Amberlite IR-120H Catalyzed Synthesis of 1,3-Diphenylpyrazolechromenoquinolin-6-one Compounds and Their Biological Evaluation
A B S T R A C T
A series of 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds were designed and synthesized by using a greener and recyclable heterogeneous Amberlite IR-120H resin as a catalyst, in the presence of ethanol reflux conditions. Interestingly, the catalyst can be recovered after completion of the reaction and can be reused without loss of catalytic property. Therefore, this method provides a green and environmentally benign much improved protocol for the synthesis of 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds. The synthesized library of thirty compounds were tested against their cytotoxicity; moreover, the compounds 5s and 5t exhibited potential cytotoxic activity with IC50 values of 1.22 and 1.64 µM, respectively, on MCF-7 cancer cells. The biophysical studies such as UV-visible, fluorescence and circular dichroism studies indicate that these compounds possess good DNA intercalation ability. In addition, these compounds efficiently inhibit topoisomerase I activity. Molecular docking and viscosity studies support that these compounds exhibited intercalative mode of binding with DNA.
Keywords
Amberlite IR-120H, pyrazoles, DNA binding, anticancer, topoisomerase I, intercalation, chromenoquinoline-6-one
Introduction
Cancer is a multifaceted debilitating disease characterized by uncontrolled proliferation of cells to form tumors that represent one of the leading causes of death worldwide and has become a most common rationale in the future [1, 2]. These are different types based on cell from which organ it has originated, treatment includes chemotherapy, radiation and surgery in which chemotherapy is the mainstay. The use of existing chemotherapeutics is often narrow due to drug resistance and undesirable side effects; therefore, there is an overwhelming need to develop new agents for cancer treatment.
At present, DNA is the most essential target for the design and discovery of drugs in pharmaceutical field and many of the drug molecules currently in clinical trials are because of DNA response to their binding ability and the topological changes in DNA effective to the anticancer, anti-bacterial and therapeutic agents, the DNA binding is in different ways such as intercalation, groove binding and alkylation [3, 4]. The translation and transcription process are associated with many enzymes one such is topoisomerase I that involves in many aspects of chromatin topology and DNA metabolism. Topoisomerase inhibitors are among the noteworthy anticancer agents due to the vital role of these enzymes in cell proliferation. DNA binders like Hoechst 33258, camptothecin, netropsin and bleomycin were found to possess broad spectrum anticancer activity. Therefore, it is imperative to identify new topoisomerase inhibitors.
Heterocycles are an important and unique class of compounds. Among them, pyrazoles are best examples of aromatic heterocycles containing five membered ring incorporated with two nitrogen heteroatoms. They have attracted much attention in recent times owing to their use in agriculture and drug discovery [5]. Pyrazoles play a key role as versatile building blocks for medicinal chemistry due to their competence to exhibit broad range of bioactivities including anti-inflammatory, anti-microbial, antioxidant, anti-depressant, anti-influenza and anticancer activities [6-10].
Pyrazole derivatives are reported to exert their anticancer activity by the inhibition of multiple targets such as topoisomerase-I, -II, EGFR, fibroblast growth factor (FGF), tumor growth factor (TGF), different kinases which are significant for the management of cancer telomerase and DNA cleavage [11]. Recently, many researchers have reported numerous pyrazole derivatives, thus demonstrating the use of pyrazole scaffold in the development of new anticancer agents. Among the anticancer pyrazoles, 1,3-diphenyl pyrazoles were accounted to be efficient and highly potent cytotoxic agents as DNA binders and topoisomerase inhibitors (Figure 1) [12]. Moreover, it has been reported that pyrazole derivatives have excellent drug-like properties and high oral bioavailability [13].
Figure 1: Representative examples of DNA binders and topoisomerase inhibitors.
On the other hand, coumarins represent a key motif for the synthesis of natural products and chemotherapeutic agents. Interest in it has been amplified because, not only they are significant synthetic endpoints, but these derivatives have shown a remarkably broad spectrum of pharmacological and physiological activities and they are used as antimicrobial, antioxidant, anticancer, anti-coagulant and anti-inflammatory agents [14]. In contrast, quinoline is also an important class of compounds with great attraction for new drug design and development owing to their wide range of biological properties [15]. The polycondensed heterocyclic systems exhibited good DNA intercalation activity (Figure 1) and considering the combination principle of drug design we are interested in synthesizing the 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds using a new method.
Multicomponent reactions are playing a key role in a number of organic transformations which has importance in medicinal chemistry [16]. At present multicomponent reactions are recognized as important tool for drug discovery because of their efficiency and productivity [17]. Moreover, when two different heterocyclic systems are coupled to synthesize new compounds, it is presumed that they will exhibit enhanced biological activities.
Previously the synthesis of chromenoquinolin-6-one compounds prepared via a three-component condensation of 4-hydroxy-coumarin, aldehydes and aniline was catalyzed by a sulfinic acidic ionic liquid under harsh dehydrating conditions (150oC) and a mixture of products were obtained, in other report under microwave conditions acetic acid was used as solvent [18]. However, the development of facile, greener and efficient method for the synthesis of chromenoquinolin-6ones is needed. Herein, we describe a new and efficient synthetic methodology for the preparation of 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds using a solid heterogeneous acid catalyst and in vitro screening of these synthesized compounds for anticancer activity.
Results and Discussion
I Chemistry
The 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds were synthesized as shown in (Scheme 1). The key aldehyde intermediates (4a-f) were prepared in two steps. Firstly, the condensation of acetophenones (1a-f) with phenyl hydrazine (2) in ethanol produced the corresponding acetophenone phenylhydrazones (3a-f). This was followed by cyclization of the acetophenone phenyl hydrazones via the Vilsmeire-Haack reaction. Finally, the condensation of subsequent aldehydes 4a-f with substituted anilines and 4-hydroxycoumarin afforded the required substituted 1,3-diphenylpyrazole-chromenoquinolin-6-one (5a-5ad) compounds in good to excellent yields.
Only a few methods are reported for the synthesis of 7,12-dihydro-6H-chromeno[4,3b] quinolin-6-one which requires high temperatures and longer reaction times. In addition, these methods produced a mixture of products, resulting in poor yields of the required product. Thus, there is still a need for the development of efficient and milder methods to overcome the shortcomings of existing protocols. In this study, we report an efficient method for the synthesis of 1,3-diphenylpyrazole-chromenoquinolin-6-one using Amberlite-IR-120H as a catalyst.
Scheme 1: Reagents and conditions: a) methanol, AcOH, rt, 5 h; b) DMF, POCl3, rt, 6 h; c) 4-hydroxy coumarin, respective aniline, Amberlite IR-120H, ethanol, reflux, 5 h.
To optimize the reaction conditions, a reaction of 4-hydroxy coumarin (1.0 mmol) with aniline (1.0 mmol) and 4a (1.0 mmol) was chosen as model reaction and the results are shown in (Table 1).
Initially, we screened different catalysts like AcOH, p-TSA, NH2SO3H, Amberlite IR120H and L-proline (Table 1, entries 1-7) to establish standard conditions. Moreover, investigation of the solvent effect on the conversion revealed that the reaction was slow in acetonitrile, chloroform, dichloromethane, water, DMF and EtOH-H2O mixture (Table 1, entries 8-13). To our delight, it was found that Amberlite IR-120H (100 mg) in ethanol refluxed for 5 h can efficiently catalyze the reaction to furnish required product (5a) with 86% yield (Table 1, entry 7). Further, the reaction was evaluated under solvent-free, catalyst-free and varying temperature conditions but without much success (Table 1, entries 14-17).
With the optimal conditions in hand, we next examined the scope of substrates on the reaction. Both electron-deficient and electron-rich substituents on aldehydes did not show much effect on the yields of the products, but the electron-deficient substituents on aniline resulted in lower yields as compared to electronrich substituents. In addition, it was observed that after completion of the reaction the catalyst was recovered, and it could be reused up to 4 cycles without loss of catalytic property. All the synthesized compounds were analyzed by 1H NMR, 13C NMR and HRMS.
Entry |
Catalyst |
Temperature (°C) |
Time (h) |
Solvent |
Yielda (%) |
1 |
p-TSA |
80 |
8 |
EtOH |
20 |
2 |
p-TSA |
100 |
8 |
H2O |
10 |
3 |
L-proline |
100 |
8 |
EtOH |
30 |
4 |
AcOH |
80 |
8 |
EtOH |
53 |
5 |
NH2SO3H |
80 |
8 |
EtOH |
65 |
6 |
NH2SO3H |
100 |
8 |
EtOH |
49 |
7 |
Amberlite IR-120 H |
80 |
5 |
EtOH |
86 |
8 |
Amberlite IR-120 H |
100 |
5 |
H2O |
32 |
9 |
Amberlite IR-120 H |
120 |
8 |
DMF |
68 |
10 |
Amberlite IR-120 H |
40 |
5 |
DCM |
30 |
11 |
Amberlite IR-120 H |
60 |
5 |
CHCl3 |
55 |
12 |
Amberlite IR-120 H |
80 |
5 |
ACN |
60 |
13 |
Amberlite IR-120 H |
85 |
8 |
EtOH-H2O |
51 |
14 |
Amberlite IR-120 H |
rt |
8 |
EtOH |
30 |
15 |
-- |
rt |
12 |
-- |
-- |
16 |
-- |
100 |
12 |
-- |
15 |
17 |
Amberlite IR-120 H |
100 |
12 |
-- |
trace |
aIsolated yields
Figure 2: Plausible mechanism for the formation of 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds.
Plausible Mechanism
The plausible mechanism for the formation of 1,3-diphenylpyrazole-chromenoquinolin-6one compounds was depicted in (Figure 2). At first the pyrazole aldehyde (4) on condensation with aniline (6) resulted in the formation of imine intermediate (A), which on the nucleophilic attack of coumarin gave the intermediate B. Then, this intermediate underwent several rearrangements (C-D) and finally undergone cyclodehydration which offered the required 1,3diphenylpyrazole-chromenoquinolin-6-one (5).
II Biology
i In Vitro Anticancer Activity
All the newly synthesized compounds (5a-ad) were evaluated for their in vitro anti proliferative activity against a panel of four human cancer cell lines, such as A549 (lung), MCF7 (breast), DU-145 (prostate) and HeLa (cervical) by using MTT assay [19]. The IC50 (µM) values (concentration required to inhibit 50% of cancer cell growth) were calculated for all the tested compounds with respect to doxorubicin as positive control and the results to this regard were summarized in (Table 2). The screening results revealed that most of the compounds exhibited good to moderate cytotoxicity against the tested cancer cell lines with IC50 values ranging from 1.22 to 62.57 µM.
All the synthesized compounds showed pronounced activity against MCF-7 cell line as compared to other cell lines. Among those 5f, 5j, 5q-5t and 5x exhibited considerable cytotoxicity against breast cancer (MCF-7) cell line (<3 µM). It was noticed that the compounds 5s and 5t were found to be most effective against MCF-7 cell line among the series exhibiting potential cytotoxic activity with IC50 values of 1.22 and 1.64 µM, respectively, and have also shown considerable cytotoxicity against the other tested cancer cell lines.
Table 2: Cytotoxicity of 1,3-diphenylpyrazole-chromenoquinolin-6-one compounds (5a‒ad) on selected human cancer cell lines.
|
Compound |
|
|
|
|
|
IC50 values (µM) a |
|
|
|
|
||||
|
|
|
A549b |
|
|
MCF-7c |
|
|
HeLad |
|
|
DU-145e |
|
|
|
|
|
|
|
|
|
|
|
|
|
|
|
||||
|
5a |
21.26 ± 1.08 |
|
9.91 ± 0.55 |
|
22.38 ± 1.55 |
|
18.32 ± 0.88 |
|
|
|||||
|
5b |
26.91 ± 1.92 |
|
8.20 ± 0.42 |
|
22.96 ± 1.32 |
|
17.51 ± 0.92 |
|
|
|||||
|
5c |
32.35 ± 1.86 |
|
10.73± 0.34 |
|
39.90 ± 2.22 |
|
21.85 ± 0.86 |
|
|
|||||
|
5d |
50.11 ± 2.78 |
|
15.27 ± 0.46 |
|
62.57 ± 3.96 |
|
30.85 ± 1.78 |
|
|
|||||
|
5e |
6.46 ± 0.99 |
|
5.46 ± 0.51 |
|
14.79 ± 2.02 |
|
6.31 ± 0.99 |
|
|
|||||
|
5f |
10.81 ± 0.63 |
|
1.98 ± 0.71 |
|
3.23 ± 0.22 |
|
4.69 ± 0.63 |
|
|
|||||
|
5g |
11.32 ± 0.89 |
|
3.68 ± 0.91 |
|
14.12 ± 1.02 |
|
6.53 ± 0.89 |
|
|
|||||
|
5h |
25.50 ± 1.54 |
|
11.70 ± 0.61 |
|
25.11 ± 1.86 |
|
18.01 ± 1.54 |
|
|
|||||
|
5i |
19.66 ± 0.98 |
|
5.02 ± 0.71 |
|
18.38 ± 1.04 |
|
10.78 ± 0.98 |
|
|
|||||
|
5j |
15.55 ± 1.52 |
|
1.82 ± 0.24 |
|
4.68 ± 0.31 |
|
6.84 ± 0.52 |
|
|
|||||
|
5k |
15.24 ± 1.26 |
|
4.68 ± 0.46 |
|
18.72 ± 1.02 |
|
9.14± 1.26 |
|
|
|||||
|
5l |
16.98 ± 0.52 |
|
3.65 ± 0.23 |
|
15.70 ± 1.03 |
|
6.61 ± 0.52 |
|
|
|||||
|
5m |
16.73 ± 1.06 |
|
3.50 ± 0.96 |
|
7.24 ± 0.98 |
|
10.47 ± 1.86 |
|
|
|||||
|
5n |
39.81 ± 2.05 |
|
12.56 ± 1.66 |
|
19.67 ±1.96 |
|
21.92 ± 1.26 |
|
|
|||||
|
5o |
24.83 ± 1.52 |
|
17.17 ± 1.03 |
|
19.61 ± 2.02 |
|
20.18 ± 0.64 |
|
|
|||||
|
5p |
14.21 ± 1.29 |
|
11.81 ± 0.94 |
|
21.72 ± 1.03 |
|
11.22 ± 1.69 |
|
|
|||||
|
5q |
13.30 ± 1.38 |
|
2.75 ± 0.54 |
|
4.26 ± 0.76 |
|
6.18 ± 0.96 |
|
|
|||||
|
5r |
15.88 ± 1.62 |
|
2.80 ± 0.84 |
|
4.36 ± 0.12 |
|
6.92 ± 0.47 |
|
|
|||||
|
5s |
10.59 ± 0.43 |
|
1.22 ± 0.94 |
|
3.51 ± 0.13 |
|
2.99 ± 0.13 |
|
|
|||||
|
5t |
5.25 ± 0.23 |
|
1.64 ± 0.76 |
|
2.71 ± 0.33 |
|
4.52 ± 0.37 |
|
|
|||||
|
5u |
19.05 ± 2.69 |
|
11.41 ± 0.52 |
|
17.37 ± 0.02 |
|
13.58 ± 2.69 |
|
|
|||||
|
5v |
17.11 ± 1.36 |
|
3.23 ± 0.98 |
|
10.56 ± 0.41 |
|
7.49 ± 0.76 |
|
|
|||||
|
5w |
21.00 ± 1.65 |
|
9.75 ± 0.33 |
|
16.18 ± 0.66 |
|
15.89 ± 1.65 |
|
|
|||||
|
5x |
15.88 ± 1.20 |
|
2.81 ± 0.87 |
|
4.36 ± 0.53 |
|
6.92 ± 0.60 |
|
|
|||||
|
5y |
11.35 ± 1.23 |
|
9.53 ± 0.91 |
|
23.77± 1.89 |
|
10.30 ± 1.23 |
|
|
|||||
|
5z |
26.30 ± 2.36 |
|
13.92 ± 0.78 |
|
24.85 ± 2.49 |
|
19.56 ± 1.36 |
|
|
|||||
|
5aa |
28.84 ± 2.13 |
|
20.14 ± 1.02 |
|
26.91 ± 1.26 |
|
22.40 ± 1.73 |
|
|
|||||
|
5ab |
17.37 ± 0.95 |
|
12.73 ± 0.51 |
|
16.87 ± 1.23 |
|
14.12 ± 0.61 |
|
|
|||||
|
5ac |
17.78 ± 1.05 |
|
13.66 ± 1.56 |
|
21.18 ± 2.01 |
|
17.00 ± 1.05 |
|
|
|||||
|
5ad |
20.41 ± 0.92 |
|
12.30 ± 1.32 |
|
20.46 ± 1.36 |
|
18.31 ± 0.76 |
|
|
|||||
|
Doxorubicin |
1.24 ± 0.59 |
|
1.32 ± 0.11 |
|
1.53 ± 0.47 |
|
2.11 ± 0.70 |
|
|
|||||
|
(Positive control) |
|
|
|
|
|
|||||||||
|
|
|
|
|
|
|
|
|
|
|
|
|
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