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Article

Synthesis of Tetrahydrocarbazole-Tethered Triazoles as Compounds Targeting Telomerase in Human Breast Cancer Cells

by
Pradeep M. Uppar
1,
Akshay Ravish
1,
Zhang Xi
2,
Keshav Kumar Harish
3,
Arun M. Kumar
1,
Lisha K. Poonacha
4,
Toreshettahally R. Swaroop
1,
Chaithanya Somu
5,
Santosh L. Gaonkar
6,
Mahendra Madegowda
3,
Peter E. Lobie
2,7,8,
Vijay Pandey
7,8,* and
Basappa Basappa
1,*
1
Laboratory of Chemical Biology, Department of Studies in Organic Chemistry, University of Mysore, Mysore 570006, Karnataka, India
2
Shenzhen Bay Laboratory, Shenzhen 518055, China
3
Department of Studies in Physics, University of Mysore, Manasagangotri, Mysore 570006, Karnataka, India
4
Department of Studies in Chemistry, University of Mysore, Manasagangotri, Mysore 570006, Karnataka, India
5
Department of Studies in Chemistry, Karnataka State Open University, Mukthagangotri, Mysore 570006, Karnataka, India
6
Department of Chemistry, Manipal Institute of Technology, Manipal Academy of Higher Education, Udupi 576104, Karnataka, India
7
Tsinghua Berkeley Shenzhen Institute, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
8
Institute of Biopharmaceutical and Health Engineering, Tsinghua Shenzhen International Graduate School, Tsinghua University, Shenzhen 518055, China
*
Authors to whom correspondence should be addressed.
Catalysts 2024, 14(10), 726; https://doi.org/10.3390/catal14100726
Submission received: 27 November 2023 / Revised: 17 March 2024 / Accepted: 18 March 2024 / Published: 16 October 2024
(This article belongs to the Section Catalysis in Organic and Polymer Chemistry)
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Versions Notes

Abstract

:
Telomere shortening and the induction of senescence and/or cell death may result from inhibition of telomerase activity in cancer cells. Herein, the properties of carbazole–triazole compounds targeting telomerase in human breast cancer cells are explored. All derivatives were evaluated for loss of viability in MCF-7 breast cancer cells, with compound 5g identified as the most potent within the examined series. Green synthesis was employed using water, a reusable nano-Fe2O3-catalyzed reaction, and an electrochemical method for the synthesis of tetrahydrocarbazole and triazoles. The crystal data of compound 4 is also reported. Furthermore, in silico analysis predicted that compound 5g may target human telomerase. Molecular docking analysis of compound 5g towards hTERT predicted a binding affinity of −6.74 kcal/mol. In flow cytometry assays, compound 5g promoted apoptosis and cell cycle arrest in the G2-M phase. Finally, compound 5g inhibited the enzymatic activity of telomerase in human breast cancer cells. In conclusion, a green synthesized series of carbazole–triazoles that target telomerase in cancer cells is reported.

Graphical Abstract

1. Introduction

Telomeres are oligonucleotide sequences (TTAGGG) present at the ends of chromosomes and exert critical functions in limiting cell replication [1]. With each cell division, the telomere length decreases, and the telomeres signal to activate telomerase. Telomerase is an enzyme complex that lengthens telomeres and is composed of telomerase reverse transcriptase (TERT), telomerase RNA (TERC), and dyskerin [2,3]. TERT extends telomeric repeats at the ends of chromosomes using TERC as its template. This process aids in maintaining genetic stability and cellular health in some cell types, such as stem cells [4]. Cells reach a state known as cellular senescence or apoptosis when the telomeres are sufficiently shortened, preventing further cell division and functioning as a natural barrier to unchecked cell proliferation. Numerous studies have reported the inhibition of telomerase by small molecules in various cancer cells [5,6,7].
In many cancer cells, the telomerase enzyme is reactivated or increased in expression [8,9]. This allows cancer cells to maintain or even lengthen their telomeres, preventing the attainment of the critical shortening point. As a result, cancer cells continue to divide indefinitely, leading to cancer cell expansion. Inhibiting telomerase activity in cancer cells could therefore lead to potential telomere shortening and the induction of cell death. Several experimental drugs and therapeutic approaches aimed at targeting telomerase have been examined in preclinical models and clinical trials [10,11]. Various natural products have also exhibited telomerase inhibition [12]. Small molecules have also been reported as inhibitors of telomerase transcription or function, such as azidothymidine (AZT), a non-specific reverse transcriptase inhibitor [13,14], retinoids [15], tamoxifen [16], EGCG (epigallocatechin gallate) [17], and other drug-like molecules that interfere with telomere structure (G-quadruplex stabilizers) [18,19].
Carbazole derivatives have previously been reported as anticancer agents; for example, Elliptinium, which was reported as a topoisomerase II inhibitor and an intercalating agent [20]. Preclinical and phase II clinical evaluations revealed that Elliptinium (Figure 1) exhibits efficacy against breast and renal cell carcinomas and both small- and non-small-cell lung cancer [21]. Elliptinium analog Celiptium (N-methyl-9-hydroxy ellipticinium acetate) has been developed and used for the treatment of metastatic breast cancer [22]. Similarly, many of the triazoles are reported as anticancer agents that target various cellular pathways in cancer development and progression [23,24,25,26,27]. Cefatrizine and Carboxyamido-triazole have been reported as potential anticancer drugs [28,29] and substituted triazole heterocycles could serve as telomerase inhibitors.
Compound A was reported as a potent dual inhibitor of CA (carbonic anhydrase) and telomerase activity in PC-3 and HT-29 cells [30], and benzimidazole-1,2,3-triazole hybrid (B) exhibited selective interaction with G-quadruplex DNA over duplex DNA and inhibited the cell cycle at the G2/M phase by inducing apoptosis in PC3 and CHO-K1 cells [31]. Bistriazolyl-dibenzo[a,c]phenazines (C) exhibit the reported activity in MCF-7 and K562 cells. The in vitro telomeric repeat amplification protocol (Q-TRAP) assay utilizing C reveals that these ligands reduce telomerase activity in cancer cells [32]. A benzimidazole–carbazole conjugate of compound D was also reported to promote apoptosis in various cancer cell types. Further, compound D demonstrated efficient telomerase inhibition activity in a TRAP assay [33]. Moreover, substituted oxadiazoles (E) also exhibit significant telomerase inhibitory activity in cancer cells [34].
Electrochemical synthesis is a versatile method to synthesize chemical entities. A wide range of organic and inorganic compounds with numerous applications can be synthesized using electrochemical methods and provide an efficient and safer reaction condition [35,36]. Various reports on the synthesis of carbazole derivatives using various protocols such as conventional methods [37,38], catalysts [39,40], and electrochemical methods [41,42,43] are published. The electrochemical technique has emerged as an influential approach due to several advantages that it provides over conventional chemical synthetic routes in synthesizing various triazole derivatives [44,45,46]. We have previously reported the electrochemical synthesis of triazoles tethered with thiouracil, and pyrimidine- and oxadiazole-tethered triazole derivatives [24,47].
Herein, the green synthesis of tetrahydrocarbazole–triazole derivatives as anticancer agents is reported. All derivatives were tested for loss of viability in MCF-7 breast cancer cells, and compound 5g was observed to be the most potent among the series examined. The crystal data of the intermediate 4 is reported, and in silico docking analysis of compound 5g towards TERT showed a binding energy of −6.74 kcal/mol. Additionally, apoptosis, cell cycle arrest, and enzymatic inhibition of telomerase were evaluated to confirm the mode of action of the lead compound.

2. Results and Discussion

2.1. Synthesis of Tetrahydrocarbazole

Carbazole is a privileged structure in many fields, and its synthesis has gained importance due to applications in medicinal chemistry. The first tetrahydrocarbazole synthesis was achieved by refluxing cyclohexanone and phenylhydrazine hydrochloride in glacial acetic acid [37]. Several reports exist for the synthesis of tetrahydrocarbazole via Fischer indolization, Ullman cross-coupling reductive cyclization, dehydrogenative reactions, Friedel–Crafts alkylation, and the use of various catalysts [38]. In the present work, a catalytic and electrochemical method for the synthesis of tetrahydrocarbazole has been developed. Ionic liquids (ILs), such as 1-butyl-3-methylimidazolium tetrafluoroborate ([BMIM]BF4) and 1-ethyl-3-methyllimidazolium tetrafluoroborate (EMIMBF4), were utilized as solvents for the synthesis of tetrahydrocarbazole. The reaction was feasible under reflux conditions (45–50 °C), whereas at room temperature, product formation was slower with a lower yield. Cyclohexanone (1) and phenylhydrazine hydrochloride (2) were refluxed in ILs for 12 h, resulting in the formation of tetrahydrocarbazole (3) with a yield of 70–75%. Additionally, an electrochemical reaction for the synthesis of tetrahydrocarbazole with and without tetrabutylammonium iodide (TBAI) was conducted using various solvents such as MeOH, EtOH, i-PrOH, MeOH:H2O (1:1), and ACN:H2O:EtOH (1:0.5:1). An improved yield of the product (yield 55–65%) was observed for ethanol solvent in the presence of a catalytic amount of TBAI under 0.5 volts for 3–4 h.
Commercially available nano-iron(III) oxide (<50 nm) was employed as a catalyst in various solvents and reaction conditions (Scheme 1). Various solvents such as DMSO, DMF, ACN, acetone, THF, EtOH, MeOH, H2O, and EtOH:H2O were employed, and the results are summarized in Table 1. The reactions were carried out at room temperature and in reflux conditions. The formation of the product was well observed with a good yield at room temperature. The reaction was more feasible using water as solvent; 0.5 eq of the catalyst, under ambient reaction conditions for 6 h, resulted in compound 3 with an improved yield (85%). Also, when 0.1 eq and 0.3 eq of catalyst were used, the reaction proceeded at slower rates and with a lesser yield.
The conventional method for the synthesis of tetrahydrocarbazole uses glacial acetic acid, which is flammable and corrosive to the eyes, skin, and respiratory tract. Hence, the aim was to develop more ecofriendly methods such as the electrochemical method and the use of a catalyst and water as solvents under mild conditions. Among the experimented protocols, the use of nano-Fe2O3 and water solvent gave a better yield in a lower reaction time.
From the above observations, tetrahydrocarbazole (3) was synthesized using nano-Fe2O3 (0.5 eq) and water as solvent at room temperature (Scheme 2). After the completion of the reaction, the reaction mixture was filtered off and the catalyst could be isolated. When the separated catalyst was employed again for synthesis, a lower product yield was seen. The filtrate was extracted with ethyl acetate, distilled under reduced pressure, and purified through column chromatography using ethyl acetate and hexane as eluents. Additionally, the electrochemical method also gave the desired product when 0.5 volts is applied to 1 and 2 in the presence of TBAI and EtOH for 8 h, using a platinum electrode and copper foil. After the completion of the reaction, the reaction mixture was extracted to an ethyl acetate layer, concentrated under reduced pressure, and purified through column chromatography and confirmed by mass spectra.

2.2. Synthesis of Tetrahydrocarbazole–Triazole Derivatives 5(a–m)

NaH, after washing with dry hexane, was suspended in dry DMF, followed by the addition of compound 3, and propargyl bromide was added drop-wise. The reaction mixture was stirred for 2 h at 0–5 °C. After the completion of the reaction, ice-cooled water was added to the reaction mixture, extracted with EtOAc; the combined organic layer was concentrated under a vacuum, and the crude reaction mass was purified by column chromatography technique to obtain compound 4 (Scheme 3).
Method A: Using CuI as a catalyst and DMSO as a solvent in basic conditions, the substituted azide–alkyne (4) cyclizes to form triazole. After the completion of the reaction, the product was purified by column chromatography.
Method B: In the presence of a platinum electrode and copper foil, a mixture containing 4 and azides, dissolved in a solvent system of ACN:EtOH:H2O (1:1:0.5), was subjected to a current of 0.3 volts for 1 h. TBATFB (0.1 mmol) was used as a catalyst. After the completion of the reaction, the reaction mass was purified using the column chromatography technique to obtain compounds 5(a–m) (Table 2).

2.3. Effect of Newly Synthesized Triazoles on MCF-7 Breast Cancer Cells

Using an AlamarBlue assay, all newly synthesized triazoles were examined for loss of cell viability in MCF-7 cells (Figure 2). The synthesized compounds’ resulting IC50 values are tabulated in Table 2, with the internal reference drugs tamoxifen and doxorubicin possessing IC50 values of 1.74 and 0.93 µM, respectively (Supplementary File). The findings showed that only compound 5g was sufficiently potent, with an IC50 value of 15.14 µM, whereas curcumin-induced loss of viability in MCF-7 cells was reported as 26.0 µM [48]. Additionally, compounds 5g and curcumin were found to have IC50 > 100 μM in cell viability assays against MCF-10A cells. This indicates the compound 5g was relatively more effective against cancer cells (MCF-7) as compared to immortalized normal mammary epithelial cells (MCF-10A).

2.4. Structural Analysis

The Cambridge Crystallographic Data Centre (CCDC) number 2291115 for the crystal of compound 4 provides complete crystallographic data, which are available online (www.ccdc.cam.ac.uk (accessed on 26 October 2023)). The Oak Ridge Thermal Ellipsoidal Plot (ORTEP) with a 50% probability is shown in (Figure S1A in the Supplementary File). The complete details of data refinement and structural parameters are tabulated (Table S1 in the Supplementary File). The 3D structure of compound 4 confirmed that it crystallizes in a triclinic crystal system having a P 1 ¯ space group. The unit cell parameters were deduced with a = 8.7295 Å, b = 11.7399 Å, c = 12.571 Å, α = 89.762 °, β = 75.097°, γ = 78.578°, and Z = 2. The structure of compound 4 resulted in a dimer (two independent molecules) via prominent hydrogen bond interaction between C24 and H1B atoms (Figure S1B, Supplementary File). The packing diagram of molecules with hydrogen bonds is shown along the a, b, and c-axes (Figure S2, Supplementary File), elucidating the crystal molecular stability and molecular packing interactions. Short contact intramolecular interactions are observed between C20 and H30B, C29 and H30A, C4 and H14B, and C13A and H14A, leading to the formation of a supramolecular motif S(5). In addition, the short interactions occurring between H13A and H14A, H4A and H14B, and H20A and H30B atoms lead to a supramolecular motif S(6). Geometry parameters such as bond lengths, bond angles, and torsional angles of the compound agree with reported standard values, as shown in Tables S2–S4 (Supplementary File), respectively.

2.5. In Silico Analysis of Novel Compound 5g Targeting Telomerase Reverse Transcriptase

Computational techniques were employed to evaluate the binding affinity and interactions of novel compound 5g with TERT (Figure 3). The molecular docking simulations yielded a binding energy of –6.74 kcal/mol for the interaction between 5g and TERT. This negative binding energy suggests a favorable binding interaction between the compound and the protein, indicating that 5g may be a potential TERT inhibitor. Analysis of the docking results revealed several critical interactions between 5g and TERT. Notable interactions included o π-cation bond forming with LYS-503 and LYS-973 and having bond distances of 4.27 Å and 4.57 Å, respectively, of TERT: hydrophobic interactions (π-sigma, Amide π-stacked, alkyl, and π-alkyl) were also observed at the binding site with residues LYS-329, HIS-500, ASN-961, and ARG-972. These interactions are indicative of the compound’s ability to interact with, and potentially inhibit, TERT function. These findings predict that compound 5g may be a candidate for the targeting of TERT.

2.6. The Title Compound Arrested Cell Cycle at the Sub-G1 and G2-M Phases in MCF-7 Cells

It has been demonstrated that curcumin inhibits telomerase activity and causes apoptosis in a variety of cancer cells [49,50]. In the current study, the effect of compound 5g on MCF-7 cell cycle progression was examined. MCF-7 cells treated with the vehicle or compound 5g were subjected to a flow cytometric analysis using propidium iodide staining. In comparison to cells treated with the vehicle, compound 5g enhanced the percentage of cells in both the sub-G1 and G2-M phases (Figure 4).

2.7. The Title Compound Inhibited Telomerase Enzymatic Activity in MCF–7 Cells

Compound 5g was further tested for the inhibition of telomerase enzymatic activity at 0, 5.0, and 10.0 μM. The result of the assay revealed that compound 5g inhibited telomerase activity with increasing concentration, as determined using the TRAPEZE® RT Telomerase Detection Kit (Millipore, cat. S7710) (Figure 5).

3. Materials and Methods

Sigma-Aldrich (Bangalore, India) procured all the chemicals and solvents. TLC plates (pre-coated silica gel) were employed to monitor the reaction progress. Agilent mass spectrophotometer (Agilent Technologies India Pvt Ltd., New Delhi, India) was used to record the molecular weight of synthesized compounds. ¹H and ¹³C NMR spectra were obtained using Agilent and Jeol NMR spectrophotometers (400 MHz) in Santa Clara, CA, USA. TMS served as the internal standard, while DMSO was used as the solvent. Chemical shifts were reported in ppm.

3.1. Synthesis of Tetrahydrocarbazole–Triazole Derivatives

Method A: Phenylhydrazine hydrochloride (1) (1.0 mmol), cyclohexane (2) (1.0 mmol), and 0.5 eq of nano-Fe2O3 were stirred at room temperature in water for 6 h. After the completion of the reaction, the reaction mixture was filtered off and the filtrate was extracted with EtOAc (3 × 15 mL); the combined organic layer was concentrated under vacuum, and the crude was purified by column chromatography technique to obtain compound 3 (Yield: 85%).
Method B: Phenylhydrazine (1) (1.0 mmol) and cyclohexane (2) (1.0 mmol) were subjected to 0.5 volts of electrolysis for 5 h in ethanol using a platinum electrode and copper foil in the presence of a catalytical amount of tetrabutylammonium iodide (TBAI). After the completion of the reaction, ethanol was removed under reduced pressure and crude was extracted with EtOAc (3 × 15 mL); the combined organic layer was concentrated under vacuum and purified by column chromatography to obtain compound 3 (Yield: 80%). Mass spectra of 3: calculated = 171.1048, found = 172.1011 [M+H]+.
NaH (1.1 mmol), after washing with dry hexane, was suspended in dry DMF (5 mL), followed by the addition of compound 3 (1 mmol). After the color change in the reaction mixture, propargyl bromide (1.5 mmol) was added drop-wise. Reaction mixture was stirred for 2 h at 0–5 °C. After the completion of the reaction, ice-cooled water (10 mL) was added to the reaction mixture and extracted with EtOAc (3 × 15 mL). The combined organic layers were then washed with water (3 × 50 mL) and dried over anhydrous Na2SO4. The organic phase was concentrated under vacuum, and the crude was purified by column chromatography technique to obtain compound 4. Mass spectra of 4: calculated = 209.1204; found = 210.1170 [M+H]+ Yield: 85%.
Method C: To a 5 mL flask with Et3N (0.4 mmol) and solvent (1.5 mL), CuI (0.1 mmol) was added at room temperature. Then, compound 4 was added to the mixture and stirred for 2 h at room temperature. After the completion of the reaction, the mixture was diluted with 25 mL of EtOAc and washed with 10 mL of H2O three times, then by brine. The organic phase was dried over anhydrous Na2SO4. After removal the of the solvent under reduced pressure, the residue was purified using column chromatography.
Method D: In the presence of a platinum electrode and copper foil, a mixture containing 4 and azides dissolved in a solvent system of ACN:EtOH:H2O (1:1:0.5) was subjected to current of 0.3 volts for 1 h. TBATFB (0.1 mmol) was used as a catalyst. After the completion of the reaction, the solvents were removed under reduced pressure and extracted with EtOAc (3 × 15 mL); the combined organic layer was concentrated under vacuum, and the crude was purified by column chromatography technique to obtain compounds 5(a–m) and characterized by spectroscopic techniques.

3.2. 9-((1-(o-Tolyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5a)

Yellow solid; M.P = 86–88 °C; 84% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.48 (s, 1H), 7.60 (d, J = 8.0 Hz, 1H), 7.43 (s, 2H), 7.37 (t, J = 6.2 Hz, 3H), 7.08 (t, J = 7.6 Hz, 1H), 6.99 (t, J = 7.3 Hz, 1H), 5.41 (s, 2H), 2.94 (s, 2H), 2.64 (s, 2H), 2.10 (s, 3H), 1.90 (d, J = 4.9 Hz, 2H), 1.80 (d, J = 4.7 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 144.36, 136.62, 136.20, 135.88, 133.36, 131.78, 130.19, 127.54, 127.39, 126.38, 125.25, 120.77, 118.99, 117.80, 109.84, 109.11, 37.72, 23.28, 23.24, 22.14, 21.19, 17.86. Mass spectra: calculated for C22H22N4 = 342.1844; found = 343.2655 [M+H]+.

3.3. 9-((1-(4-Chlorophenyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5c)

Yellow solid; M.P = 132–134 °C; 96% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.80 (s, 1H), 7.89 (d, J = 8.9 Hz, 2H), 7.62 (d, J = 8.9 Hz, 2H), 7.55 (d, J = 8.1 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.07 (t, J = 7.3 Hz, 1H), 6.97 (t, J = 7.4 Hz, 1H), 5.39 (s, 2H), 2.92 (t, J = 5.8 Hz, 2H), 2.62 (t, J = 5.7 Hz, 2H), 1.93–1.86 (m, 2H), 1.82–1.76 (m, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.63, 136.13, 135.81, 135.77, 133.37, 130.24, 127.54, 122.19, 121.89, 120.80, 119.01, 117.79, 109.82, 109.17, 37.75, 23.25, 23.18, 22.04, 21.16. Mass spectra: calculated for C21H19ClN4 = 362.1298; found = 363.1808 [M+H]+.

3.4. 9-((1-(3,4-Dichlorophenyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5d)

Yellow solid; M.P = 130–132 °C; 94% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.86 (s, 1H), 8.21 (d, J = 2.3 Hz, 1H), 7.91 (dd, J = 8.8, 2.3 Hz, 1H), 7.81 (d, J = 8.8 Hz, 1H), 7.54 (d, J = 8.1 Hz, 1H), 7.34 (s, 1H), 7.07 (t, J = 7.5 Hz, 1H), 6.97 (t, J = 7.4 Hz, 1H), 5.40 (s, 2H), 2.91 (t, J = 5.4 Hz, 2H), 2.62 (t, J = 5.3 Hz, 2H), 1.90 (d, J = 5.2 Hz, 2H), 1.79 (d, J = 4.6 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.78, 136.47, 136.12, 135.77, 132.74, 132.15, 131.38, 127.53, 122.14, 122.08, 120.81, 120.48, 119.02, 117.78, 109.79, 109.20, 37.75, 23.25, 23.18, 22.01, 21.16. Mass spectra: calculated for C21H18Cl2N4 = 396.0909; found = 397.0625 [M+H]+.

3.5. 9-((1-(4-Bromophenyl)-1H-1,2,3-triazol-4-yl) methyl)-2,3,4,9-tetrahydro-1H-carbazole (5e)

Yellow solid; M.P = 150–152 °C; 92% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.81 (s, 1H), 7.84 (s, 2H), 7.76 (d, J = 8.8 Hz, 2H), 7.55 (d, J = 8.1 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.06 (t, J = 7.5 Hz, 1H), 6.97 (t, J = 7.4 Hz, 1H), 5.39 (s, 2H), 2.92 (t, J = 5.8 Hz, 2H), 2.62 (t, J = 5.7 Hz, 2H), 1.90 (d, J = 5.6 Hz, 2H), 1.80 (d, J = 5.5 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.65, 136.18, 136.12, 135.82, 133.18, 127.53, 122.45, 121.86, 121.75, 120.80, 119.01, 117.79, 109.83, 109.17, 37.75, 23.25, 23.18, 22.04, 21.16. Mass spectra: calculated for C21H19BrN4 = 406.0793; found = 407.0469 [M+H]+.

3.6. 9-((1-(3-Chlorophenyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5f)

Yellow solid; M.P = 130–132 °C; 90% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.87 (s, 1H), 8.01 (s, 1H), 7.87 (d, J = 8.1 Hz, 1H), 7.59–7.50 (m, 3H), 7.35 (d, J = 7.6 Hz, 1H), 7.07 (t, J = 7.4 Hz, 1H), 6.97 (t, J = 7.3 Hz, 1H), 5.40 (s, 2H), 2.92 (t, J = 5.5 Hz, 2H), 2.62 (t, J = 5.4 Hz, 2H), 1.90 (d, J = 5.4 Hz, 2H), 1.80 (d, J = 5.2 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.64, 138.00, 136.12, 135.80, 134.61, 131.99, 128.89, 127.53, 122.03, 120.81, 120.25, 119.06, 119.02, 117.79, 109.82, 109.17, 37.75, 23.26, 23.18, 22.03, 21.17. Mass spectra: calculated for C21H19ClN4 = 362.1298; found = 363.1808 [M+H]+.

3.7. 9-((1-(4-Methoxyphenyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5g)

Brown solid; M.P = 156–158 °C; 86% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.67 (s, 1H), 7.74 (d, J = 8.9 Hz, 2H), 7.56 (d, J = 8.1 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.10–7.05 (m, 3H), 6.96 (d, J = 7.3 Hz, 1H), 5.37 (s, 2H), 3.80 (s, 3H), 2.93 (t, J = 5.5 Hz, 2H), 2.62 (t, J = 5.3 Hz, 2H), 1.89 (d, J = 5.2 Hz, 2H), 1.79 (d, J = 4.8 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 159.71, 145.20, 136.14, 135.84, 130.42, 127.53, 122.20, 121.77, 120.77, 118.98, 117.78, 115.26, 109.85, 109.11, 56.00, 37.80, 23.26, 23.20, 22.07, 21.17. Mass spectra: calculated for C22H22N4O = 358.1794; found = 359.1361 [M+H]+.

3.8. 9-((1-(p-Tolyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5h)

Yellow solid; M.P = 92–94 °C; 90% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.72 (s, 1H), 7.72 (d, J = 8.4 Hz, 2H), 7.56 (d, J = 8.1 Hz, 1H), 7.35 (dd, J = 7.8, 3.4 Hz, 3H), 7.06 (d, J = 7.3 Hz, 1H), 6.98 (d, J = 7.3 Hz, 1H), 5.38 (s, 2H), 2.93 (t, J = 5.7 Hz, 2H), 2.62 (t, J = 5.6 Hz, 2H), 2.34 (s, 3H), 1.89 (d, J = 5.5 Hz, 2H), 1.79 (d, J = 5.4 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.33, 138.72, 136.13, 135.83, 134.75, 130.62, 127.53, 121.67, 120.78, 120.37, 118.99, 117.78, 109.85, 109.12, 37.78, 23.26, 23.19, 22.06, 21.17, 21.00. Mass spectra: calculated for C22H22N4 = 342.1844; found = 343.2655 [M+H]+.

3.9. 9-((1-(3-Bromophenyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5i)

Yellow solid; M.P = 146–148 °C; 87% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.87 (s, 1H), 8.13 (s, 1H), 7.91 (dd, J = 8.2, 1.0 Hz, 1H), 7.64 (d, J = 8.5 Hz, 1H), 7.56 (d, J = 8.1 Hz, 1H), 7.49 (t, J = 8.1 Hz, 1H), 7.35 (d, J = 7.7 Hz, 1H), 7.07 (t, J = 7.4 Hz, 1H), 6.97 (t, J = 7.4 Hz, 1H), 5.39 (s, 2H), 2.92 (t, J = 5.6 Hz, 2H), 2.62 (t, J = 5.4 Hz, 2H), 1.89 (d, J = 5.3 Hz, 2H), 1.79 (d, J = 4.3 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.62, 138.07, 136.12, 135.79, 132.18, 131.79, 127.53, 122.95, 122.86, 122.01, 120.81, 119.42, 119.01, 117.79, 109.81, 109.17, 37.76, 23.27, 23.19, 22.03, 21.17. Mass spectra: calculated for C21H19BrN4 = 406.0793; found = 407.0469 [M+H]+.

3.10. 9-((1-Phenyl-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5j)

White solid; M.P = 114–116 °C; 88% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.78 (s, 1H), 7.85 (d, J = 8.0 Hz, 2H), 7.56 (t, J = 7.8 Hz, 3H), 7.46 (t, J = 7.4 Hz, 1H), 7.36 (d, J = 7.7 Hz, 1H), 7.07 (t, J = 7.5 Hz, 1H), 6.98 (d, J = 7.4 Hz, 1H), 5.40 (s, 2H), 2.93 (t, J = 5.8 Hz, 2H), 2.62 (t, J = 5.6 Hz, 2H), 1.93–1.87 (m, 2H), 1.82–1.76 (m, 2H); 13C NMR (100 MHz, DMSO-d6) δ 145.45, 136.99, 136.15, 135.85, 130.29, 129.12, 127.54, 121.83, 120.79, 120.54, 119.00, 117.79, 109.85, 109.14, 37.78, 23.26, 23.19, 22.07, 21.17. Mass spectra: calculated for C21H20N4 = 328.1688; found = 329.1264 [M+H]+.

3.11. 9-((1-(5-(Furan-2-yl)-1H-pyrazol-3-yl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5k)

Brown solid; M.P = 184–186 °C; 76% yield; 1H NMR (400 MHz, DMSO-d6) δ 13.77 (s, 1H), 8.54 (s, 1H), 7.84 (d, J = 1.0 Hz, 1H), 7.59 (d, J = 8.1 Hz, 1H), 7.36 (d, J = 7.7 Hz, 1H), 7.07 (t, J = 7.5 Hz, 1H), 6.98 (d, J = 4.0 Hz, 2H), 6.93 (s, 1H), 6.66 (dd, J = 3.3, 1.8 Hz, 1H), 5.41 (s, 2H), 2.93 (t, J = 5.7 Hz, 2H), 2.63 (t, J = 5.6 Hz, 2H), 1.93–1.87 (m, 2H), 1.80 (d, J = 5.4 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 146.88, 144.96, 144.17, 144.01, 136.24, 136.14, 135.88, 127.55, 121.33, 120.82, 119.03, 117.81, 112.48, 109.87, 109.20, 108.76, 93.35, 37.60, 23.24, 23.20, 22.08, 21.16. Mass spectra: calculated for C22H20N6O = 384.1699; found = 385.1348 [M+H]+.

3.12. 9-((1-(4-Nitrophenyl)-1H-1,2,3-triazol-4-yl) methyl)-2,3,4,9-tetrahydro-1H-carbazole (5l)

Orange solid; M.P = 230–232 °C; 90% yield; 13C NMR (100 MHz, DMSO) δ 147.78, 143.97, 136.02, 135.57, 134.74, 132.98, 127.34, 126.93, 126.38, 121.69, 121.39, 126.38, 121.69, 121.39, 199.66, 118.15, 110.18, 109.58, 37.34, 23.21, 23.07, 21.94, 21.00. Mass spectra: calculated for C21H19N5O2 = 373.1539; found = 374.1289 [M+H]+.

3.13. 9-((1-(3-Nitro-4-methyl-phenyl)-1H-1,2,3-triazol-4-yl)methyl)-2,3,4,9-tetrahydro-1H-carbazole (5m)

Yellow solid; M.P = 186–188 °C; 86% yield; 1H NMR (400 MHz, DMSO-d6) δ 8.60 (s, 1H), 8.02 (s, 1H), 7.84 (s, 1H), 7.70–7.68 (m, 1H), 7.55 (d, J = 8.1 Hz, 1H), 7.36 (d, J = 7.8 Hz, 1H), 6.99 (s, 1H), 6.95–6.91 (m, 1H), 5.42 (s, 2H), 2.89 (t, J = 5.7 Hz, 2H), 2.63 (d, J = 5.2 Hz, 2H), 2.47 (s, 3H), 1.92–1.87 (m, 2H), 1.79 (dd, J = 7.6, 2.8 Hz, 2H); 13C NMR (100 MHz, DMSO-d6) δ 147.57, 145.04, 142.29, 136.04, 135.57, 135.04, 127.79, 127.33, 125.94, 125.00, 121.81, 120.82, 119.01, 117.79, 109.80, 109.18, 37.68, 23.25, 23.20, 21.17, 20.85, 20.82. Mass spectra: calculated for C22H21N5O2 = 387.1695; found = 388.1410 [M+H]+.

3.14. Cell Lines and Culture Conditions

MCF-7 cells were procured from Procell Life Science and Technology Co., Ltd. (Wuhan, China). MCF-7 cells were grown in MEM with 2% FBS in a humidified environment containing 5% CO2 and a temperature of 37 °C. In order to be stored as stock solutions, the chemicals of interest were dissolved in DMSO. These stock solutions were then diluted to the necessary concentrations using a cell culture medium. Triazoles at concentrations of 0, 0.01, 0.1, 10, 100, and 1000 M were applied to the cells for 72 h. Cell viability was assessed using the AlamarBlue reagent (Procell Life Science and Technology Co., Ltd. Wuhan, China) [51].

3.15. X-ray Data Collection and Refinement Methods

The X-ray intensity data were collected for a block-shaped transparent crystal with dimensions of 0.200 × 0.140 × 0.04 mm. MoKα radiation with a wavelength of 0.71073 Å at 293 K was used to collect data using a Bruker D8 VENTURE diffractometer equipped with a PHOTON II detector (Sophisticated Analytical Instrumentation Facility, IIT Madras, Chennai, India). SAINT PLUS software (Version 8.34A) was used to collect and process the data [52]. Using the SHELXS and SHELXL programs, the structure was solved using direct methods and refined using the full-matrix least-squares method on F2 [53,54]. All the hydrogen atom positions were fixed at acceptable chemical locations and were allowed to ride on the parent atoms with a range of Uiso(H) = 1.2 to 1.5 Ueq (carrier atom). In total, 5004 unique reflections with 291 parameters were subjected to refinement, resulting in a convergence of R1 to 0.095 (wR2 = 0.2406) and a goodness-of-fit score of 1.536. The geometries were computed using PLATON (Version no.200322) [55]. Mercury was used to generate ORTEP (Oak Ridge Thermal Ellipsoidal Plot) and molecular packing diagrams [56].

3.16. Molecular Docking Studies

In silico analysis was carried out with AutoDock4 tools-1.5.7 [57]. TERT’s three-dimensional structure was acquired from a protein database (PDB ID: 7TRD, https://www.rcsb.org/structure/7TRD, accessed on 26 October 2023). The new chemical 5g’s structure was designed and optimized using relevant software. Docking simulations were performed using the Lamarckian genetic process, which is implemented in AutoDock4 (Auto Docking 4.2.6 version). Ten docking experiments were conducted to investigate the binding interactions of 5g and TERT. The grid box was centered on the active site of TERT, with proportions adequate to contain the binding pocket grid of 50 Å × 50 Å × 50 Å and spacing of 0.500 Å. The binding energy of 5g–TERT complexes was determined, and the most advantageous docking pose with the lowest binding energy was chosen for further investigation. The resulting docking stances were visualized and analyzed using Discovery Studio (Discovery studio 2021 version) [58] and UCSF Chimera (chimera version 1.8) [59].

3.17. Annexin V Cell Cycle Analysis Assay

MCF-7 cells were procured from Procell Life Science and Technology Co., Ltd. (Wuhan, China). To assess cell cycle distribution, 1 × 105 MCF-7 cells were collected, washed once in ice-cold PBS, and permeabilized with 100 L of 0.5% Triton X-100. One hundred and five (1 × 105) cells were fixed with 75% ethanol at −20 °C overnight and then were stained for one hour at 4 °C using 50 µg/mL PI in 200 µL PBS supplemented with 20 μg/mL (w/v) RNase A (Abbkine, KTA2020, Wuhan, China). Cytofluorometric acquisitions were carried out in low flow rate mode on a BECKMAN Coulter CytoFlex. (Beckman Coulter, Inc., Brea, CA, USA) using Annexin-V-FLUOS and PI-stained (Neobioscience, Shenzhen, China) cells as per the manufacturer’s instructions [60].

3.18. Telomerase Enzymatic Activity

MCF-7 cells were exposed to the compound at the indicated time and concentrations, and 1 × 106 cells were harvested for analysis. Telomerase catalytic activity (TRAP) was measured using the TRAPEZE® RT Telomerase Detection Kit (Millipore, cat. S7710, Wuhan, China) according to the manufacturer’s instructions. In detail, for each sample, 1 million cells were resuspended in 200 µL CHAPS and incubated on ice for 30 min. Samples were centrifuged at 12,000× g for 20 min at 4 °C. 5 μL of the lysates was further diluted 200-fold and used for the TRAPeze RT Telomerase assay along with a positive control (a telomerase-positive extract provided by the manufacturer also diluted in 200 µL CHAPS), a negative telomerase control (only CHAPS lysis buffer), and a no template control (only nuclease-free water). Real-time quantitative PCR was performed. All reactions were run in triplicate using the master mix provided with the kit and Hieff® Taq DNA Polymerase (Yeasen, No.10101ES, Wuhan, China) following the manufacturer’s protocol. Telomerase activity was calculated using the generated TSR8 standard curve deduced from known concentrations of TSR8.

3.19. Data Analysis and Statistics

The mean and standard deviation of the results are provided. To examine the statistical difference between treatment groups, a one-way analysis of variance (one-way ANOVA) with Bonferroni’s multiple comparison tests was employed. The cut-off for substantial change was set at a confidence level of 0.05.

4. Conclusions

The synthesis of tetrahydrocarbazole–triazole derivatives and their efficacy in cancer cells is reported. All of the derivatives were tested for loss of viability in MCF-7 cells, and compound 5g was observed as the most potent among the series. Additionally, an in silico docking analysis of compound 5g towards TERT showed a favorable binding energy of 6.74 kcal/mol. Compound 5g decreased telomerase activity and promoted cell cycle arrest and apoptosis of MCF-7 cells. To conclude, a novel method for the synthesis of tetrahydrocarbazole–triazole derivatives, using reusable iron(III) oxide nano-particles and an electrochemical method, that target telomerase in cancer cells is reported.

Supplementary Materials

The following supporting information can be downloaded at: https://www.mdpi.com/article/10.3390/catal14100726/s1: S3–S5: Figure S1. Crystal image of compound 4. Figure S2. Crystal structure packing along the a, b and c-axis, respectively, showing hydrogen bonds between C24 and H1B, C5 and H32, and C6 and H32 in blue dashed lines. Table S1. Crystal structure data and refinement parameters; Table S2. Geometry bond lengths; Table S3. Selected geometry bond angles; Table S4. Selected geometry torsional angles of compound 4; S6–S25: Spectral data of 5(a–m); S26–S31: IC50 values of 5(a–m), Tamoxifen, Doxorubicin, and Curcumin.

Author Contributions

P.M.U., A.R., Z.X., K.K.H., A.M.K., L.K.P., C.S. and T.R.S.: conceptualization, methodology, formal analysis, and writing; S.L.G. and M.M.: formal analysis, P.E.L., V.P. and B.B.: conceptualization, methodology, software, data curation, original draft, validation, writing, and editing. All authors have read and agreed to the published version of the manuscript.

Funding

This research was further supported by the National Natural Science Foundation of China (82172618); the Shenzhen Key Laboratory of Innovative Oncotherapeutics (ZDSYS20200820165400003) (Shenzhen Science and Technology Innovation Commission), China; Universities Stable Funding Key Projects (WDZC20200821150704001), China; The Shenzhen Bay Laboratory, Oncotherapeutics (21310031), China; Overseas Research Cooperation Project (HW2020008) (Tsinghua Shenzhen International Graduate School), China; P.M.U. (NTA Ref. No.: 221610108292) thanks CSIR-UGC for providing fellowship, and B.B. thank VGST-CESEM for providing fellowship.

Data Availability Statement

All data are freely available within this article.

Conflicts of Interest

The authors declare no conflicts of interest.

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Catalysts 14 00726 g001
Figure 1. Reported drugs and telomerase inhibitors containing carbazole/tetrahydrocarbazole (blue), triazole (red), and aryl (pink) motifs.
Figure 1. Reported drugs and telomerase inhibitors containing carbazole/tetrahydrocarbazole (blue), triazole (red), and aryl (pink) motifs.
Catalysts 14 00726 g001
Catalysts 14 00726 sch001
Scheme 1. Synthesis of tetrahydrocarbazole.
Scheme 1. Synthesis of tetrahydrocarbazole.
Catalysts 14 00726 sch001
Catalysts 14 00726 sch002
Scheme 2. Optimized reaction for the synthesis of tetrahydrocarbazole.
Scheme 2. Optimized reaction for the synthesis of tetrahydrocarbazole.
Catalysts 14 00726 sch002
Catalysts 14 00726 sch003
Scheme 3. Synthesis of tetrahydrocarbazole–triazole 5(a–m) derivatives.
Scheme 3. Synthesis of tetrahydrocarbazole–triazole 5(a–m) derivatives.
Catalysts 14 00726 sch003
Catalysts 14 00726 g002
Figure 2. IC50 of compound 5g using loss of viability in MCF-7 breast cancer cells.
Figure 2. IC50 of compound 5g using loss of viability in MCF-7 breast cancer cells.
Catalysts 14 00726 g002
Catalysts 14 00726 g003
Figure 3. (A) A cartoon illustration of the docked complex 5g (yellow) with the TERT active site. (B) Intermolecular interactions observed after molecular docking between 5g and TERT.
Figure 3. (A) A cartoon illustration of the docked complex 5g (yellow) with the TERT active site. (B) Intermolecular interactions observed after molecular docking between 5g and TERT.
Catalysts 14 00726 g003
Catalysts 14 00726 g004
Figure 4. Effects of compound 5g on cell cycle progression in MCF-7 cells: MCF-7 cells were treated with the compound at the indicated concentrations for 48 h and harvested for cell cycle analysis. The percentage (%) of the cell cycle phase is quantified. Data are presented in the histograms as means ± SD. * p < 0.05, ** p < 0.01, *** p < 0.005, **** p < 0.0001, two-way ANOVA, compared with no treatment control.
Figure 4. Effects of compound 5g on cell cycle progression in MCF-7 cells: MCF-7 cells were treated with the compound at the indicated concentrations for 48 h and harvested for cell cycle analysis. The percentage (%) of the cell cycle phase is quantified. Data are presented in the histograms as means ± SD. * p < 0.05, ** p < 0.01, *** p < 0.005, **** p < 0.0001, two-way ANOVA, compared with no treatment control.
Catalysts 14 00726 g004
Catalysts 14 00726 g005
Figure 5. Compound 5g inhibited telomerase activity in MCF-7 cells: MCF-7 cells were exposed to the compound at the indicated concentrations (5 μM and 10 μM) for 48 h and harvested for the TRAPeze™ RT Telomerase assay. Data represent three independent experiments. Data are presented in the histogram as means ± SD. * p < 0.05, ** p < 0.01, *** p < 0.005, **** p < 0.0001, one-way ANOVA, compared with no treatment control.
Figure 5. Compound 5g inhibited telomerase activity in MCF-7 cells: MCF-7 cells were exposed to the compound at the indicated concentrations (5 μM and 10 μM) for 48 h and harvested for the TRAPeze™ RT Telomerase assay. Data represent three independent experiments. Data are presented in the histogram as means ± SD. * p < 0.05, ** p < 0.01, *** p < 0.005, **** p < 0.0001, one-way ANOVA, compared with no treatment control.
Catalysts 14 00726 g005
Table 1. Optimization of reaction conditions for the synthesis of tetrahydrocarbazole.
Table 1. Optimization of reaction conditions for the synthesis of tetrahydrocarbazole.
EntrySolventCatalystReaction ConditionTime Yield (%)
1.[BMIM]BF4Reflux1275
2.[EMIM]BF4Reflux1270
3.Electrochemical methodrt880
4. DMSO0.1 eq nano-Fe2O3rt1250
5.DMSO0.3 eq nano-Fe2O3rt1265
6.DMSO0.5 eq nano-Fe2O3rt1275
7.DMSO0.5 eq nano-Fe2O3Reflux860
8.DMF0.5 eq nano-Fe2O3rt1270
9.DMF0.5 eq nano-Fe2O3Reflux855
10.ACN0.5 eq nano-Fe2O3rtnrnr
11.Dioxane0.5 eq nano-Fe2O3rt1255
12.Acetone0.5 eq nano-Fe2O3rtnrnr
13. THF0.5 eq nano-Fe2O3rtnrnr
14.EtOH0.5 eq nano-Fe2O3rt1070
15.MeOH0.5 eq nano-Fe2O3rt1165
16.H2O0.5 eq nano-Fe2O3rt685
17.EtOH:H2O0.5 eq nano-Fe2O3rt780
nr = no reaction; rt = room temperature.
Table 2. List of newly synthesized derivatives and IC50 for loss of viability in MCF-7 breast cancer cells.
Table 2. List of newly synthesized derivatives and IC50 for loss of viability in MCF-7 breast cancer cells.
EntryR–N3ProductIC50
(µM)
5aCatalysts 14 00726 i001Catalysts 14 00726 i002>100
5bCatalysts 14 00726 i003Catalysts 14 00726 i00421.38
5cCatalysts 14 00726 i005Catalysts 14 00726 i006>100
5dCatalysts 14 00726 i007Catalysts 14 00726 i008>100
5eCatalysts 14 00726 i009Catalysts 14 00726 i010>100
5fCatalysts 14 00726 i011Catalysts 14 00726 i012>100
5gCatalysts 14 00726 i013Catalysts 14 00726 i01415.14
5hCatalysts 14 00726 i015Catalysts 14 00726 i016>100
5iCatalysts 14 00726 i017Catalysts 14 00726 i018>100
5jCatalysts 14 00726 i019Catalysts 14 00726 i02027.19
5kCatalysts 14 00726 i021Catalysts 14 00726 i02234.8
5lCatalysts 14 00726 i023Catalysts 14 00726 i02464.33
5mCatalysts 14 00726 i025Catalysts 14 00726 i02679.76
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Uppar, P.M.; Ravish, A.; Xi, Z.; Kumar Harish, K.; Kumar, A.M.; Poonacha, L.K.; Swaroop, T.R.; Somu, C.; Gaonkar, S.L.; Madegowda, M.; et al. Synthesis of Tetrahydrocarbazole-Tethered Triazoles as Compounds Targeting Telomerase in Human Breast Cancer Cells. Catalysts 2024, 14, 726. https://doi.org/10.3390/catal14100726

AMA Style

Uppar PM, Ravish A, Xi Z, Kumar Harish K, Kumar AM, Poonacha LK, Swaroop TR, Somu C, Gaonkar SL, Madegowda M, et al. Synthesis of Tetrahydrocarbazole-Tethered Triazoles as Compounds Targeting Telomerase in Human Breast Cancer Cells. Catalysts. 2024; 14(10):726. https://doi.org/10.3390/catal14100726

Chicago/Turabian Style

Uppar, Pradeep M., Akshay Ravish, Zhang Xi, Keshav Kumar Harish, Arun M. Kumar, Lisha K. Poonacha, Toreshettahally R. Swaroop, Chaithanya Somu, Santosh L. Gaonkar, Mahendra Madegowda, and et al. 2024. "Synthesis of Tetrahydrocarbazole-Tethered Triazoles as Compounds Targeting Telomerase in Human Breast Cancer Cells" Catalysts 14, no. 10: 726. https://doi.org/10.3390/catal14100726

APA Style

Uppar, P. M., Ravish, A., Xi, Z., Kumar Harish, K., Kumar, A. M., Poonacha, L. K., Swaroop, T. R., Somu, C., Gaonkar, S. L., Madegowda, M., Lobie, P. E., Pandey, V., & Basappa, B. (2024). Synthesis of Tetrahydrocarbazole-Tethered Triazoles as Compounds Targeting Telomerase in Human Breast Cancer Cells. Catalysts, 14(10), 726. https://doi.org/10.3390/catal14100726

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