molecules Molecules Molecules Molecules 1420-3049 MDPI 10.3390/molecules17044717 molecules-17-04717 Article Synthesis, Molecular Docking and Preliminary in-Vitro Cytotoxic Evaluation of Some Substituted Tetrahydro-naphthalene (2',3',4',6'-Tetra-O-Acetyl-β-D-Gluco/-Galactopyranosyl) Derivatives Al-Mutairi Maha S. 1 Al-Abdullah Ebtehal S. 1 Haiba Mogedda E. 1 2 Khedr Mohammed A. 3 Zaghary Wafaa A. 1 3 * Department of Pharmaceutical Chemistry, Faculty of Pharmacy, King Saud University, Riyadh 11451, Saudi Arabia Department of Medicinal Chemistry, National Research Center, Dokki, Cairo 12622, Egypt Department of Pharmaceutical Chemistry, Faculty of Pharmacy, Helwan University, Ain Helwan, Cairo 11795, Egypt Author to whom correspondence should be addressed; Email: wzaghary@ksu.edu.sa; Tel.: +966-1-291-4843; Fax: +966-1-206-4501. 23 04 2012 04 2012 17 4 4717 4732 14 02 2012 09 04 2012 13 04 2012 © 2012 by the authors; licensee MDPI, Basel, Switzerland. 2012

This article is an open-access article distributed under the terms and conditions of the Creative Commons Attribution license (http://creativecommons.org/licenses/by/3.0/).

A facile, convenient and high yielding synthesis of novel S-glycosides and N-glycosides incorporating 1,2,3,4-tetrahydronaphthalene and or 1,2-dihydropyridines moieties has been described. The aglycons 2, 4, and 7 were coupled with different activated halosugars in the presence of basic and acidic medium. The preliminary in-vitro cytotoxic evaluation revealed that compounds 3c, 3f, 5c and 7b show promising activity. A molecular docking study was performed against tyrosine kinase (TK) (PDB code: 1t46) by Autodock Vina. The docking output was analyzed and some compounds have shown hydrogen bond (H-B) formation with reasonable distances ranged from 2.06 A° to 3.06 A° with Thr 670 and Cys 673 residues found in the specified pocket. No hydrogen bond was observed with either Glu 640 nor Asp 810 residues, as was expected from pdbsum.

 tetrahydronaphthalene pyridine glycoside cytotoxic molecular docking 1. Introduction

Tetrahydronaphthalene derivatives have attracted significant attention in the field of drug discovery because of their wide array of pharmacological activities, including action as non-steroidal glucocorticoid receptor modulators, anticancer, analgesic, anti-inflammatory, antimicrobial, antiplatelet aggregation, hypotensive, antiarrhythmic and anti-HIV effects [1,2,3,4,5,6,7,8,9,10,11]. Additionally, pyridine analogs are very important class of heterocyclic compounds that have remarkable pharmacological activities as PDE4 inhibitors, analgesic, antifungal, antimalarial, anti-inflammatory, antibacterial, anti-HIV, antitumor and antiviral properties [12,13,14,15,16,17].

On the other hand recent advances have implicated the role of tyrosine kinases (TK) in the physiology of cancer. Though their activity is tightly regulated in normal cells, they may acquire transforming functions due to mutation(s), over expression leading to malignancy [18,19]. The activation of cancer cells can be blocked by selective tyrosine kinase inhibitors and thus considered to be a promising target for anticancer drug discovery. Tyrosine kinases are important mediators of the signal transduction process, leading to cell proliferation, differentiation, migration, metabolism and apoptosis. Tyrosine kinases are a family of enzymes, which catalyzes phosphorylation of select tyrosine residues in target proteins, using ATP. They are implicated in several steps of neoplastic development and progression. Tyrosine kinase signaling pathways normally prevent deregulated proliferation or contribute to sensitivity towards apoptotic stimuli. These signaling pathways are often genetically or epigenetically altered in cancer cells to impart a selection advantage to the cancer cells [20,21,22].

Regarding the above mentioned findings and our previous reports [23] and [24], the main goal of the present work was to design, synthesize and investigate the anticancer activity of some novel pyridine-tetrahydronaphthalene derivatives carrying carbohydrate residues attached through S-glycosidic or N-glycosidic bond formation. A molecular docking study was performed in order to interpret the activity expressed by compounds 3c, 3f, 5b, 5c, 7a and 7b.

 2. Results and Discussion 2.1. Chemistry

A series of S-glycosides and N-glycosides was designed in such a way that they incorporate a tetrahydronaphthalene derivative attached to a glycosyl moiety through a S-linkage or N-linkage. Synthesis of our desired compounds was achieved by allowing the acetyl derivative 1-(1,2,3,4-tetrahydronaphthaline-6-yl)ethanone (1) to react directly with the appropriate aromatic aldehyde and cyanothioacetamide in the presence of ammonium acetate, to afford the corresponding 2-thioxo(1H)pyridines 2a–c, respectively (Scheme 1, Table 1). The coupling between the aglycon and the activated cyclic sugars (2',3',4',6'-O-acetyl-α-D-gluco- (or galato-) pyranosyl bromide was achieved in a basic medium to give the corresponding thioglycoside derivatives 3a–f in a good yields, respectively (Scheme 1, Table 1). The structures of thioglycosides 3a–f were established and confirmed on the basis of their elemental analysis and spectral data (IR, 1H-NMR, 13C-NMR and MS, cf. Experimental).

molecules-17-04717-f001_Scheme 1

Synthetic pathways to compounds 2a–c, 3a–f, 4a,b and 5a–d.

 molecules-17-04717-t001_Table 1

Physicochemical properties of the newly synthesized compounds 2a, 3a–f, 5a–d, 7a, 7b, 8a and 8b.

Comp No. Ar R1 R2 MP (°C) Cryst.Solv. Yield % Molecular Formula (Mol. Wt.)
2a -C4H3O --- --- 245–247 Ethanol/H2O 80 C20H16N2OS (332)
3a -C4H3O H OAc 194–196 Ethanol/H2O 76 C34H34N2O10S (662)
3b 4-NO2-C6H5 H OAc 172–174 Ethanol/H2O 75 C36H35N3O11S (717)
3c 3-EtO,4-OH-C6H4 H OAc 118–120 Ethanol/H2O 68 C38H40N2O11S (732)
3d -C4H3O OAc H 215–217 Ethanol/H2O 75 C34H34N2O10S (662)
3e 4-NO2-C6H5 OAc H 140–142 Ethanol/H2O 76 C36H35N3O11S (717)
3f 3-EtO-4-OH-C6H4 OAc H 175–177 Ethanol/H2O 79 C38H40N2O11S (732)
5a 2,6-Cl2-C6H4 H OAc 192–194 Ethanol/H2O 65 C36H35Cl2N3O9 (724)
5b 2,6-Cl2-C6H4 OAc H 205–207 Ethanol/H2O 70 C36H35Cl2N3O9 (724)
5c 2,6-F2-C6H4 H OAc 107–109 Ethanol/H2O 66 C36H35F2N3O9 (691)
5d 2,6-F2-C6H4 OAc H 132–134 Ethanol/H2O 72 C36H35F2N3O9 (691)
7a 2,6-Cl2-C6H4 --- --- 180–182 Ethanol/H2O 95 C22H18Cl2N2O2 (413)
7b 2,6-F2-C6H4 --- --- 170–172 Ethanol/H2O 92 C22H18F2N2O2 (380)
8a 2,6-Cl2-C6H4 OAc H 230–232 Ethanol/H2O 86 C36H36Cl2N2O11 (743)
8b 2,6-F2-C6H4 OAc H 155–157 Ethanol/H2O 85 C36H36F2N2O11 (710)

Also, one-step synthesis of 2-imino (1H)pyridines 4a,b was accomplished by heating the acetyl derivative 1 with malononitrile and the appropriate aldehyde in the presence of ammonium acetate (Scheme 1, Table 1). The authors used these intermediate aglycones for the preparation of the new glycosides 5a–d (Scheme 1, Table 1). The formation of N-glycosides 5a–d was proven using spectral data (IR, 1H-NMR, 13C-NMR and MS).

On the other hand, the one pot reaction of compound 1 with the appropriate aromatic aldehyde and ethyl cyanoacetate in the presence of ammonium acetate, afforded the corresponding pyridones 6a,b, respectively (Scheme 2, Table 1). Hydrolysis of 6a,b in the presence of conc. sulphuric acid afforded the amide derivatives 7a,b in good yield. Finally the coupling between the aglycons 7a,b and the activated cyclic sugar 2',3',4',6'-tetra-O-α-D-galactopyranosyl bromide gave the corresponding N-glycosides 8a,b in a good yield respectively. The structures of N-glycosides 8a,b were established and confirmed for the reaction products on the basis of their spectral data.

molecules-17-04717-f002_Scheme 2

Synthetic pathways to compounds 6a,b, 7a,b and 8a,b.

 2.2. Molecular Modeling Study Docking Using Autodock Vina

The tyrosine kinase (TK) crystal structure (PBD code = 1t46) was downloaded (Figure 1). In order to find the important residues that form interactions with that inhibitor, the pdbsum server was used. It was found that Cys 673, Thr 670, Glu 640 and Asp 810 formed some interactions with different moieties of the inhibitor (Figure 2).

Showing the active site at which the inhibitor complexed.

A representation image simulating the interactions that was found in pdbsum, showing the most visible interactions that were formed with the complexed ligand.

The affinity of any small molecule can be considered to be a unique tool in the field of drug design, as there is a relationship between the affinity of organic molecules and the free binding energy and this can contribute in prediction and interpretation of the activity of organic compounds toward a specific target protein. Here we used the Autodock Vina [25,26] program for docking and to obtain the affinities and RMSD (root mean square deviation) of all compounds.

The most visible feature that was observed in the docking output that all compounds fitted well inside the same docking site and hence, the next step was to compare their affinities and try to rank them as observed in the previous table and then to measure the ligands’ interaction to find out which ones interact well and correlate that to the activity.

The six compounds with the highest calculated affinities were found to be compounds 7b, 3f, 5c, 5b, 3c and 7a, respectively (−11.6, −11.4, −11.2, −11.0, −10.7 and −10.3 Kcal/mol). Compounds 3c and 7b were found to have low RMSD values that reflect their better fit as they were expected to have a conformation with a low deviation from the expected best binding mode. No clear correlation between the biological activity and the calculated affinity was observed. The only observation that was found that the active compounds have the best affinities regardless of their ranking in activity.

Regarding the best mode of interaction for each compound of these six compounds, the docking output was visualized to determine these interactions. It was important to concentrate on the previously mentioned residues (Cys 673, Thr 670, Glu 640 and Asp 810) whether they were involved in these interactions or not. For compound 3c THR 670 (Figure 3) was the major residue for making hydrogen bond with one of the acetyl groups found in the side chains of this compound.

Compound 3c showing hydrogen bond with Thr 670 with the -CH3CO of the compound.

Compound 3f shows two hydrogen bonds with Thr 670 and Cys 673 (Figure 4). Compounds 5c, 5b, and 7b have shown the same hydrogen bond with the previously mentioned residues as well (Thr 670, and Cys 673), as shown in Figure 5, Figure 6, Figure 7.

Compound 3f hydrogen bond formation with Thr 670 and Cys 673.

Compound 5c hydrogen bond formation with Thr 670 and Cys 673.

Compound 5b hydrogen bond formation with Thr 670 and Cys 673.

Compound 7b hydrogen bond formation with Cys 673.

 2.3. <italic>In Vitro</italic> Cytotoxic Screening

Some of the newly synthesized compounds were tested at the Department of Tumor Pathology, National Cancer Institute, Cairo, Egypt. Ehrlich Ascites Carcinoma (EAC) cells were used for cytotoxic activity screening. The selected synthesized analogues 2b, 3a–f, 5b, 5c, 7a and 7b were tested for in vitro cytotoxic activity at two different concentrations. The results (Table 2) are expressed in the form of the percentage of non-viable cells [27]. The in vitro evaluation revealed that 3c, 3f, 5c and 7b show promising activity. This provides a new class of antitumor agents for further biological evaluation.

molecules-17-04717-t002_Table 2

The effect of the tested compounds on the viability of tumor cell in vitro. The calculated affinities and RMSD for some of the newly synthesized compounds.

Compound Anticancer effect % inhibition of cell viability Affinity Kcal/mol RMSD Deviation from best mode
100 µg/mL 50 µg/mL
2b 0 0 −9.5 7.07
3a 0 0 −8.3 9.5
3b 0 0 −7.7 11.6
3c 70% 50% −10.7 4.02
3d 0 0 −6.6 10.3
3e 0 0 −7.4 9.2
3f 10% 0 −11.4 9.0
5b 0 0 −11.0 9.3
5c 40% 7% −11.2 9.5
7a 0 0 −10.3 7.2
7b 20% 15% −11.6 4.6
3. Experimental 3.1. Chemistry 3.1.1. General

Melting points (°C, uncorrected) were determined in open glass capillaries using a Barnstead 9001 Electrothermal melting point apparatus. Infrared (IR) spectra were recorded on a Perkin Elmer FT-IR Spectrum BX Spectrometer at cm−1 scale using KBr discs. 1H-NMR and 13C-NMR were recorded on a JEOL 300 MHz Spectrometer; chemical shifts are expressed in δ (ppm) with reference to TMS. The mass spectra were run at 70 ev with Packard 5890 Thewlett GC/MS Spectrometer, using the Electron Ionization (EI) technique. Elemental analyses (C, H, N) were carried out at the Microanalytical Data Center, Faculty of Science, Cairo, Egypt, and were in full agreement with the proposed structures within ±0.4% of the theoretical values. Thin layer chromatography was performed on precoated (0.75 mm) silica gel GF254 plates (E. Merck, Germany). Visualization was performed by illumination with UV light source (254 nm). Compounds 2b, 2c, 4a, 4b, 6a and 6b were prepared using the previously published procedures [10] and [11] as described below (Scheme 1 and Scheme 2).

 3.1.2. Synthesis of <italic>4-Aryl-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-thioxo-1,2-dihydropyridine-3-carbonitriles</italic> <bold>2a–c</bold>

A mixture of 6-acetyltetraline 1 (0.3 g, 0.0017 mol), 2-cyanothioacetamide (0.17 g, 0.0017 mol), the an appropriate aromatic aldehyde, namely 2-furfural, p-nitrobenzaldehyde, and/or 3-ethoxy-4-hydroxybenzaldehyde (0.00172 mol) and excess ammonium acetate (1.05 g, 0.0137 mol) was gently refluxed in absolute ethanol (15 mL) for 3–8 h. On cooling, the separated solid was filtered off, washed successively with water, and then with ether and recrystallized with aqueous ethanol to give 2a–c respectively (Table 1).

4-(Furan-2-yl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-thioxo)-1,2-dihydropyridine-3-carbonitrile (2a). IR: (υ, cm−1) 3,300 (NH), 2,200 (CN) and 1,206 (C-O). 1H-NMR (DMSO-d6): δ 1.76 (m, 4H, -CH2-CH2-), 2.78 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 6.89–8.61 (m, 7H, aromatic protons & pyridine-H) and 13.9 (NH). 13C-NMR (DMSO-d6): δ 22.9 (-CH2-CH2-), 29.2 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 114.2 (CN), 106.2, 107.6, 117.7, 117.9, 125.66, 128.7, 129.3, 129.8, 137.8, 141.5, 142.1, 147.5, 148.3, 152.6, 180.4 (Ar-C), MS, m/z (%): (M+, 332, 0.05%).

 3.1.3. Synthesis of <italic>4-Aryl-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-<sc>D</sc>-gluco and galactopyranosyl thio)pyridine-3-carbonitriles</italic> <bold>3a–f</bold>

A mixture of 2a–c (0.01 mol) in ethanol (10 mL) and potassium hydroxide (0.56 g, 0.01 mol) in distilled water (6 mL) was added to a solution of 2,3,4,6-tetra-O-acetyl-α-D-gluco- or galactopyranosyl bromide (4.10 g, 0.01 mol) in acetone (30 mL). The reaction mixture was stirred at room temperature until completion (TLC) 20–24 h. and then the solution was evaporated and poured onto ice/cold water. The formed solid product was collected by filtration. The residue was washed with distilled water to remove the formed potassium bromide. The resulting solid product was dried and crystallized from dilute ethanol (Table 1).

4-(Furan-2-yl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosylthio)pyridine-3-carbonitrile (3a). IR: (υ, cm−1) 2937 (CH, alkane), 2,216 (CN), 1,748 (C=O) and 1,230 (C-O). 1H-NMR (DMSO-d6): δ 1.78 (m, 4H, -CH2-CH2-), 2.02–2.03 (4s, 12H, 4 × CH3CO), 2.88 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 4.02–4.06 (m, 2H, 6'-H2) 4.31 (m, 1H, 5'-H), 5.03 (t, 1H, 4'-H) 5.26 (t, 1H, 3'-H), 5.71 (t, 1H, 2'-H), 6.24 (d, 1H, 1'-H) and 6.84–8.13 (m, 7H, aromatic protons and pyridine-H). 13C-NMR (DMSO-d6): δ 22.9 (-CH2-CH2-), 29.2 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 115.7 (CN), 62.29 (CH2, C-6'), 68.20 (C-4'), 69.76 (C-2'), 73.1 (C-3'), 75.17 (C-5'), 83.90 (C-1'), 106–180 (Ar-C) and 169.5–170.3 (4 × CO). MS, m/z (%): (M+, 662, 0.03%).

4-(4-Nitrophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosylthio)pyridine-3-carbonitrile (3b). IR: (υ, cm−1) 2,930 (CH, alkane), 2,217 (CN), 1,752 (C=O) and 1,348 & 1,528 (NO2). 1H-NMR (DMSO-d6): δ 1.75 (m, 4H, -CH2-CH2-), 2.04 (4s, 12H, 4 × CH3CO), 2.76 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 4.04–4.06 (m, 2H, 6'-H2) 4.35 (m, 1H, 5'-H), 5.05 (t, 1H, 4'-H) 5.24 (t, 1H, 3'-H), 5.74 (t, 1H, 2'-H), 6.31 (d, 1H, 1'-H) and 7.1–8.4 (m, 8H, aromatic protons and pyridine-H). 13C-NMR (DMSO-d6): δ 22.18 (-CH2-CH2-), 19.62–19.90 (4 × -COCH3), 28.65 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 61.5 (CH2, C-6'), 67.2 (C-4'), 69.5 (C-2'), 72.9 (C-3'), 74.6 (C-5'), 79.6 (C-1'), 115.46 (CN), 102–147 (Ar-C), 169.5 (4 × CO).MS, m/z (%): (M+, 717, 1.34%).

4-(3-Ethoxy-4-hydroxyphenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosyl thio)pyridine-3-carbonitrile (3c). IR: (υ, cm−1) 3,458 (OH), 2,937 (CH, alkane), 2,216 (CN), 1,754 (C=O) and 1,125 (C-O). 1H-NMR (DMSO-d6): δ 1.36 (t, 3H, OCH2CH3), 1.78 (m, 4H, -CH2-CH2-), 1.9–2.03 (4s, 12H, 4 × CH3CO), 2.87 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 4.01–4.35 (m, 5H, 6'-H2, 5'-H & OCH2CH3), 4.9 (t, 1H, 4'-H) 5.2 (t, 1H, 3'-H), 5.7 (t, 1H, 2'-H), 6.29 (d, 1H, 1'-H) 6.94–8.1 (m, 7H, aromatic protons & pyridine-H) and 9.6 (OH). 13C-NMR (DMSO-d6): δ 14.49 (-OCH2CH3), 20.28 (4 × -COCH3), 22.49 (-CH2-CH2-), 28.63 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 61.54 (CH2, C-6'), 63.89 (-O-CH2-CH3), 67.52 (C-4'), 69.50 (C-2'), 72.89 (C-3'), 74.63 (C-5'), 79.60 (C-1'), 115.75 (CN), 113–158 (Ar-C) and 169.45 (4 × CO). MS, m/z (%): (M+, 732, 12.15%).

4-(Furan-2-yl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl thio)pyridine-3-carbonitrile (3d). IR: (υ, cm−1) 2,936 (CH, alkane), 2,216 (CN), 1,754 (C=O) and 1,239 (C-O). 1H-NMR (DMSO-d6) δ 1.78 (m, 4H, -CH2-CH2-), 1.96–2.14 (4s, 12H, 4 × CH3CO), 2.88 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 3.95 (m, 2H, 6'-H2), 4.10 (m, 1H, 5'-H), 4.53 (t, 1H, 4'-H) 5.25 (t, 1H, 3'-H), 5.41 (t, 1H, 2'-H), 6.22 (d, 1H, 1'-H), 6.8–8.1 (m, 7H, aromatic protons and pyridine-H). 13C-NMR (DMSO-d6): δ 22.9 (-CH2-CH2-), 29.2 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 115.7 (CN), 61.70 (CH2, C-6'), 67.74 (C-4'), 69.45 (C-2'), 72.64 (C-3'), 74.97 (C-5'), 84.74 (C-1'), 106–180 (Ar-C) and 169.03–169.87 (4 × CO). MS, m/z (%): (M+, 662, 0.71%).

4-(4-Nitrophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl thio)pyridine-3-carbonitrile (3e). IR: (υ, cm−1) 2,932 (CH, alkane), 2,217 (CN), 1751 (C=O) and 1,348 & 1,528 (NO2). 1H-NMR (DMSO-d6): δ 1.76 (m, 4H, -CH2-CH2-), 1.97–2.14 (4s, 12H, 4 × CH3CO), 2.77 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 3.94 (m, 2H, 6'-H2), 4.08 (m, 1H, 5'-H), 4.55 (t, 1H, 4'-H) 5.30 (t, 1H, 3'-H), 5.40 (t, 1H, 2'-H), 6.25 (d, 1H, 1'-H) and 7.21–8.43 (m, 8H, aromatic protons and pyridine-H). 13C-NMR (DMSO-d6): δ 22.2 (-CH2-CH2-), 19.6–19.9 (4 × -COCH3), 28.82 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 61.28 (CH2, C-6'), 65.23 (C-4'), 66.67 (C-2'), 71.34 (C-3'), 74.46 (C-5'), 80.75 (C-1'), 115.46 (CN), 102–147 (Ar-C), 169.56–169.70 (4 × -CO of COCH3 groups). MS, m/z (%): (M+ −1,716, 8.9%).

4-(3-Ethoxy-4-hydroxyphenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl thio)pyridine-3-carbonitrile (3f). IR: (υ, cm−1) 3,458 (OH), 2,217 (CN), 1,752 (C=O) and 1,056 (C-O). 1H-NMR (DMSO-d6): δ 1.39 (t, 3H, OCH2CH3), 1.80 (m, 4H, -CH2-CH2-), 1.96–2.06 (4s, 12H, 4 × CH3CO), 2.79 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 4.08 (m, 2H, 6'-H2) 4.11 (m, 1H, 5'-H), 4.13 (t, 2H, -OCH2CH3) 4.5 (t, 1H, 4'-H) 5.26–5.65 (t, 2H, 3'-H & 2'-H), 6.25 (d, 1H, 1'-H) and 6.98–8.08 (m, 7H, aromatic protons and pyridine-H). 13C-NMR (DMSO-d6): δ 13.96 (-OCH2CH3) 19.62–19.85 (4 × -COCH3), 22.17 (-CH2-CH2-), 28.81 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 61.25 (CH2, C-6'), 64.06 (-O-CH2-CH3), 65.27 (C-4'), 66.73 (C-2'), 71.40(C-3'), 74.34 (C-5'), 80.69 (C-1'), 115.6 (CN), 110–147 (Ar-C) and 168.56–169.52 (4 × CO). MS, m/z (%): (M+, 732, 6.9%).

 3.1.4. Synthesis of <italic>4-Aryl-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-<sc>D</sc>-gluco and galactopyranosyl imino)pyridine-3-carbonitriles</italic> <bold>5a–d</bold>

To a solution of 4a and/or 4b (0.001 mol) in acetone (10 mL), 2,3,4,6-tetra-O-acetyl-α-D-gluco- or galactopyranosyl bromide (4.10 g, 0.01 mol) was added. A few drops of acetic acid were added and the reaction mixture was heated with stirring on a water bath at 40–50 °C for 25 h. The reaction mixture was cooled and then poured onto ice water. The formed precipitate was washed for several times with water and recrystallized from aqueous ethanol (Table 1).

4-(2,6-Dichlorophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-gluco-pyranosyl imino)pyridine-3-carbonitrile (5a). IR: (υ, cm−1) 3,450 (NH), 2,990 (CH2), 2,216 (CN), 1,750 (C=O). 1H-NMR (DMSO-d6): δ 1.79 (m, 4H, tetrahydronaphthalene CH2), 1.98–2.29 (4s, 12H, 4 × CH3CO) 2.81 (m, 4H, tetrahydronaphthalene CH2), 4.09 (s, 2H, 6'-H), 4.54 (m, 1H, 5'-H), 4.64 (m, 2H, 4'-H, 3'-H), 5.46 (t, 1H, 2'-H), 5.95 (d, 1H, 1'H), 7.14–7.84 (m, 7H, Ar-H and pyridine-H). 13C-NMR (DMSO-d6): 20.65–20.87 (4 × -COCH3), δ 22.2 (-CH2-CH2-), 28.7 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 61.9 (CH2, C-6'), 68.4 (C-4'), 68.8 (C-2'), 73.9 (C-3'), 75.25 (C-5'), 81.9 (C-1'), 115 (CN), 106–176 (Ar-C & pyridine-C), 169.5–170.3 (4 × CO). MS, m/z (%): (M+ +1, 725, 4.47%).

4-(2,6-Dichlorophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl imino)pyridine-3-carbonitrile (5b). IR: (υ, cm−1) 3,360 (NH), 2,929 (CH2), 2,212 (CN), 1,737 (C=O). 1H-NMR (DMSO-d6): δ 1.74 (m, 4H, tetrahydronaphthalene CH2), 2–2.01 (4s, 12H, 4 × CH3CO) 2.76 (m, 4H, tetrahydronaphthalene CH2), 4.01–4.06 (s, 2H, 6'-H), 4.51 (m, 1H, 5'-H), 4.71 (t, 1H, 4'), 5.47 (t, 1H, 3'-H), 5.62 (t, 1H, 2'-H), 6.53 (d, 1H, 1'H), 7.14–7.84 (m, 7H, Ar-H and pyridine-H). 13C-NMR (DMSO-d6): 20.69–19.89 (4 × -COCH3), 22.17 (-CH2-CH2-), 28.81 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 61.94 (CH2, C-6'), 66.22 (C-4'), 68.01 (C-2'), 71.73(C-3'), 74.33 (C-5'), 82.28 (C-1'), 115.6 (CN), 111–180 (Ar-C & pyridine C) and 169.56–170.33(4 × CO).MS, m/z (%): (M+ +1, 725, 3%).

4-(2,6-Difluorophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-glucopyranosyl imino)pyridine-3-carbonitrile (5c).IR: (υ, cm−1) 3,359 (NH), 2,932 (CH2), 2,214 (CN), 1,750 (C=O). 1H-NMR (DMSO-d6): δ 1.75 (m, 4H, tetrahydronaphthalene CH2), 2–2.02 (4s, 12H, 4 × CH3CO) 2.77 (m, 4H, tetrahydronaphthalene CH2), 4.02 (s, 2H, 6'-H), 4.18 (m, 1H, 5'-H), 4.70 (t, 1H, 4'), 4.92 (t, 1H, 3'-H), 5.25 (t, 1H, 2'-H), 6.62 (d, 1H, 1'H), 7.15–8.55 (m, 7H, Ar-H and pyridine-H). MS, m/z (%):13C-NMR (DMSO-d6): 20.65–20.87 (4 × -COCH3), δ 22.4 (-CH2-CH2-), 28.91 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 61.9 (CH2, C-6'), 68.4 (C-4'), 68.8 (C-2'), 73.9 (C-3'), 75.25 (C-5'), 81.9 (C-1'), 115.8 (CN), 111.52–174.1 (Ar-C and pyridine-C), 169.5–170.3 (4 × CO). MS, m/z (%): (M+, 691, 16%).

4-(2,6-Difluorophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl imino)pyridine-3-carbonitrile (5d). IR: (υ, cm−1) 3,430 (NH), 2,990 (CH2), 2,217 (CN), 1,750 (C=O). 1H-NMR (DMSO-d6): δ 1.75 (m, 4H, tetrahydronaphthalene CH2), 1.99–2.01 (4s, 12H, 4 × CH3CO) 2.76 (m, 4H, tetrahydronaphthalene CH2), 4.05 (s, 2H, 6'-H), 4.2 (m, 1H, 5'-H), 4.68 (t, 1H, 4'), 4.95 (t, 1H, 3'-H), 5.37 (t, 1H, 2'-H), 6.65 (d, 1H, 1'H), 7.15–9.54 (m, 7H, Ar-H and pyridine-H). 13C-NMR (DMSO-d6): 20.69–19.89 (4 × -COCH3), 22.17 (-CH2-CH2-), 28.81 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 61.94 (CH2, C-6'), 66.22 (C-4'), 68.01 (C-2'), 71.73(C-3'), 74.33 (C-5'), 82.28 (C-1'), 115 (CN), 111–176 (Ar-C and pyridine C) and 169.56–170.33 (4 × CO). MS, m/z (%): (M+, 691, 2%).

 3.1.5. Synthesis of <italic>4-Aryl-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-oxo-1,2-dihydropyridine-3-carboxamides</italic> <bold>7a,b</bold>

A mixture of 6a,b (0.01 mol) and conc. sulphuric acid (15 mL) was stirred at room temperature 6 h, and then poured on cold water. The formed solid product was collected by filtration and recrystallized from ethanol to give 7a,b (Table 1).

4-(2,6-Dichlorophenyl-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-oxo)-1,2-dihydropyridine-3-carboxamide (7a). IR: (υ, cm−1) br. 3,382 (NH & NH2), 2,931 (CH2) and 1,668 (C=O). 1H-NMR (DMSO-d6): δ 1.69 (m, 4H, -CH2-CH2-), 2.70 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 4.03 (br. s, 2H, NH2) and 6.40–8.89 (m, 7H, aromatic protons and pyridine-H). 13C-NMR (DMSO-d6): δ 22.97 (-CH2-CH2-), 29.23 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 107.17, 118.39, 124.78, 128.05, 128.42, 129.20, 129.56, 131.71, 137.98, 140.12, 140.68, 149.39, 153.11 (Ar-C), 163.88, 164.97 (2C=O). MS, m/z (%): (M+, 413, 14%).

4-(2,6-Difluorophenyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-oxo-1,2-dihydropyridine-3-carboxamide (7b). IR: (υ, cm−1) br. 3,380 (NH & NH2), 2,932 (CH2) and 1,666 (C=O). 1H-NMR (DMSO-d6): δ 1.69 (m, 4H, -CH2-CH2-), 2.71 (m, 4H, 2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 3.34 (br. s, 2H, NH2), 6.55–8.72 (m, 7H, aromatic protons & pyridine-H) and 12.5 (NH). 13C-NMR (DMSO-d6): δ 22.98 (-CH2-CH2-), 29.18 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene, 108.16, 111.59, 112.45, 118.37, 120.53, 123.07, 124.80, 128.41, 129.45, 130.15, 137.91, 140.51, 145.09, 148.75, 157.87, 159.81 (Ar-C), 163.20, 165.54 (2C=O). MS, m/z (%): (M+, 380, 23%).

 3.1.6. <italic>Synthesis of 4-Aryl-N-(2',3',4',6'-tetra-O-acetyl-β-<sc>D</sc>-galactopyranosyl)-6-(1,2,3,4-tetrahydro-naphthalen-6-yl)-2-oxo-1,2-dihydro pyridine-3-carboxamides</italic> <bold>8a,b</bold>

To a solution of 7a and/or 7b (0.001 mol) in acetone (10 mL), 2,3,4,6-tetra-O-acetyl-α-D-gluco- or galactopyranosyl bromide (4.10 g, 0.01 mol) was added. Few drops of acetic acid were added and the reaction mixture was heated with stirring on a water bath at 40–50 °C for 25 h. The reaction mixture was cooled and then poured onto ice water. The formed precipitate was washed for several times with water and recrystallized from ethanol (Table 1).

4-(2,6-Dichlorophenyl-N-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-oxo)-1,2-dihydropyridine-3-carboxamide (8a). IR: (υ, cm−1) 1H-NMR (DMSO-d6): δ 1.73 (m, 4H, -CH2-CH2-), 1.90–2.08 (4s, 12H, 4 × CH3CO), 2.75 [m, 4H, 2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 3.93 (m, 2H, 6'-H2) 4.08 (m, 1H, 5'-H), 4.20 (t, 1H, 4'-H) 5.15–5.17 (t, 2H, 3'-H & 2'-H), 5.35 (d, 1H, 1'-H), 6.42–8.99 (m, 7H, aromatic protons and pyridine-H) and 12.67 (NH). 13C-NMR (DMSO-d6): δ 19.85–20.04 (4 × -COCH3), 22.98 (-CH2-CH2-), 29.14 [2(CH2)] attached to the aromatic ring of tetrahydronaphthalene), 61.25 (CH2, C-6'), 65.88 (C-4'), 67.34 (C-2'), 72.1 (C-3'), 74.34 (C-5'), 80.23 (C-1'), 107.17–153.09 (Ar-C) and 163.87–190.99 (6 × CO). MS, m/z (%): (M+ +1, 744, 10.96).

4-(2,6-Difluorophenyl-N-(2',3',4',6'-tetra-O-acetyl-β-D-galactopyranosyl)-6-(1,2,3,4-tetrahydronaphthalen-6-yl)-2-oxo)-1,2-dihydropyridine-3-carboxamide (8b). IR: (υ, cm−1). 1H-NMR (DMSO-d6): δ 1.73 (m, 4H, -CH2-CH2-), 1.99–2.08 (4s, 12H, 4 × CH3CO), 2.74 (m, 4H, 2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 3.92 (m, 2H, 6'-H2) 4.08 (m, 1H, 5'-H), 4.56 (t, 1H, 4'-H) 5.15–5.17 (t, 2H, 3'-H & 2'-H), 5.40 (d, 1H, 1'-H), 6.59–9.48 (m, 7H, aromatic protons and pyridine-H) and 12.66 (NH). 13C-NMR (DMSO-d6): δ 19.85–20.04 (4 × -COCH3), 22.98 (-CH2-CH2-), 29.14 (2(CH2) attached to the aromatic ring of tetrahydronaphthalene), 61.25 (CH2, C-6'), 65.88 (C-4'), 67.34 (C-2'), 72.1(C-3'), 74.34 (C-5'), 80.23 (C-1'), 108.17–159.79 (Ar-C) and 163.22–170.33 (6 × CO). MS, m/z (%): (M+, 710, 8.66).

 3.2. Molecular Modelling

Autodock vina allows the flexible docking of ligands into their site of action. It has the ability to use all the rotable bonds of the ligands to give a number of conformations from which the best mode could be deduced. The crystal structure of tyrosine kinase was downloaded from protein data bank [28]. Pdb code = 1t46 was written in search area of the pdbsum by clicking on find tap the complexed inhibitor will be viewed showing all possible interactions with the binding site [29]. All compounds were built and saved as pdbqt format and docking with Autodock Vina was performed according to the specified condition in which the grid box was adjusted to have center x = 24.15, center_y = 22.8, and center_z = 12.9 by these centres the pocket with the main residues were involved inside the box.

 3.3. <italic>In Vitro</italic> Cytotoxic Screening 3.3.1. Tumor

Ehrlich Ascites Carcinoma (EAC) cells was kindly provided by the National Cancer Institute (Cairo University, Cairo, Egypt). The tumor line was maintained in female Swiss albino mice by weekly intra-peritoneal injection of 2.5 × 105 cells/mouse according to the method recommended by the Egyptian National Cancer Institute, Cairo University. Such developed tumor is characterized by its moderate rapid growth which could not kill the animal due to the accumulation of ascites before about 14 days after transplantation. Cells were counted before injection using the bright line haemocytometer and dilutions made by physiological saline. The desired number of cells was injected in a volume of 0.5 mL/mouse. Solid Ehrlich carcinoma was induced by inoculation of 2.5 × 105 cells in the back between the thighs of each animal [30].

 3.3.2. Animals

Adult female Swiss albino mice, obtained from the animal house of Cairo Cancer Institute (Cairo University, Egypt) weighing 18–22 g were used. The local committee approved the design of the experiments, and the protocol conforms to the guidelines of the National Institutes of Health (NIH). The animals were maintained on a standard pellet diet and tap water ad libitum.

 3.3.3. <italic>In Vitro</italic> Test for Cytotoxic Effect

A set of sterile test tubes were used, where 2.5 × 105 tumor cells per ml were suspended in phosphate buffer saline, then 25, 50, 100 µg/mL of the test compound were added to the suspension, kept at 37 °C for 2 h. Trypan blue dye exclusion test was then carried out to calculate the percentage of non-viable cells [27].

 4. Conclusions

Some substituted tetrahydronaphthalene (2,3,4,6-tetra-O-acetyl-β-D-gluco/-galactopyranosyl) derivatives were synthesized and tested for their anticancer activity. The preliminary in vitro cytotoxicity evaluation revealed that five compounds show promised activity. This encouraged us to do a molecular docking study to find out a suitable binding mode for these compounds. The docking was done against TK and the docking output was analyzed. The compounds have shown hydrogen bond formation with a reasonable distance ranging from 2.06 A° to 3.06 A° with Thr 670 and Cys 673 residues. No hydrogen bond was observed with neither Glu 640 nor Asp 810 residues as was expected from pdbsum. From that we can conclude that substituted tetrahydronaphthalene (2,3,4,6-tetra-O-acetyl-β-D-gluco/-galactopyranosyl) compounds may provide more activity by further study trying to modify their substitutions to give new derivatives with expected improved anticancer activity and that may be the subject of our future work.

 Acknowledgments

This research project was supported by a grant from the “Research Center of the Center for Female Scientific and Medical Colleges”, Deanship of Scientific Research, King Saud University.

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Sample Availability: Samples of the compounds 1, 2 and 4 are available from the authors.