Synthesis of S-Phenacylated Trisubstituted 1,2,4-Triazole Incorporated with 5-(Benzofuran-2-yl)-1-Phenyl-1H-Pyrazol-3-yl Moiety and their Antibacterial Screening

Mohammad Idrees1*, Roshan D Nasare2 and Naqui J Siddiqui1

1Department of Chemistry, Government Institute of Science, Nagpur, Maharashtra, India

2Department of Chemistry, Government Science College, Gadchiroli, Maharashtra, India

Visit for more related articles at Der Chemica Sinica

Abstract

Starting with a concise and practical synthesis of acyl thiosemicarbazides (3a-h), a series of new 1,2,4-triazole derivatives (4a-h), have been synthesized by intramolecular cyclization in alkaline medium. The acyl thiosemicarbazides required for this purpose were obtained by reaction of carbohydrazides (1a-b) with appropriate aromatic isothiocyanates (2a-h). Subsequently, 4a-h which upon treatment with phenacyl bromide underwent S-phenacylation in presence of triethylamine afforded 5a-h. The structural identities of 3a, 4a and 5a compound were established on the basis of elemental analysis and spectral studies such as 1H NMR, IR, 13C NMR and mass while rest of the compounds were characterized by elemental analysis and IR spectroscopy. The synthesized compound acyl thiosemicarbazide (3a) and 1,2,4-triazole (5a) were evaluated for their in vitro antibacterial activity against pathogenic bacteria and the results were comparable with Chloramphenicol antibiotic.

Keywords

1,2,4-triazole, Acylthiosemicarbazide, Arylisothiocyate, Carbohydrazides

Introduction

The rapid development of bacterial resistance to conventional drugs is one of the major difficulties in the treatment of bacterial infection, thus it is still necessary to search for new antibacterial agent. Triazole derivatives have occupied a unique position in heterocyclic chemistry due to their antimicrobial activities. 1,2,4-triazoles as antibacterial agents can be grouped according to the mode of action, i.e., the ability to inhibit the synthesis of the cell wall, cell membrane, proteins and nucleic acids of bacteria. 1,2,4-triazoles exhibit a wide range of therapeutical properties like antibacterial [1-5], antifungal [6], anti-inflammatory [7], antituberculosis [8], anticancer [9], antioxidant [10], InhA inhibitory activity [11], antidepressant [12], etc. Some of the modern day drugs with triazole nucleus are as fluconazole, itraconazole, terconazole, posaconazole, voriconazole. Moreover, now a day researchers prefer to synthesize hybrids of heterocycles to enhance the therapeutically activities. 1,2,4-triazoles with other heterocyclic derivatives possess a wide spectrum of biological activities. The huge number of 1,2,4-triazoles containing hybrid systems exhibits anticonvulsant and CNS depressant [13], anticancer [14], antioxidant [15] activity, etc.

1,2,4-triazole have been prepared by different methods. One of the most common routes to these compounds involves cyclodehydration of acylthiosemicarbazides with a variety of basic reagents, such as sodium hydroxide [16-18], potassium hydroxide [19], sodium carbonate [20], triethylamine [21], etc. In addition, it is known that acylthiosemicarbazides, the versatile key intermediates itself has various pharmacological activities like analgesic [22], antibacterial [23], antifungal [24,25], antitubercular [26], etc.

In view of these above findings the present paper reports on the synthesis of a some new 1,2,4-triazoles derivatives bearing 5-(benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl obtained through cyclodehydration of acyl thiosemicarbazides in basic medium followed by S-phenacylation with phenacyl bromide in weak base and investigates the potential antibacterial activity.

Materials and Methods

The melting points were recorded in open capillary in paraffin bath and are uncorrected. IR spectra were recorded on a Shimadzu IR Spectrophotometer (KBr, v max in cm-1). 1H NMR spectra are recorded on a Bruker AM 400 instrument (400 MHz) using tetramethylsilane (TMS) as an internal reference and DMSO-d6 as solvent and 13C NMR spectra are recorded on a Bruker AM 400 instrument (100 MHz) and DMSO-d6 as solvent. Chemical shifts are given in parts per million (ppm). Positive-ion Electro Spray Ionization (ESI) mass spectra were obtained with a Waters Micromass Q-TOF Micro, Mass Spectrophotometer. Elemental (CHN) analysis was done using Thermo Scientific (Flash-2000). The compounds were analyzed for carbon, hydrogen, nitrogen and sulphur and the results obtained are in good agreement with the calculated values. Chemicals used for the synthesis were of AR grade of Merck, S.D. Fine and Aldrich. The reactions were monitored by E. Merck TLC aluminum sheet silica gel60F254 and visualizing the spot in UV Cabinet and iodine chamber.

Experimental

General procedure for the synthesis of 1-(5-(5-H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)- 4-substituted/unsubstituted phenyl thiosemicarbazides (3a-h): A mixture of 1a-b (10 mmol) and appropriate aromatic isothiocyanates 2a-h (11 mmol) in chloroform (30 mL) was refluxed for 1.5 h. The reaction mixture was cooled, excess of solvent was removed under reduced pressure, solid obtained was washed with water, filtered and further purified by recrystallization using 1,4-dioxane to give 3a-h (Scheme 1).

der-chemica-sinica-unsubstituted-pheny

Scheme 1: Synthesis of 1-(5-(5-H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-substituted/unsubstituted phenyl thiosemicarbazides (3a-h).

1-(5-(benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-p-tolylthiosemicarbazide (3a): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 224-226°C; yield, 94%; IR (KBr v max in cm-1): 3114, 3146, 3227, 3312 (NH), 3035, 3066 (ArH), 1650 (C=O), 1234 (C=S), 1441, 1481 (C=C), 1261, 1063 (C-O-C), 1513 (C=N); 1H NMR(DMSO-d6) δ (ppm): 2.28 (s, 3H, Ar-CH3), 6.60 (s, 1H, pyrazole CH), 7.11-7.61 (m, 14H, ArH), 9.73 (s, 1H, NH-CS-NHC6H5), 9.78 (s, 1H, NH-CS-NHC6H5), 10.44 (s, 1H, -CONH NH-CS-NHC6H5); MS: m/z 468 [M+H]+, 469 [M+2]+, 470 [M+3]+, 490 [M+Na]+, 491 [(M+H)+Na]+. Elemental Anal. Calcd: for C26H21O2N5S; C, 66.79; H, 4.53; N, 14.98; S, 6.86; Found: C, 66.12; H, 4.24; N, 14.33; S, 6.23.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-(4-bromophenyl) thiosemicarbazide (3b): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 255-257°C; yield, 89%; IR (KBr v max in cm-1): 3146, 3226, 3315 (NH), 3030, 3056 (ArH), 1618 (C=O), 1227 (C=S), 1435, 1486 (C=C), 1267 (C-O-C), 1502 (C=N). Elemental Anal. Calcd: for C25H17Br2N5O2S; N, 11.46; S, 5.25; Found: N, 11.03; S, 5.11.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-(4-chlorophenyl) thiosemicarbazide (3c): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 246-250°C; yield, 82%; IR (KBr v max in cm-1): 3148, 3223, 3315 (NH), 3027, 3038 (ArH), 1618 (C=O), 1228 (C=S), 1436, 1488 (C=C), 1267 (C-O-C), 1510 (C=N). Elemental Anal. Calcd: for C25H17BrClN5O2S; N, 12.35; S, 5.66; Found: N, 12.17; S, 5.02.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-(3-chlorophenyl) thiosemicarbazide (3d): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 260-262°C; yield, 80%; IR (KBr v max in cm-1): 3198, 3227, 3312 (NH), 3027, 3053 (ArH), 1647 (C=O), 1222 (C=S), 1432, 1478 (C=C), 1261 (C-O-C), 1508 (C=N). Elemental Anal. Calcd: for C25H17Br2N5O2S; N, 12.35; S, 5.66; Found: N, 12.40; S, 5.36.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-o-tolyl thiosemicarbazide (3e): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 243-245°C; yield, 86%; IR (KBr v max in cm-1): 3195, 3226, 3317 (NH), 3024, 3048 (ArH), 1652 (C=O), 1234 (C=S), 1432, 1488 (C=C), 1253, 1060 (C-O-C), 1517 (C=N). Elemental Anal. Calcd: for C26H20BrN5O2S; N, 12.82; S, 5.87; Found: N, 12.26; S, 5.54.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-m-tolyl thiosemicarbazide (3f): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 236-240°C; yield, 84%; IR (KBr v max in cm-1): 3251, 3307 (NH), 3022, 3033 (ArH), 1645 (C=O), 1242 (C=S), 1433, 1485 (C=C), 1262 (C-O-C), 1567 (C=N). Elemental Anal. Calcd: for C26H20BrN5O2S; N, 12.82; S, 5.87; Found: N, 12.31; S, 5.38.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-p-tolyl thiosemicarbazide (3g): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 238-240°C; yield, 78%; IR (KBr v max in cm-1): 3241, 3314 (NH), 3066 (ArH), 1642 (C=O), 1228 (C=S), 1434, 1494 (C=C), 1265 (C-O-C), 1516 (C=N). Elemental Anal. Calcd: for C26H20BrN5O2S; N, 12.82; S, 5.87; Found: N, 12.13; S, 5.46.

1-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-phenyl thiosemicarbazide (3h): White crystalline solid; recrystallization solvent, 1,4-dioxane; mp, 243-245°C; yield, 86%; IR (KBr v max in cm-1): 3193, 3245, 3326 (NH), 3045, 3053 (ArH), 1646 (C=O), 1231 (C=S), 1454, 1489 (C=C), 1261 (C-O-C), 1513 (C=N). Elemental Anal. Calcd: for C25H18BrN5O2S; N, 13.15; S, 6.02; Found: N, 12.94; S, 5.86.

General procedure for the synthesis 5-(5-(H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-Substituted/ unsubstituted phenyl-2H-1,2,4-triazole-3(4H)-thione (4a-h): Thiosemicarbazide 3a-h (0.002 M) in sodium hydroxide (4N, 6 mL) solution and ethanol (20 mL) was heated under reflux for 3 h. The reaction mixture was cooled to room temperature and acidified with diluted acetic acid. The product thus separated was filtered, washed with excess of water and recrystallized from ethanol to afford compound 4a-h (Scheme 2).

der-chemica-sinica-Substituted-unsubstituted

Scheme 2: Synthesis 5-(5-(H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-Substituted/unsubstituted phenyl-2H-1,2,4-triazole-3(4H)-thione (4a-h).

5-(5-(benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-p-tolyl-2H-1,2,4-triazole-3(4H)-thione (4a): White crystalline solid; recrystallization solvent, Ethanol; mp, 230-232°C; yield, 88%; IR (KBr v max in cm-1): 3316 (N-H), 3064 (ArH), 1610 (C=N), 1435 (C=C), 1248 (C-O-C), 1154 (C=S); 1H NMR(DMSO-d6) δ (ppm): 2.47 (s, 3H, Ar-CH3), 6.61 (s, 1H, C3-H of Benzofuran), 6.30 (s, 1H, pyrazole CH), 7.18-7.48 (m, 14H, ArH); 13C NMR δ (ppm): 21, 106, 107, 111, 121, 123, 125, 127, 128, 129, 130, 131, 135, 139, 140, 141, 146, 154, 169; Elemental Anal. Calcd: for C26H19 N5OS; N, 15.58; S, 7.13; Found: N, 15.21; S, 6.98.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-(4-bromophenyl)-2H-1,2,4-triazole-3(4H)-thione (4b): White crystalline solid; recrystallization solvent, Ethanol; mp, 222-224°C; yield, 83%; IR (KBr v max in cm-1): 3314 (N-H), 3066 (ArH), 1609 (C=N), 1434, 1494 (C=C), 1256, 1228 (C-O-C), 1152 (C=S). Elemental Anal. Calcd: for C25H15Br2N5OS; N, 11.80; S, 5.40; Found: N, 11.24; S, 5.22.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-(4-chlorophenyl)-2H-1,2,4-triazole-3(4H)-thione (4c): White crystalline solid; recrystallization solvent, Ethanol; mp, 246-248°C; yield, 80%; %; IR (KBr v max in cm-1): 3312 (N-H), 3055 (ArH), 1597 (C=N), 1432, 1491 (C=C), 1245 (C-O-C), 1153 (C=S). Elemental Anal. Calcd: for C25H15BrClN5OS; N, 12.76; S, 5.84; Found: N, 12.54; S, 5.68.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-(3-chlorophenyl)-2H-1,2,4-triazole-3(4H)-thione (4d): White crystalline solid; recrystallization solvent, Ethanol; mp, 226-228°C; yield, 78%; IR (KBr v max in cm-1): 3316 (N-H), 3062 (ArH), 1597 (C=N), 1432, 1489 (C=C), 1245 (C-O-C), 1152 (C=S). Elemental Anal. Calcd: for C25H15BrClN5OS; N, 12.76; S, 5.84; Found: N, 12.48; S, 5.57.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-o-tolyl-2H-1,2,4-triazole-3(4H)-thione (4e): White crystalline solid; recrystallization solvent, Ethanol; mp, 243-245°C; yield, 83%; IR (KBr v max in cm-1): 3313 (N-H), 3061 (ArH), 1607 (C=N), 1432 (C=C), 1253 (C-O-C), 1154 (C=S). Elemental Anal. Calcd: for C26H18BrN5OS; N, 13.25; S, 6.07; Found: N, 12.97; S, 6.02.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-m-tolyl-2H-1,2,4-triazole-3(4H)-thione (4f): White crystalline solid; recrystallization solvent, Ethanol; mp, 252-254°C; yield, 84%; IR (KBr v max in cm-1): 3317 (N-H), 3068 (ArH), 1579 (C=N), 1444, 1493 (C=C), 1251 (C-O-C), 1152 (C=S). Elemental Anal. Calcd: for C26H18BrN5OS; N, 13.25; S, 6.07; Found: N, 13.08; S, 5.99.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-p-tolyl-2H-1,2,4-triazole-3(4H)-thione (4g): White crystalline solid; recrystallization solvent, Ethanol; mp, 242-244°C; yield, 84%; IR (KBr v max in cm-1): 3315 (N-H), 3066 (ArH), 1595 (C=N), 1437, 1499 (C=C), 1249 (C-O-C), 1152 (C=S). Elemental Anal. Calcd: for C26H18BrN5OS; N, 13.25; S, 6.07; Found: N, 13.03; S, 6.03.

5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-phenyl-2H-1,2,4-triazole-3(4H)-thione (4h): White crystalline solid; recrystallization solvent, Ethanol; mp, 258-260°C; yield, 84%; IR (KBr v max in cm-1): 3314 (N-H), 3049 (ArH), 1583 (C=N), 1445, 1479 (C=C), 1252 (C-O-C), 1153 (C=S). Elemental Anal. Calcd: for C25H16BrN5OS; N, 13.61; S, 6.23; Found: N, 13.23; S, 6.09.

General procedure for the synthesis 2-(5-(5-(H/Bromo benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4- substituted/unsubstituted phenyl-4H-1,2,4-triazol-3-ylthio)-1-phenylethanone (5a-h): A mixture of 4a-h (0.001 mmol) and phenacyl bromide (0.001 mmol) were dissolved in ethanol (15 mL) and 2-3 drops of triethylamine was added as a catalyst. The reaction mixture was heated for 3h and cooled to room temperature then content was poured into cold water and product separated was filtered, washed with ethanol and recrystallized from 1,4-dioxane to give 5a-h (Scheme 3).

der-chemica-sinica-Bromo-benzofuran

Scheme 3: Synthesis 2-(5-(5-(H/Bromo benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-substituted/unsubstituted phenyl-4H-1,2,4-triazol-3-ylthio)-1-phenylethanone (5a-h).

2-(5-(5-(benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-p-tolyl-4H-1,2,4-triazol-3-ylthio)-1-phenylethanone (5a): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 218-220°C; yield, 86%; IR (KBr v max in cm-1): 3056, 3037 (ArH), 2954, 2917, 2849 (CH3 and CH2), 1685 (C=O), 1466, 1579, 1595 (C=C), 1513 (C=N), 1256, 1072 (C-O-C), 1045 (N-N), 691 (C-S-C); 1H NMR(DMSO-d6) δ (ppm): 2.41 (s, 3H, Ar-CH3), 4.99 (s, 2H, CH2), 6.65 (s, 1H, pyrazole CH), 7.03-8.06 (m, 19H, ArH); MS: m/z 568 [M+H]+, 569 [M+2]+, 590 [M+Na]+. Elemental Anal. Calcd: for C34H25N5O2S; C, 71.94; H, 4.44; N, 12.34; S, 5.65; Found: C, 71.12; H, 4.21; N, 12.13; S, 5.58.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-(4-bromophenyl)-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5b): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 254-256°C; yield, 82%; IR (KBr v max in cm-1): 3052, 3033 (ArH), 2949, 2915 (CH3 and CH2), 1673 (C=O), 1434, 1493 (C=C), 1585 (C=N), 1248 (C-O-C), 685 (C-S-C). Elemental Anal. Calcd: for C33H21Br2N5O2S; N, 9.84; S, 4.51; Found: N, 9.13; S, 4.26.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-(4-chlorophenyl)-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5c): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 256-258°C; yield, 80%; IR (KBr v max in cm-1): 3044, 3037 (ArH), 2948, 2917 (CH3 and CH2), 1671 (C=O), 1430, 1494 (C=C), 1583 (C=N), 1248 (C-O-C), 683 (C-S-C). Elemental Anal. Calcd: for C33H21BrClN5O2S; N, 10.50; S, 4.81; Found: N, 9.98; S, 4.37.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-(3-chlorophenyl)-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5d): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 214-218°C; yield, 79%; IR (KBr v max in cm-1): 3060, 3036 (ArH), 2946, 2911 (CH3 and CH2), 1676 (C=O), 1429, 1484 (C=C), 1582 (C=N), 1252 (C-O-C), 685 (C-S-C). Elemental Anal. Calcd: for C33H21BrClN5O2S; N, 10.50; S, 4.81; Found: N, 10.12; S, 4.32.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-o-tolyl-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5e): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 290-294°C; yield, 77%; IR (KBr v max in cm-1): 3056, 3040 (ArH), 2942, 2916 (CH3 and CH2), 1670 (C=O), 1430, 1484 (C=C), 1583 (C=N), 1256, 1062 (C-O-C), 685 (C-S-C). Elemental Anal. Calcd: for C34H24BrN5O2S; N, 10.83; S, 4.96; Found: N, 10.52; S, 4.77.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-m-tolyl-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5f): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 206-208°C; yield, 77%; 3058, 3038 (ArH), 2952, 2917 (CH3 and CH2), 1672 (C=O), 1431, 1488 (C=C), 1585 (C=N), 1256 (C-O-C), 687 (C-S-C). Elemental Anal. Calcd: for C34H24BrN5O2S; N, 10.83; S, 4.96; Found: N, 10.52; S, 4.67.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-p-tolyl-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5g): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 218-220°C; yield, 74%; IR (KBr v max in cm-1): 3053, 3042 (ArH), 2929, 2917 (CH3 and CH2), 1671 (C=O), 1433, 1490 (C=C), 1585 (C=N), 1253, 1028 (C-O-C), 687 (C-S-C). Elemental Anal. Calcd: for C34H24BrN5O2S; N, 10.83; S, 4.96; Found: N, 10.18; S, 4.72.

2-(5-(5-(5-bromobenzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-phenyl-4H-1,2,4-triazol-3-ylthio)-1- phenylethanone (5h): White crystalline solid; solvent for recrystallization, 1,4-dioxane; mp, 218-220°C; yield, 74%; IR (KBr v max in cm-1): 3062, 3046 (ArH), 2927, 2914 (CH3 and CH2), 1676 (C=O), 1449, 1493 (C=C), 1584 (C=N), 1258, 1022 (C-O-C), 687 (C-S-C). Elemental Anal. Calcd: for C33H22BrN5O2S; N, 11.07; S, 5.07; Found: N, 10.88; S, 4.87.

Antibacterial activity

The novel synthesized acyl thiosemicarbazide 3a and 1,2,4-triazole 5a were screened for their in vitro antimicrobial activity using cup plate agar disc-diffusion method against two Gram positive bacterial strains, B. thurengienesis and S. aureus and two Gram negative strains, E. coli and E. aerogenes. Chloramphenicol was used as standard drug for bacteria.

General procedure

Determination of zone of inhibition by agar disc-diffusion method: Test solutions were prepared with known weight of compound in DMSO and half diluted suitably to give the resultant concentration of 31 μg/mL to 1000 μg/ mL. Whatmann no. 1 sterile filter paper discs (6 mm) were impregnated with solution and allowed to dry at room temperature. In vitro antibacterial activity was determined by using Mueller Hinton Agar obtained from Himedia Ltd., Mumbai. Petri plates were prepared by pouring 10 mL of Mueller Hinton Agar for bacteria containing microbial culture was allowed to solidify. The discs were then applied and the plates were incubated at 37°C for 24 h (bacteria) and the inhibition zone was measured as diameter in four directions and expressed as mean. The results were compared using chloramphenicol as a standard antibacterial agent. The results of antibacterial activity (i.e. zone of inhibition in mm) of some of the synthesized compounds are given in the Table 1.

S. No. Conc.(µg/mL) Zone of Inhibition in mm
Gram +ve Gram -ve
B. thurengienesis S. aureus E. coli E. aerogenes
3a
1 1000 16 8 15 10
2 500 12 15 22 12
3 250 10 14 15 15
4 125 10 8 24 8
5 63 8 10 22 8
6 31 - 8 8 -
5a
1 1000 15 13 18 10
2 500 13 8 20 14
3 250 18 14 24 12
4 125 14 18 16 8
5 63 16 12 16 10
6 31 16 20 20 14
Standard Chloramphenicol
1 1000 22 26 24 16
2 500 20 30 20 16
3 250 21 27 18 17
4 125 16 21 17 16
5 63 15 18 17 15
6 31 16 20 21 15

Table 1: Antibacterial Activity of 3a and 5a.

Results and Discussion

The schemes of the targeted synthesized compounds 3a-h, 4a-h and 5a-h are described in Schemes 1-3 respectively. The purity of synthesized compound at every synthetic stage was monitored by TLC technique. The structures of the newly synthesized products were substantiated based on elemental and spectral analysis such as IR, 1H NMR and mass. The synthesis of the starting compound, 5-(5-H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazides (1a-b) were achieved in quantitative yields by adopting published literature method [27].

The reaction of 1a-b with aryl isothiocyanates 2a-h in chloroform as a solvent led to the formation of 3a-h. The IR spectrum of 3a showed -NH stretch of amine at 3312 cm-1 and C=O stretching in amide group at 1650 cm-1. The 1H NMR spectrum showed singlet at δ 2.3 ppm for -CH3 protons, hence it confirms that aryl isothiocyanates has condensed with 5-(benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbohydrazide to afford 1-(5-(H/Br benzofuran- 2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-substituted/unsubstituted phenyl thiosemicarbazide derivatives 3a-h. The elemental analysis of this product gave C, 66.12; H, 4.24; N, 14.33 and S, 6.23. The mass spectra of the products revealed a molecular ion peak at m/z 468 [M+H]+ which is in agreement with the molecular formula C26H21O2N5S.

The reaction of 1-(5-(5-H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazole-3-carbonyl)-4-substituted/unsubstituted phenyl thiosemicarbazides 3a-h with NaOH (4N) yielded 5-(5-(H/Br benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)- 4-substituted/unsubstituted phenyl-2H-1,2,4-triazole-3(4H)-thione derivatives 4a-h. The IR spectrum of 4a reveals that C=O stretching in amide group has disappeared and 1,2,4-triazole endocyclic C=N stretch has appeared at 1610 cm-1. The 1H-NMR spectra revealed singlet signal at δ 2.47 ppm which was attributed to the -CH3 protons. 1H-NMR spectra showed expected signals for aromatic and aliphatic protons, obtained data assigned to the proposed structure 4a confirms that thiosemicarbazide has been cyclized to form 1,2,4-triazole.

Further, 5-(5-(benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4-p-tolyl-2H-1,2,4-triazole-3(4H)-thione (4a) treated with phenacyl bromide in presence of triethylamine afforded 2-(5-(5-(benzofuran-2-yl)-1-phenyl-1H-pyrazol-3-yl)-4- p-tolyl-4H-1,2,4-triazol-3-ylthio)-1-phenyl ethanone (5a).

4a exhibits thione-thiol tautomerization hence undergoes phenacylation when treated with phenacyl bromide in presence of a base. In this reaction, selective S-phenacylation was observed in presence of triethylamine; a weak base to afford 5a, which was confirmed from its spectral data. The IR spectra of 5a showed moderately strong bands around 2954 cm-1, 2917 cm-1, 2849 cm-1, 1685 cm-1 and 1045 cm-1, characteristic of the CH3 and CH2, C=O and N-N groups respectively. In the 1H NMR spectra, characteristic signal due to the -S-CH2-CO- protons appeared at δ 4.99 ppm. The signal due to the -CH3 protons appeared at δ 2.41 ppm. The signals due to the aromatic protons appeared as multiples at δ 7.03-8.06 ppm. Its elemental analysis reveals that % of C, H, N and S are 71.12, 4.21, 12.13 and 5.58 respectively, while its mass spectrum shows a molecular ion peak at m/z 568 [M+H]+ matches with the molecular formula C34H25N5O2S.

Antibacterial activity

Obtained results of in vitro antimicrobial activity of 3a and 5a are summarized in the Table 1 and their comparative study has done. Dark value in the Table 1 indicated that either zone of inhibition of tested compound at that particular concentration is greater or equal as standard drug. Data revealed that the acylthiosemicarbazide 3a showed good antibacterial activity against Gram positive bacteria, S. aureus and B. thurengienesis. It is inactive against S. aureus only at a concentration of 31 μg/mL. In case of Gram negative bacteria, 3a showed good activity against E.coli, and at a concentration of 500 μg/mL it showed high activity compared with standard drug while moderately active against E. aerogenes and inactive at 31 μg/mL.

1,2,4-triazole 5a showed good activity against all tested microorganisms at all concentrations. The part of interest is that it possesses high activity against E. coli at concentration of 500 μg/mL and 250 μg/mL. At lower concentration that is 31 μg/mL, 5a showed equal zone of inhibition against both the Gram positive bacteria compared with the standard drug chloramphenicol.

Conclusion

A series of novel 1,2,4-triazoles (4a-h, 5a-h) were successfully synthesized in good yields. In first step acyl thiosemicarbazides (3a-h) obtained by condensation of carbohydrazides (1a-b) with aromatic isothiocynates (2ah) then cyclization of acyl thiosemicarbazides to triazole thiones (4a-h) in presence of sodium hydroxide. Finally, 1,2,4-triazole thione was selectively S-phenacylated by phenacyl bromide in presence of triethylamine to give 5ah. Their purity and confirmation was checked by physical, analytical and spectral data. Antibacterial screening of selected compounds were found to possess high to moderate activity against selected strains of bacteria.

Acknowledgements

The authors are thankful to The Principal, Government Science College, Gadchiroli, for his support and cooperation. The authors are also thankful to Dr. S. D. Narkhede, Head, Department of Botany, GSC, Gadchiroli for permitting to carry out the antimicrobial activity, similarly the authors are also thankful to The Director, SAIF, Punjab University, Chandigarh for providing CHN analysis, IR, 1H NMR and Mass Spectra.

References

Select your language of interest to view the total content in your interested language

Viewing options

Flyer image
journal indexing image

Share This Article

T�rkiye'nin Yeni Nesil Bahis Adresi Matadorbet giris Adresi G�ncellenmistir!