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1,2,4-Oxadiazole Moiety Molecules Synthesis for Cancer

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26/01/18 Chemistry Reference this

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2.4. Synthesis of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole derivatives for their MTT assay using MCF-7 breast cancer cell line and degradation of DNA in EAT cells

2.4.1. INTRODUCTION

In the biological and pharmacological importance, heterocycles plays a significance role. Oxadiazole molecules show biologically activity includes angiogenesis inhibitor [246] and also HIV inhibitor [247], tyrosine kinase inhibition [45], histamine H3 antagonism [48], muscarinic agonism [49], potent histamine H2 receptor antagonists [50, 51], muscarinic receptor antagonists [53, 54], interleukin-8 (IL-8) receptor antagonists [65], cytotoxic activities [68], monoamine oxidase inhibition [66], potent therapeutic agents for prostate cancer [72], anticonvulsant activity [67], tumor-selective and apoptosis-inducing agents [70, 71], antitumor [4f] and apoptosis-inducing anticancer agents [73, 74].

Breast cancer is a most terrifying disease in which cells in breast tissue grow and divide without normal control. This type of growth of cells without control forms a lump called tumor. In breast cancer, tumors are called benign or malignant. Malignant tumors will grow by eating food. They get the food by forming new blood vessels in a process called angiogenesis. These blood vessels are the main reason to promote the growth of the tumors. After this tumor growing it will spread to nearby tissue, which is called as invasion.

The breakage of main tumor cells will spread into other parts of the body and it will lead to metastatic breast cancer. This happens through blood stream or lymphatic system and this process is called metastasis. The main disadvantage of the malignant breast cancer is dividing and grows out of control which leads to form number of new tumors. If those new tumors are in other parts of the body, then also we call those as breast cancer.

Especially in women, breast cancer leading to the cause of cancer related death. In developing and developed countries, breast cancer is the second most common malignancy type diagnosed disease in women. In India breast cancer is the most discussing problem in the current health problem (248). By the survey conceded by the Indian Council of Medical Research (ICMR), the percentage of breast cancer patients has been nearly doubled. In the past few years nearly one lakh new patients are being detected from 1985 to 2001 (249, 250). It has been estimated that the breast cancer in 2004 is nearly 90,273 and they predicted that in 2015 the patient’s number may be nearly 1, 12,680 (251).

Due to the damage in DNA, normal cells will become cancer cells. DNA is present in every cell and it directs to all its actions. When DNA gets damaged in normal cells, the cell either repairs the damage or it dies. But in the cancer cells, damaged DNA is not repaired. The damaged cell undergoes splitting. As a result cell goes on making new cells that the body doesn’t need and those cells have same damaged DNA as the first cells does. This conjecture the design and synthesis of new anticancer drugs, and drug combination and treatment modalities is still the need for effective treatment of breast cancer patients [252].

1,2,4-Oxadiazole moiety molecules show signs of vide variety of biological activities [40, 253-255]. In connection to the above studies, our molecules are subjected to the angiogenesis using MCF-7 breast cancer cell lines and degradation of DNA studies using in EAT cells.

2.4.2. MATERIALS

Melting points were recorded (uncorrected) on a Buchi Melting Point B-545 instrument. Infrared (IR) spectra were recorded using a Jasco FTIR-4100 series. All reagents and solvents used were commercially procured and used as received. 1H-NMR spectra’s were recorded on Shimadzu AMX-400-Bruker with 400 MHz with TMS as internal standard. The 13C NMR spectra were examined on a Bruker DPX-400 at 100.6 MHz. The mass spectra were recorded on a JEOL JMS-AX505HA mass spectrometer.

2.4.3. EXPERIMENTAL

2.4.3.1. Chemistry

General procedure for synthesis of (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2).

A solution of hydroxylamine hydrochloride (1.529 g, 22.004 mmol) (2.5eq) and sodium carbonate (1.492 g, 14.082 mmol) (1.6eq) was taken in a round bottom flask. Stir for 10min to dissolve completely, then to this mixture 4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorobenzonitrile (1) (2.0 g, 8.801 mmol) (1.0 eq) is dissolved with ethanol was added. Then the mixture is heated to 60 0C about 5-6 hr. After that the steps forward of the reaction fusion was examined by the thin layer chromatography (TLC). After reaction completion, the solvent and the product was separated in vacuum pump under reduced pressure. Then the product was poured to water and extracted with ethyl ethanoate. The organic layer was washed 2-3 times with distilled water. The organic layer was washed 2-3 times with distilled water. The extracted ethyl ethanoate layer was dried over sodium sulphate (anhydrous) and the solvent was evaporated to get (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2).

2.4.3.2. Synthesis of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole 4(a-f) derivatives.

(Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2) (1.0 eq) is dissolved in dry dichloromethane and cooled to 0-5 0C in ice bath. Then N,N-diisopropylethylamine (1.1 eq) was added to cold reaction mixture and stirred for 10 minutes, then different aromatic acid chlorides (3a-e) (1 eq) were added. The reaction mixture was allowed to room temperature under stirring for 5-6 hr. After that the steps forward of the reaction fusion was examined by the thin layer chromatography (TLC). After reaction completion, the solvent and the product was separated in vacuum pump under reduced pressure. Then the product was poured to water and extracted with ethyl ethanoate. The organic layer was washed 2-3 times with distilled water. The organic layer was washed 2-3 times with distilled water. The extracted ethyl ethanoate layer was dried over sodium sulphate (anhydrous) and the product was purified with the help of column chromatography over silica gel (60-120 mesh) using hexane and ethyl acetate (1:1).

Scheme 1.

Reagents and conditions: (i) Sodium carbonate, water, ethanol, 60 0C, 6 h; (ii) dichloromethane, N,N-diisopropylethylamine, 0-5 0C, 6 h; 3(a-e) Where 3a = 4-chloro benzoyl chloride; 3b = 4-Fluoro benzoyl chloride; 3c = 4-(trifluoromethyl)benzoyl chloride; 3d = 4-Fluoro-3-Nitrobenzoyl chloride; 3e = 4-EthylPhenylbenzoyl chloride.

2.4.3.2.1. Synthesis of 5-(4-chlorophenyl)-3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-1,2,4-oxadiazole (4a)

Pale yellow color from (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2) (0.1 g, 0.384 mmol), 4-chlorobenzoylchloride (3a) (0.067 g, 0.384 mmol) and N,N-diisopropylethylamine (0.049 g, 0.461 mmol). 1H NMR (400 MHz, CDCl3): 8.32 (d, 1H, Ar-H), 7.75 (dd, 2H, Ar-H), 7.70, (d, 1H, imid-H), 7.55 (d, 1H, Ar-H), 7.50 (dd, 2H, Ar-H), 7.35 (d, 1H, imid-H), 7.30 (d, 1H, Ar-H), 5.05 (d, 1H, pyrrole-H), 2.56-2.30 (d, 4H, pyrrole-H); MS (ESI) m/z: 381.081 (100.0%), Anal. calcd. for C20H14ClFN4O (in %): C- 63.08, H- 3.71, N- 14.71.

2.4.3.2.2. Synthesis of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-(4-fluorophenyl)-1,2,4-oxadiazole (4b)

Orange color from (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2) (0.1 g, 0.384 mmol), 4-Fluoro benzoyl chloride (3b) (0.060 g, 0.384 mmol)and N,N-diisopropylethylamine (0.049 g, 0.461 mmol). 1H NMR (400 MHz, CDCl3): 8.31 (d, 1H, Ar-H), 7.30 (dd, 2H, Ar-H), 7.72, (d, 1H, imid-H), 7.56 (d, 1H, Ar-H), 7.34 (d, 1H, imid-H), 7.31 (d, 1H, Ar-H), 7.29 (dd, 2H, Ar-H), 5.02 (d, 1H, pyrrole-H), 2.58-2.31 (d, 4H, pyrrole-H); MS (ESI) m/z: 365.114 (100.0%), Anal. calcd. for C20H14F2N4O (in %): C- 65.93, H- 3.87, N- 15.38.

2.4.3.2.3. Synthesis of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-(4-(trifluoromethyl)phenyl)-1,2,4-oxadiazole (4c)

Dark brown color from (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2) (0.1 g, 0.384 mmol), 4-(trifluoromethyl)benzoyl chloride (3c) (0.080 g, 0.384 mmol) and N,N-diisopropylethylamine (0.049 g, 0.461 mmol). 1H NMR (400 MHz, CDCl3): 8.33 (d, 1H, Ar-H), 8.10 (dd, 2H, Ar-H), 7.74 (d, 1H, imid-H), 7.70 (dd, 2H, Ar-H), 7.58 (d, 1H, Ar-H), 7.37 (d, 1H, imid-H), 7.33 (d, 1H, Ar-H), 5.06 (d, 1H, pyrrole-H), 2.59-2.29 (d, 4H, pyrrole-H); MS (ESI) m/z: 415.110 (100.0%), Anal. calcd. for C21H14F4N4O (in %): C- 60.87, H- 3.41, N- 13.52.

2.4.3.2.4. Synthesis of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-(4-fluoro-3-nitrophenyl)-1,2,4-oxadiazole (4d)

Pale yellow color from (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2) (0.1 g, 0.384 mmol), 4-Fluoro-3-Nitrobenzoyl chloride (3d) (0.078 g, 0.384 mmol)and N,N-diisopropylethylamine (0.049 g, 0.461 mmol). 1H NMR (400 MHz, CDCl3): 8.71 (d, 1H, Ar-H), 8.65 (d, 1H, Ar-H), 8.34 (d, 1H, Ar-H), 7.74 (d, 1H, imid-H), 7.61 (dd, 1H, Ar-H), 7.58 (d, 1H, Ar-H), 7.37 (d, 1H, imid-H), 7.33 (d, 1H, Ar-H), 5.06 (d, 1H, pyrrole-H), 2.59-2.29 (d, 4H, pyrrole-H); MS (ESI) m/z: 410.099 (100.0%), Anal. calcd. for C20H13F2N5O3 (in %): C- 58.68, H- 3.20, N- 13.52.

2.4.3.2.5. Synthesis of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-(5-ethyl-[1,1′-biphenyl]-2-yl)-1,2,4-oxadiazole (4e).

White color from (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N‘-hydroxybenzimidamide (2) (0.1 g, 0.384 mmol), 4-EthylPhenylbenzoyl chloride (3e) (0.094 g, 0.384 mmol) and N,N-diisopropylethylamine (0.049 g, 0.461 mmol). 1H NMR (400 MHz, CDCl3): 8.31 (d, 1H, Ar-H), 7.95 (d, 1H, Ar-H), 7.80 (dd, 2H, Ar-H), 7.75 (d, 1H, Ar-H), 7.72, (d, 1H, imid-H), 7.53 (dd, 2H, Ar-H), 7.56 (d, 1H, Ar-H), 7.45 (d, 1H, Ar-H), 7.34 (d, 1H, imid-H), 7.30 (d, 1H, Ar-H), 7.31 (d, 1H, Ar-H), 5.03 (d, 1H, pyrrole-H), 2.65 (q, 2H, -CH2), 2.58-2.31 (d, 4H, pyrrole-H), 1.27 (t, 3H, -CH3),; MS (ESI) m/z: 451.186 (100.0%), Anal. calcd. for C28H23FN4O (in %): C- 74.65, H- 5.15, N- 12.44.

2.4.4. Biology

2.4.4.1. Culture of MCF-7 cells:

MCF-7 cells were cultured with minor modification in Minimal Essential medium (Invitrogen) supplemented with 10% fetal bovine serum, 100units/ml penicillin-G, 100 µg/ml streptomycin and 1% sodium bicarbonate (Invitrogen). MCF-7 cells were obtained from Cell repository unit of National Center for Cell Sciences (NCCS), Pune, India. All cell lines were maintained at 37°C in a humidified atmosphere with 5% CO2 [256].

2.4.4.2. Culture of EAT cells:

Animals, in vivo tumor generation and imidazole derivatives treatment Six to eight weeks old female mice were acclimated for one week while caged in-group of five. Mice were housed and fed a diet of animal chow and water ad libitum throughout the experiment. All the experiments were approved by the institutional animal care and use committee of the University of Mysore, Mysore, India. Ehrlich Ascites Tumor (EAT) cells (5×106 cells/mouse) were injected intraperitoneally. These cells grow in mouse peritoneum forming an ascites tumor with massive abdominal swelling. The animals showed a dramatic increase in body weight over the growth period and the animals succumbed to the tumor burden 14–16 days after implantation.

2.4.4.2.1. Isolation of EAT cells from mice peritoneal cavity and compound treatment: From the peritoneal cavity of tumor-bearing mice the EAT cells were isolated (control and treated). 2-3 mm of sterile PBS was injected in to the peritoneal cavity of the mice and the peritoneal fluid containing tumor cells withdrawn, collect in sterile petri dishes and incubated at 370C for 2 h. The cells of macrophage linage adhered to the bottom of Petri dishes. The non-adherent population was aspirated out gently and washed repeatedly with PBS. Moreover, viability of these cells was assessed and was found to be >95% by trypan blue dye exclusion. The viable EAT cells were processed for further experiments. The EAT cells (5 x 106) were treated with or without compounds of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole series 4(a-e) and incubated at 370 C for different time interval or for known period of time. After the incubation period the cells were used for the further analysis [258].

2.4.4.2.2. Cell count by Trypan blue dye exclusion assay.

EAT cells were treated with different concentrations of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole compounds 4(a-e) at various time periods (0–4 h). Cell viability was assessed by mixing aliquots of cell suspension with 0.4% trypan blue and counted using heamocytometer. Cells that picked up the dye were considered to be dead [259(a)].

2.4.5. Result and Discussion

2.4.5.1. Chemistry

Synthesis of the key intermediate (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N’-hydroxybenzimidamide (2) is outlined in Scheme 1. Briefly, hydroxylamine hydrochloride and sodium carbonate was taken in water and stirred. 4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorobenzonitrile (1) was dissolved in ethanol and added to the reaction mixture. The presence of –NH2 and =N-OH proton peaks NMR spectra indicates the formation of (Z)-4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluoro-N’-hydroxybenzimidamide (2). The key intermediate compound (2) was taken in dry dichloromethane and cooled to 0-5 0C, and N,N-diisopropylethylamine was added. Stirred for 10 min, then different aromatic acid chlorides 3(a-e) was added drop by drop. The reaction mixture was allowed to room temperature under stirring for 5-6 h and after that the steps forward of the reaction fusion was examined by the thin layer chromatography (TLC). After reaction completion, the solvent and the product was separated in vacuum pump under reduced pressure. Then the product was poured to water and extracted with ethyl ethanoate. The organic layer was washed 2-3 times with distilled water to get target 3-(4-(3-(1H-imidazol-5-yl)propyl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole 4(a-e). Upon completion crude products 4(a-e) were obtained with a good yield of 81–93% and which the product was purified with the help of column chromatography over silica gel (60-120 mesh) using hexane and ethyl acetate (1:1). The absence of –CO proton peak in synthesized derivatives in 1H spectra confirmed the identity of the products. The details of chemical structures, physical data and purity of compounds are given in Table 1.

Compound

R1

Yield

MP (oC)

Purity

4a

90

277

90

4b

85

100

93

4c

81

110

89

4d

82

142

92

4e

79

95

81

Table 1. Chemical structures, physical data and purity of compounds 4(a–e)

2.4.5.2. Biology

2.4.5.2.1. MTT assay:

The MTT assay was performed according to the protocol previously reported [257]. MCF-7 cells were plated at a density of 1 X 105 cells in 96-well plates. (Subsequently, the 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole series 4(a-e) were assayed using concentrations from 0.05 to 0.5 mM). After 24 h of incubation, 10 µL of 5% 3-(4,5- dimethylthiazol-2-yl)-2,5-diphenyl tetrazolium bromide (MTT) (Sigma Aldrich) (0.05 mg/mL) were added to the culture medium. After 4 h at 370C the culture medium was removed and 200 µL of DMSO were added to dissolve the salts of formazan. The absorbance was measured with a 96-wells plate spectrophotometer at 570 nm. The experiments were independently performed three times and each experiment contained triple replicates. Control samples containing a complete culture medium devoid of cells or control cells with 0.1% DMSO were also included in each experiment.

Figure 1. The MTT assay of compounds 4(a-e) in MCF-7 breast cancer cell lines.

Sl.No.

Name of the compound

IC50 Value

1

Cisplatin

10μg

2

4a

100ug

3

4b

200ug

4

4c

100ug

5

4d

800ug

6

4e

200ug

Table 2. Compounds 4(a-e) and their IC50 value (µg/ml) on MCF-7 breast cancer cell lines.

2.4.5.3. DNA fragmentation assay:

EAT cells were collected from mice treated with or without 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazole series 4(a-e). Thein vivo and DNA was isolated using the phenol–chloroform method. In brief, cells were lysed in a buffer containing 50mM Tris–HCl, pH 8.0, and 0.5% SDS, and incubated for 30min at 37°C. The cell lysate was subjected to 8M potassium acetate precipitation and left for 1h at 4°C. The supernatant was subjected to phenol/chloroform/isoamyl alcohol (25:24:1) extraction and once to chloroform extraction. DNA was precipitated by adding 1:2 volumes of ice-cold ethanol. The precipitated DNA was dissolved in 50μL TE buffer (pH 8.0). The DNA was digested with 20μg/mL RNase at 37°C for 1h. The DNA was quantitated and equal concentration of DNA (25μg) was resolved on 1.5% agarose gel, viewed under UV light, and documented using BIORAD gel documentation system Figure 2 [259(b)].

Figure 2. The DNA degradation of compounds 4(a-e) in Ehrlich Ascites Tumor (EAT) cells.

Conclusion:

A series of 3-(4-(6,7-dihydro-5H-pyrrolo[1,2-c]imidazol-5-yl)-3-fluorophenyl)-5-substituted-1,2,4-oxadiazoles 4(a-e) has been synthesized by using simple synthetic procedures and were screened for their MTT assay using MCF-7 breast cancer cell line and degradation of DNA in Ehrlich Ascites Tumor (EAT) cells activity. All the final compounds exhibited good in all the in-vitro activity.

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