An efficient synthesis, characterization and docking studies of 2-methoxy-3-(1-substituted-1H-pyrazol-3-yl)quinoxalines

Cite this paper: Vietnam J. Chem., 2021, 59(2), 153-158 Article DOI: 10.1002/vjch.202000139 153 Wiley Online Library © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH An efficient synthesis, characterization and docking studies of 2-methoxy-3-(1-substituted-1H-pyrazol-3-yl)quinoxalines Muralidhar Reddy Rachala 1 , Laxminarayana Eppakayala 2 , Giri Tharikoppula 2 , Thirumala Chary Maringanti 3* 1 Vidya Jyothi Institute of Technology, Aziz Nagar Gate, Hyderabad-500 075, Telangana, India 2 Sreenidhi Institute of Science and Technology (Autonomous), Ghatkesar, -501301 Telangana, India 3 Jawaharlal Nehru Technological University Hyderabad, Kukatpally, Hyderabad, -500 085 Telangana India Submitted August 13, 2020; Accepted October 18, 2020 Abstract A basic, proficient and P-TSA catalyzed synthesis of quinoxalines beginning from ethyl 3-methoxyquinoxaline-2- carboxylate in great yields is introduced. All the compounds synthesized were analyzed by spectral analysis. Keywords. Quinoxalines, P-TSA, pyrazole, Docking studies. 1. INTRODUCTION Quinoxaline subsidiaries are a significant class of nitrogen-containing heterocycles, as they establish helpful intermediates in organic synthesis. This substructure plays a significant role as an essential skeleton for the plan of various heterocyclic compounds with various biological activities, hence thesecompounds significant in the fields of antitumor, anticonvulsant, antimalarial, anti- inflammatory, antiamoebic, antioxidant, antidepressant, antiprotozoal, antibacterial, anti-HIV agents, [1-10] fluorescent dying agents, electroluminescent materials, chemical switches, cavitands and semiconductors. [11-17] Pyrazole subsidiaries are a fascinating class of organic compounds, which are seen as related with different pharmacological properties, for example,antimicrobial, [18,19] anti-inflammatory, [20] antihypertensive, [21] antidepressant, [22] antiviral [23] and anticancer [24] activities. Owing biological significance of Quinoxaline and Pyrazole subsidiaries, we herein report the synthesis of title compounds. 2. MATERIALS AND METHODS All the chemical, reagents and solvents used in this work were purchased either from sd/Fluka or Merck. The progress of the reactions was monitored by Thin-layer chromatography (TLC) which was performed on E. Merck AL silica gel 60 F254 plates and visualized under ultraviolet (UV) light. 1 H NMR and 13 C NMR spectra were recorded using Varian NMR‐400 MHz and 100 MHz instruments respectively. All the chemical shifts were reported in δ (ppm) using TMS as an internal standard. Signals are indicated as s (singlet), d (doublet), t (triplet), q (quartet), m (multiplet), br (broad); and coupling constants in Hz. Mass spectra were recorded with a PESciex model API 3000 mass spectrometer. Synthesis of 3-methoxyquinoxaline-2-carboxylic acid (2): To a stirred solution of ethyl 3- methoxyquinoxaline-2-carboxylate 1 (10 g, 43.08 mmol) in EtOH H2O (100 mL, 3:1) was added LiOH.H2O (4.3 g, 86.17 mmol) and stirred the reaction at 90 o C for 6 h. Reaction was monitored by TLC. After completion of reaction, solvent was evaporated from reaction mixture up to three times, poured the reaction mixture into ice water, acidified with 2 N HCl (up to pH = 2) and filtered the formed precipitate, washed the precipitate with water, dried the product under reduced pressure to afford 3- methoxyquinoxaline-2-carboxylic acid 2 (8 g, 91 %) as off white solid. 1 HNMR (DMSO-d6, 400 MHz): 10.31 (brs, 1H), 8.09 (d, 2H, J = 8.2 Hz), 7.82 (t, 2H, J = 4.0 Hz), 3.78 (s, 3H); ESI-MS: m/z, 205.1 (M+H) + . Synthesis of N,3-dimethoxy-N- methylquinoxaline-2-carboxamide (3): To a stirred solution of 3-methoxyquinoxaline-2-carboxylic acid 2 (8 g, 39.21 mmol) in DMF (40 mL) was added Vietnam Journal of Chemistry Thirumala Chary Maringanti et al. © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 154 DIPEA(20.2 g, 156.8 mmol), HOBT(10.59 g, 78.43 mmol), EDC.HCl (15 g, 78.43 mmol) and stirred the reaction at room temperature for 15 min. then added N,O dimethyl hydroxylamine (2.87 g, 47.05 mmol) and stirred the reaction at room temperature for 18 h. After completion of reaction, reaction mixture was poured into water and filtered the formed precipitate, dried the precipitate under reduced pressure to afford N,3-dimethoxy-N-methylquinoxaline-2- carboxamide 3 (8 g, 83 %) as brown solid. 1 HNMR (DMSO-d6, 400 MHz): 8.11 (d, 2H, J = 8.0 Hz), 7.81 (t, 2H, J = 8.0 Hz, 3.2 Hz);2.79 (s, 3H), 3.52 (s, 3H), 3.72 (s, 3H). ESI-MS: m/z, 247.9 (M+H) + . N N N N O N N O O N N N O O HO N N O O O 1 2 3 4 6 a-d O NH N N O O N O N N O O R-NH-NH2, P-TSA 5 R DMF-DMA MeMgBr, THF EtOH, 90 0C, 6 h EDC.HCl, HOBT DMF, DIPEA RT, 12 h 0 0C-RT, 6 h DMF, 90 0C, 18 h EtOH, 100 0C, 6 h R= H, Methyl, Ethyl, Phenyl LiOH.H2O Scheme 1: Synthesis of 2-methoxy-3-(1-substituted-1H-pyrazol-3-yl) quinoxalines Synthesis of 1-(2-methoxyquinoxalin-3-yl) ethanone (4): To a stirred solution of N,3- dimethoxy-N-methylquinoxaline-2-carboxamide 3 (6g, 24.29 mmol) in THF (60 mL) at -78 o C was added methyl magnesium bromide solution (16.19 mL, 3 M, 48.58 mmol) in diethyl ether as drop wise and stirred the reaction at room temperature for 6h. Reaction was monitored by TLC. After completion of reaction, cooled the reaction mixture to 0 o C and quenched with sat. NH4Cl solution, poured the reaction mixture into ice water, extracted with EtOAc, combined extracts were washed with water followed by brine solution. Dried the extracts over anhy.Na2SO4 and evaporated the solvent to afford crude product. Crude product was purified by silica gel (60-120) column chromatography; product was eluted at 70 % ethyl acetate in pet ether to afford 1- (2-methoxyquinoxalin-3-yl) ethanone 4 (4.1 g, 85 %) as off brown solid. 1 H-NMR (DMSO-d6, 400 MHz): 8.02 (d, 2H, J = 8.0 Hz), 7.75 (t, 2H, J = 8.0 Hz), 3.78 (s, 3H), 2.24 (s, 3H); ESI-MS: m/z, 202.9 (M+H) + Synthesis of 3-(dimethylamino)-1-(3- methoxyquinoxalin-2-yl)prop-2-en-1-one (5): To a stirred solution of 1-(2-methoxyquinoxalin-3-yl) ethanone 4 (4 g, 19.80 mmol) in DMF (20 mL) was added DMF-DMA (2.17 g, 29.70 mmol) at room temperature and stirred the reaction at 100 o C for 18 h. Reaction was monitored by TLC. After completion of reaction, reaction mixture was poured into ice water, extracted with EtOAc, combined extracts were washed with water, brine solution. Dried the extracts over anhy.Na2SO4 and evaporated the solvent to afford crude product. Crude product was purified by silica gel (60-120) column chromatography; product was eluted at 3 % MeOH in DCM to afford 2-methoxy-3-(1-alkyl-1H-pyrazol- 3-yl) quinoxaline 5 (3.75 g, 75 %) as gummy liquid. 1 H-NMR (DMSO-d6, 400 MHz): 8.02 (d, 2H, J = 7.8 Hz), 7.78 (t, 2H, J = 7.8 Hz), 7.22 (d, 1H, J = 8.0 Hz), 6.73 (d, 8 Hz), 3.78 (s, 3H), 2.8 (s, 3H), 2.68 (s, 3H); ESI-MS: m/z, 257.9 (M+H) + Synthesis of 2-methoxy-3-(1-alkyl-1H-pyrazol-3- yl) quinoxaline (6): To a stirred solution of 3- (dimethylamino)-1-(3-methoxyquinoxalin-2- yl)prop-2-en-1-one 5 (1 g, 3.88 mmol) in EtOH (10 mL) was added hydrazine derivatives (3.88 mmol), P-TSA (134 mg, 0.77 mmol) at room temperature and stirred the reaction at 100 o C for 18 h. Reaction was monitored by TLC. After completion of reaction, reaction mixture was poured into water and filtered the formed precipitate, dried the precipitate under reduced pressure to afford crude product. Crude product was purified by silica gel (60-120) column chromatography, product was eluted at 2-3 % MeOH in DCM to afford 2-methoxy-3-(1-alkyl- Vietnam Journal of Chemistry An efficient synthesis, characterization and docking © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 155 1H-pyrazol-3-yl) quinoxaline 6(a-d) and yields of the products varied between 80-95 %. By adapting this procedure the compounds 6(a-d) were synthesized. 2-methoxy-3-(1H-pyrazol-3-yl)quinoxaline (6a): Yield: 89 %; 1 H-NMR (DMSO-d6, 400 MHz):  10.26 (brs, 1H), 8.11 (d, 2H, J = 7.8 Hz), 7.94 (d, 1H, J = 9.8 Hz), 7.82 (t, 2H, J = 8.0 Hz), 7.63 (d, 1H, J = 9.8 Hz), 3.75 (s, 3H); ESI-MS: m/z 227 (M+H) + 2-methoxy-3-(1-methyl-1H-pyrazol-3- yl)quinoxaline (6b): Yield: 80 %; 1 H-NMR (DMSO-d6, 400 MHz): 8.13 (d, 2H, J = 7.8 Hz), 7.93 (d, 1H, J = 9.8 Hz), 7.80 (t, 2H, J = 4.0 Hz), 7.62 (d, 1H, J = 9.8 Hz), 3.74 (s, 3H), 2.61 (s, 3H); ESI–MS: m/z, 241 (M+H)+. 2-methoxy-3-(1-ethyl-1H-pyrazol-3- yl)quinoxaline (6c): Yield: 85 %; 1 H-NMR (DMSO-d6, 400 MHz):  8.10 (d, 2H, J = 7.8 Hz), 7.91 (d, 1H, J = 9.8 Hz), 7.79 (t, 2H, J = 8.0 Hz), 7.64 (d, 1H, J = 9.8 Hz), 3.75 (s, 3H), 2.62 (m, 2H), 1.31 (t, 3H, J = 3.5 Hz); ESI-MS: m/z, 255 (M+H) + . 2-methoxy-3-(1-phenyl-1H-pyrazol-3- yl)quinoxaline (6d): Yield 95 %; 1 H-NMR (DMSO- d6, 400 MHz): 8.12 (d, 2H, J = 7.8 Hz), 7.95 (d, 1H, J = 9.8 Hz), 7.80 (t, 2H, J = 8.0 Hz), 7.61 (d, 1H, J = 9.8 Hz), 7.40 (m, 5H), 3.78 (s, 3H); 13 C NMR (DMSO-d6, 100 MHz):  155.02, 148.08, 142.01, 139.01, 138.0, 137.8, 132.2, 131.2, 128.8, 126.2, 122.05, 119.8, 110.80, 56.10; ESI-MS: m/z, 302.9 (M+H) + . 3. RESULTS AND DISCUSSION 3.1. Chemistry The target compounds 6a-d was prepared as outlined in scheme 1. The compound ethyl 3- methoxyquinoxaline-2-carboxylate 1 was reacted with LiOH.H2O in presence EtOH:Water to afford 3- methoxyquinoxaline-2-carboxylic acid 2 as 90 % yield. The resulting product was treated with N,O dimethyl hydroxylamine in presence of EDC.HCl, HOBT and afford N,3-dimethoxy-N- methylquinoxaline-2-carboxamide 3 as 87 % yield. Resulted amide was treated with methyl magnesium bromide in THF then formed corresponding 1-(2- methoxyquinoxalin-3-yl)ethanone 4 as 85 % yield. This ketone was further treated with DMF-DMA and get 2-methoxy-3-(1-alkyl-1H-pyrazol-3-yl) quinoxaline 5 as 80 % yield. This compound 5 was treated with different hydrazine derivatives in EtOH in presence of P-TSA to afford corresponding substituted pyrazole products 6(a-d) in excellent yield. The structures of synthesized compounds were confirmed by spectral analysis. The 1 H NMR spectrum of compound 6d showed a doublet peak at δ 8.12, 7.95, 7.80, 7.61 corresponding to quinoxaline and pyrazole rings, multiplet at 7.40 indicating phenyl group and 3.78 singlet for three protons suggested the presence of methyl group. In the 13 C NMR spectrum of compound 8a peak at δ 56.1 indicated the presence of ether group and the other signals corresponding to aromatic carbons. Further support was also obtained from the mass spectrum which showed peak at m/z = 302.9 corresponding to [(M+H) + ] of the compound 6d. 3.2. Docking studies The protein 1jff (tubulin) was downloaded from RSC PDB and was docked. [25] Compound 6d was the most efficient for inhibiting the structural protein as shown in tables 1 and 2. The major aminoacids which were involved in the binding of the compounds were tyrosine, asparagines, alanine, glutamine, glutamic acid, leucine, serine (figure 1). Table 1: Docking results for Free energy of Binding Rank Est. Free Energy of Binding Est. Inhibition Constant, Ki vdW + Hbond + desolv Energy Electrostatic Energy Total Intermolec. Energy Frequency Interact. Surface 1. -4.45 kcal/mol 547.79 M -5.21 kcal/mol -0.07 kcal/mol -5.28 kcal/mol 50 % 586.527 Vietnam Journal of Chemistry Thirumala Chary Maringanti et al. © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 156 Table 2: Docking results of hydrogen bonding Hydrogen bonds Polar Hydrophobic pi-pi Other N2 () [3.27] – SER38 (O, OG) N4 () [3.63] – SER38 (OG) C14 () [3.39] – PRO35 (CB) C13 () [3.31] – TYR55 (CD1, CE1) C7 () [3.90] – SER38 (CB) N3 () [2.66] – SER38 (CB, OG) C9 () [3.89] – PRO40 (CG) C14 () [3.79] – TYR55 (CD1) C8 () [3.53] – SER38 (CB, OG) C10 () [3.46] – TYR55 (CE1, CZ) C18 () [3.64] – SER38 (CB) C12 () [3.78] – TYR55 (CE1) C9 () [3.35] – SER38 (OG) C13 () [3.89] – SER38 (OG) N2 () [3.67] – PRO40 (CB, CG) N3 () [3.83] – PRO40 (CG) C2 () [3.04] – GLN42 (CD, NE2, OE1) C1 () [3.31] – GLN42 (OE1) N4 () [3.74] – TYR55 (CE1) C11 () [3.76] – TYR55 (OH) C10 () [3.51] – TYR55 (OH) C2 () [3.87] – LYS468 (NZ) Figure 1: Bonding involved in the binding of the ligand to the tubulin Vietnam Journal of Chemistry An efficient synthesis, characterization and docking © 2021 Vietnam Academy of Science and Technology, Hanoi & Wiley-VCH GmbH www.vjc.wiley-vch.de 157 Acknowledgements. 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