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Спутники
РН
SpaceX
Роскосмос
NASA
СпутникиРНSpaceXРоскосмосNASABackground Antibacterial agents containing β-lactam derivatives have been widely used in medicine because of their broad-spectrum effectiveness against various infectious diseases. β-Lactam antibiotics remain one of the most important classes of antibacterial agents, and the development of new β-lactam derivatives continues to be essential for overcoming microbial resistance. Therefore, the discovery of novel β-lactam compounds remains an important area in medicinal chemistry for the development of improved antibacterial agents. Objective The present study aimed to synthesize new β-lactam derivatives derived from sulfapyridine Schiff bases and to evaluate their biological activity using laboratory investigations and molecular docking analysis. Methods Sulfapyridine-derived Schiff bases were prepared through condensation reactions with different aromatic aldehydes and used as key intermediates for the synthesis of β-lactam derivatives. The structures of the synthesized compounds were confirmed using FT-IR, 1H-NMR, and 13C-NMR spectroscopic techniques. Two series of β-lactam derivatives were synthesized. The first series [A5–A8] was obtained through the reaction of Schiff bases [A1–A4] with chloroacetyl chloride in the presence of triethylamine. The second series [A9–A12] was synthesized through cycloaddition reactions between the prepared Schiff bases and diclofenac acid in the presence of ρ-toluenesulfonyl chloride and trimethylamine. The synthesized compounds were biologically evaluated, and molecular docking studies were carried out against biologically relevant bacterial targets, including Escherichia coli (PDB ID: 2EG7) and Staphylococcus aureus (PDB ID: 2W9S). Results Molecular docking studies were performed to evaluate the antibacterial activity of compounds A5–A12 against Escherichia coli and Staphylococcus aureus. Several synthesized derivatives, particularly A7–A9 and A12, exhibited enhanced antibacterial activity compared with the reference drug. Experimental and theoretical findings suggested that β-lactam-based compounds may serve as promising scaffolds for the development of new antibacterial agents. Compared with amoxicillin (−7.5 kcal/mol), compounds A10 and A11 demonstrated lower binding energies (−9.0 and − 8.4 kcal/mol, respectively), indicating strong interactions with bacterial target proteins. Conclusion Molecular docking studies supported the experimental antibacterial findings and provided insight into possible ligand–protein interactions, confirming the biological potential of the synthesized β-lactam derivatives. These findings support the continued investigation of β-lactam scaffolds as promising candidates for future antibacterial drug development.
Chemicals were obtained from Fluka/Merck, with M.P. recorded via electrothermal melting point apparatus (Gallenkamp). FT-IR (KBr disk) spectra of the prepared compounds were recorded on a Shimadzu FT-IR 8400 s spectrometer at the Department of Chemistry at the College of Science; 1H NMR (DMSO-d6, TMS) and 13C NMR (DMSO-d6, TMS) spectra were recorded using a Bruker Ultra Shield™ 400 MHz NMR spectrometer.
General procedure for the synthesis of Schiff bases [A1-A4]:
Sulphapyridine of 2.49 g (0.01 mol) was mixed with an equivalent amount of an aromatic aldehyde (0.01 mol) to give a final volume of 30 mL of absolute ethanol, and then glacial acetic acid was added as a catalyst (3–4 drops) into the mixed reaction mixture, and it was refluxed for approximately three hours, with agitation.
The progress of the reaction was monitored by TLC. After the completion of the reaction, the mixture was cooled to room temperature, and the solid phase was filtered from the reaction vessel, washed with cold ethanol and dried under reduced pressure, providing Schiff bases A1–A4 in high yield. Complete NMR spectra analysis of all the newly synthesized compounds is included in the Supplementary Materials/Zenodo Repository.7–9,18
4-((4-chlorobenzylidene) amino)-N-(pyridin-2-yl) benzene sulfonamide [A1]: Pale yellow solid, yield: 90%, m.p. 200–202 °C. FT-IR: 3390 (NH), 3024 (CH aromatic), 1681 (C=N pyridine), 1631 (C=N), 1384 (SO2 asy.), 1085 (SO2 sy.), 1005 (C-Cl); 1H NMR δ 11.73 (s, 1H, NH), 1H, N=CH), 6.87–8.07 (m, 12H, Ar-H). 13CNMR δ: 112.58–154.85 (C-Ar), 162.24 (C=N).
4-((4-nitrobenzylidene) amino)-N-(pyridin-2-yl) benzene sulfonamide [A2]: Yellow solid, yield: 85%, m.p. 190–192 °C. FT-IR: 3244 (NH), 3055 (CH aromatic), 1679 (C=N), 1629 (C=N), 1575 (NO2 asy.), 1319 (NO2 sy.), 1388 (SO2 asy.), 1083 (SO2 sy.).
4-((4-(dimethylamino)benzylidene)amino)-N-(pyridin-2-yl) benzene sulfonamide [A3]: Yellow solid, yield: 85%, m.p. 188–190 °C. FT-IR: 3305 (NH), 3047 (CH aromatic), 1708 (C=N pyridine), 1679 (C=N), 1008 (C-N), 1359 (SO2) asy., 1087(SO2)sy.
4-((4-methoxybenzylidene) amino)-N-(pyridin-2-yl) benzene sulfonamide [A4]: Pale brown solid, yield: 88%, m.p. 185–187 °C. FT-IR: 3225 (NH), 3047 (CH aromatic), 1708(C=N pyridine), 1683 (C=N), 1283 (Ar-O), 1380 (SO2) asy., 1085 (SO2)sy. 1H NMR δ 11.57 (s, 1H, NH), 8.51 (s, 1H, N=CH), 6.88–7.71 (m, 12H, Ar-H), 3.73 (s, 3H, OCH3). 13CNMR δ: 56.16 (CH3), 112.58–154.85 (C- Ar), 162.24 (C=N).
General procedure for the synthesis of β-lactam derivatives [A5-A8]:
0.01 mol of a Schiff base was stirred in dry dichloromethane (20 mL), and triethylamine (0.02 mol) was added dropwise to this solution via an inert atmosphere. The reaction was cooled in an ice bath, and then chloroacetyl chloride (0.012 mol) was added in a slow manner while keeping the temperature of the reaction mixture below 10 °C. The reaction mixture was then stirred for a total of 6 hours once it had been allowed to reach room temperature. After completion, the mixture was washed with distilled water, followed by 5% NaHCO3 and then with brine. The organic phase was dried using anhydrous Na2SO4, filtered, and evaporated under reduced pressure to yield β-lactam derivatives A5 - A8 after recrystallization of the product from ethanol.10,14,15
4-(3-chloro-2-(4-chlorophenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A5]: Yellow solid, yield: 85%, m.p. 148–150 °C. FT-IR: 3307 (NH), 3058 (CH aromatic), 1706 (C=O amide), 1679 (C=N pyridine), 1359 (SO2 asy.), 1085 (SO2 sy.), 1002 (C-Cl).
4-(3-chloro-2-(4-nitrophenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A6]: Brown solid, yield: 86%, m.p. 158–160 °C. FT-IR: 3299 (NH), 3056 (CH aromatic), 1703 (C=O amide). 1670 (C=N pyridine), 1533, 1394 (NO2), 1361 asy., 1087 (SO2) sy. 1H NMR δ: 12.39 (s, 1H, NH), 6.40–7.97 (m, 12H, Ar-H), 5.77 (d, 1H, CH-Cl), 4.29 (d, 1H, CH-N). 13CNMR δ: 166.01 (C=O), 114.41–154.28 (C-Ar), 70.68 (C-N), 64.19 (C-Cl).
4-(3-chloro-2-(4-(dimethylamino)phenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A7]: Brown solid, yield: 89%, m.p. 145–147 °C. FT-IR: 3309 (NH), 3029 (CH aromatic), 1728 (C=O amide), 1672 (C=N pyridine), 1359 asy., 1039 (SO2) sy. 1H-NMR δ: 10.90 (s, 1H, NH), 6.77–8.03 (m, 12H, Ar-H), 5.77 (d, 1H, CH-Cl), 4.34 (d, 1H, CH-N), 3.03 (s, 6H, CH3-N). 13CNMR δ: 165.73 (C=O), 111.55–154.67 (C-Ar), 65.34 (C-N), 64.18 (C-Cl), 41.99 (2CH3).
4-(3-chloro-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A8]: Brown solid, yield: 90%, m.p. 159–161 °C. FT-IR: 3269 (NH), 3068 (CH aromatic), 1712 (C=O amide), 1677 (C=N pyridine), 1259 (Ar-O), 1332 (SO2) asy., 1049 (SO2 sy.).
General procedure for the synthesis of β-lactam derivatives [A9-A12]:
A mixture of diclofenac acid (1.5 mmol, 0.6 g), Schiff base (1 mmol), p-toluenesulfonyl chloride (1.5 mmol, 0.4 g), and triethylamine (5 mmol) in dry dichloromethane (10 mL) was stirred at room temperature for 35–60 h. The reaction progress was monitored by TLC. After completion, the mixture was washed sequentially with 1 N HCl (10 mL), NaHCO3 solution (10 mL), and brine (10 mL). The organic layer was dried over anhydrous MgSO4, filtered, and the solvent was removed to yield crude β-lactams (A9–A12), which were recrystallized from ethanol.12,13,17
4-(2-(4-chlorophenyl)-3-(2-((2,6-dichlorophenyl)amino)phenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A9] : Dark yellow solid, yield: 88%, m.p. 190–192 °C. FT-IR 3379 (NH), 3031 (CH aromatic), 1680 (C=O amide), 1361 (SO2 asy.), 1054 (SO2 sy.), 1008 (C-Cl).
4-(3-(2-((2,6-dichlorophenyl)amino)phenyl)-2-(4-nitrophenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A10]: Pale yellow solid, yield: 80%, m.p. 210–212 °C. FTIR: 3261 (NH), 3072 (CH aromatic), 1714 (C=O amide), 1506 (NO2 asy.), 1307 (SO2) asy., 1045(SO2) sy, 1000(C-Cl). 1H-NMR δ: 10.03(s, 1H, NH), 6.42–7.96 (m,19H, Ar-H), 5.62 (d, 1H, CH), 4.12 (d,1H, CH-N). 13CNMR δ: 169.90 (C=O), 112.39–140.80 (C- Ar), 58.74 (C-N), 44.53 (CH).
4-(3-(2-((2,6-dichlorophenyl)amino)phenyl)-2-(4-(dimethylamino)phenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A11]: Yellow solid, yield: 83%, m.p. 239–241 °C. FTIR: 3323 (NH), 3074 (CH aromatic), 1724(C=O amide), 1371(SO2) asy., 1014(SO2) sy., 1015(C-Cl).
4-(3-(2-((2,6-dichlorophenyl)amino)phenyl)-2-(4-methoxyphenyl)-4-oxoazetidin-1-yl)-N-(pyridine-2-yl) benzenesulfonamide [A12]: Brown solid, yield: 89%, m.p. 204–206 °C. FT-IR 3234 (NH), 3080 (CH aromatic), 1681 (C=O amide), 1083 (C-O), 1348 (SO2) asy., 1043(SO2) sy., 1001 (CCl). 1H NMR δ: 9.82 (s, 1H, NH), 6.79–8.10 (m, 19H, Ar-H), 6.31(d,1H, CH), 5.83 (d,1H, CH-N) 3.12 (s, 3H, OCH3). 13C NMR δ: 166.99 (C=O), 112.39–140.80 (C-Ar), 60.90 (C-N), 55.40 (CH3), 44.15 (CH).
Tested microorganisms included:
• Staphylococcus aureus (Gram-positive)
• Escherichia coli (Gram-negative)
• Candida albicans (fungus)
In this method, 30 μg of each compound dissolved in DMSO was deposited on sterile filter paper disks for antimicrobial susceptibility testing. DMSO alone was included as a negative control to verify that it has no effect on microbial growth. Using the disk diffusion method, the antimicrobial activity of all synthesized compounds was evaluated in this preliminary screening. The inoculated plates were incubated at 37 °C and 28 °C for bacteria and fungi, respectively, and the zone of inhibition of each compound was measured. In addition, ceftriaxone and fluconazole were used as standard reference antimicrobial agents. Results were calculated and reported as mean ± standard deviation for all replicates (n = 3). Additional studies are needed to determine the minimum inhibitory concentration (MIC) of each of the synthesized compounds.
Molecular docking
ChemOffice 2016, Discovery Studio 2021, and the AutoDock Vina module incorporated into PyRx 0.8 were used for molecular docking investigations.12
The crystal structures of the antibacterial target proteins, Escherichia coli (PDB ID: 2EG7) and Staphylococcus aureus (PDB ID: 2W9S), were retrieved from the Protein Data Bank and prepared in Discovery Studio by removing water molecules and heteroatoms and verifying structural completeness. The optimized protein structures were saved in pdb format.19,20
The synthesized compounds (A5–A12) were drawn using ChemDraw and converted into.pdb files. AutoDock Tools was used to convert protein and ligand structures into pdbqt format, and Open Babel was used for ligand energy minimization. The active site was defined based on the co-crystallized ligand (ceftriaxone), and the grid box was centered accordingly during the Vina Wizard docking procedure. Binding affinities were evaluated using the lowest Vina score values, and ligand–protein interactions were analyzed using Discovery Studio Visualizer 2021.21