key: cord-0843412-xb69ob9u
authors: Abdel-Latif, E.; Khatab, T. K.; Fekri, A.; Khalifa, M. E.
title: Synthesis of New Binary Thiazole-Based Heterocycles and Their Molecular Docking Study as COVID-19 Main Protease (M(pro)) Inhibitors
date: 2021-10-27
journal: Russ J Gen Chem
DOI: 10.1134/s1070363221090231
sha: 4bb31005dee0d930fa80724efcbc6d4491d1220a
doc_id: 843412
cord_uid: xb69ob9u

Isolated polynuclear binary heterocyclic compounds containing thiazole building block combined with benzofuran, pyrrole, thiazole, or thiophene via carboxamide and/or secondary amine as a junction are presented. The synthetic strategy of those is based on utilization of 2-chloroacetamido-4-phenylthiazole in the synthesis of binary heterocyclic compounds by cyclocondensation with salicylic aldehyde, acetonitrile derivatives, ammonium thiocyanate, 3-mercaptoacrylonitrile derivatives, and/or 3-mercaptoacrylate derivatives. The prepared binary thiazole-based heterocycles have been studied as protease (M(pro)) inhibitors by molecular docking for visualization of their orientation and interactions with COVID-19 units using hydroxychloroquine as a reference molecule.

Polynuclear heterocycles containing thiazole ring are considered as a specific scaffolds in the synthesis of pharmacologically active compounds and efficient drugs [1] . Thiazole derivatives are components of molecules that demonstrate a broad spectrum of biologically activities [2] [3] [4] [5] [6] . For example, the efficient drug Famotidine is used in treatment of peptic ulcer and controlling gastro esophageal reflux [7] , Cefdinir is the third generation broad spectrum cephalosporin antibiotic [8] . The biological and synthetic significance of aminothiazole derivatives stimulated our design of some new molecules for COVID-19 main protease (M pro ) inhibitor based on molecular docking studies.

Covid-19 is considered as one of the biggest disasters that occurred in the modern era of mankind [9] . Up to now, no decisive treatment of it has been found yet. In modern drug discovery the molecular docking tools are considered as an important approach to design of agonists of drugs by calculating the ligand-receptor affinity.

2-Chloroacetamido-4-phenylthiazole (2) has been synthesized in 75% yield by the earlier developed method [10] . Reactions of the intermediate 2 with various nucleophiles led to new heterocyclic structures containing thiazole nucleus linked with furan, pyrrole, thiazole, and/or thiophene ring system. Reaction of compound 2 with salicylaldehyde and anhydrous K 2 CO 3 in dimethyl sulfoxide led to the corresponding N-(4-phenylthiazol-2-yl)benzofuran-2-carboxamide (3) (Scheme 1). The reaction of compound 2 with acetonitrile derivatives (malononitrile, cyanoacetamide and 2-benzothiazolyl acetonitrile) in presence of sodium ethoxide gave the corresponding 3-substituted-1-(4-phenylthiazol-2-yl)pyrroles 4a-4c. Chemical structures of the products 4a-4c were elucidated from their elemental analyses and spectroscopic data. Refluxing of compound 2 with ammonium thiocyanate in ethanol afforded 2-[(4-phenylthiazol-2-yl)imino]thiazolidin-4-one (5), which underwent the reaction with p-chlorobenzaldehyde in AcOH and fused AcONa to furnish the corresponding condensation product 5-(4-chlorobenzylidene)-2-[(4phenylthiazol-2-yl)imino]thiazolidin-4-one (6) . Chemical structures of thiazolidin-4-one derivatives 5 and 6 were based on elemental analysis and spectral data.

Cyclocondensation of compound 2 with 3-mercapto-3-phenylamino-acrylonitrile derivatives 7a-7c under the action of sodium ethoxide. The corresponding 3-amino-5-phenylamino-2-(4-phenylthiazol-2-yl-carbamoyl)-4substitutedthiophene derivatives 9a-9c were formed. Formation of thiophene derivatives 9 could proceed via nucleophilic attack of the thiol function leading to the sulfide intermediate 8, which upon intramolecular cyclization via nucleophilic addition of the methylene group to the activated nitrile could produce the corresponding 3-amino-4-substituted-thiophenes 9 (Scheme 2). IR, NMR and mass spectra of the products 9a-9c were in agreement with their molecular structures. proteins by an enzyme called the main protease (M pro ), which was proposed to be a good target in coronavirus therapy and discovery of new series of anti-coronavirus drugs [12] [13] [14] [15] . Molecular docking was carried out by using the standard docking MOE2015.10 software. The "pdb file" of X-ray crystallographic structure of COVID-19 main protease (M pro ) (PDB ID: 7BUY) was obtained from the protein data bank (PDB). Our research group is experienced in the study of the drug-receptor interactions of a wide variety of newly synthesized molecules using molecular docking databases [16] [17] [18] [19] [20] [21] [22] . The presented docking protocol allowed us to calculate the important factor for interpretation of ligand-enzyme interactions between the synthesized heterocycles and M pro enzyme in terms of E-score (kcal/mol) as follows: Most of the synthesized compounds were characterized by good interactions that formed two or more electrostatic bonds. The molecule 15 is a sample of the ligandenzyme electrostatic bonding (Fig. 2) . The presented example demonstrates two hydrogen bonds between the carbonyl and hydroxyl groups of the molecule on one hand and Gly143 and Arg194 in the enzyme pocket on the other with the lengths measured as 2.23 and 1.94 Ǻ, respectively.

Melting points (uncorrected) were measured on a Gallenkamp electric melting point instrument. IR spectra (KBr disks) were recorded on a Thermo Scientific Nicolet iS 10 FT-IR spectrophotometer. 1 H and 13 C NMR spectra were measured on a Bruker WP 300 MHz (Faculty of Science, Cairo University) using DMSO-d 6 as a solvent. Mass spectra were measured on a Shimadzu Qp-2010 mass spectrometer (Faculty of Science, Mansoura University) at 70 eV (EI mode). Elemental analysis was carried out on a Perkin-Elmer 2400 analyzer.

. Salicylaldehyde (2 mmol, 0.25 mL) was added to a stirred solution of 2-chloroacetamido-4phenylthiazole (2) (2 mmol, 0.50 g) in DMSO (10 mL) solution containing anhydrous K 2 CO 3 (0.50 g). The reaction mixture was stirred for 8 h at room temperature, then 10% HCl solution (20 mL) was added, and the product was filtered off. The separated precipitate was recrystallized from ethanol. Yield 80%, mp 234-236°C. IR spectrum, ν, cm -1 : 3115 (N-H), 1676 (C=O). 1 1H-pyrroles (4a-4c) . The appropriate substituted acetonitrile (2 mmol) was mixed with sodium ethoxide (0.09 g) and compound 2 (0.50 g; 2 mmol) in ethanol (20 mL), and the mixture was refluxed for 6 h. The mixture was poured into ice-cold water and then neutralized by dilute HCl. The precipitate was filtered off and recrystallized from ethanol to give the corresponding pure product.

274-275°C (mp 276-277°C [23] ). IR spectrum, ν, cm -1 : 3343, 3205 (NH 2 ), 2194 (C≡N), 1737 (C=O). 

Yield 82%, mp 148-150°C. IR spectrum, ν, cm -1 : 3434, 3315 (NH 2 ), 1754 (C=O). 1 H NMR spectrum, δ, ppm: 3.80 s (2H, CH 2 ), 6.85 s (2H, NH 2 ), 7.25-8.05 m (10H, H Ar , and C 5 H thiazole ). 13 

A mixture of solution of compound 2 (4 mmol, 1.00 g) in 20 mL of absolute ethanol and ammonium thiocyanate (6 mmol, 0.46 g) was refluxed for 5 h followed by cooling down to room temperature. The yellow precipitate was filtered off and dried. Yield 76%, mp 257-259°C. IR spectrum, ν, cm 5-(4-Chlorobenzylidene)-2-((4-phenylthiazol-2-yl)imino)thiazolidine-4-one (6) . A mixture of the derivative 5 (2 mmol, 0.55 g) with p-chlorobenzaldehyde (2 mmol, 0.28 g) was refluxed in acetic acid (25 mL) containing anhydrous sodium acetate (0.5 g) for 4 h, then cooled down and poured into ice-cold water. Synthesis of 5-phenylamino-2-(4-phenylthiazol-2yl-carbamoyl)-4-substituted-thiophene derivatives 9, 12, and 15. A mixture of compound 2 (2 mmol, 0.50 g) with the appropriate thiocarbamoyl derivative 7, 10 or 13 (2 mmol) was refluxed for 4 h with sodium ethoxide solution (0.09 g) in 20 mL of absolute ethanol. The reaction mixture was cooled down to room temperature, poured into ice-cold water and neutralized by dilute HCl. The precipitate was filtered off, dried and recrystallized from ethanol. 3-Amino-4-carbamoyl-5-phenylamino-2-(4phenylthiazol-2-yl-carbamoyl)thiophene (9b). Yield 72%, mp 218-220°C. IR spectrum, ν, cm -1 : 3447, 3410, 3384, 3336, 3237 (NH 2 and N-H), 1635 (broad, C=O). 1 H NMR spectrum, δ, ppm: 6.35 s (2H, NH 2 ), 7.10-7.85 m (11H, H Ar , and C 5 H thiazole ), 8.75 s (2H, NH 2 ), 10.85 s thiazole linked benzofuran, pyrrole, thiazolidine, and/or thiophene ring systems have been determined using IR, 1 H and 13 C NMR, and mass spectra. Docking procedure has exposed the more efficient interactions of the products 4c, 6, 9a-9c, 12, and 15 with COVID-19 main protease (M pro ) binding site than hydroxychloroquine used as a reference ligand. 

12.15 s (1H, NH). 13 C NMR spectrum, δ

1655 (C=O). 1 H NMR spectrum, δ, ppm: 6.70 s (2H, NH 2 ), 7.10-8.10 m (15H, H Ar , and C 5 H thiazole ), 11.05 s (1H, NH), 11.85 s (1H, NH). 13 C NMR spectrum, δ

N 13.64. MS: m/z: 513 [M] + . 4-(4-Hydroxyphenylazo

1 H NMR spectrum, δ, ppm: 2.70 s (3H, CH 3 ), 6.70-7.95 m (15H, H Ar , and C 5 H thiazole ), 9.90 s (1H, OH), 12.25 s (1H, NH), 13.18 s (1H, NH). 13 C NMR spectrum, δ

MS: m/z: 511 [M] + . CONCLUSIONS In summary, new thiazole-based derivatives have been synthesized by the reactions of 2-chloroacetamido-4-phenylthiazole with various oxygen, carbon and/or sulfur nucleophilic reagents

Proc. Nat. Acad. Sci

No conflict of interest was declared by the authors.