Ramesh Babu H.a, M. Ravinderb, Sirassu Narsimhab*
aDepartment of Physical Sciences/Chemistry, Kakatiya Institute of Technology and Science, Warangal,
T. S-506015, India
bDepartment of Chemistry, Chaitanya Degree College (Autonomous), Warangal, TS -506 001, India
*Address for Corresponding Author:
Dr. Sirassu Narsimha,
Department of Chemistry, Chaitanya Degree College (Autonomous), Warangal, TS -506 001, India
Abstract
Objectives:Microwave-assisted one-pot synthesis of fused [1,2,3]triazolyl[4',5':4,5]pyrano[3,2-h]quinolines and evaluation of their anticancer activity. Materials and Methods: The newly synthesized compoundswere characterized by spectroscopic (FTIR, 1H NMR, 13C NMR and Mass) analysis after synthesis. All compounds were screened for theirin vitro cytotoxic activity against MCF-7, A-549, and HeLa tumor cell lines using MTT analysis. Results: The results of cytotoxic activity revealedthat compound 3jhas shown potent activity against MCF-7 and HeLa with IC50 values 16.88 ± 0.5 & 11.42 ± 0.6 μM, which are comparable to the standard drug, doxorubicin. Conclusions: We have developed a new method for the synthesis of fused 1,2 3-triazole derivatives and the protocol involves a Cu-catalyzed one pot [3+2] cycloaddition followed by C-C bond coupling reaction under microwave condition. Most of the analogues showed strong activity against HeLa and moderate activity against MCF-7 and A-549. The results indicate that these compounds have the potential to develop as leads, and their additional simple structural modifications in the title compounds can produce promising anti-cancer agents for the human cervical cancer HeLa cell line.
Keywords: Microwave synthesis, fused [1,2,3]triazole, anticancer activity
Introduction
1,2,3-Triazoles are an important class of heterocycles that exhibit a wide range of structural and biological activities and are widely used in organic, medicinal, and materials science (Fournier et al., 2007;Hartmuth and Sharpless, 2003;Michael et al., 2008; Alvarez et al., 1994; Tienanet al., 2004; Angell and Burgess, 2007). As compounds containing fused 1,2,3-triazoles become increasingly common in anticancer active substances (Sheng-Jiao et al., 2010; Chung-Yu et al., 2013; Kishna et al., 2015; Narsimha et al., 2016a, 2018b) (Figure 1). Based on their structural and biological importance of fused 1,2,3-triazoles, new strategies to synthesize this class of molecules are highly desirable. There are numerous methods available for the synthesis of 1, 4, 5-trisubstituted 1,2,3-triazoles. A classical method involves C-C bond formation of 1, 4-disubstituted 1,2,3-triazole with aryl halide using palladium or copper catalysts in high temperature and longtime refluxing condition (Ackermann et al., 2008, 2009, 2010; Panteleev et al., 2010; Rajkumar et al., 2012).
Figure 1. Representative examples of anticancer active fused 1,2,3-triazole moieties
On the other hand, the quinoline nucleus is an important scaffold found in a variety of biologically active compounds, including natural products and synthetic drugs (Musiol et al., 2007, 2010; Michael, 2007; Kaur et al., 2010). Quinoline and its derivatives have been described as antibacterial (Desai et al., 2012), anticancer (Atwell et al., 1989) and antimalarial (Insuasty et al., 2013). The association of quinoline with the 1,2,3-triazole ring has recently led to the synthesis of new antimicrobial and antitubercular drugs (Sumangala et al., 2010; Thomas et al., 2010, 2011; Harjinder et al., 2014)(Figure 2).
Figure 2. Representative examples of bioactive quinolone containing 1,2,3-triazole moieties
Based on the above successful synthesis of fused 1,2,3-triazole derivatives via intramolecular C–H arylation of in situ generated 1,4-disubstituted 1,2,3-triazoles and previous therapeutic properties of triazoles and quinolines, as well as continuation of our research on 1,2,3-triazoles (Narsimha et al., 2014, 2016b, 2018a; Ranjithet al., 2017; Swamy et al., 2016, 2017, 2017a; Vasudeva Reedy et al., 2016a, 2016b), we report an efficient method for the synthesis of fused hetrocyclic derivatives having triazole and quinoline moieties in a single scaffold by using copper and palladium catalyzed intramolecular C–H arylation of in situ generated 1,4-disubstituted 1,2,3-triazoles from 7-bromo-8-(prop-2-ynyloxy) quinoline with different aryl azides in one pot microwave irradiation method and evaluated for their anticancer activity (Scheme 1).
Scheme 1. Synthesis of novel fused [1,2,3]triazolyl[4',5':4,5]pyrano[3,2-h]quinolines.
Materials and methods
All the reagents and solvents were purchased from Aldrich/Merck and used without further purifications. Thin-layer chromatography (TLC) was performed using Merck silica gel 60 F254 precoated plates (0.25 mm) and Silica gel (100-200 mesh) was used for column chromatography. The progress of the reactions as well as purity of the compounds was monitored by thin layer chromatography with using ethylacetate /hexane (7/3) as eluent. Melting points were determined using a Cintex apparatus and are uncorrected. IR spectra (KBr pellet) were recorded on a Perkin-Elmer BX seriesFT-IR spectrometer. 400 MHz and 100 MHz NMR spectrometers were used to get 1H-NMR and 13C NMR spectra respectively. Coupling constant (J) values are presented in Hertz, spin multiples are given as s (singlet), d (doublet), t (triplet), and m (multiplet). Mass spectra were recorded by using ESI-MS method.
Synthesis and Spectral data
Synthesis of 7-bromo-8-(prop-2-ynyloxy) quinoline (2)
To a mixture of 7-bromoquinolin-8-ol (0.02 mol) andK2CO3 (0.05 mol) in DMF (50 ml) was added propargylbromide (0.025 mol) and stirred at room temperature for 6h.After completion of the reaction by TLC analysis, the reaction mixture was poured carefully into ice-cold water (25 mL)and the product was extracted with ethyl acetate (2 x 50 mL). The combined organic layer was dried over anhydrous Na2SO4. After filtration, the solvent was evaporated under vacuum and the crude product obtained was purified by column chromatography to afford the pure desired product2(86%).Yellow solid.1H NMR (CDCl3, 400 MHz): δ 8.72 (d, J = 8.6 Hz, 1H), 8.32 (d, J=8.0 Hz, 1H), 7.84 (d, J=8.4 Hz, 1H), 7.69-7.74 (m, 1H), 7.42 (d, J =8.4Hz, 1H), 4.89 (d, J =2.2Hz, O-CH2, 2H), 2.77 (t, J= 2.5 Hz, 1H, CH); ESI-MS: 262 [M+2H].
Synthesis of 3-aryl-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano [3,2-h]quinoline(3a-k)
7-bromo-8-(prop-2-ynyloxy) quinoline (1mmol), aryl azide (1.2mmol) and tBuOK (2mmol) were suspended inDMF (10 mL) in a 25-mL glass vialequipped with a small magnetic stirring bar. To this was added copperiodide (10mol %), and the vialwas tightly sealed with an aluminum/Teflon crimp top. The mixture was heated at 150°C for 30 min. Progress of the reaction was monitored by TLC. Then, the vial was cooled to room temperatureand the reaction mixture was poured carefully into ice-cold water (10 mL) and the product was extracted with ethyl acetate (2 x 15 mL). The combined organic layer was dried over anhydrous Na2SO4. After filtration, the solvent was evaporated under vacuum and the crude product obtained was purified by column chromatography (hexane/ethyl acetate gradient) to afford the pure desired product.
3-phenyl-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline (3a):pale red solid; IR(KBr, cm-1)νmax3074 (Ar-H),1638 (C=N),1567(C=C); 1H NMR (400 MHz, CDCl3): δH8.89 (d,J=8.6 Hz,1H), 8.35 (d, J=8.0 Hz, 1H),7.72- 7.83 (m,3H), 7.60-7.67 (m, 2H), 7.47-7.53 (m, 2H), 7.27-7.36(m, 1H), 5.62 (s, 2H, O-CH2); 13C-NMR(100 MHz, CDCl3): δC154.3, 153.2, 144.4, 139.3, 133.4, 131.1, 130.3, 128.9,124.6, 122.5,121.6,120.4,118.7,61.7; ESI-MS: 301[M+H]+;Anal. Calcd for C18H12N4O: C, 71.99; H, 4.03; N, 18.66. Found: C, 71.86; H, 4.11; N, 18.79.
3-(4-methoxyphenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3b): White solid; IR(KBr, cm-1)νmax3074 (Ar-H), 1638 (C=N),1567(C=C);1H NMR (400 MHz, CDCl3): δH 8.75 (d, J=8.2 Hz, 1H), 8.32 (d, J=8.0 Hz, 1H),7.69-7.78(m, 1H), 7.68 (d, J= 8.6 HZ, 2H), 7.46-7.53(m, 1H), 7.27-7.31 (m, 1H), 7.02 (d, J= 8.6 HZ, 2H), 5.65 (s, 2H, O-CH2), 3.86 (s, -OCH3, 3H); 13C-NMR(100 MHz, CDCl3): δC 158.1, 153.7, 144.1, 138.9, 133.5, 132.2, 131.0, 127.8, 124.1, 121.9, 121.2, 119.8, 118.2, 61.5, 57.6; ESI-MS: 331 [M+H]+;Anal. Calcd for C19H14N4O2: C, 69.08; H, 4.27; N, 16.96. Found: C, 68.09; H, 4.19; N, 17.04.
3-(3-methoxyphenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3c): White solid; IR(KBr, cm-1)νmax3074 (Ar-H), 1638 (C=N),1567(C=C); 1H NMR (400 MHz, CDCl3): δH 8.73 (d, J=8.2 Hz, 1H), 8.31 (d, J=7.8 Hz, 1H),7.76-7.84 (m, 2H), 7.56-7.62 (m, 2H), 7.34-7.42 (m, 2H), 7.20 (s, 1H), 5.62 (s, 2H, O-CH2), 3.88 (s, -OCH3, 3H); 13C-NMR(100 MHz, CDCl3): δC 157.1, 153.8, 144.6, 138.2, 134.1, 133.0, 131.4, 128.1, 125.3, 124.6, 123.4, 122.7, 121.3, 120.1, 119.4, 117.6, 61.3, 57.3; ESI-MS: 331 [M+H]+;Anal. Calcd for C19H14N4O2: C, 69.08; H, 4.27; N, 16.96. Found: C, 69.00; H, 4.21; N, 17.01.
3-(4-chlorophenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3d):
Pale yellow solid; IR(KBr, cm-1)νmax3069 (Ar-H), 1641 (C=N),1558(C=C),1329 (C-Cl); 1H NMR (400 MHz, CDCl3): δH 8.86 (d, J=8.6 Hz, 1H), 8.30 (d, J=8.2 Hz, 1H), 7.75-7.88(m, 3H), 7.56-7.64(m, 2H), 7.33-7.43 (m, 2H), 5.65 (s, 2H, O-CH2); 13C-NMR(100 MHz, CDCl3): δC 153.2, 144.4, 137.8, 136.2, 132.4, 131.6, 127.5, 126.0, 123.3, 122.3, 120.9, 120.1, 119.8, 118.6, 116.4, 62.0; ESI-MS: 335[M+H]+;Anal. Calcd for C18H11ClN4O: C, 64.58; H, 3.31; N, 16.74. Found: C, 64.52; H, 3.25; N, 16.87.
3-(3-chlorophenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3e):
Pale yellow solid; IR(KBr, cm-1)νmax3084 (Ar-H), 1668 (C=N),1549(C=C),1341 (C-Cl); 1H NMR (400 MHz, CDCl3): δH 8.82 (d, J=8.0 Hz, 1H), 8.33 (d, J=7.6 Hz, 1H), 7.88-7.94(m, 2H), 7.52-7.63(m, 2H), 7.30-7.42 (m, 3H), 5.62 (s, 2H, O-CH2); 13C-NMR(100 MHz, CDCl3): δC 153.6, 144.6, 138.1, 137.0, 133.6, 132.8, 127.6, 126.4, 124.8, 124.2, 123.6, 122.9, 121.4, 120.4, 119.8, 117.3, 116.9, 61.8; ESI-MS: 335 [M+H]+; Anal. Calcd for C18H11ClN4O: C, 64.58; H, 3.31; N, 16.74. Found: C, 64.49; H, 3.22; N, 16.85.
3-(4-nitrophenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3f):
Yellow solid; IR (KBr, cm-1)νmax, 3064 (Ar-H), 1653 (C=N),1555 (C=C),1351 (NO2); 1H NMR (400 MHz, CDCl3): δH 8.89 (d, J=8.0 Hz, 1H), 8.32 (d, J=7.2 Hz, 1H), 8.22 (d, J=2.4 Hz, 1H),8.10 (d, J =8.2Hz, 1H), 7.71-7.83(m, 2H), 7.54-7.69(m, 2H), 7.34-7.46 (m, 1H), 5.68 (s, 2H, O-CH2); 13C-NMR(100 MHz, CDCl3): δC 153.7, 148.1, 144.7, 138.9, 134.6, 132.7, 131.8, 129.6, 127.8, 125.4, 124.2, 123.8, 121.3, 120.4, 116.7, 62.2; ESI-MS: 346[M+H]+; Anal. Calcd for C18H11N5O3: C, 62.61; H, 3.21; N, 20.28. Found: C, 62.54; H, 3.14; N, 20.37.
3-(3-nitrophenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3g)
White solid; IR (KBr, cm-1)νmax3074 (Ar-H), 1639 (C=N),1565(C=C), 1340 (C-NO2); 1H NMR (400 MHz, CDCl3): δH 8.83 (d, J=8.6 Hz, 1H), 8.35 (d, J=8.0 Hz, 1H), 8.21 (s, 1H),8.07 (m, 1H), 7.76-7.88 (m, 1H), 7.58-7.60 (m, 2H), 7.29-7.56 (m, 2H), 5.69 (s, 2H, O-CH2); 13C-NMR(100 MHz, CDCl3): δC 153.4, 148.3, 144.7, 138.3, 135.0, 132.4, 131.3, 129.4, 127.6, 125.8, 124.7, 124.0, 123.8, 122.2, 121.6, 120.8, 119.2, 62.5; ESI-MS: 346 [M+H]+; Anal. Calcd for C18H11N5O3: C, 62.61; H, 3.21; N, 20.28. Found: C, 62.53; H, 3.11; N, 20.35.
3-(p-tolyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline (3h)
Pale yellow solid; IR(KBr, cm-1)νmax3062 (Ar-H), 1641 (C=N),1557(C=C); 1H NMR (400 MHz, CDCl3): δH 8.80 (d, J=8.0 Hz, 1H), 8.27 (d, J=7.2 Hz, 1H), 7.72-7.88 (m, 2H), 7.52-7.62 (m, 2H),7.20-7.50 (m, 3H), 5.62 (s, 2H, O-CH2), 2.39 (s, 3H, -CH3); 13C-NMR(100 MHz, CDCl3): δC 153.1, 143.5, 138.4, 133.4, 131.3, 127.8, 124.3, 123.4, 122.7, 122.1, 120.8, 120.1, 119.6, 118.7, 61.5, 21.3; ESI-MS: 315[M+H]+; Anal. Calcd for C19H14N4O: C, 72.60; H, 4.49; N, 17.82. Found: C, 72.66; H, 4.42; N, 17.77.
3-(m-tolyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline (3i)
Pale yellow solid; IR (KBr, cm-1)νmax3080 (Ar-H), 1639 (C=N),1577(C=C); 1H NMR (400 MHz, CDCl3): δH 8.82 (d, J=8.0 Hz, 1H), 8.26(d, J=7.8 Hz, 1H), 7.65-7.76 (m, 2H), 7.54-7.62 (m, 2H),7.42-7.48 (m, 1H), 7.30-7.37 (m, 2H), 5.65 (s, 2H, O-CH2), 2.43 (s, 3H, -CH3); 13C-NMR(100 MHz, CDCl3): δC 153.5,143.7, 138.7, 133.6, 132.1, 128.1, 124.7, 123.3, 122.8, 120.6, 120.0, 119.4, 118.6, 61.7, 19.8; ESI-MS: 315 [M+H]+; Anal. Calcd for C19H14N4O: C, 72.60; H, 4.49; N, 17.82. Found: C, 72.69; H, 4.45; N, 17.73.
3-(3,5-dimethylphenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3j) Pale yellow solid; IR (KBr, cm-1)νmax3066 (Ar-H), 1644 (C=N),1564(C=C); 1H NMR (400 MHz, CDCl3): δH8.83 (d, J=8.6 Hz, 1H), 8.26 (d, J=8.0 Hz, 1H),7.78-7.86 (m, 2H), 7.49-7.64(m, 2H), 7.44-7.49(m, 2H), 7.35(s, 2H), 7.14(s, 1H), 5.62 (s, 2H, O-CH2), 2.41 (s, 6H, -CH3); 13C-NMR(100 MHz, CDCl3): δC 153.1, 143.6, 138.4, 131.4, 127.1, 126.7, 125.3, 123.6, 122.4, 121.3, 120.6, 119.8, 118.2, 61.5, 21.1; ESI-MS: 329[M+H]+;Anal. Calcd for C20H16N4O: C, 73.15; H, 4.91; N, 17.06. Found: C, 73.23; H, 4.97; N, 17.01.
3-(3,5-dichlorophenyl)-3,11-dihydro-[1,2,3]triazolo[4',5':4,5]pyrano[3,2-h]quinoline(3k): Yellow solid; IR (KBr, cm-1)νmax3087 (Ar-H), 1648 (C=N),1557(C=C), 1327 (C-Cl); 1H NMR (400 MHz, CDCl3): δH8.88 (d, J=8.0 Hz, 1H), 8.23 (d, J=7..2 Hz, 1H), 7.89-8.02 (m, 1H), 7.77(s, 2H), 7.53-7.68(m, 2H), 7.37-7.50 (m, 1H), 5.65 (s, 2H, O-CH2); 13C-NMR(100 MHz, CDCl3): δC 153.8, 144.2 138.9, 134.1, 132.7, 131.2, 126.8, 123.4, 122.3, 121.4, 118.7, 62.2; ESI-MS: 370[M+H]+;Anal. Calcd for C18H10Cl2N4O: C, 58.56; H, 2.73; N, 15.18. Found: C, 58.48; H, 2.67; N, 15.11.
Cytotoxic activity
All of the synthesized compounds were evaluated for their invitro cytotoxic activity against three different cancer cell linessuch as MCF-7 (breast), A-549 (alveolar) and HeLa (cervical). Allthe cancer cell lines used in this research work was obtainedfrom National Centre for Cell Sciences (NCCS), Pune, India. Cellviability in the presence of the test samples was measured usingthe MTT-microculturedtetrazolium assay (Shekan et al., 1990; Monks et al., 1991). This assay isa quantitative colorimetric method for the determination of cellcytotoxicity. The assessed parameter is the metabolic activity ofviable cells. Metabolically active cells reduce pale yellow tetrazolium salt (MTT) to a dark blue water-insoluble formazan, which can be directly quantified after solubilization with DMSO. The absorbance of the formazan directly correlates with the number of viable cells. Human cells were plated into a 96-well plate at a density of 1X104 cells per well. Cells were grownovernight in the full medium and then switched to the lowserum media. DMSO was used as a control. After 48 h of treatmentwith different concentrations of test compounds, the cellswere incubated with MTT (2.5 mg mL-1) in the CO2 chamber for2 h. The medium was then removed and 100 L of DMSO wasadded into each well to dissolve the formazan crystals. Afterthoroughly mixing, the plates were read at 570 nm for opticaldensity, which is directly correlated with cell quantity. Theresults were represented as a percentage of cytotoxicity/viability.All of the experiments were carried out in triplicates. The IC50values were calculated from the percentage of cytotoxicity andcompared with the reference drug.
Result and discussion
The synthetic procedure adopted to obtain the target compounds is shown in Scheme 1.The intermediate 7-bromo-8-(prop-2-ynyloxy) quinoline (2) was prepared with high yields (86%) using 7-bromoquinolin-8-ol (1) and propargyl bromide in the presence of anhydrous K2CO3 in DMF.With the aim of preparing fused 1, 2, 3-triazoles, our initial investigation began with the reaction of 2 and phenyl azide with 10mol % of CuI in THF at 80°C for 20 h. The desired product was formed in 17% yield (Table 1, entry 1). Similarly, the reaction was carried out using different solventsDMSO, DMF, and H2O (Table 1, entries 2–4), the product was formed with yields not exceeding 27%, with DMF being the most favorable solvent (26% yield). Then, the reaction was carried out using 10 mol % of CuI at 120°C for 24 h, the desired product was obtained with 36% yield (Table 1, entry 5). When t-BuOK was replaced with t-BuOLi, K2PO3 and Cs2CO3, we could not get the desired products in good yield compared to t-BuOK (Table 1, entries 6–8). When the reaction was carried out at higher temperatures (above 140°C) using t-BuOK and DMF the product was obtained in 58% yield (Table 1, entry 9). Encouraged by these results the reaction was carried out under microwave irradiation, which resulted in the generation of the desired product in excellent yields (Table 1, entry 10, 11). After the complete optimization studies, it was clear that the use of catalyst load of CuI (10 mol %) with 2 equivalents of t-BuOK in DMF under the microwave irradiation (150 W) was the optimal reaction conditions to obtain the desired products in good yields. Several substituted phenyl azides containing electron-donating groups (methyl, and methoxy groups) and electron-withdrawing groups (chloro and nitro groups), were all compatible with this transformation under the optimal reaction conditions (Figure 3).
Table 1.Optimization of CuI-catalyzed intramolecular C-C couplinga
|
Entry |
Catalyst (10 mol%) |
Solvent |
Base |
Temp (oC) |
Time(h) |
Yieldb(%) |
|
1 |
CuI |
THF |
t-BuOK |
80 |
20 |
17 |
|
2 |
CuI |
DMSO |
t-BuOK |
80 |
20 |
20 |
|
3 |
CuI |
DMF |
t-BuOK |
80 |
20 |
26 |
|
4 |
CuI |
THF-H2O |
t-BuOK |
80 |
20 |
16 |
|
5 |
CuI |
DMF |
t-BuOK |
120 |
24 |
36 |
|
6 |
CuI |
DMF |
t-BuOLi |
120 |
24 |
23 |
|
7 |
CuI |
DMF |
K2PO3 |
120 |
24 |
N.R |
|
8 |
CuI |
DMF |
Cs2CO3 |
120 |
24 |
N.R |
|
9 |
CuI |
DMF |
t-BuOK |
140 |
24 |
58 |
|
10 |
CuI |
DMF |
t-BuOK |
150W(MW) |
15 min |
78 |
|
11 |
CuI |
DMF |
t-BuOK |
200W(MW) |
20 min |
74 |
aReactions were performed with 2 (1.0 mmol), azide (1.0 mmol) and tBuOK (2.0 mmol); bIsolated yield; N.R. = No Reaction.
The structures of the newly synthesized compounds 3a-3k were confirmed by spectral data (1H NMR, 13C NMR, IR, and ESI-MS) and elemental (CHN) analysis. All the spectral and analytical data of the synthesized compounds were in full agreement with the proposed structures and also discussed for a representative compound 3b. From the IR spectrum, the appearance of a broad absorption band at sharp bands at 3074, 1638 and 1567 cm-1 are ascribed to Ar-H, C=N and -C=C stretching frequencies, respectively. From the 1H NMR spectrum, the signals appearance at d 3.86 (s, 3H, O-CH3), d 5.65 (s, 2H, O-CH2 ), d 7.02 to 8.75 (m, 9H, Ar-H), and from the 13C NMR, the presence of signals at 158.1 ppm (C-OCH3), 153.7 ppm (C-O-CH2), 61.5 ppm (-OCH2), 57.6 ppm (-OCH3) and the ESI- mass spectra of 3b showed [M+H] ion peak at m/z 331, which confirmed the structure of compound 3b. The elemental analyses (CHN) data (C, 68.09; H, 4.19; N, 17.04) confirmed the purity of compound 3b.
Figure 3. Cu/Pd catalyzed one pot microwave synthesis of fused [1,2,3]triazolyl[4',5':4,5] pyrano[3,2-h]quinolines. The isolated yields are given as percentages.
Anticancer activity
In vitro anticancer activity results revealed that all the compounds were activeagainst all the three tested cell lines such as breast carcinoma (MCF-7), alveolar carcinoma (A-549) and cervical carcinoma (HeLa). Cellviability in the presence of the test samples was measured using the MTT-microcultured tetrazolium assay. Doxorubicin was used as a positive control and the results are summarized in table 2.
Table 2.Cytotoxic activityof fused 1,2,3-triazoles (3a-3k) on MCF-7, A-549 and HeLa [in vitroa (IC50µM]b
|
Product |
MCF-7 |
A-549 |
HeLa |
|
3a |
41.86 ± 0.7 |
62.88± 1.2 |
46.39±1.0 |
|
3b |
89.21± 0.9 |
77.52± 1.3 |
24.92± 0.8 |
|
3c |
31.44± 0.5 |
44.52± 1.1 |
15.67± 0.6 |
|
3d |
47.67± 0.8 |
59.62± 1.1 |
49.14± 1.0 |
|
3e |
55.27± 1.4 |
75.89± 1.6 |
54.57± 0.9 |
|
3f |
79.88± 1.3 |
96.87± 1.5 |
68.21± 1.1 |
|
3g |
81.37± 1.6 |
69.54± 1.0 |
51.79± 0.8 |
|
3h |
39.18± 1.0 |
42.97± 1.3 |
21.27± 0.7 |
|
3i |
40.66± 0.8 |
63.47± 1.1 |
31.66± 0.9 |
|
3j |
16.88± 0.5 |
32.47± 1.0 |
11.42± 0.6 |
|
3k |
49.55± 1.0 |
67.88± 1.4 |
43.68± 1.1 |
|
Doxorubicin |
3.01 ± 0.2 |
1.08 ± 0.08 |
1.35 ± 0.04 |
aValues are expressed as mean ± SEM. bCytotoxicity,
Among them, the compound derived from the 3,5-dimethylphenygroup on fused triazole ring i.e. 3j has shown potent activity against MCF-7 & HeLa with IC50 values 16.88 ± 0.5 & 11.42 ± 0.6μM and moderate activity against A-549 with IC50 value 32.47 ± 1.0μM respectively. Compound 3c, having a 3-methoxyphenyl group on triazole ring exhibited potent activity against HeLa with IC50 value 15.67 ± 0.6μM and moderate activity against the MCF-7 cell line with an IC50 value of 31.44 ± 0.5μM. These results are comparable to those of the standard drug doxorubicin. Similarly, the introduction of 4-methoxyphenyl group and 4-methylphenyl group on fused triazole ring i.e. 3b and 3h have shown good activity against HeLa cell line with IC50 values 24.92 ± 0.8 & 21.27 ± 0.7μM respectively. Remaining compounds have shown moderate activity with IC50 values ranging from 39.18± 1.0 -96.87± 1.5μM against the three cell lines. It is necessary to point out that all of the potent analogues contain methyl, dimethyl and methoxy substituents on the triazole ring (3b, 3c, 3h, 3i & 3j) and this preference was uniform and irrespective to the substitution pattern on the aromatic ring. The electron withdrawing substituents such as chloro and nitro groups on the triazole ring exhibited moderate to poor activity against all three tested cell lines.
Conclusion
In summary, we have developed a new method for the synthesis of [1,2,3] triazolyl [4 ', 5': 4,5] pyrano [3,2-h] quinoline derivatives. The protocol involves a Cu-catalyzed one pot [3+2] cyclo addition followed by C-C bond coupling reaction under microwave condition without isolating the intermediate 1,4-disubstituted 1,2,3-triazole. These new compounds were tested for their in vitro cytotoxic activity against the cancer cell lines MCF-7, A-549 and HeLa. Among them, compounds 3c and 3j showed strong activity against HeLa. Interestingly, most of the analogues showed strong activity against HeLa and moderate activity against MCF-7 and A-549. In general, the results indicate that these compounds have the potential to develop as leads, and their additional simple structural modifications in the title compounds can produce promising anti-cancer agents for the human cervical cancer HeLa cell line.
Acknowledgments
The authors are thankful to the Director of Indian Institute of Chemical Technology in Hyderabad for recording 1H, 13C NMR and mass spectra. The authors are thankful to the Head, Department of Bio-Technology, Kakatiya University, and Warangal for providing data of biological activity.
Conflicts of interest
The authors declare no conflict of interest.
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