1. Introduction

IJOC

International Journal of Organic Chemistry

2161-4687

Scientific Research Publishing

10.4236/ijoc.2021.111003

IJOC-107622

Articles

Biomedical&Life Sciences Chemistry&Materials Science

3-(Tetrazol-5-yl)-2-imino-coumarins Derivatives: Synthesis, Characterization, and Evaluation on Tumor Cell Lines

Ali

Bouattour

¹Mehdi

Fakhfakh

¹Souhir

Abid El-Gharbi

²Majdi

Abid

²Ludovic

Paquin

³Rémy

Le Guevel

⁴Thierry

Charlier

⁴Houcine

Ammar

¹Jean-Pierre

Bazureau

⁵^*

Institut des Sciences Chimiques de Rennes, ISCR UMR CNRS 6226, Campus Beaulieu, Université de Rennes 1, Bat. 10A, Rennes Cedex, France

Laboratoire de Chimie Appliquée: Hétérocycles, Corps Gras et Polymères, Faculté des Sciences de Sfax, Université de Sfax, Sfax, Tunisie

Chemistry Department, College of Science and Arts, Jouf University, Al Qurayyat, Al Jawf, KSA

S2Wave Platform, ScanMAT UMS 2001 CNRS, Campus Beaulieu, Université de Rennes 1, Bat. 10A, Rennes Cedex, France

ImPACcell Platform, SFR Biosit Bat. 8, Campus Villejean, Rennes Cedex, France

28012021

110124347, January 20216, March 2021 9, March 2021

2014

This work is licensed under the Creative Commons Attribution International License (CC BY). http://creativecommons.org/licenses/by/4.0/

The first report of new 3-(tetrazol-5-yl)-2-iminocoumarin derivatives is described. The title compounds were prepared in two steps and were obtained in good yields (55-93%). They have been fully characterized by ¹H, ¹³C NMR, FTIR, UV-Visible and HRMS. They were tested for their antiproliferative activities against six representative human tumor cell lines (Huh 7-D12, Caco2, MDA-MB231, HCT 116, PC3 and NCI-H727) and HaCat keratinocytes. Among them, compound 5e was active on HCT 116 (IC ₅₀ 15 μM).

2-Iminocoumarin Tetrazole Fluorescence Tumor Cell Lines HCT 116

1. Introduction

Tetrazole [1] belongs to a family of compounds bearing the highest number of nitrogen atoms and surprisingly, they do not exist in nature. Tetrazole is an important scaffold because they are integrated in many compounds that have applications in numerous fields such as in medicine, biochemistry, and pharmacology [2] [3] [4]. It’s noteworthy that in pharmacology, 5-substituted-1H-tetrazoles are bio-isosters of carboxylic acids because they presented comparable pK_a (tetrazole 4.5 - 4.9 vs carboxylic acid 4.2 - 4.4), they have a similar size and a near molecular electrostatic potential [5]. They undergo very similar receptor-ligand interactions [6], exhibit a prolonged half-life time because they enhanced the metabolic stability [7] [8] and the membrane penetration [9]. Food Drug Administration (FDA) approved 23 drugs that contain 1H- or 2H-tetrazole substituents [10]. Among them as examples (Figure 1): losartan as angiotensin II receptor [11], irbesartan as Angiotensin Receptor Blocker (ARB) for the treatment of hypertension [12], cilostazol for peripheral vascular disease [13] and cefazolin as antibiotic [14].

In our group and as part of our program aimed at developing new methods for the preparation of new building blocks or, for the synthesis of 2-iminocoumarins showing potential biological properties dedicated to protection of rat tissues from isoproterenol toxicity [15] or, for cancer [16] [17], we were motivated in this work respectively for: 1) to prepare a class of hybrid derivatives of 2-iminocoumarins bearing a tetrazole pharmacophore, 2) to evaluate their antiproliferative activities on tumor cell lines and iii) to study their UV/visible properties.

2. Results and Discussion2.1. Synthesis and Characterizations

The synthetic route towards the preparation of the title compounds 5 is outlined below. In the first step (Scheme 1), the 3-cyano-2-iminocoumarins 3 were synthesized from an equimolecular mixture of various substituted 2-hydroxy benzaldehyde 1 (1a: 2-hydroxy-3-methoxybenzaldehyde, 1b: 4-diethylamino-2-hydroxybenzaldehyde, 1c: 2,4-dihydroxybenzaldehyde, 1d: 2-hydroxynaphthaldehyde, 1e: 2-hydroxybenzaldehyde, 1f: 2-hydroxy-4-methoxybnezaldehyde, 1g: 5-bromo-2-hydroxybenzaldehyde, 1h: 3-ethoxy-2-hydroxybenzaldehyde) and

Scheme 1. Synthesis of 3-cyano-2-iminocoumarins 3(a-h) from various substituted 2-hydroxybenzaldehydes 1(a-h) and propanedinitrile 2.

propanedinitrile 2 in ethanol with 0.5% of piperidine at room temperature. After a reaction time of 8 - 9 hours and elimination of volatile compounds in vacuo, the 3-cyano-2-iminocoumarins 3 were prepared easily according to this classical protocol previously developed in our laboratory [18] [19] [20].

In the second step (Scheme 2), transformation of the nitrile group of 3-cyano2-iminocoumarins 3 into desired tetrazole moiety [21] was accomplished by using one equivalent of zinc chloride as catalyst and sodium azide 4. The reaction was conducted in a solution of THF and deionized water (4:1 v/v) under reflux during 4 - 7 h. Completion of the reaction was monitored by thin layer chromatography on 0.2-mm precoated plates of silica gel 60F-254 (Merck). After cooling down to room temperature, the precipitated material was collected by filtration on a Buchner funnel (porosity N˚4) and purified by washing with deionized water. The desired 3-(tetrazol-5-yl)-2-iminocoumarins 5 were synthesized in yields ranging from 55 to 92 (Table 1). Moderate yields must be mentioned for compounds 5c (61%) and 5g (55%) bearing respectively a phenolic function in C-7 position for 5c and a bromine atom in C-6 position for 5g. On the contrary, the presence of electron-donating groups, such as methoxy or ethoxy groups provide yields greater than 90%, this concerns 5a (92%) and 5h (93%).

Scheme 2. Synthesis of substituted 3-(tetrazol-5-yl)-2-iminocoumarins 5(a-h) from various substituted 3-cyano-2-iminocoumarins 3(a-h) and sodium azide 4.

Table 1 Results for the preparation of 3-(tetrazol-5-yl)-2-iminocoumarins 5(a-h)


Compound	R⁵		R⁶	R⁷	R⁸	Reaction time (h)	Yield (%)^a
5a	H		H	H	MeO	4	92
5b	H		H	Et₂N	H	4	87
5c	H		H	OH	H	7	61
5d				H	H	4	73
5e	H	H		H	H	4	72
5f	H	H		MeO	H	6	84
5g	H	Br		H	Br	6	55
5h	H	H		H	EtO	6	93

^aIsolated yields.

The structures for hybrid derivatives of 2-iminocoumarins 5(a-h) were confirmed by ¹H, ¹³C NMR, HRMS and FTIR. In the IR spectrum, the presence of NH stretching frequencies of the tetrazole group of 5 was detected at 3400 cm⁻¹ [22] and associated to disappearance of the characteristic band at 2200 - 2300 cm⁻¹ for CN group of the 3-cyano-2-iminocoumarins 3. This is also confirmed in ¹³C NMR by the disappearance of a peak located at δ115 (attributed to the CN group of the starting compound 3) after synthesis of compounds 5. For MS, the [M + 1]⁺ molecular ion signal for all compounds 5 were obtained as base signal.

UV/Visible experiments were realized in DMSO and analytical data are reported in Table 2. Examination of these results shows that absorption maxima λ_abs of compounds 5 are located between 320 to 444 nm. Their emission peaks appears in purple-blue region due to a large Stokes shift (see Figure 2 for compound 5b in DMSO) and their fluorescence excitation spectra were similar. Highest values of quantum yields f were observed respectively for compounds 5c (f = 0.68) and moderate values for compounds 5b (f = 0.362), 5f (f = 0.335)

Table 2 Maximum absorption (λ<sub>abs</sub>) and emission (λ<sub>em</sub>) wavelengths, and fluorescence quantum yields for the 3-(tetrazol-5-yl)-2-iminocoumarins 5(a-h)

Compound	λ_abs (nm)	λ_em (nm)	f
5a	328	449	0.042
5b	444	512	0.362
5c	372	440	0.680
5d	392	460	0.208
5e	340	414	0.034
5f	366	439	0.335
5g	322	464	0.037
5h	320	454	0.081

bearing a substituent in C-7 position. The presence of a donor group leaded to potential interesting quantum yields.

2.2. Cytotoxic Assays

The potential in vitro cytotoxic character of 3-(tetrazol-5-yl)-2-iminocoumarins 5(a-h) has been evaluated on six selected tumor cell lines, which are respectively Huh7-D12, Caco 2, MDA-MB231, HCT 116, PC3 and NCI-H727 and are representative of different cancers (leukemia, melanoma and cancers for liver, colon, breast, prostate, lung and kidney). HaCat keratinocyte was also used as normal cell line. For each tumor cell line, the % of cell survival was measured at a single dose of 25 μM (after 48 h) in triplicate. When the survival rate is less than 50%, the IC₅₀ value for this compound is determined, using roscovitine and doxorubicine as references for positive controls (Table 3). It can be observed that only compound 5e exhibited antiproliferative activity with a marked effect on HCT116 (5e: IC₅₀ 15 μM).

3. Conclusion

This work described an easy method for the synthesis of new 3-(tetrazol-5-yl)-2-imino-coumarins derivatives. Introduction of the tetrazol moiety on the 3-cyano function of 2-iminocoumarins 3(a-h) involves a very simple method by using zinc chloride as catalyst that provided the desired compounds in yields ranging from 55% to 92%. UV/Visible analytical data were also realized by measuring the absorption maxima λ_abs, the emission maxima λ_em associated to fluorescence quantum yields f. Antiproliferative activities of all the

Table 3 Antiproliferative activities of 3-(tetrazol-5-yl)-2-iminocoumarins 5(a-h) on six tumor cell lines and HaCat keratinocyte

Compound	Percentage of survival^a (IC₅₀, μM of selected compounds)^b
Compound	Huh7-D12	Caco 2	MDA-MB231	HCT 116	PC3	NCI-H727	HaCat
5a	113	79	64	73	81	116	87
5b	126	83	129	77	90	75	97
5c	137	80	104	88	99	95	108
5d	119	86	96	87	91	121	90
5e	79 (33)	64 (21)	54 (39)	95 (15)	79 (44)	70 (>25)	92 (38)
5f	118	81	124	93	123	124	102
5g	143	92	127	110	98	95	114
5h	226	86	96	95	133	198	85
Roscovitine	21 (15)	3 (15)	21 (12)	10 (9)	24 (13)	30 (43)	6 (11)
Doxorubicine	63 (0.03)	43 (0.03)	82 (0.01)	22 (0.03)	34	65	88 (0.02)
DMSO	100 (>25)	100 (>25)	100 (>25)	100 (>25)	100 (>25)	100 (>25)	100 (>25)

^aPercentage of survival measured at 25 μM (after 48 h using a single dose, triplicate). ^bIC₅₀ values in parentheses are expressed in μM and are the average of three assays, standard error ± 0.5 μM.

new compounds were also examined on six representative human tumor cell lines and we observed that compound 5e was active on HCT 116 (IC₅₀ 15 μM). These current results are the starting point of a new larger program within our group to investigate intensively the biological properties of these new compounds with potential applications in cancer.

4. Experimental Sections4.1. Chemistry4.1.1. General Information

Solvents were evaporated with a BUCHI rotary evaporator (New Castle, PA, USA). All reagents and solvents were purchased from Acros Fisher (Illkirch, France), Sigma-Aldrich Chimie (St Quentin Fallavier, France) and were used without further purification. ¹H NMR spectra were recorded on Bruker AC 300 P (300 MHz) spectrometer and ¹³C NMR spectra on Bruker AC 300 P (75 MHz) spectrometer (Bruker France Scientifique, Voisins-le-Bretonneux, France). Chemical shifts are expressed in parts per million downfield. Data are given in the following order: δvalue, multiplicity (s, singlet; d, doublet; t, triplet; q, quartet; quint: quintuplet, m, multiplet; br, broad), number of protons, coupling constants J is given in Hertz. The High-Resolution Mass Spectra (HRMS) were recorded in positive mode using direct Electrospray infusion, respectively on Waters Q-TOF 2 or on Thermo Fisher Scientific Q-Exactive spectrometers (Thermo Electron, Villebon-sur-Yvette, France) at the “Centre Régional de Mesures Physiques de l’Ouest” platform (CRMPO platform, ScanMAT UMS 2001 CNRS, Rennes, France). Melting points were determined on a Kofler melting point apparatus and were uncorrected. Infrared spectra were recorded on a Perkin Elmer 100 (Perkin Elmer France, Paris, France). UV/VIS absorption spectra were recorded on a Hewlett Packard 8452A diode array spectrophotometer (Hewlett Packard Enterprise, Paris, France). For solutions, corrected steady state fluorescence spectra were recorded with a Perkin Elmer LS55 spectrofluorometer using cells of 1 cm optical pathway (Perkin Elmer France, Paris, France). Elemental microanalyses were performed on an EA1112 analyzer from CE Instruments Hi Tech Detection Systems HTDS, ZI Charguia II 2035, Tunis-Carthage, Tunisie).

4.1.2. General Procedure for the Synthesis of 3-(tetrazol-5-yl)-2-iminocoumarins 5(a-h)

To a stirred solution of 2-iminocoumarin-3-carbonitrile 3 (0.27 mmol) in a solution of 4 mL of THF and 1 mL of deionized water, was added successively zinc chloride (37 mg, 0.32 mml) and sodium azide (20 mg, 0.32 mmol). The resulting mixture was refluxed under magnetic stirring (500 rpm) for a reaction time from 4 to 7 h. After cooling down to room temperature, the desired compound 5 was collected by filtration on a Büchner funnel (porosity N˚4), washed with cooled deionized water (2 × 2 mL), dried under vacuum (10 - 2 Torr) at 25˚C for 1 h to give a powder.

1)8-Methoxy-3-(tetrazol-5-yl)-2-iminocoumarin (5a)

Yield = 92%. Reaction time = 4 h. Mp > 260˚C. IR (cm⁻¹): ν = 3295 (NH), 1634 (C=N); ¹H NMR (300 MHz, CDCl₃) δ: 11.21 (br s, 1H, NH), 9.32 (s, 1H, H₄), 7.54 (m, 3H, H_Ar), 4.02 (s, 3H, OCH₃); ¹³C NMR (75 MHz, CDCl₃) δ: 147.5, 121.3, 120.9, 120.1, 119.2, 118,3 116.3, 112.5, 108.7, 56.6. Anal. Calcd for C₁₁H₉N₅O₂: C, 54.32; H, 3.73; N, 28.79. Found C, 54.26; H, 3.66; N, 28.71.

2)7-N,N-Diethylamino-3-(tetrazol-5-yl)-2-iminocoumarin (5b)

Yield = 87%. Reaction time = 4 h. Mp > 260˚C. IR (cm⁻¹): ν = 3229 (NH), 1643 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 11.20 (br s, 1H, NH), 8.81 (s, 1H, H₄), 7.69 (d, ³J = 8.7 Hz, 1H, H₅), 6.82 (d, ³J = 8.7 Hz, 1H, H₆), 6.56 (s, 1H, H₈), 3.50 (q, ³J = 13.8 Hz, 2H, CH₂), 1.17 (t, ³J = 13.8 Hz, 3H, CH₃); ¹³C NMR (75 MHz, DMSO-d₆) δ: 161.9, 155.8, 154.5, 151.4, 143.05, 130.3, 110.1, 107.9, 106.7, 95.61, 44.2, 12.2. Anal. Calcd for C₁₄H₁₆N₆O: C, 59.14; H, 5.67; N, 29.56. Found C, 59.23; H, 5.61; N, 29.59.

3)7-Hydroxy-3-(tetrazol-5-yl)-2-iminocoumarin (5c)

Yield = 61%. Reaction time = 7 h. Mp > 260˚C. IR (cm⁻¹): ν = 3321 (NH), 1646 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 8.97 (br s, 1H, NH), 8.89 (s, 1H, H₄), 7.78 (d, ³J = 8.1 Hz, 1H, H₅), 6.88 (d, ³J = 8.4 Hz, 1H, H₆), 6.80 (s, 1H, H₈); ¹³C NMR (75 MHz, DMSO-d₆) δ: 163.1, 160.6, 155.7, 153.8, 139.4, 130.9, 114.4, 111.0, 110.8, 101.7. Anal. Calcd for C₁₀H₇N₅O₂: C, 52.40; H, 3.08; N, 30.56. Found C, 52.35; H, 3.05; N, 30.22.

4)2-(Tetrazol-5-yl)-3-imino-3H-naphtho[2,1-b]pyran (5d)

Yield = 73%. Reaction time = 4 h. Mp > 260˚C. IR (cm⁻¹): ν = 3262 (NH), 1636 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 9.51 (br s, 1H, NH), 8.91 (s, 1H, H₄), 8.72 (d, ³J = 9.0 Hz, 1H, H_5’/6’), 8.36 (d, ³J = 9.0 Hz, 1H, H₇), 8.13 (d, ³J = 9.0 Hz, 1H, H_5’/6’), 7.81 (t, ³J = 6.1 Hz, 1H, H_5”/6”), 7.72 (t, ³J = 3.0 Hz, 1H, H_5”/6”); 6.76 (d,³J = 9.0 Hz, 1H, H₈), ¹³C NMR (75 MHz, DMSO-d₆) δ: 154.0, 149.7, 139.9, 135.4, 129.9, 128.9, 126.5, 122.3, 120.9, 116.4, 113.3, 112.6, 111.2, 109.4. Anal. Calcd for C₁₄H₉N₅O: C, 63.87; H, 3.45; N, 26.61. Found C, 63.95; H, 3.41; N, 26.54.

5)3-(Tetrazol-5-yl)-2-iminocoumarin (5e)

Yield = 72%. Reaction time = 4 h. Mp > 260˚C. IR (cm⁻¹): ν = 3313 (NH), 1641 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 8.55 (br s, 1H, NH), 8.27 (s, 1H, H₄), 8.02 (dd, 1H, H₈), 7.76 (m, 1H, H₆), 7.55 (dd, 1H, H₅), 7.48 (m, 1H, H₇); ¹³C NMR (75 MHz, DMSO-d₆) δ: 153.5, 149.5, 144.2, 133.7, 129.8, 125.0, 120.8, 118.3, 112.3, 109.3. Anal. Calcd for C₁₀H₇N₅O: C, 56.34; H, 3.31; N, 32.85. Found C, 56.37; H, 3.29; N, 32.88.

6)7-Methoxy-3-(tetrazol-5-yl)-2-iminocoumarin (5f)

Yield = 84%. Reaction time = 6 h. Mp > 260˚C. IR (cm⁻¹): ν = 3311 (NH), 1640 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 8.99 (br s, 1H, NH), 8.52 (s, 1H, H₄), 7.93 (d, ³J = 9.0 Hz, 1H, H5), 7.05 (d, ³J = 6.0 Hz, 1H, H₆), 6.99 (s, 1H, H₈), 3.92 (s, 1H, OCH₃); ¹³C NMR (75 MHz, DMSO-d₆) δ: 164.3, 155.8, 149.7, 144.5, 131.15, 121.4, 111.9, 109.8, 108.2, 100.5, 56.2. Anal. Calcd for C₁₁H₉N₅O₂: C, 54.32; H, 3.73; N, 28.79. Found C, 54.41; H, 7.67; N, 28.82.

7)6,8-Dibromo-3-(tetrazol-5-yl)-2-iminocoumarin (5g)

Yield = 55%. Reaction time = 6 h. Mp > 260˚C. IR (cm⁻¹): ν = 3205 (NH), 1651 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 9.46 (br s, 1H, NH), 8.62 (s, 1H, H₄), 8.22 (s, 1H, H₇), 8.09 (s, 1H, H₅); ¹³C NMR (75 MHz, DMSO-d₆) δ: 160.4, 150, 146.4, 136.3, 135.3, 130.3, 129.6, 120.9, 115.9, 107.6. Anal. Calcd for C₁₀H₅N₅OBr₂: C, 32.34; H, 1.35; N, 18.87. Found C, 32.39; H, 1.30; N, 18.92.

8)8-Ethoxy-3-(tetrazol-5-yl)-2-iminocoumarin (5h)

Yield = 93%. Reaction time = 6 h. Mp > 260˚C. IR (cm⁻¹): ν = 3305 (NH), 1636 (C=N); ¹H NMR (300 MHz, DMSO-d₆) δ: 8.85 (br s, 1H, NH), 8.23 (s, 1H, H₄), 7.35 - 7.43 (m, 3H, H_Ar), 4.23 (q, ³J = 12.0 Hz, 2H, OCH₂), 1.43 (t, ³J = 12.0 Hz, 3H, CH₃); ¹³C NMR (75 MHz, DMSO-d₆) δ: 145.6, 144.5, 142.9, 125.1, 121.0, 120.8, 119.0, 116.6, 112.4, 109.5, 64.4, 14.4. Anal. Calcd for C₁₂H₁₁N₅O₂: C, 56.03; H, 4.31; N, 27.22. Found C, 55.98; H, 4.29; N, 27.29.

4.2. Cell Culture and Survival Assays

Caco2 (differentiated colorectal adenocarcinoma, Ref ECACC: 86010202), Huh-7D12 (differential hepatocellular carcinoma, Ref ECACC: 01042712), MDA-MB-231 (breast carcinoma, Ref ECACC: 92020424), HCT-116 (actively proliferating colorectal adenocarcinoma, Ref ECACC: 91091005), PC3 (prostate carcinoma, Ref ECACC: 90112714), NCI-H727 (lung carcinoma, Ref ECACC: 94060303) cell lines were obtained from the ECACC collection and HaCaT (keratinocyte from Cell Lines Service, Eppelheim, Germany). Cells were grown according to ECACC recommendations [23]. The toxicity test of the compounds on these cells was as follows: 2 × 10³ cells for HCT-116 cells or 4 × 10³ for the other cells were seeded in 96 multi well plates in triplicate and left for 24 h for attachment, spreading and growing. Then, cells were exposed for 48 h to increasing concentrations of the compounds, ranging from 0.1 to 25 mM in a final volume of 120 mL of culture medium. Cells were fixed in cooled ethanol-acetic acid solution (90:5 v/v), nuclei were stained with Hoechst 3342 (Sigma) and counted using automated imaging analysis (Cellomics Arrayscan VTI/HCS Reader, Thermo/Scientific). The IC₅₀ were graphically determined.

Funding

One of us (A.B.) wishes to thank the “Ministère de l’Enseignement Supérieur et de la Recherche de Tunisie” for the grant. Financial support of this program carried out under the French cancer Institute “Cancéropôle Grand Ouest” in network “Marin molecules, Metabolism and Cancer” contract, is gratefully acknowledged.

Acknowledgments

The authors are grateful to the assistance of the staff (N. Le Yondre, P. Jéhan, F. Lambert) of CRMPO analytical chemistry core facility for HRMS analysis (CRMPO platform ScanMAT UMS 2001 CNRS, Université de Rennes 1, Bat. 11A, Campus de Beaulieu, Rennes, France).

Supplementary Materials

Supplementary materials can be found at: https://www.researchgate.net/profile/Jean_Bazureau.

Conflicts of Interest

The authors declare no conflicts of interest regarding the publication of this paper.

Cite this paper

Bouattour, A., Fakhfakh, M., El-Gharbi, S.A., Abid , M., Paquin, L., Le Guevel, R., Charlier, T., Ammar, H. and Bazureau, J.-P. (2021) 3-(Tetrazol-5-yl)-2-imino-coumarins Derivatives: Synthesis, Characterization, and Evaluation on Tumor Cell Lines. International Journal of Organic Chemistry, 11, 24-34. https://doi.org/10.4236/ijoc.2021.111003

Abbreviations

FTIR: Fourier Transformed Infra Red

HRMS: High Resolution Mass Spectrometry

NMR: Nuclear Magnetic Resonance

UV: Ultra Violet

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