity, while compounds 8e, 8m, 8c were found to be less cytotoxic. Some of them displayed luminous antibacterial activity and reasonable antituberculosis activity as compared with the first line drugs.
1. Introduction
Malaria and tuberculosis (TB) are the most disturbing infectious diseases in the world, due to their high mortality and morbidity. The protozoan parasite Plasmodium falciparum and the pathogen Mycobacterium tuberculosis (MTB) are respectively responsible for their occurrence. It has been estimated that around 500 million people get infected in subtropical and tropical countries by malaria and 2.5 million deaths occur annually.1–3 The World Health Organization has declared TB to be a ‘global emergency’ and a recent estimation by WHO showed that within the next 20 years around 30 million people will be infected by M. tuberculosis.4,5 The recurrence of TB infection has been connected to co-infection with the human immunodeficiency virus (HIV),6 the appearance of multidrug-resistant (MDR) and extensively drug-resistant (XDR) M. tuberculosis strains that are resistant to the existing therapies.7 Thus to overcome the threat of MDR-TB and XDR-TB, there is an imperative need for the development of new drugs with divergent and unique structures and possibly with a different mechanism of action from that of the existing drugs.8
Multi-component reactions (MCRs) are the most efficient and powerful methods in the context of modern drug discovery for the preparation of bioactive heterocyclic compounds because of their atom economy, high yields of the products and simple experimentation.9,10 Ultrasound irradiation is also a superior technique in green synthetic approach, which is being used to accelerate organic reactions. It is considered as a processing aid in terms of energy conservation compared with conventional methods as it provides uniform and noncontact heating.11,12 The significant features of the ultrasound approach are improved rate of reaction, easier handling and formation of pure products in prominent yields.
Fluorine substituted quinolones (Fig. 1) such as norfloxacin, ofloxacin, ciprofloxacin, temafloxacin, defloxacin, sparfloxacin, delafloxacin, lomefloxacin etc. are used clinically as they possess effective antibacterial potency.13 The substitution of fluorine in to a potential drug molecule can extend not only pharmacokinetic properties but also enhances the properties of pharmacodynamics, toxicology and efficacy of drugs.14
 |
| Fig. 1 Fluorine substituted quinolone drugs. | |
Pyrazole and its derivatives are the key structural motifs in heterocyclic chemistry and occupy a significant position in biological and medicinal chemistry. They exhibited a broad spectrum of pharmacological activities such as such as anticancer,15 antibacterial,16 antiviral,17 analgesic,18 anti-inflammatory,19 antimalarial, antituberculosis and antifungal activities.20 Polyhydroquinoline derivatives have experienced tremendous upsurge in the modern era. They exhibited diverse therapeutic and pharmacological importance, such as calcium channel blockers, hepatoprotective agents, vasodilators, antiatherosclerotic agents, bronchodilators, geroprotective agents, antitumor agents, antidiabetic agents, etc.21–25 Substituted 1,4-dihydropyridines are also well known as calcium channel blockers (CCB) which are often used to treat orderly cardiovascular diseases including hypertension.26–28
Lichitsky and co-workers reported the conventional synthesis of fused N-substituted 1,4-dihydropyridines by reacting cyclic enhydrazinoketones and arylidene derivatives of malononitrile in two step without biological evaluation. They employed simple aromatic aldehydes and only two substituted phenyl hydrazine hydrochlorides for the synthesis.29 In the context of our interest we designed and synthesized fluorinated 5-(substituted aryloxy)-pyrazole nucleus based on polyhydroquinoline scaffold Fig. 2. In current work, we have concentrated on following points: (a) synthesis of target compounds by single step one-pot three-component cyclocondensation reaction employing conventional as well as ultrasonic irradiation method (b) use of heteroaromatic aldehydes (3-methyl-5-substituted-aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes) and variously substituted phenyl hydrazine hydrochlorides (4-F, 4-Br, 4-Cl, 4-OMe) in synthesizing the target molecules (c) biological evaluation including antibacterial, antimalarial and antituberculosis studies and cytotoxicity.
 |
| Fig. 2 Present study. | |
In continuation of our efforts to synthesize some novel heterocyclic motifs with biological interest,30–37 herein we report for the synthesis and biological screening of novel polyhydroquinoline derivatives bearing a fluorinated 5-aryloxypyrazole nucleus using ultrasonic irradiation. In the context of biological importance, we intended to develop novel approach for structural diversity of heterocycles incorporating polyhydroquinoline scaffold. The modifications made on quinolone core for probing antibacterial, antimalarial and antitubercular activity includes; (A) fluorinated 5-substituted aryloxypyrazole at C-4 position (B) 4-substituted phenylamino nucleus at N-1 position and (C) methyl group on C-7 position to validate lipophilicity of the target molecules.
2. Chemistry
The synthesis of targeted 5-(variously fluorinated aryloxy)-pyrazole incorporated polyhydroquinoline derivatives are summarized in Scheme 1. The starting material 5-chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde 1 was prepared according to Vilsmeier–Haack reaction of 3-methyl-1-phenyl-1H-pyrazol-5(4H)-one.38 3-Methyl-5-substituted aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes 3a–d were prepared by refluxing compound 1 and substituted phenols 2a–d in presence of anhydrous K2CO3 as basic catalyst in DMF as solvent. The required enhydrazinoketones 6a–e were prepared by the reaction of β-diketone dimedone 4 with 4-substituted phenyl hydrazine hydrochlorides 5a–e under aqueous condition. The targeted compounds fluorinated pyrazole incorporated polyhydroquinoline derivatives 8a–p were synthesized by cyclocondensation reaction of 3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes 3a–d, substituted enhydrazinoketones 6a–e and malononitrile 7 in absolute ethanol using piperidine as the basic catalyst by conventional and ultrasonic irradiation methods (Scheme 1 and Table 1).
 |
| Scheme 1 Synthesis of 2-amino-7,7-dimethyl-4-(3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazol-4-yl)-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydro quinoline-3-carbonitrile 8a–p (i) DMF, K2CO3, reflux 2 h. (ii) H2O stirring RT, 6 h. (iii) (A) Ethanol, piperidine, reflux 1.5–2.5 h (iii) (B) ethanol, piperidine RT 15–30 min. | |
Table 1 Reaction parameters under conventional method and sonication (8a–p)
Entry |
R |
R1 |
Conventional method |
Ultrasonic method |
Time (h) |
Yielda (%) |
Time (min) |
Yielda (%) |
Isolated. |
8a |
2-F |
4-Br |
2.5 |
79 |
25 |
88 |
8b |
2-F |
4-F |
2.0 |
78 |
20 |
91 |
8c |
2-F |
4-Cl |
2.5 |
64 |
30 |
79 |
8d |
2-F |
–H |
2.5 |
76 |
20 |
87 |
8e |
4-F |
–H |
1.5 |
73 |
15 |
84 |
8f |
2-F |
4-OMe |
1.5 |
76 |
15 |
88 |
8g |
3-F |
–H |
2.0 |
65 |
15 |
76 |
8h |
3-CF3 |
–H |
2.5 |
73 |
20 |
85 |
8i |
3-CF3 |
4-OMe |
2.0 |
76 |
15 |
83 |
8j |
3-CF3 |
4-Br |
2.5 |
75 |
25 |
87 |
8k |
3-CF3 |
4-F |
2.0 |
61 |
20 |
74 |
8l |
3-F |
4-OMe |
1.5 |
71 |
20 |
81 |
8m |
3-F |
4-Br |
2.0 |
77 |
20 |
86 |
8n |
3-F |
4-F |
2.5 |
79 |
25 |
89 |
8o |
4-F |
4-Br |
2.0 |
62 |
30 |
78 |
8p |
4-F |
4-F |
1.5 |
68 |
20 |
80 |
A plausible mechanism for the reaction is outlined in Scheme 2. The reaction occurs via in situ initial formation of the heterylidenenitrile, containing the electron-poor C
C double bond, from the Knoevenagel condensation between 3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes 3a–d and malononitrile 7 by loss of water molecule, Michael addition of enhydrazinoketones 6a–e to the ylidenic bond to form an acyclic intermediate which undergoes cyclization by nucleophilic attack of the –NH group on the electron deficient cyano carbon, followed by tautomerisation to the final products 8a–p.
 |
| Scheme 2 Plausible mechanistic pathway for the synthesis of polyhydroquinoline. | |
3. Pharmacology
3.1. In vitro antimicrobial activity
The antimicrobial activity of the newly synthesized compounds 8a–p was carried out by broth micro dilution method according to National Committee for Clinical Laboratory Standards (NCCLS).39 Antibacterial activity was screened against three Gram positive (Bacillus subtilis MTCC 441, Clostridium tetani MTCC 449, and Streptococcus pneumoniae MTCC 1936) and three Gram negative (Salmonella typhi MTCC 98, Escherichia coli MTCC 443, and Vibrio cholerae MTCC 3906) bacteria by using ampicillin, ciprofloxacin, norfloxacin and chloramphenicol as the standard antibacterial drugs. Antifungal activity was screened against two fungal species (Aspergillus fumigatus MTCC 3008 and Candida albicans MTCC 227) where griseofulvin and nystatin were used as the standard antifungal drugs. The strains employed for the activity were procured from the Institute of Microbial Technology, Chandigarh (MTCC-Micro Type Culture Collection). Mueller Hinton broth was used as nutrient medium to grow and dilute the drug suspension for the test. DMSO was used as the diluent to get the desired concentration of compounds to test upon the standard bacterial strains. The result of antimicrobial screening data is shown in Table 2.
Table 2 In vitro antimicrobial activity of polyhydroquinoline derivatives 8a–p (MICs, μg mL−1)a
Comp. |
Gram positive bacteria |
Gram negative bacteria |
Fungi |
S.P. |
B.S. |
C.T. |
E.C. |
S.T. |
V.C. |
C.A. |
A.F. |
MTCC |
MTCC |
MTCC |
MTCC |
MTCC |
MTCC |
MTCC |
MTCC |
1936 |
441 |
449 |
443 |
98 |
3906 |
227 |
3008 |
S. P.: Streptococcus pneumoniae, B. S.: Bacillus subtilis, C. T.: Clostridium tetani, E. C.: Escherichia coli, S. T.: Salmonella typhi, V. C.: Vibrio cholerae, C. A.: Candida albicans, A. F.: Aspergillus fumigatus, MTCC: microbial type culture collection. A: ampicillin, B: norfloxacin, C: chloramphenicol, D: ciprofloxacin. n.t.: not tested. |
8a |
200 |
500 |
250 |
200 |
250 |
500 |
1000 |
500 |
8b |
500 |
500 |
125 |
125 |
500 |
250 |
1000 |
1000 |
8c |
100 |
250 |
125 |
250 |
100 |
250 |
1000 |
500 |
8d |
125 |
62.5 |
500 |
100 |
250 |
200 |
500 |
500 |
8e |
500 |
200 |
200 |
250 |
250 |
250 |
500 |
1000 |
8f |
125 |
250 |
250 |
250 |
200 |
100 |
>1000 |
500 |
8g |
200 |
100 |
250 |
250 |
200 |
250 |
1000 |
500 |
8h |
250 |
200 |
100 |
500 |
250 |
125 |
1000 |
1000 |
8i |
62.5 |
250 |
125 |
200 |
100 |
100 |
250 |
100 |
8j |
100 |
62.5 |
100 |
62.5 |
200 |
250 |
250 |
500 |
8k |
125 |
100 |
500 |
250 |
250 |
250 |
1000 |
1000 |
8l |
500 |
200 |
500 |
100 |
200 |
62.5 |
1000 |
100 |
8m |
500 |
500 |
250 |
200 |
500 |
200 |
500 |
1000 |
8n |
125 |
100 |
200 |
250 |
500 |
250 |
200 |
500 |
8o |
200 |
200 |
250 |
200 |
100 |
250 |
1000 |
>1000 |
8p |
250 |
500 |
250 |
100 |
500 |
200 |
1000 |
>1000 |
A |
100 |
250 |
250 |
100 |
100 |
100 |
n. t.b |
n. t. |
B |
10 |
100 |
50 |
10 |
10 |
10 |
n. t. |
n. t. |
C |
50 |
50 |
50 |
50 |
50 |
50 |
n. t. |
n. t. |
D |
25 |
50 |
100 |
25 |
25 |
25 |
n. t. |
n. t. |
E |
n. t. |
n. t. |
n. t. |
n. t. |
n. t. |
n. t. |
100 |
100 |
F |
n. t. |
n. t. |
n. t. |
n. t. |
n. t. |
n. t. |
500 |
100 |
3.2. In vitro antituberculosis activity
A primary in vitro antituberculosis activity of the newly synthesized compounds 8a–p was conducted at 250 μg mL−1 against Mycobacterium tuberculosis H37Rv strain by using Lowenstein–Jensen medium as described by Rattan.40 The obtained results are presented in Table 3 in form of % inhibition. Isoniazid and rifampicin were used as the standard drugs.
Table 3 In vitro antituberculosis activity (% inhibition) of polyhydroquinoline derivatives 8a–p against M. tuberculosis H37Rv (at concentration 250 μg mL−1)
Comp. |
% Inhibition |
Comp. |
% Inhibition |
8a |
26 |
8j |
21 |
8b |
16 |
8k |
95 |
8c |
52 |
8l |
88 |
8d |
48 |
8m |
91 |
8e |
94 |
8n |
20 |
8f |
63 |
8o |
36 |
8g |
14 |
8p |
89 |
8h |
25 |
Rifampicin |
98 |
8i |
30 |
Isoniazid |
99 |
3.3. In vitro antimalarial activity
In vitro antimalarial activity of the newly synthesized compounds 8a–p against P. falciparum strain was performed using quinine and chloroquine as the reference compounds. The consequences of the antimalarial screening are expressed as the drug concentration resulting in 50% inhibition (IC50) of parasite growth and are listed in Table 4.
Table 4 In vitro antimalarial activity of polyhydroquinoline derivatives 8a–p
Comp. |
IC50 (μg mL−1) |
Comp. |
IC50 (μg mL−1) |
8a |
0.58 |
8j |
0.073 |
8b |
0.95 |
8k |
1.54 |
8c |
0.090 |
8l |
0.067 |
8d |
1.45 |
8m |
0.088 |
8e |
1.24 |
8n |
1.47 |
8f |
1.56 |
8o |
0.42 |
8g |
2.10 |
8p |
0.78 |
8h |
0.59 |
Chloroquine |
0.020 |
8i |
0.042 |
Quinine |
0.268 |
4. Results and discussion
4.1. Optimization of reaction conditions for the target compounds
The reactions leading to the desired products were performed using conventional method (Path A in Scheme 1) as well as ultrasonic irradiation (Path B in Scheme 1). It was observed that, all the reactions by conventional route consumed very long time (1.5–2.5 h) for completion with relatively lower yields (61–79%). The same transformations could be successfully accomplished under ultrasound irradiation in comparatively shorter duration (15–30 min) with moderate to excellent yields (Table 1). The differences in yield and reaction time as compared to conventional method may be ascribed to cavitation in irradiated reaction mixture enhancing the mass transfer which allows chemical reactions to occur at the faster rate.41 Thus ultrasonic irradiation method was found to be more advantageous for the synthesis of novel polyhydroquinoline derivatives bearing a fluorinated 5-substituted aryloxypyrazole nucleus.
4.2. Analytical results
The structures of the newly synthesized compounds were confirmed by 1H NMR, FT-IR, mass spectrometry and elemental analysis. The IR spectrum of compounds 8a–p exhibited characteristic absorption band in the range 1263–1224 cm−1. This can be attributed to the presence of ether linkage. The carbonyl group stretching frequency was observed at 1665–1645 cm−1. The absorption band in the range of 2188–2210 cm−1 observed for all the compounds are due to –C
N stretching. The strong absorption band was also observed in the range of 1375–1364 cm−1 due to –CH3 rocking. The characteristic absorption band in the range 3486–3321 cm−1 may be attributed to asymmetric & symmetric stretching of –NH2. The 1H NMR spectra of compounds 8a–p exhibited the presence of the –CH proton (C4–H of polyhydroquinoline ring) as a sharp singlet around δ 4.56–4.53 ppm and a broad singlet at δ 8.70–8.22 ppm arising due to –NH proton. Multiplets in the range between δ 7.53–5.78 ppm appeared for amine and aromatic protons. The mass spectrum of all the compounds showed molecular ion peak at (M+) corresponding to their respective molecular weights, which confirmed the chemical structures.
4.3. Biological section
4.3.1. In vitro antibacterial activity. The antibacterial screening of the tested compounds 8a–p showed moderate to excellent inhibitory activity (Table 2). It has been observed that against S. pneumonia, compound 8i (R = 3-CF3, R1 = 4-OCH3) was found to be more potent i.e. 62.5 μg mL−1 as compared to ampicillin i.e. 100 μg mL−1. While compounds 8c (R = 2-F, R1 = 4-Cl) and 8j (R = 3-CF3, R1 = 4-Br) showed comparable activity to that of ampicillin. Against B. subtilis, compounds 8d (R = 2-F, R1 = 4-H) and 8j (R = 3-CF3, R1 = 4-Br) showed maximum potency i.e. 62.5 μg mL−1 as compared to ampicillin i.e. 250 μg mL−1 as well as norfloxacin i.e. 100 μg mL−1. Compounds 8c (R = 2-F, R1 = 4-Cl), 8f (R = 2-F, R1 = 4-OCH3), 8i (R = 3-CF3, R1 = 4-OCH3) MIC = 250 μg mL−1 showed equivalent potency to that of ampicillin. Compounds 8e (R = 4-F, R1 = 4-H), 8h (R = 3-CF3, R1 = 4-H), 8l (R = 3-F, R1 = 4-OCH3) and 8o (R = 4-F, R1 = 4-Br) i.e. 200 μg mL−1 were found to be more effective as compared to ampicillin MIC = 250 μg mL−1. Against C. tetani, compounds 8a (R = 2-F, R1 = 4-Br), 8f (R = 2-F, R1 = 4-OCH3), 8m (R = 3-F, R1 = 4-Br), 8o (R = 4-F, R1 = 4-Br), 8p (R = 4-F, R1 = 4-F), and 8g (R = 3-F, R1 = 4-H), MIC = 250 μg mL−1 showed same influence as that of ampicillin. Compounds 8h (R = 3-CF3, R1 = 4-H), 8j (R = 3-CF3, R1 = 4-Br) MIC = 100 μg mL−1 and compound 8b (R = 2-F, R1 = 4-F), 8c (R = 2-F, R1 = 4-Cl), 8i (R = 3-CF3, R1 = 4-OCH3) MIC = 125 μg mL−1 were found to more active than ampicillin MIC = 250 μg mL−1.In case of inhibiting Gram negative bacteria, compounds 8j (R = 3-CF3, R1 = 4-Br) and 8l (R = 3-F, R1 = 4-OCH3) MIC = 62.5 μg mL−1 were found to have higher potency against E. coli and V. cholera respectively as compared to ampicillin. Compounds 8c (R = 2-F, R1 = 4-Cl), 8i (R = 3-CF3, R1 = 4-OCH3), 8o (R = 4-F, R1 = 4-Br) and compounds 8f (R = 2-F, R1 = 4-OCH3), 8i (R = 3-CF3, R1 = 4-OCH3) also exhibited the similar activity as that of ampicillin i.e. 100 μg mL−1 respectively against S. typhi and V. cholera (Table 2).
4.3.2. In vitro antifungal activity. The antifungal screening data from Table 2 revealed that against C. albicans, compound 8n (R = 3-F, R1 = 4-F) i.e. 200 μg mL−1, compounds 8i (R = 3-CF3, R1 = 4-OCH3) and 8j (R = 3-CF3, R1 = 4-Br) i.e. 250 μg mL−1 were found to have significant activity as compared to griseofulvin. Compounds 8i (R = 3-CF3, R1 = 4-OCH3) and 8l (R = 3-F, R1 = 4-OCH3) exhibited equivalent potency i.e. 100 μg mL−1 against A. fumigates. From the above results, it can be concluded that compound 8j showed the potential to become new class of antimicrobial agent in future.
4.3.3. In vitro antituberculosis activity. Antituberculosis screening of the novel compounds 8a–p was conducted at 250 μg mL−1 concentrations against Mycobacterium tuberculosis H37Rv strain. Compounds 8e (R = 4-F, R1 = 4-H), 8k (R = 3-CF3, R1 = 4-F) and 8m (R = 3-F, R1 = 4-Br) were found to possess brilliant activity (i.e. 94%, 95% and 91% at 250 μg mL−1) against M. tuberculosis H37Rv. The compounds 8l (R = 3-F, R1 = 4-OCH3) and 8p (R = 4-F, R1 = 4 F) are moderately active and remaining all other compounds showed poor inhibition against M. tuberculosis H37Rv growth (Table 3).
4.3.4. In vitro antimalarial activity. The newly synthesized compounds 8a–p were evaluated for their antimalarial screening against chloroquine and quinine sensitive strain of P. falciparum. All the experiments were performed in duplicate and a mean value of IC50 is mentioned in Table 4. The compounds 8c (R = 2-F, R1 = 4-Cl), 8i (R = 3-CF3, R1 = 4-OCH3), 8j (R = 3-CF3, R1 = 4-Br), 8l (R = 3-F, R1 = 4-OCH3) and 8m (R = 3-F, R1 = 4-Br) were found to have IC50 in the range of 0.042 to 0.090 upon P. falciparum strain. Above compounds displayed fabulous activity against P. falciparum strain as compared to quinine IC50 0.268.
4.3.5. Cytotoxicity. Cytotoxicity of synthesized compounds was tested using bioassay of S. pombe cells at the cellular level. From the result, cell death caused by toxicity of the synthesized compounds could be easily monitored by vital staining (Table 5). The toxicity was found to vary with the type of substituent present and concentrations of the synthesized compounds. It has been observed that cytotoxicity was found to increase with concentration of drugs. Compounds 8i, 8j, 8k and 8l were found to have maximum toxicity, while compounds 8e, 8m, 8c were found to be less cytotoxic (Fig. 3). After 17 h of the treatment, many of the S. pombe cells were killed due to toxic nature of the compound.
Table 5 The percentage viability of different chemically synthesized compounds was listed in table
Conc. |
8C |
8M |
8K |
8L |
8I |
8J |
8E |
DMSO |
Untreated cell |
— |
— |
— |
— |
— |
— |
— |
— |
97 |
98 |
2.5 |
94 |
95 |
76 |
78 |
82 |
66 |
85 |
|
|
5 |
90 |
91 |
74 |
74 |
80 |
62 |
76 |
|
|
7.5 |
84 |
90 |
72 |
64 |
76 |
60 |
73 |
|
|
10 |
78 |
88 |
63 |
51 |
71 |
58 |
70 |
|
|
12.5 |
75 |
85 |
57 |
55 |
64 |
56 |
63 |
|
|
 |
| Fig. 3 Effect of synthesized compounds on viability of S. Pombe at different concentrations. | |
4.4. Structure–activity relationship (SAR)
The results of the biological screening showed that the activity was significantly affected by introducing fluorinated 5-substituted aryloxypyrazole at C-4 position and phenylamino nucleus at N-1 position on polyhydroquinoline scaffold (Fig. 4).
 |
| Fig. 4 Structure–activity relationships for antimicrobial, antituberculosis, antimalarial and cytotoxicity activity of the synthesized compounds 8a–p. | |
We perceived that the methoxy group existing at R1 position in N-phenyl moiety at N-1 in polyhydroquinoline and –CF3 group at meta position of aryloxy ring in pyrazole nucleus exhibited excellent antimalarial activity against P. falciparum strain as compared to quinine as well as improved antibacterial activity against S. pneumonia. Without any substitution at R1 position and fluoro group at ortho position of aryloxy ring revealed highest activity against B. subtilis. The fluoro group prevailing at R1 positions and –CF3 group at meta position of aryloxy ring displayed superior antituberculosis activity against M. tuberculosis H37Rv. The replacement of electron donating methoxy group with electron withdrawing chloro groups at R1 position increased antimalarial activity. The bromo group present at R1 position and –CF3 group at meta position in aryloxy ring exhibited brilliant activity against B. subtilis and improved antimalarial activity. The bromo, fluoro and methoxy groups present at R1 position and –CF3 and –F groups at meta position in aryloxy ring demonstrate higher cytotoxicity against S. pombe cells at a cellular level. But the chloro and bromo groups existing at R1 positions and –F group at ortho and meta positions of aryloxy ring displayed inferior cytotoxicity against S. pombe cells at a cellular level. It can be concluded that electron donating and withdrawing groups at R1 position and –CF3 group at meta position of aryloxy ring are observed to be chiefly responsible for deviation in biological potency.
5. Conclusion
We designed and synthesized some novel polyhydroquinoline derivatives bearing a fluorinated 5-substituted aryloxypyrazole nucleus advantageously using ultrasonic irradiation and examined their antimicrobial, antimalarial and antituberculosis activities. The results indicated that majority of the compounds were found to be most active against B. subtilis and C. tetani. Amongst the tested compounds, 8e, 8k, and 8m showed prominent antituberculosis activities. The Compounds 8c, 8i, 8l and 8m displayed superior antimalarial activity. Finally compound 8i could be recognized as the most biologically active member within the synthesized series showing an interesting dual antimalarial and antibacterial profile. The SAR results revealed that the presence of electron donating and withdrawing groups at R1 position and –CF3 group at meta position of aryloxy ring played effective role in boasting the prepared polyhydroquinoline derivatives as potent antimicrobial, antimalarial and antitubercular agents. The chloro and bromo groups existing at R1 positions and –F group at ortho and meta positions of aryloxy ring displayed inferior cytotoxicity against S. pombe cells at a cellular level. Consequently, polyhydroquinoline scaffold represents a class that needs further investigation with the hope of discovering new antimicrobial and antimalarial agents.
6. Experimental section
6.1. Chemistry
All the reagents were obtained commercially and used without further purification. Solvents used were of analytical grade. Melting points (°C, uncorrected) were determined in open capillaries on μThermoCal10 melting point apparatus (Analab Scientific Pvt. Ltd, India). Precoated silica gel plates (silica gel 0.25 mm, 60 G F 254; Merck, Germany) were used for thin layer chromatography. Electron impact Mass Spectra were recorded on Shimadzu LCMS 2010 spectrometer (Shimadzu, Tokyo, Japan) purchased under PURSE programme of DST at Sardar Patel University, Vallabh Vidyanagar, India. The IR spectra were recorded on Shimadzu FTIR 8401 spectrophotometer using potassium bromide pellets in the range 4000–400 cm−1 and frequencies of only characteristic peaks are expressed in cm−1. The elemental analysis was performed on Perkin-Elmer 2400 series-II elemental analyzer (Perkin-Elmer, USA) at Sophisticated Instrumentation Centre for Applied Research & Training (SICART), Vallabh Vidyanagar, India. All the compounds were found to be within ±0.4% of their theoretical values. The reaction mixtures were irradiated by ultrasound at room temperature in a D-compact ultrasonic cleaner with a frequency of 30 kHz and an output power of 250 W. The reaction flask was kept at the maximum energy area in the cleaner and the level of the reactants was kept slightly lower than the level of water in the bath. 1H NMR spectra (in DMSO-d6) were recorded on Bruker Avance 400F (MHz) NMR Spectrometer at 400 MHz using TMS as the internal standard.
6.1.1. General procedure for the synthesis of 3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes (3a–d). 5-Chloro-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde 1 (1 mmol), substituted phenols 2a–d (1 mmol) and anhydrous potassium carbonate (2 mmol) in dimethylformamide (10 mL) were charged in a 100 mL round bottom flask equipped with a mechanical stirrer and a condenser. The reaction mixture was heated at 90 °C for 2 h and the progress of the reaction was monitored by TLC. After the completion of reaction confirmed by the TLC, the reaction mixture was poured in to 100 mL ice-water and filtered, washed thoroughly with water, dried and recrystallized from hot ethanol (10 mL) to obtain a white solid.
6.1.1.1 5-(2-Fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (3a). Yield 85%; m.p. 225–227 °C; 1H NMR (400 MHz, DMSO-d6): δ 2.46 (s, 3H, –CH3), 7.13–7.64 (m, 9H, Ar–H), 9.56 (s, 1H, –CHO).
6.1.1.2 5-(3-Fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (3b). Yield 78%; m.p. 210–212 °C; 1H NMR (400 MHz, DMSO-d6): δ 2.47 (s, 3H, –CH3), 6.92–7.63 (m, 9H, Ar–H), 9.61 (s, 1H, –CHO).
6.1.1.3 5-(4-Fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazole-4-carbaldehyde (3c). Yield 82%; m.p. 245–247 °C; 1H NMR (400 MHz, DMSO-d6): δ 2.46 (s, 3H, –CH3), 7.17–7.64 (m, 9H, Ar–H), 9.54 (s, 1H, –CHO).
6.1.2. General procedure for the synthesis of substituted 5,5-dimethyl-3-(2-phenylhydrazinyl)-cyclohex-2-enones (6a–e). 1,3-Dimedone 4 (10 mmol), substituted phenyl hydrazine hydrochlorides 5a–e (10 mmol) and water (10 mL) were charged in a 100 mL round bottom flask equipped with a mechanical stirrer. The reaction mixture was stirred at room temperature for 6 h. After the completion of reaction (checked by TLC), the separated substituted enhydrazinoketones 6a–e were filtered and washed with water to obtain the pure solid product.
6.1.3. General procedure for the conventional synthesis of 2-amino-7,7-dimethyl-4-(3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazol-4-yl)-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydro quinoline-3-carbonitriles (8a–p). A 100 mL round bottomed flask was charged with a mixture of 3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes 3a–d (1 mmol), malononitrile 7 (1 mmol), substituted enhydrazinoketones 6a–e (1 mmol), and catalytic amount of piperidine (2–3 drops) in ethanol (10 mL). The reaction mixture was refluxed for an appropriate time period till the completion of the reaction as indicated by TLC (Table 1). After the completion of reaction, the reaction mixture was stirred magnetically for further 10 min. After cooling the separated solid mass was collected by filtration, washed well with ethanol (10 mL) and crystallized from hot ethanol (10 mL).
6.1.3. General procedure for the synthesis of 2-amino-7,7-dimethyl-4-(3-methyl-5-substituted aryloxy-1-phenyl-1H-pyrazol-4-yl)-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydro quinoline-3-carbonitriles (8a–p) using sonochemical method. A 100 mL round bottomed flask was charged with a mixture of 3-methyl-5-aryloxy-1-phenyl-1H-pyrazole-4-carbaldehydes 3a–d (1 mmol), malononitrile 7 (1 mmol), substituted enhydrazinoketones 6a–e (1 mmol) and catalytic amount of piperidine (2–3 drops) in ethanol (10 mL). The reaction flask was located in the ultrasonic bath so as to keep the level of reactants slightly lower than the level of water in bath. The reaction mixture was sonicated at room temperature for an appropriate time period till the completion of the reaction as indicated by TLC (Table 1). After the completion of reaction, the reaction mixture was stirred magnetically for further 10 min. The separated solid mass was collected by filtration, washed well with cold ethanol (10 mL) and crystallized from hot ethanol (10 mL). The physicochemical and spectroscopic characterization data of the synthesized compounds 8a–p are given below.
6.1.3.1. 2-Amino-1-((4-bromophenyl)amino)-4-(5-(2-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8a). Yield 88%; m.p. 215–217 °C; IR (KBr, νmax, cm−1): 3478 & 3336 (asym. & sym. str. of –NH2), 2188 (C
N str.), 1650 (C
O str.), 1368 (–CH3 rocking), 1260 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.85 (s, 3H, –CH3), 0.91 (s, 3H, –CH3), 1.68–2.20 (m, 4H, 2 × –CH2), 2.31 (s, 3H, –CH3), 4.56 (s, 1H, –CH), 5.98–7.50 (m, 15H, Ar–H and –NH2), 8.62 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.93 (pyrazole–CH3), 26.68, 28.46 (C(CH3)2), 32.31 (C4), 37.65 (CH2), 49.21 (CH2–CO), 56.33 (C–CN), 109.98, 110.84, 111.47, 114.13, 117.40, 120.69, 120.77, 121.86, 122.14, 123.59, 125.10, 126.90, 127.15, 130.78, 131.85, 132.81, 134.55, 134.70, 135.07, 138.15, 142.86, 144.08, 152.97, 154.16, 161.18 (25C, Ar–C), 195.07 (C
O); ESI-MS (m/z): 653.1 (M+), 655.1 (M + 2); anal. calcd (%) for C34H30BrFN6O2: C, 62.48; H, 4.63; N, 12.86. Found: C, 62.24; H, 4.40; N, 12.63.
6.1.3.2. 2-Amino-4-(5-(2-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-((4-fluorophenyl)amino)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8b). Yield 91%; m.p. 202–204 °C; IR (KBr, νmax, cm−1): 3472 & 3340 (asym. & sym. str. of –NH2), 2198 (C
N str.), 1645 (C
O str.), 1375 (–CH3 rocking), 1231 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.83 (s, 3H, –CH3), 0.89 (s, 3H, –CH3), 1.69–2.02 (m, 4H, 2 × –CH2), 2.31 (s, 3H, –CH3), 4.56 (s, 1H, –CH), 597–7.50 (m, 15H, Ar–H and –NH2), 8.46 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.57 (pyrazole–CH3), 26.35, 28.03 (C(CH3)2), 31.92 (C4), 37.65 (CH2), 49.35 (CH2–CO), 56.67 (C–CN), 109.75, 109.93, 113.93, 114.38, 121.54, 121.88, 122.22, 129.65, 137.99, 138.17, 142.05, 143.51, 143.90, 144.03, 144.34, 144.61, 147.76, 150.16, 151.20, 152.59, 152.72, 152.88, 152.24, 154.18, 161.25 (25C, Ar–C), 195.04 (C
O); ESI-MS (m/z): 593.2 (M+); anal. calcd (%) for C34H30F2N6O2: C, 68.91; H, 5.10; N, 14.18. Found: C, 68.68; H, 4.83; N, 13.97.
6.1.3.3. 2-Amino-1-((4-chlorophenyl)amino)-4-(5-(2-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8c). Yield 79%; m.p. 218–220 °C; IR (KBr, νmax, cm−1): 3439 & 3334 (asym. & sym. str. of –NH2), 2210 (C
N str.), 1660 (C
O str.), 1371 (–CH3 rocking), 1224 (C–O–C ether str.); 760 (C–Cl stretching); 1H NMR (400 MHz, DMSO-d6): 1H NMR (400 MHz, DMSO-d6): δ 0.85 (s, 3H, –CH3), 0.91 (s, 3H, –CH3), 1.68–2.20 (m, 4H, 2 × –CH2), 2.31 (s, 3H, –CH3), 4.56 (s, 1H, –CH), 5.99–7.50 (m, 15H, Ar–H and –NH2), 8.61 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.54 (pyrazole–CH3), 28.08, 28.55 (C(CH3)2), 31.96 (C4), 37.72 (CH2), 49.82 (CH2–CO), 56.74 (C–CN), 109.95, 109.97, 113.86, 114.26, 121.57, 121.85, 122.19, 124.14, 129.71, 138.01, 138.26, 143.93, 144.49, 145.15, 146.10, 147.77, 147.82, 147.93, 150.18, 152.25, 152.48, 152.79, 153.10, 154.15, 161.22 (25C, Ar–C), 195.07 (C
O); ESI-MS (m/z): 610.1 (M+); anal. calcd (%) for C34H30ClFN6O2: C, 67.04; H, 4.96; N, 13.80. Found: C, 66.79; H, 4.75; N, 13.53.
6.1.3.4. 2-Amino-4-(5-(2-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8d). Yield 87%; m.p. 196–198 °C; IR (KBr, νmax, cm−1): 3431 & 3321 (asym. & sym. str. of –NH2), 2188 (C
N str.), 1658 (C
O str.), 1369 (–CH3 rocking), 1232 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.83 (s, 3H, –CH3), 0.90 (s, 3H, –CH3), 1.74–2.20 (m, 4H, 2 × –CH2), 2.31 (s, 3H, –CH3), 4.56 (s, 1H, –CH), 5.95–7.51 (m, 16H, Ar–H and –NH2), 8.49 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.62 (pyrazole–CH3), 28.28, 28.49 (C(CH3)2), 31.95 (C4), 38.01 (CH2), 49.64 (CH2–CO), 56.74 (C–CN), 109.78, 111.73, 112.13, 116.45, 117.58, 120.37, 120.73, 121.56, 121.86, 122.05, 122.17, 124.34, 125.32, 127.04, 129.55, 129.70, 129.85, 130.32, 144.39, 144.73, 147.05, 147.88, 152.74, 153.36, 154.09 (25C, Ar–C), 195.07 (C
O); ESI-MS (m/z): 575.2 (M+); anal. calcd (%) for C34H31FN6O2: C, 71.06; H, 5.44; N, 14.62. Found: C, 70.78; H, 5.21; N, 14.36.
6.1.3.5. 2-Amino-4-(5-(4-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8e). Yield 84%; m.p. 192–194 °C; IR (KBr, νmax, cm−1): 3452 & 3332 (asym. & sym. str. of –NH2), 2210 (C
N str.), 1646 (C
O str.), 1350 (–CH3 rocking), 1232 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.83 (s, 3H, –CH3), 0.88 (s, 3H, –CH3), 1.73–2.19 (m, 4H, 2 × –CH2), 2.40 (s, 3H, –CH3), 4.55 (s, 1H, –CH), 5.84–7.53 (m, 16H, Ar–H and –NH2), 8.55 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.62 (pyrazole–CH3), 28.13, 28.37 (C(CH3)2), 32.11 (C4), 37.79 (CH2), 49.52 (CH2–CO), 56.33 (C–CN), 109.55, 111.99, 112.14, 113.93, 116.91, 117.10, 120.51, 121.42, 121.93, 122.08, 126.83, 126.95, 129.57, 129.68, 129.91, 138.08, 145.08, 145.40, 147.06, 147.81, 152.57, 152.77, 153.32, 154.21, 159.55 (25C, Ar–C), 195.07 (C
O); ESI-MS (m/z): 575.1 (M+); anal. calcd (%) for C34H31FN6O2: C, 71.06; H, 5.44; N, 14.62. Found: C, 70.85; H, 5.15; N, 14.36.
6.1.3.6. 2-Amino-4-(5-(2-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-((4-methoxyphenyl)amino)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8f). Yield 88%; m.p. 240–242 °C; IR (KBr, νmax, cm−1): 3470 & 3339 (asym. & sym. str. of –NH2), 2192 (C
N str.), 1655 (C
O str.), 1362 (–CH3 rocking), 1262 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.84 (s, 3H, –CH3), 0.91 (s, 3H, –CH3), 1.76–2.20 (m, 4H, 2 × –CH2), 2.38 (s, 3H, –CH3), 3.69 (s, 3H, –OCH3), 4.55 (s, 1H, –CH), 5.91–7.51 (m, 15H, Ar–H and –NH2), 8.22 (s, 1H, –NH); 13C NMR (100 MHz, DMSO–d6) δ: 13.94 (pyrazole–CH3), 28.19, 28.48 (C(CH3)2), 32.57 (C4), 36.31 (CH2), 49.20 (CH2–CO), 51.04 (Ar–C–OCH3), 55.97 (C–CN), 104.97, 106.41, 110.22, 111.14, 114.19, 117.20, 117.86, 121.71, 124.76, 125.53, 125.92, 126.85, 127.53, 129.80, 131.89, 137.89, 143.76, 145.68, 147.70, 148.46, 149.77, 152.22, 155.71, 157.23, 161.20 (25C, Ar–C), 195.05 (C
O); ESI-MS (m/z): 605.1 (M+); anal. calcd (%) for C35H33FN6O3: C, 69.52; H, 5.50; N, 13.90. Found: C, 69.29; H, 5.26; N, 13.62.
6.1.3.7. 2-Amino-4-(5-(3-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8g). Yield 76%; m.p. 195–197 °C; IR (KBr, νmax, cm−1): 3471 & 3340 (asym. & sym. str. of –NH2), 2191 (C
N str.), 1656 (C
O str.), 1372 (–CH3 rocking), 1263 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.82 (s, 3H, –CH3), 0.88 (s, 3H, –CH3), 1.68–2.18 (m, 4H, 2 × –CH2), 2.28 (s, 3H, –CH3), 4.55 (s, 1H, –CH), 5.87–7.53 (m, 16H, Ar–H and –NH2), 8.56 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.58 (pyrazole–CH3), 28.44, 29.08 (C(CH3)2), 32.11 (C4), 37.80 (CH2), 49.48 (CH2–CO), 56.80 (C–CN), 109.42, 109.75, 110.48, 111.46, 114.14, 120.67, 121.52, 121.91, 126.99, 129.62, 129.73, 129.89, 131.57, 138.15, 139.27, 144.31, 144.66, 147.03, 147.79, 152.60, 153.44, 154.27, 154.72, 157.64, 161.89 (25C, Ar–C), 194.92 (C
O); ESI-MS (m/z): 575.2 (M+); anal. calcd (%) for C34H31FN6O2: C, 71.06; H, 5.44; N, 14.62. Found: C, 70.81; H, 5.21; N, 14.33.
6.1.3.8. 2-Amino-7,7-dimethyl-4-(3-methyl-1-phenyl-5-(3-(trifluoromethyl)phenoxy)-1H-pyrazol-4-yl)-5-oxo-1-(phenylamino)-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8h). Yield 85%; m.p. 201–203 °C; IR (KBr, νmax, cm−1): 3481 & 3333 (asym. & sym. str. of –NH2), 2197 (C
N str.), 1665 (C
O str.), 1371 (–CH3 rocking), 1259 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.80 (s, 3H, –CH3), 0.86 (s, 3H, –CH3), 1.62–2.21 (m, 4H, 2 × –CH2), 2.34 (s, 3H, –CH3), 4.56 (s, 1H, –CH), 5.84–7.52 (m, 16H, Ar–H and –NH2), 8.56 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.58 (pyrazole–CH3), 27.97, 28.25 (C(CH3)2), 32.10 (C4), 37.78 (CH2), 49.48 (CH2–CO), 56.79 (C–CN), 109.37, 111.95, 112.77, 113.85, 114.06, 119.38, 120.70, 121.73, 122.23, 127.17, 129.62, 129.92, 131.51, 131.69, 137.91, 138.05, 144.11, 146.99, 147.89, 152.60, 152.72, 152.95, 153.42, 154.32, 156.69, 156.77 (26C, Ar–C), 194.84 (C
O); ESI-MS (m/z): 625.1 (M+); anal. calcd (%) for C35H31F3N6O2: C, 67.30; H, 5.00; N, 13.45. Found: C, 67.06; H, 4.73; N, 13.18.
6.1.3.9. 2-Amino-1-((4-methoxyphenyl)amino)-7,7-dimethyl-4-(3-methyl-1-phenyl-5-(3-(trifluoromethyl)phenoxy)-1H-pyrazol-4-yl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8i). Yield 83%; m.p. 245–247 °C; IR (KBr, νmax, cm−1): 3472 & 3338 (asym. & sym. str. of –NH2), 2197 (C
N str.), 1664 (C
O str.), 1367 (–CH3 rocking), 1254 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.80 (s, 3H, –CH3), 0.86 (s, 3H, –CH3), 1.63–2.23 (m, 4H, 2 × –CH2), 2.41 (s, 3H, –CH3), 3.73 (s, 3H, –OCH3), 4.53 (s, 1H, –CH), 5.78–7.52 (m, 15H, Ar–H and –NH2), 8.28 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.60 (pyrazole–CH3), 28.06, 28.25 (C(CH3)2), 32.17 (C4), 37.79 (CH2), 49.51 (CH2–CO), 55.79 (Ar–C–OCH3), 56.73 (C–CN), 109.27, 109.66, 113.17, 113.93, 114.16, 115.00, 115.24, 119.60, 121.72, 122.30, 127.16, 129.62, 129.91, 131.71, 137.91, 138.07, 140.50, 140.63, 144.50, 147.59, 153.11, 153.55, 153.05, 154.28, 154.47, 156.72 (26C, Ar–C), 195.11 (C
O); ESI-MS (m/z): 655.1 (M+); anal. calcd (%) for C36H33F3N6O3: C, 66.05; H, 5.08; N, 12.84. Found: C, 65.82; H, 4.81; N, 12.63.
6.1.3.10. 2-Amino-1-((4-bromophenyl)amino)-7,7-dimethyl-4-(3-methyl-1-phenyl-5-(3-(trifluoromethyl)phenoxy)-1H-pyrazol-4-yl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8j). Yield 87%; m.p. 232–234 °C; IR (KBr, νmax, cm−1): 3482& 3338 (asym. & sym. str. of –NH2), 2196 (C
N str.), 1663 (C
O str.), 1366 (–CH3 rocking), 1257 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.81 (s, 3H, –CH3), 0.87 (s, 3H, –CH3), 1.58–1.99 (m, 4H, 2 × –CH2), 2.33 (s, 3H, –CH3), 4.55 (s, 1H, –CH), 5.90–7.54 (m, 15H, Ar–H and –NH2), 8.70 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.52 (pyrazole–CH3), 27.20, 28.13 (C(CH3)2), 32.12 (C4), 37.74 (CH2), 49.44 (CH2–CO), 56.82 (C–CN), 109.57, 109.84, 111.71, 113.85, 113.95, 114.46, 119.70, 121.75, 122.28, 127.13, 129.59, 131.70, 132.38, 132.52, 137.88, 138.03, 144.26, 146.39, 147.87, 152.38, 152.71, 153.08, 153.45, 154.96, 156.64, 156.74 (26C, Ar–C), 194.87 (C
O); ESI-MS (m/z): 703.1 (M+), 705.1 (M + 2); anal. calcd (%) for: C35H30BrF3N6O2: C, 59.75; H, 4.30; N, 11.95. Found: C, 59.49; H, 4.05; N, 11.67.
6.1.3.11. 2-Amino-1-((4-fluorophenyl)amino)-7,7-dimethyl-4-(3-methyl-1-phenyl-5-(3-(trifluoromethyl)phenoxy)-1H-pyrazol-4-yl)-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8k). Yield 74%; m.p. 224–226 °C; IR (KBr, νmax, cm−1): 3486 & 3338 (asym. & sym. str. of –NH2), 2193 (C
N str.), 1662 (C
O str.), 1370 (–CH3 rocking), 1263 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.83 (s, 3H, –CH3), 0.89 (s, 3H, –CH3), 1.61–2.21 (m, 4H, 2 × –CH2), 2.33 (s, 3H, –CH3), 4.54 (s, 1H, –CH), 5.87–7.53 (m, 15H, Ar–H and –NH2), 8.54 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.63 (pyrazole–CH3), 28.08, 28.23 (C(CH3)2), 32.09 (C4), 37.88 (CH2), 49.48 (CH2–CO), 56.75 (C–CN), 109.50, 109.88, 114.04, 116.43, 119.26, 121.71, 122.21, 127.16, 129.58, 129.73, 131.47, 131.71, 138.08, 143.51, 144.10, 144.48, 147.96, 152.50, 152.88, 153.27, 153.71, 153.89, 156.12, 156.38, 156.47, 156.81 (26C, Ar–C), 195.07 (C
O); ESI-MS (m/z): 643.1 (M+); anal. calcd (%) for: C35H30F4N6O2: C, 65.41; H, 4.71; N, 13.08. Found: C, 65.17; H, 4.42; N, 12.85.
6.1.3.12. 2-Amino-4-(5-(3-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-((4-methoxyphenyl)amino)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8l). Yield 81%; m.p. 248–250 °C; IR (KBr, νmax, cm−1): 3477 & 3334 (asym. & sym. str. of –NH2), 2185 (C
N str.), 1658 (C
O str.), 1365 (–CH3 rocking), 1259 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.81 (s, 3H, –CH3), 0.86 (s, 3H, –CH3), 1.63–2.22 (m, 4H, 2 × –CH2), 2.33 (s, 3H, –CH3), 3.74 (s, 3H, –OCH3), 4.54 (s, 1H, –CH), 5.79–7.52 (m, 15H, Ar–H and –NH2), 8.37 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.82 (pyrazole–CH3), 26.78, 28.41 (C(CH3)2), 32.45 (C4), 36.24 (CH2), 49.43 (CH2–CO), 51.52 (Ar–C–OCH3), 56.39 (C–CN), 105.13, 106.18, 111.67, 114.53, 116.73, 117.97, 120.78, 121.86, 122.74, 123.89, 125.50, 126.70, 127.75, 130.88, 131.89, 132.71, 134.85, 134.95, 135.15, 138.75, 142.96, 144.58, 157.77, 160.93, 164.37 (25C, Ar–C), 194.47 (C
O); ESI-MS (m/z): 605.2 (M+); anal. calcd (%) for: C35H33FN6O3: C, 69.52; H, 5.50; N, 13.90. Found: C, 69.29; H, 5.23; N, 13.62.
6.1.3.13. 2-Amino-1-((4-bromophenyl)amino)-4-(5-(3-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8m). Yield 86%; m.p. 228–230 °C; IR (KBr, νmax, cm−1): 3475 & 3339 (asym. & sym. str. of –NH2), 2190 (C
N str.), 1665 (C
O str.), 1371 (–CH3 rocking), 1258 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.83 (s, 3H, CH3), 0.89 (s, 3H, CH3), 1.40–2.18 (m, 4H, 2 × CH2), 2.33 (s, 3H, CH3), 4.54 (s, 1H, CH), 6.45–7.72 (m, 15H, Ar–H and NH2), 8.70 (s, 1H, NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.58 (pyrazole–CH3), 28.40, 28.29 (C(CH3)2), 32.80 (C4), 37.95 (CH2), 49.51 (CH2–CO), 56.33 (C–CN), 109.88, 110.28, 111.45, 111.76, 114.13, 117.40, 120.75, 121.76, 122.24, 123.49, 125.19, 126.93, 127.17, 130.88, 131.75, 132.71, 134.65, 134.79, 135.17, 138.35, 142.76, 144.88, 152.87, 154.26, 161.38 (25C, Ar–C), 195.07 (C
O); ESI-MS (m/z): 653.1 (M+), 655.1 (M + 2); anal. calcd (%) for: C34H30BrFN6O2: C, 62.48; H, 4.63; N, 12.86. Found: C, 62.24; H, 4.36; N, 12.63.
6.1.3.14. 2-Amino-4-(5-(3-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-((4-fluorophenyl)amino)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8n). Yield 89%; m.p. 204–206 °C; IR (KBr, νmax, cm−1): 3483 & 3340 (asym. & sym. str. of –NH2), 2195 (C
N str.), 1662 (C
O str.), 1364 (–CH3 rocking), 1257 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.83 (s, 3H, –CH3), 0.90 (s, 3H, –CH3), 1.36–2.19 (m, 4H, 2 × –CH2), 2.33 (s, 3H, –CH3), 4.54 (s, 1H, –CH), 5.90–7.53 (m, 15H, Ar–H and –NH2), 8.53 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.55 (pyrazole–CH3), 28.01, 28.36 (C(CH3)2), 32.13 (C4), 37.80 (CH2), 49.48 (CH2–CO), 56.83 (C–CN), 109.55, 109.91, 111.44, 113.37, 113.67, 113.92, 114.13, 116.34, 116.56, 121.53, 121.87, 122.06, 126.98, 129.60, 129.72, 131.56, 138.15, 143.51, 147.59, 152.65, 153.64, 154.77, 154.82, 157.54, 161.79 (25C, Ar–C), 194.92 (C
O); ESI-MS (m/z): 593.2 (M+); anal. calcd (%) for: C34H30F2N6O2: C, 68.91; H, 5.10; N, 14.18. Found: C, 68.63; H, 4.86; N, 13.97.
6.1.3.15. 2-Amino-1-((4-bromophenyl)amino)-4-(5-(4-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8o). Yield 78%; m.p. 238–240 °C; IR (KBr, νmax, cm−1): 3473 & 3338 (asym. & sym. str. of –NH2), 2197 (C
N str.), 1664 (C
O str.), 1372 (–CH3 rocking), 1261 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.85 (s, 3H, –CH3), 0.89 (s, 3H, –CH3), 1.70–2.19 (m, 4H, 2 × –CH2), 2.32 (s, 3H, –CH3), 4.53 (s, 1H, –CH), 5.89–7.52 (m, 15H, Ar–H and –NH2), 8.68 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.55 (pyrazole–CH3), 27.68, 28.23 (C(CH3)2), 32.14 (C4), 37.74 (CH2), 49.52 (CH2–CO), 56.50 (C–CN), 109.75, 110.00, 111.67, 113.80, 114.13, 116.67, 116.90, 121.47, 122.15, 123.75, 125.18, 126.85, 129.53, 129.68, 129.96, 138.27, 145.28, 145.50, 147.46, 147.71, 152.47, 152.67, 153.38, 154.48, 159.59 (25C, Ar–C), 194.95 (C
O); ESI-MS (m/z): 653.1 (M+), 655.1 (M + 2); anal. calcd (%) for: C34H30BrFN6O2: C, 62.48; H, 4.63; N, 12.86. Found: C, 62.22; H, 4.40; N, 12.58.
6.1.3.16. 2-Amino-4-(5-(4-fluorophenoxy)-3-methyl-1-phenyl-1H-pyrazol-4-yl)-1-((4-fluorophenyl)amino)-7,7-dimethyl-5-oxo-1,4,5,6,7,8-hexahydroquinoline-3-carbonitrile (8p). Yield 80%; m.p. 226–228 °C; IR (KBr, νmax, cm−1): 3483 & 3342 (asym. & sym. str. of –NH2), 2198 (C
N str.), 1662 (C
O str.), 1367 (–CH3 rocking), 1262 (C–O–C ether str.); 1H NMR (400 MHz, DMSO-d6): δ 0.84 (s, 3H, –CH3), 0.89 (s, 3H, –CH3), 1.70–2.19 (m, 4H, 2 × –CH2), 2.32 (s, 3H, –CH3), 4.54 (s, 1H, –CH), 5.87–7.53 (m, 15H, Ar–H and –NH2), 8.52 (s, 1H, –NH); 13C NMR (100 MHz, DMSO-d6) δ: 13.55 (pyrazole–CH3), 28.15, 28.27 (C(CH3)2), 32.13 (C4), 37.79 (CH2), 49.54 (CH2–CO), 56.87 (C–CN), 109.70, 110.00, 113.36, 113.79, 113.88, 116.32, 116.59, 116.89, 117.22, 121.46, 121.87, 122.15, 126.85, 129.53, 129.68, 138.08, 143.50, 145.08, 145.38, 147.79, 152.48, 153.10, 154.50, 156.90, 159.27 (25C, Ar–C), 194.93 (C
O); ESI-MS (m/z): 593.2 (M+); anal. calcd (%) for: C34H30F2N6O2: C, 68.91; H, 5.10; N, 14.18. Found: C, 68.69; H, 4.84; N, 13.91.
Acknowledgements
The authors wish to express thanks to Head, Department of Chemistry, Sardar Patel University for providing research facilities. We are also thankful to Dhanji P. Rajani, Microcare Laboratory, Surat for antimicrobial, antituberculosis and antimalarial screening of the compounds reported herein and Sophisticated Instrumentation Centre for Applied Research and Training (SICART), Vallabh Vidyanagar for FT-IR analysis at concessional rate. SCK and VBP wish to acknowledge the University Grants Commission – New Delhi, India for meritorious fellowships awarded to them during 2013–2015.
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Footnote |
† Electronic supplementary information (ESI) available: The spectral data of synthesized compound are shown in ESI. See DOI: 10.1039/c5ra00388a |
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