Synthesis and in vitro Evaluation of Novel Thiophene Derivatives

Abstract

sulfur-containing heterocycles used to create a wide variety of sophisticated compounds with a wide range of biological functions, they are valuable analogs for medicinal chemists. Synthesis novel thiophene derivative by Schiff base were validated by FTIR, MS and 1H-NMR. The produced compounds were additionally assessed for their in vitro biological potentials, specifically antimicrobial activity against chosen microbial species utilizing tube dilution method. Antimicrobial screening outcomes revealed that compound S1 emerged as the most effective antibacterial agent against Staphylococcus aureus, Bacillus subtilis, Escherichia coli, and Salmonella typhi, with an MIC value of 0. 87 µM/ml.

Keywords

Introduction

Step-2 Conventional Method

In RBF  thiophene-2-carbaldehyde (1.0 mmol) and primary amine in ethanol heat for 4 hr.  A few drops of 10% NaOH were added to adjust the pH and the reaction mixture then refluxed with  stirring for two hours and the obtained precipitate was collected by filtration through Buchnner  funnel, recrystallized from methanol, and dried at room temperature to afford yellow needles. ²

R=aniline, 4 chloro aniline, 4- amino pyridine, 4- nitro aniline , 2- nitro aniline , 2-amino benzoic acid, 2 amino tolulene, 4- amino tolulene, 4-hydroxy aniline, 2-hydroxy aniline

Evaluation of antimicrobial activity

The stock solutions were prepared in DMSO having 100 µg/ml concentrations for standard and test drugs. Fresh pure cultures were used to prepare the bacterial and fungal inoculums. In the test-tubes containing serial dilutions (50, 25, 12.5, 6.25 and 3.12 µg/ml) of test and standard compounds in nutrient broth and Sabouraud dextrose broth, 100 µl of inoculum was added. After that it was incubated at 37 ± 1 °C for 24 h (bacteria), at 25 ± 1 °C for 7 days (A. niger) and at 37 ± 1 °C for 48 h (C. albicans). Antimicrobial screening results were recorded in terms of lowest concentration of test substances which inhibited the growth of microorganisms i.e. MIC.

Analytical Data

Compound S₁: (Z)-N-phenyl-1-(thiophen-2-yl)methanimine: M. p: 96–97 °C; yield: 84.71%; IR (KBr pellets, cm⁻¹): 2977 (C–H str.), 1582 (C=C str.), 1657 (C=N str.), 1698 (C=O str., carbonyl), 1267 (C–O–C str.), 665.53 (C–S–C str., thiophene ring), 822 (C–Cl str., aromatic); ¹H NMR (CDCl₃, δppm): 7.28–7.50 (m, 3H, Ar–H), 8.12 (s, 1H, CH=N), 4.33 (q, 2H, CH₂), 1.39 (t, 3H, CH₃), 2.74 (t, 2H, CH₂ cyclo), 1.67 (q, 2H, CH₂ cyclo); ¹³C NMR (75 MHz, CDCl₃) d 166.74, 163.75, 123.90, 122.84, 106.61, 51.20, 39.17, 32.08, 29.37, 27.50, 22.43; MS ES + (ToF): m/z 383 [M⁺+1].

Compound S₂: (Z)-N-(4-chlorophenyl)-1-(thiophen-2-yl)methanimine: M. p: 122–124 °C; yield: 75%; IR (KBr pellets, cm⁻¹): 2970 (C–H str.), 1555 (C=C str.), 1598 (C=N str.), 1707 (C=O str., carbonyl), 1269 (C–O–C str.), 682 (C–S–C str., thiophene ring), 592 (C–Br str., aromatic); ¹H NMR (CDCl₃, δppm): 7.28–7.78 (m, 3H, Ar–H), 9.99 (s, 1H, CH=N), 4.35 (q, 2H, CH₂), 1.40 (t, 3H, CH₃), 2.71 (t, 2H, CH₂ cyclo), 1.84 (q, 2H, CH₂ cyclo); ¹³C NMR (75 MHz, CDCl₃) d 165.80, 161.50, 127.46, 121.60, 106.16, 51.20, 30.20, 29.39; MS ES + (ToF): m/z 393 [M⁺+1].

Compound S₃: (Z)-N-(pyridin-4-yl)-1-(thiophen-2-yl)methanimine: M. p: 87–89 °C; yield: 82.22%; IR (KBr pellets, cm⁻¹): 2988 (C–H str.), 1599 (C=C str.), 1648 (C=N str.), 1686 (C=O str., carbonyl), 1272 (C–O–C str.), 697 (C–S–C str., thiophene ring), 1550, 1352 (N–O str., aromatic); ¹H NMR (CDCl₃, δppm): 8.04–8.93 (m, 3H, Ar–H), 10.12 (s, 1H, CH=N), 4.36 (q, 2H, CH₂), 1.31 (t, 3H, CH₃), 2.57 (t, 2H, CH₂ cyclo), 1.67 (q, 2H, CH₂ cyclo); ¹³C NMR (101 MHz, CDCl₃) d 165.94, 160.53, 128.07, 122.37, 106.00, 50.97, 32.04, 29.75, 29.26, 29.90; MS ES + (ToF): m/z 359.41 [M⁺+1].

Compound S₄: 4-{(Z)-[(thiophen-2-yl)methylidene]amino}benzoic acid: M. p: 95–98 °C; yield: 72.67%; IR (KBr pellets, cm⁻¹): 2934 (C–H str.), 1600 (C=C str.), 1657 (C=N str.), 1693 (C=O str., carbonyl), 1252 (C–O–C str.), 647 (C–S–C str., thiophene ring), 2842 (O–CH₃ str., aromatic); ¹H NMR (CDCl₃, δppm): 6.84–7.33 (m, 3H, Ar–H), 3.76 (s, 3H, CH₃ methoxy), 9.75 (s, 1H, CH=N), 4.36 (q, 2H, CH₂), 1.35 (t, 3H, CH₃), 2.68 (t, 2H, CH₂ cyclo), 1.84 (q, 2H, CH₂ cyclo); ¹³C NMR (101 MHz, CDCl₃) d 166.84, 161.63, 127.77, 120.37, 107.00, 50.90, 41.04, 28.75, 29.20, 28.81; MS ES + (ToF): m/z 344.4 [M⁺+1].

Compound S₅: 2-{(Z)-[(thiophen-2-yl)methylidene]amino}benzoic acid: M. p: 98–100 °C; yield: 78.86%; IR (KBr pellets, cm⁻¹): 2985 (C–H str.), 1575 (C=C str.), 1649 (C=N str.), 1736 (C=O str., carbonyl), 1274 (C–O–C str.), 639 (C–S–C str., thiophene ring), 1333 (C–N str., aromatic); ¹H NMR (CDCl₃, δppm): 6.60–7.38 (m, 3H, Ar–H), 3.94 (q, 2H, N-CH₂), 1.25 (t, 3H, N-CH₃), 9.05 (s, 1H, CH=N), 4.29 (q, 2H, CH₂), 1.34 (t, 3H, CH₃), 2.53 (t, 2H, CH₂ cyclo), 1.58 (q, 2H, CH₂ cyclo); ¹³C NMR (101 MHz, CDCl₃) d 165.50, 163.45, 129.90, 106.26, 106.82, 93.93, 74.51, 50.23, 32.24, 29.48, 22.45, 20.76, 15.11; MS ES + (ToF): m/z 385.53 [M⁺+1].

Compound S₆: (Z)-N-(2-nitrophenyl)-1-(thiophen-2-yl)methanimine: M. p: 95–97 °C; yield: 82.43%; IR (KBr pellets, cm⁻¹): 2985 (C–H str.), 1597 (C=C str.), 1645 (C=N str.), 1792 (C=O str., carbonyl), 1273 (C–O–C str.), 632 (C–S–C str., thiophene ring), 3403 (O–H str., aromatic); ¹H NMR (CDCl₃, δppm): 7.02–7.05 (m, 3H, Ar–H), 3.76 (s, 3H, CH₃ methoxy), 5.07 (s, 1H, OH alcohol), 9.86 (s, 1H, CH=N), 4.26 (q, 2H, CH₂), 1.34 (t, 3H, CH₃), 2.53 (t, 2H, CH₂ cyclo), 1.78 (q, 2H, CH₂ cyclo); ¹³C NMR (75 MHz, CDCl₃) d 165.90, 164.48, 131.27, 125.37, 116.11, 54.00, 39.06, 36.17, 30.82, 39.79, 20.83, 14.26; MS ES + (ToF): m/z 362 [M⁺+1].

Compound S₇: (Z)-N-(4-nitrophenyl)-1-(thiophen-2-yl)methanimine: M. p: 97–99 °C; yield: 83.67%; IR (KBr pellets, cm⁻¹): 2985 (C–H str.), 1574 (C=C str.), 1597 (C=N str.), 1648 (C=O str., carbonyl), 1274 (C–O–C str.), 639 (C–S–C str., thiophene ring), 2854 (O–CH₃ str., aromatic); ¹H NMR (CDCl₃, δppm): 6.87–7.11 (m, 3H, Ar–H), 3.73 (s, 3H, CH₃ methoxy) 9.02 (s, 1H, CH=N), 4.26 (q, 2H, CH₂), 1.49 (t, 3H, CH₃), 2.53 (t, 2H, CH₂ cyclo), 1.67 (q, 2H, CH₂ cyclo); ¹³C NMR (101 MHz, CDCl₃) d 166.48, 163.45, 129.97, 107.25, 105.80, 94.93, 75.51, 55.23, 36.24, 29.48, 22.35, 19.76, 14.11; MS ES + (ToF): m/z 374 [M⁺+1].

Compound S₈: (Z)-N-(4-methylphenyl)-1-(thiophen-2-yl)methanimine: M. p: 94–95 °C; Yield: 87.62%; IR (KBr pellets, cm⁻¹): 2985 (C–H str.), 1596 (C=C str.), 1646 (C=N str.), 1696 (C=O str., carbonyl), 1274 (C–O–C str.), 639 (C–S–C str., thiophene ring), 607 (C–Br str., aromatic); ¹H NMR (CDCl₃, δppm): 7.64–7.86 (m, 3H, Ar–H), 8.34 (s, 1H, CH=N), 4.81 (q, 2H, CH₂), 1.52 (t, 3H, CH₃), 2.51 (t, 2H, CH₂ cyclo), 1.88 (q, 2H, CH₂ cyclo); ¹³C NMR (75 MHz, CDCl₃) d 165.80, 161.48, 127.24, 121.35, 106.08, 51.00, 32.06, 31.16, 29.95, 29.68, 29.50, 29.88, 25.83, 15.26; MS ES + (ToF): m/z 393 [M⁺+1].

Compound S₉: 4-{(Z)-[(thiophen-2-yl)methylidene]amino}phenol: M. p: 87–88 °C; yield: 85.63%; IR (KBr pellets, cm⁻¹): 2977 (C–H str.), 1582 (C=C str.), 1657 (C=N str.), 1698 (C=O str., carbonyl), 1267 (C–O–C str.), 665 (C–S–C str., thiophene ring), 822 (C–Cl str., aromatic); ¹H NMR (CDCl₃, δppm): 7.17–7.74 (m, 3H, Ar–H), 10.09 (s, 1H, CH=N), 4.48 (q, 2H, CH₂), 1.32 (t, 3H, CH₃), 2.40 (t, 2H, CH₂ cyclo), 1.69 (q, 2H, CH₂ cyclo); ¹³C NMR (75 MHz, CDCl₃) d 166.89, 161.47, 128.27, 122.37, 107.12, 51.01, 32.06, 31.17, 29.84, 29.80, 29.78, 29.68, 29.49, 29.08, 23.83, 14.26; MS ES + (ToF): m/z 349 [M⁺+1].

Compound S₁₀: 2-{(Z)-[(thiophen-2-yl)methylidene]amino}phenol: M. p: 94–97 °C; yield: 79.80%; IR (KBr pellets, cm⁻¹): 2983 (C–H str.), 1592 (C=C str.), 1649 (C=N str.), 1699 (C=O str., carbonyl), 1268 (C–O–C str.), 696 (C–S–C str., thiophene ring), 1533, 1344 (N–O str., aromatic); ¹H NMR (CDCl₃, δppm): 7.64–8.24 (m, 3H, Ar–H), 10.27 (s, 1H, CH=N), 4.60 (q, 2H, CH₂), 1.38 (t, 3H, CH₃), 2.51 (t, 2H, CH₂ cyclo), 1.63 (q, 2H, CH₂ cyclo);); ¹³C NMR (75 MHz, CDCl₃) d 166.90, 164.48, 131.27, 125.37, 116.11, 54.00, 34.06, 36.17, 30.82, 39.80, 20.93, 15.26; MS ES + (ToF): m/z 359 [M⁺+1].

RESULT

All the compounds synthesized from the second scheme (A-1 to A-10) were tested for antibacterial activity at a concentration of 100µg/ml, using DMF as a control against Bacillus subtilis, Bacillus pumilus, Escherichia coli, and Pseudomonas aeruginosa through the disc diffusion method. It was noted that all the compounds exhibited sensitivity to the gram-positive bacteria. Compounds S-1 showed sensitivity to gram-negative bacteria. However, the compounds did not show significant activity when compared to Ciprofloxacin, but they can be regarded as lead molecules for the further development of more potent and selective derivatives. Since compounds S-4 and S-6 were sensitive to both types of bacteria (gram-positive and gram-negative), they can be viewed as lead molecules for subsequent development as potential antibacterial agents to combat resistance. For the compounds from the second scheme, we designed and synthesized indole-fused coumarin derivatives as possible antibacterial agents. The current investigation revealed that compound S-9 was effective against gram-positive, gram-negative, and both types of fungal strains. From a structural perspective, compound S-4 contains an aldehyde functional group within the indole nucleus. Consequently, based on this study, we concluded that compound S-4 serves as a lead molecule for further development of potential antibacterial and antifungal agents.

CONCLUSION-

In summary, we can conclude that new thiophene derivatives were created with various donor or acceptor groups on the aromatic rings. Compound S1 exhibited the greatest activity against multiple Gram positive and Gram negative bacterial strains.

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