Utility of N-aryl 2-aroylhydrazono-propanehydrazonoyl chlorides as precursors for synthesis of new functionalized 1,3,4-thiadiazoles with potential antimicrobial activity

Graphical abstract

Abstract

Starting from N-aryl 2-aroylhydrazono-propanehydrazonoyl chlorides, a series of new functionalized 1,3,4-thiadiazoles were prepared. The structures of the compounds prepared were confirmed by both elemental and spectral analyses as well as by alternate synthesis. The mechanisms of the studied reactions are outlined. The antimicrobial activities of the compounds prepared were screened and the results showed that most of such compounds exhibit considerable activities.

Introduction

The chemistry of hydrazonoyl halides of the general formula, R—C(X) NNHR’, 1, has attracted the interest of many research groups since their discovery in 1882 [1]. Their reactions with various reagents and their applications in synthesis of various heterocyclic compounds have been extensively reviewed by Shawali and/or his colleagues [2], [3], [4], [5], [6], [7], [8], [9], [10], [11], [12], [13], [14] and others [15], [16]. A survey of literature reveals the presence of two contradicting reports [17], [18], [19]. In one report [17], it was indicated that reaction of N-aryl 2-oxopropane-hydra-zonoyl bromide 2a with acylhydrazines 3 yielded the corresponding substitution products 4 which upon oxidation afforded the corresponding formazan derivatives 5 (Scheme 1). In contrast, it was recently reported that reaction of N-aryl 2-oxopropanehydrazonoyl chlorides 2b with acylhydrazines 3 yielded the condensation products 6 [18], [19] (Scheme 1). In an attempt to provide further evidence for the actual pathway for the reaction of 2b with acid hydrazides, it was thought interesting to study the reaction of the products 6 with some sulfur dipolarophiles. This is because products of type 6 still have the hydrazonoyl chloride moiety. Our objective after such a study was to explore the utility of compounds of type 6 as precursors in syntheses of new thiadiazoline derivatives of expected biological activities. This is because many 1,3,4-thiadiazoles have been reported to possess several biological activities such as anticancer, antihistaminic and hypoglycemic activities [20], [21], [22].

Scheme 1.

Experimental

All melting points were measured on Electrothermal IA 9000 series digital melting point apparatus. The IR spectra were recorded in potassium bromide disks on a Pye Unicam SP 3300 and Shimadzu FT IR 8101 PC infrared spectrophotometer. ¹H NMR (300 MHz) was run in deuterated dimethyl sulfoxide (DMSO-d₆). Chemical shifts were related to that of the solvent. Mass Spectra were recorded on a Shimadzu GCMS-QP1000 EX mass spectrometer at 70 eV. Elemental analyses were carried out at the Microanalytical Center of Cairo University, Giza, Egypt. All reactions were followed by TLC (Silica gel, Aluminum Sheets 60 F254, Merck). 2-(2-benzoylhydrazono)-N′-phenylpropanehydrazonoyl chloride 6a, 2-(2-benzoylhydrazono)-N′-p-tolylpropanehydrazonoyl chloride 6b, 2-(2-(4-methylbenzoyl)hydrazono)-N′-(p-tolyl)propanehydrazonoyl chloride 6c, methyl N-phenyldithiocarbamate, methyl benzylidenedithiocarbazate, methyl dithiocarbazate, methyl benzoylcarbodithioate, and 5-phenyl-1,3,4-oxadiazole-2-thiol were prepared as reported in the literature [18], [19], [23], [24].

Synthesis of phenyl 2-(2-benzoylhydrazono)-N′-phenylpropanehydrazonothioate (7)

Method A

A mixture of 6 (0.31 g, 1 mmol) and sodium thiophenolate (0.13 g, 1 mmol) in ethanol (20 mL) was stirred at rt for 2 h, and the solid formed was filtered off, washed with ethanol, dried and recrystallized from ethanol to give 7 as yellow crystals (94%); m.p. 180–182 °C (EtOH); IR: v 1591 (C N), 1653 (C O), 3193, 3443 (2NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.19 (s, 3H, CH₃), 6.90–7.89 (m, 15H, ArH’s), 9.81 (s, br, 1H, NH), 12.58 (s, br, 1H, NH); Anal. Calcd for C₂₂H₂₀N₄O_S (388.49): C, 68.02; H, 5.19; N, 14.42; S, 8.25 Found C, 68.14; H, 5.21; N, 14.23; S, 8.34%.

Method B

A mixture of 8 (0.27 g, 1 mmol) and benzoylhydrazide (0.13 g, 1 mmol) in ethanol (20 mL) was heated under reflux for 2 h, allowed to cool and the solid formed was filtered off, washed with ethanol, dried and recrystallized from ethanol to give product in 78% yield identical in all aspects (mp., mixed mp. and spectra data) with 7 obtained by method A.

Synthesis of phenyl 2-oxo-N′-phenylpropanehydrazonothioate (8)

A mixture of 2b (0.19 g, 1 mmol) and sodium thiophenolate (0.13 g, 1 mmol) in ethanol (30 mL) was stirred at rt for 1 h, and then it was left overnight. The solid precipitate formed was filtered off, dried and crystallized from ethanol to give the corresponding product 8 as yellow crystals (83%); m.p. 118 °C (AcOH). IR: ν 3264 (NH), 1659 (CO), 1600 (C N) cm⁻¹. ¹H NMR (DMSO-d6): δ 2.33 (s, 3H, CH₃), 6.90–7.41 (m, 10H, ArH’s), 9.87 (s, br., 1H, NH). Anal. Calcd for C₁₅H₁₄N₂OS (270.35): C, 66.64; H, 5.22; N, 10.36; S, 11.86. Found C, 66.59; H, 5.10; N, 10.28; S, 11.68%.

Synthesis of iminothiadiazolines 9a,b

Method A

A mixture of the appropriate 6 (5 mmol) and potassium thiocyanate (0.6 g, 6 mmol) in ethanol (25 mL) was stirred at rt for 24 h. The resulting solid was collected, washed with water, and crystallized from ethanol to give the corresponding product 9.

Method B

A mixture of the appropriate 6 (0.005 mol) and thiourea (0.38 g, 5 mmol) in ethanol (25 mL) was refluxed for 3 h. The solid product that formed after cooling was collected and crystallized from ethanol to give the corresponding product 9 in 75% yield which proved identical in all aspects with that obtained by method A.

N′-(1-(5-Imino-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)-benzo-hydrazide (9a)

Yellow solid (78%); m.p. 210–2 °C (EtOH); IR: v 1600 (C N), 1658 (C O), 3308, 3184 (2NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.32 (3H, s, CH₃), 6.90–7.90 (10H, m, ArH’s), 10.13 (1H, s, NH), 10.83 (1H, s, NH); ¹³C NMR: δ 13.4 (CH₃), 126.2, 128.1, 128.9, 130.2, 130.8, 134.5, 140.1, 148.4, 155.3, 161.5, 165.2; MS m/z (%): 338 (M⁺+1, 5), 337 (M⁺, 32), 278 (33), 161 (19), 105 (100), 77 (100). Anal. Calcd for C₁₇H₁₅N₅OS (337.40): C, 60.52; H, 4.48; N, 20.76. Found C, 60.58; H, 4.40; N, 20.56%.

N′-(1-(5-Imino-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)-benzo-hydrazide (9b)

Yellow solid (72%); m.p. 210 °C (EtOH); IR: v 1610 (C N), 1674 (C O), 3169, 3310 (2NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.31 (3H, s, CH₃), 2.50 (3H, s, CH₃), 6.63–8.19 (10H, m, ArH’s), 10.63 (1H, s, NH), 11.37 (1H, s, NH); ¹³C NMR: δ 13.4, 21.1, 121.1, 128.6, 129.9, 131.5, 134.6, 140.4, 148.4, 155.4, 161.4, 164.8; MS m/z (%): 352 (M⁺+1, 4), 351 (M⁺, 14), 161 (12), 105 (100), 77 (54). Anal. Calcd for C₁₈H₁₇N₅OS (351.43): C, 61.52; H, 4.88; N, 19.93. Found C, 61.46; H, 4.92; N, 19.69%.

Preparation of the N-nitroso derivatives 10a,b

A cold saturated solution of sodium nitrite (10 mL) was added dropwise to a solution of the appropriate 9 (1 g) in acetic acid (20 mL) in an ice bath while stirring. The reaction mixture was stirred for 30 min. The resulting solid was collected, washed with water, and crystallized from acetone to give the corresponding 10a and 10b, respectively.

N′-(1-[5-(nitrosoimino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl]ethylidene)benzohydrazide (10a)

Orange solid (69%); m.p. 187–9 °C; IR: v 1581 (N O), 1640 (C N), 1681 (C O), 3442 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.29 (3H, s, CH₃), 6.63–8.18 (10H, m, ArH’s), 10.63 (1H, s, NH); ¹³C NMR (DMSO-d6): δ 1.3.4, 126.5, 127.4, 128.9, 130.2, 123.8, 134.7, 139.8, 155.7, 160.9, 161.8, 165.1; MS m/z (%): 367 (M⁺+1, 4), 367 (M⁺, 16), 314 (8), 278 (32), 161 (15), 105 (100), 77 (73). Anal. Calcd for C₁₇H₁₄N₆O₂S (366.40): C, 55.73; H, 3.85; N, 22.94. Found C, 55.89; H, 3.96; N, 22.74%.

N′-(1-[4-(4-methylphenyl)-5-(nitrosoimino)-4,5-dihydro-1,3,4-thiadiazol-2-yl]-ethylidene)benzohydrazide (10b)

Orange solid (72%); m.p. 182–4 °C; IR: v 1581 (N O), 1643 (C N), 1686 (C O), 3448 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.29 (3H, s, CH₃), 2.42 (3H, s, CH₃), 6.62–8.08 (9H, m, ArH’s), 10.69 (1H, s, NH); ¹³C NMR (DMSO-d6): δ 13.4, 20.9, 121.5, 128.9, 130.1, 134.8, 140.8, 156.1, 161.4, 161.7, 164.9; MS m/z (%): 380 (M⁺, 65), 237 (42), 193(43), 151(26), 77(100). Anal. Calcd for C₁₈H₁₆N₆O₂S (380.42): C, 56.83; H, 4.24; N, 22.09. Found C, 56.76; H, 4.35; N, 22.01%.

N′-(1-(5-oxo-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)benzo-hydrazide (11b)

A solution of compound 10b (0.5 g) in xylene (20 mL) was refluxed for 15 min and the solvent was evaporated under reduced pressure. The oil residue was triturated with petroleum ether (40–60 °C), and the solid formed was collected and crystallized from ethanol to give 11b as yellow solid (78%); m.p. 232–4 °C; IR: v 1666, 1708 (2C O), 3448(NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.26 (3H, s, CH₃), 2.39 (3H, s, CH₃), 7.32–7.79 (9H, m, ArH’s), 11.17 (1H, s, NH); ¹³C NMR (DMSO-d6): δ 13.4, 21.3, 120.3, 130.1, 130.9, 131.4, 123.5, 134.3, 134.6, 139.7, 149.2, 156.5, 160.2, 163.1; MS m/z (%): 353(M⁺+1, 18), 352(M⁺, 43), 239(23), 119(100), 84(65). Anal. Calcd for C₁₈H₁₆N₄O₂S (352.41): C, 61.35; H, 4.58; N, 15.90. Found C, 61.33; H, 4.51; N, 15.76%.

Synthesis of N-((E)-5-((Z)-1-(2-benzoylhydrazono)ethyl)-3-phenyl-1,3,4-thiadiazol-2(3H)-ylidene)acetamide (12a)

A mixture of 9a (1 g) in acetic acid (10 mL) and acetic anhydride (5 mL) was heated for 5 min at 70 °C. The reaction mixture was poured onto ice water (40 mL). The solid precipitate was collected and crystallized to give 12a as yellow solid (71%); m.p. 198 °C (EtOH); IR: v 1632, 1651, 1709 (3C O), 3234 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.17 (3H, s, CH₃), 2.28 (3H, s, CH₃), 2.39 (3H, s, CH₃), 7.31–7.83 (9H, m, ArH’s), 11.17 (1H, s, NH); ¹³C NMR (DMSO-d6): δ 13.3, 25.1, 125.6, 127.8, 128.9, 129.7, 130.6, 134.5, 140.2, 146.5, 155.1, 161.2, 164.8, 174.6; MS m/z (%): 380 (M⁺+1, 2), 379 (M⁺, 8), 314 (32), 278 (31), 161 (17), 105 (100), 77(75). Anal. Calcd for C₁₉H₁₇N₅O₂S (379.11): C, 60.14; H, 4.52; N, 18.46. Found C, 60.28; H, 4.64; N, 18.67%.

Synthesis of 1,3,4-thiadiazoline derivatives 13a–c

Method A

Triethylamine (0.75 mL, 5 mmol) was added dropwise with stirring to a mixture of methyl N-phenyldithiocarbamate (5 mmol) and the appropriate 6a–c (5 mmol) in ethanol (20 mL) for 30 min. The resulting solid was collected and recrystallized from ethanol to give the corresponding 13.

Method B

A mixture of the appropriate 6a–c (5 mmol) and phenylthiourea (0.38 g, 5 mmol) in ethanol (25 mL) was refluxed for 3 h. The solid product that formed after cooling was collected and crystallized from ethanol to give the product 13 which proved identical in all aspects (mp, mixed mp, and spectra) with 13 which obtained by method A.

The products 13a–c prepared together with their physical constants are given below.

N′-(1-(4-phenyl-5-(phenylimino)-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)-benzohydrazide (13a)

Yellow solid (73%); m.p. 194–6 °C (EtOH); IR: v 1610 (C N), 1661 (C O), 3336 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.33 (s, 3H, CH₃), 6.91–7.98 (m, 15H, ArH’s), 10.73 (s, 1H, NH); ¹³C NMR (DMSO-d6): δ 13.5, 124.3, 126.4, 127.9, 129.1, 129.7, 129.9, 130.2, 134.4, 140.1, 147.6, 155.7, 161.3, 164.8; MS m/z (%): 414 (M⁺+1, 3), 413 (M⁺, 8), 374(5), 338 (19), 306 (56), 278 (13), 161 (56), 105 (100), 77 (96), 51 (46). Anal. Calcd for C₂₃H₁₉N₅OS (413.49): C, 66.81; H, 4.63; N, 16.94. Found C, 66.65; H, 4.54; N, 16.76%.

4-Methyl-N′-(1-(4-phenyl-5-(phenylimino)-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethyl-idene)benzohydrazide (13b)

Yellow solid (78%); m.p. 213–5 °C (EtOH); IR: v 1619 (C N), 1670(C O), 3324 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.32 (s, 3H, CH₃), 2.49 (s, 3H, CH₃), 7.03–7.89 (m, 14H, ArH’s), 10.79 (s, 1H, NH); MS m/z (%): 428 (M⁺+1, 2), 427 (M⁺, 5), 333 (32), 261 (5), 243 (4), 209 (17), 105 (100), 77 (70). Anal. Calcd for C₂₄H₂₁N₅OS (427.52): C, 67.43; H, 4.95; N, 16.38. Found C, 67.33; H, 4.78; N, 16.30%.

4-Methyl-N′-(1-((Z)-5-(phenylimino)-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)benzohydrazide (13c)

Yellow solid (73%); m.p. 196–8 °C (EtOH); IR: v 1614 (C N), 1674 (C O), 3313 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.15 (s, 3H, CH₃), 2.38 (s, 3H, CH₃), 2.50 (s,3H, CH₃), 6.94–7.82 (m, 13H, ArH’s), 10.71 (s, 1H, NH); ¹³C NMR (DMSO-d6): δ 13.4, 20.8, 21.5, 121.2, 124.2, 127.8, 129.8, 131.2, 131.3, 134.2, 135.4, 145.1, 147.5, 147.8, 156.1, 161.2, 164.8; MS m/z (%): 442(M⁺+1, 5), 441(M⁺, 3), 306 (9), 225 (8), 175 (15), 119 (100), 105 (27), 77 (24). Anal. Calcd for C₂₅H₂₃N₅OS (441.55): C, 68.00; H, 5.25; N, 15.86. Found C, 67.70; H, 5.29; N, 15.57%.

Synthesis of 1,3,4-thiadiazoline derivatives 14a–g

Method A

Triethylamine (0.75 mL, 5 mmol) was added dropwise with stirring to a mixture of methyl arylidenedithiocarbazate (5 mmol) and the appropriate 6a–c (0.005 mol) in ethanol (20 mL) for 30 min. The resulting solid was collected and crystallized from DMF to give the corresponding product 14a–g.

N′-(1-(5-(benzylidenehydrazono)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)benzohydrazide (14a)

Orange solid (86%); m.p. 268 °C (DMF); IR: v 1604 (C N), 1663 (C O), 3184 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.43 (3H, s, CH₃), 7.29–8.05 (15H, m, ArH’s), 8.47 (1H, s, CH N), 11.25 (1H, s, NH); MS m/z (%): 442 (M⁺+2, 4), 441 (M⁺+1, 15), 440 (M⁺, 52), 323 (12), 161 (45), 105 (56), 77 (98). Anal. Calcd for C₂₄H₂₀N₆OS (440.52): C, 65.44; H, 4.58; N, 19.08. Found C, 65.36; H, 4.34; N, 19.02%.

N′-(1-(5-(benzylidenehydrazono)-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)benzo-hydrazide (14b)

Orange solid (80%); m.p. 240–2 °C (DMF); IR: v 1604 (C N), 1666 (C O), 3176 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.19 (3H, s, CH₃), 2.44 (3H, s, CH₃), 6.94–7.82 (14H, m, ArH’s), 8.45 (1H, s, CH N), 11.23 (1H, s, NH); MS m/z (%): 455 (M⁺+1, 14), 454 (M⁺, 39), 337 (12), 161 (34), 105 (100), 77 (79). Anal. Calcd for C₂₅H₂₂N₆OS (454.55): C, 66.06; H, 4.88; N, 18.49. Found C, 66.12; H, 4.67; N, 18.39%.

N′-(1-(5-(benzylidenehydrazono)-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)-4-methylbenzohydrazide (14c)

Orange solid (83%); m.p. 278 °C (DMF); IR: v 1610 (C N), 1659 (C O), 3172 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.51 (3H, s, CH₃), 3.30 (3H, s, CH₃), 7.17–7.89 (13H, m, ArH’s), 8.34 (1H, s, CH N), 11.15 (1H, s, NH); MS m/z (%): 455 (M⁺+1, 14), 454 (M⁺, 39), 337 (12), 161 (34), 105 (100), 77 (79). Anal. Calcd for C₂₆H₂₄N₆OS (468.57): C, 66.64; H, 5.16; N, 17.94. Found C, 66.69; H, 5.12; N, 17.72%.

N′-(1-(5-((4-chlorobenzylidene)hydrazono)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)benzohydrazide (14d)

Yellow solid (84%); m.p. 274–6 °C (DMF); IR: v 1610 (C N), 1663 (C O), 3177 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.49 (3H, s, CH₃), 7.34–8.04 (14H, m, ArH’s), 8.47 (1H, s, CH N), 11.25 (1H, s, NH); MS m/z (%): 477 (M⁺+2, 3), 475 (M⁺+1, 10), 474 (M⁺, 10), 161 (30), 105 (100), 77 (68). Anal. Calcd for C₂₄H₁₉ClN₆OS (474.97): C, 60.69; H, 4.03; 7.46; N, 17.69. Found C, 60.47; H, 4.01; N, 17.53%.

N′-(1-(5-((4-nitrobenzylidene)hydrazono)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene) benzohydrazide (14e)

Orange solid (83%); m.p. 260 °C (DMF); IR: v 1604 (C N), 1663 (C O), 3187 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.31 (3H, s, CH₃), 7.22–7.90 (14H, m, ArH’s), 8.44 (1H, s, CH N), 11.27 (1H, s, NH); ¹³C NMR (DMSO-d6): δ 13.4, 20.9, 21.6, 119.4, 124.7, 127.9, 129.8, 131.2, 132.4, 133.4, 134.9, 138.1, 144.3, 145.1, 154.9, 158.8, 160.4, 161.3, 164.8; MS m/z (%): 486 (M⁺+1, 8), 485 (M⁺, 25), 290 (31), 262 (11), 105 (100), 77 (66). Anal. Calcd for C₂₄H₁₉N₇O₃S (485.52): C, 59.37; H, 3.94; N, 20.19. Found C, 59.30; H, 3.87; N, 20.03%.

N′-(1-(5-((4-chlorobenzylidene)hydrazono)-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)-4-methylbenzohydrazide (14f)

Orange solid (80%); m.p. 318 °C (DMF); IR: v 1608 (C N), 1660 (C O), 3172 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.33 (3H, s, CH₃), 2.43 (3H, s, CH₃), 3.34 (3H, s, CH₃), 7.27–7.90 (12H, m, ArH’s), 8.45 (1H, s, CH N), 11.26 (1H, s, NH); MS m/z (%): 504 (M⁺+1, 19), 503 (M⁺, 29), 297 (39), 262 (19), 119 (100), 105 (75), 77 (41). Anal. Calcd for C₂₆H₂₃ClN₆OS (503.02): C, 62.08; H, 4.61; N, 16.71. Found C, 62.01; H, 4.54; N, 16.24%.

4-Methyl-N′-(1-(5-((4-nitrobenzylidene)hydrazono)-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)benzohydrazide (14g)

Orange solid (84%); m.p. 292 °C (DMF); IR: v 1591 (C N), 1661 (C O), 3171 (NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.37 (3H, s, CH₃), 2.49 (3H, s, CH₃), 3.32 (3H, s, CH₃), 7.32–7.89 (12H, m, ArH’s), 8.44 (1H, s, CH N), 11.14 (1H, s, NH); MS m/z (%): 514 (M⁺+1, 5), 513 (M⁺, 14), 119 (100), 105 (6), 77 (5). Anal. Calcd for C₂₆H₂₃N₇O₃S (513.57): C, 60.81; H, 4.51; N, 19.09. Found C, 60.67; H, 4.59; N, 19.01%.

Method B

A mixture of 15a (0.35 g, 1 mmol) and benzaldehyde (0.106 g, 1 mmol) in isopropyl alcohol (15 mL) was refluxed for 30 min. The solid product that formed after cooling was collected and crystallized from acetic acid to give a product proved identical in all aspects (mp, mixed mp, and spectra) with 14a which was obtained by method A.

Synthesis of N′-(1-(5-hydrazono-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)benzohydrazide 15a

Triethylamine (0.75 mL, 5 mmol) was added dropwise with stirring to a mixture of methyl dithiocarbazate (0.61 g, 5 mmol) and 6a (0.98 g, 5 mmol) in ethanol (20 mL) for 30 min. The resulting solid was collected and recrystallized from ethanol to give 15a as a yellow solid (79%); m.p. 242–4 °C; IR: v 1600(C N), 1647 (C O), 3184, 3435 (NH₂, NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.18 (3H, s, CH₃), 6.90–7.90 (12H, m, ArH’s, NH₂), 10.25 (1H, s, NH); MS m/z (%): 353(M⁺+1, 2), 352 (M⁺, 12), 284 (13), 174 (14), 105 (51), 55 (100). Anal. Calcd for C₁₇H₁₆N₆OS (352.41): C, 57.94; H, 4.58; N, 23.85. Found C, 57.78; H, 4.45; N, 23.78%.

Synthesis of N′-(1-(5-(2-benzoylhydrazono)-4-aryl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)-benzohydrazides 16a,b

Method A

Triethylamine (0.75 mL, 5 mmol) was added dropwise with stirring to a mixture of methyl 2-benzoylhydrazinecarbodithioate (1.13 g, 5 mmol) and the equimolar amount of 6a,b (5 mmol) in ethanol (20 mL). The resulting solid, which formed after 30 min, was collected and crystallized from DMF to give the corresponding product 16.

Method B

Triethylamine (0.75 mL, 5 mmol) was added dropwise with stirring to a mixture of 5-phenyl-1,3,4-oxadiazole-2-thiol (0.89 g, 5 mmol) and the equimolar amount of 6a,b (5 mmol) in ethanol (20 mL). The resulting solid, which formed after 6 h, was collected and recrystallized from DMF to give the corresponding product 16 in 82% yield as in method A.

N′-(1-(5-(2-benzoylhydrazono)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)-benzohydrazide (16a)

Orange solid (82%); m.p. 284–6 °C (DMF); IR: v 1647 (C O), 3175, 3448 (2NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.34 (s, 3H, CH₃), 7.11–7.80 (m, 15H, ArH’s), 8.98 (s, 1H, br, NH), 11.10 (1H, s, br, NH); MS m/z (%): 457 (M⁺+1, 76), 456 (M⁺, 57), 290 (97), 225 (100), 192 (95), 116 (93), 53 (55). Anal. Calcd for C₂₄H₂₀N₆O₂S (456.52): C, 63.14; H, 4.42; N, 18.41. Found C, 63.11; H, 4.35; N, 18.32%.

N′-(1-(5-(2-benzoylhydrazono)-4-(p-tolyl)-4,5-dihydro-1,3,4-thiadiazol-2-yl)-ethylidene)-benzohydrazide (16b)

Orange solid (85%); m.p. 216–8 °C (DMF); IR: v 1655 (C O), 3187, 3441 (2NH) cm⁻¹; ¹H NMR (DMSO-d6): δ 2.21 (s, 3H, CH₃), 2.36 (s, 3H, CH₃), 7.19–7.96 (m, 14H, ArH’s), 9.08 (s, br, 1H, NH), 11.17 (s, br, 1H, NH); ¹³C NMR (DMSO-d6): δ 11.4, 20.8, 119.3, 126.4, 127.8, 128.7, 129.3, 132.6, 133.4, 134.4, 140.1, 153.2, 158.5, 162.4, 164.4, 165.7; MS m/z (%): 471 (M⁺+1, 38), 470 (M⁺, 28), 403 (39), 286 (43), 206 (39), 137 (54), 105 (72), 77 (100). Anal. Calcd for C₂₅H₂₂N₆O₂S (470.55): C, 63.81; H, 4.71; N, 17.86. Found C, 63.68; H, 4.67; N, 17.67%.

Antimicrobial assay

The biological evaluation was carried out in the Medical Mycology Laboratory of the Regional Center for Mycology and Biotechnology of Al-Azhar University, Cairo, Egypt. The method adopted for such tests is the Agar diffusion method. The microorganism inoculums were uniformly spread using sterile cotton swab on a sterile Petri dish Malt extract agar (for fungi) and nutrient agar (for bacteria). One hundred μL of each sample was added to each well (10 mm diameter holes cut in the agar gel, 20 mm apart from one another). The systems were incubated for 24–48 h at 37 °C (for bacteria) and at 28 °C (for fungi). After incubation, the microorganism’s growth was observed. Inhibition of the bacterial and fungal growth was measured as IZD in mm. Tests were performed in triplicate [25].

Results and discussion

In our hands, reaction of benzoylhydrazine with each of the hydrazonoyl chlorides 2b in refluxing ethanol yielded, in each case, the corresponding condensation product 6 as previously reported [18]. The structures of the latter products were confirmed by their chemical reaction as outlined below. Treatment of 6 each with sodium thiophenolate afforded phenyl 2-(2-benzoylhydrazono)-N′-phenylpropanehydrazonothioate 7 (Scheme 2). The latter product 7 was alternatively prepared by reacting the hydrazonoyl chloride 2b with sodium thiophenolate to give phenyl 2-oxo-N′-phenylpropanehydrazonothioate 8 and treatment of the latter with benzoylhydrazine (Scheme 2).

Scheme 2.

Next, reactions of 6 with various sulfur reagents were examined. Thus, treatment of each of compounds 6a, b with potassium thiocyanate in ethanol gave the corresponding 1,3,4-thiadiazoline derivatives 9a,b, respectively. The structures of the latter products 9a, b were elucidated based on their elemental and spectral analyses (IR, MS and ¹H NMR) (see Experimental). In addition, structure 9 was confirmed by alternate synthesis. Thus, treatment of 6 with thiourea in ethanol afforded products identical in all respects with the product obtained by reaction of 6 with potassium thiocyanate (Scheme 3). Furthermore, the assigned structure 9 was confirmed by its chemical reactions. For example, treatment of 9a,b each with sodium nitrite in acetic acid yielded the corresponding N-nitroso derivatives 10a,b, respectively. Heating of 10b in xylene gave the thiadiazolone derivative 11b. In addition, treatment of 9a with acetyl chloride yielded the corresponding N-acetyl derivative 12a (Scheme 3).

Scheme 3.

Reaction of 6a–c each with either methyl N-phenyldithiocarbamate or phenylthiourea in ethanol yielded in both cases one and same product that proved to be the corresponding 2-phenyliminothiadizoline derivative 13 (Scheme 4). The structures of the isolated products 13a–c were elucidated based on their elemental and spectral analyses (see Experimental). For example, the infrared spectrum of 13a showed bands at v 3336 (NH), 1661 (C O), 1610 (C N) cm⁻¹ and their ¹H NMR, in addition to the aromatic proton signals, revealed characteristic signals at δ 2.33 (CH₃) and 10.73 (NH).

Scheme 4.

Reaction of 6 with methyl 2-(4-substituted benzylidene)hydrazinecarbodithioate in ethanol in the presence of triethylamine afforded, in each case, one isolable product that was identified based upon its spectral (IR, MS and ¹H NMR) and elemental analyses as the corresponding thiadiazoline derivative 14 (Scheme 5) (see Experimental). Structure 14 was confirmed by alternate synthesis. Thus, reaction of 6a with methyl dithiocarbazate in ethanol in the presence of triethylamine yielded the thiadiazoline derivative 15a. Treatment of the latter with benzaldehyde in ethanol afforded product that proved identical in all respects (mp., mixed mp., IR, ¹H NMR) with 14a obtained above (Scheme 5).

Scheme 5.

Similar reaction of 6a,b each with methyl 2-benzoylhydrazinecarbodithioate yielded the thiadiazoline derivatives 16a,b, respectively (Scheme 6). The structures of the latter were elucidated based on by elemental and spectral analyses and also by alternate syntheses (see Experimental). Thus, treatment of 6a,b each with 5-phenyl-1,3,4-oxadiazole-2-thione in refluxing ethanol in the presence of triethylamine afforded products that proved identical in all aspects (mp., mixed mp., and spectra) with those 16a,b obtained from the foregoing reaction of 6a,b with methyl 2-benzoylhydrazinecarbodithioate (Scheme 6).

Scheme 6.

Antimicrobial activity

The newly synthesized compounds 9a, 10a, 11a, 12a, 13a,b, 14a,b, and 16a,b were tested for their in vitro antibacterial activity against two Gram-positive bacteria namely Staphylococcus pneumoniae (SP) and Bacillis subtilis (BS) and two Gram-negative bacteria namely Pseudomonas aeruginosa (PA) and Escherichia coli (EC). They were also tested for their in vitro antifungal activity against three fungi species namely Aspergillus fumigatus (AF), Geotrichum candidum (GC), Candida albicans (CA) and Syncephalastrum racemosum (SR). The organisms were tested against the activity of solutions of concentration (5 μg/mL) of each compound and using inhibition zone diameter (IZD) in mm as criterion for the antimicrobial activity (agar diffusion well method). The fungicides Amphotericin B and the bactericides Ampicillin, Gentamicin were used as references to evaluate the potency of the tested compounds under the same conditions. The results are summarized in Table 1, Table 2. Such results indicate the following: (1) Compounds 9a, 10a, 11a, 12a, 13a, 13b, 14a and 16b exhibit high inhibitory effects against of S. pneumoni, (2) Compounds 9a, 10a, 11a, 12a, 13a, 13b, 14a, 14b, 16a and 16b exhibit high inhibitory effects against of B. subtilis while have no inhibitory effect toward P. aeruginosa, (3) Compounds 11a, 12a, 13b and 16b exhibit high inhibitory effects against E. coli, (4) Compound 14b has moderate inhibitory effect against S. pneumoniae. On the other hand, compounds 9a, 10a, 13a, 14a, 14b, and 16a have moderate inhibitory effect toward E. coli and (5) Compounds 9a, 10a, 11a, 12a, 13a, 13b, 14a, 14b, 16a and 16b exhibit high inhibitory activities against each of A. fumigatus, S. racemosum and G. candidum, while compound 14b has moderate inhibitory activity and all compounds have no activity against C. albicans.

Table 1.

Antibacterial activity of the synthesized compounds (9–16).^⁎

Compounds	Minimal inhibitory concentration in μg/mL (zone of inhibition in mm)
	Gram-positive bacteria		Gram-negative bacteria
	Staphylococcus pneumoniae	Bacillis subtilis	Pseudomonas aeruginosa	Escherichia coli
9a	16.8 ± 0.37	15.9 ± 0.44	NA	12.6 ± 0.25
10a	15.8 ± 0.44	14.2 ± 0.37	NA	12.0 ± 0.58
11a	18.2 ± 0.44	20.2 ± 0.58	NA	18.0 ± 0.25
12a	19.2 ± 0.17	20.8 ± 0.29	NA	19.5 ± 0.42
13a	16.2 ± 0.44	15.3 ± 0.44	NA	12.8 ± 0.25
13b	16.3 ± 0.44	21.0 ± 0.37	NA	18.0 ± 0.44
14a	13.7 ± 0.44	15.0 ± 0.37	NA	10.0 ± 0.44
14b	9.4 ± 0.37	12.1 ± 0.19	NA	8.3 ± 037
16a	13.8 ± 0.44	17.2 ± 0.25	NA	10.7 ± 0.25
16b	16.5 ± 0.44	21.4 ± 0.37	NA	19.7 ± 0.44
Ampicillin	23.8 ± 0.2	32.4 ± 0.3	–	–
Gentamicin	–	–	17.3 ± 0.1	19.9 ± 0.3

^∗NA: No activity, data are expressed in the form of mean ± SD.

Table 2.

Antifungal activity of the synthesized compounds (9–16).^⁎

Compounds	Minimal inhibitory concentration in μg/Ml (zone of inhibition in mm)
	Aspergillus fumigatus	Syncephalastrum racemosum	Geotrichum candidum	Candida albicans
9a	15.7 ± 0.44	17.4 ± 0.25	13.9 ± 0.32	NA
10a	14.2 ± 0.44	15.8 ± 0.58	12.4 ± 0.4	NA
11a	17.9 ± 0.22	19.9 ± 0.44	16.8 ± 0.44	NA
12a	18.9 ± 0.22	20.2 ± 0.25	16.8 ± 0.44	NA
13a	14.9 ± 0.58	16.4 ± 0.19	14.7 ± 0.25	NA
13b	18.3 ± 0.44	19.9 ± 0.58	18.0 ± 0.19	NA
14a	13.3 ± 0.25	12.4 ± 0.44	13.6 ± 0.44	NA
14b	9.3 ± 0.15	8.3 ± 0.19	13.3 ± 0.38	NA
16a	13.4 ± 0.58	12.7 ± 0.37	14.3 ± 0.58	NA
16b	19.3 ± 0.44	20.0 ± 0.58	18.2 ± 0.19	NA
Amphotericin B	23.7 ± 0.1	19.7 ± 0.2	28.7 ± 0.2	25.4 ± 0.1

^∗NA: No activity, data are expressed in the form of mean ± SD.

Conclusion

In conclusion, reaction of acylhydrazines with α-ketohydrazonoyl chlorides yielded the condensation products 6. The latter products 6 proved to be useful precursors for synthesis of various functionalized 1,3,4-thiadiazole derivatives. The structures of the newly synthesized compounds were confirmed by spectral data, elemental analyses and alternate syntheses. Most of the compounds prepared exhibit considerable antimicrobial activities.

Conflict of Interest

The authors have declared no conflict of interest.

Compliance with Ethics Requirements

This article does not contain any studies with human or animal subjects.