This paper describes the synthesis of a new series of functionalized 1,2,4‒triazinones and containing sulfonamide moieties by 1,3‒dipolar cyclocondensation reaction of nitrilimines with α‒amino‒esters. The structures of the newly synthesized compounds were elucidated by spectral methods (IR, ¹H‒NMR, ¹³C‒NMR and MS spectrometry) and elemental analysis. The newly synthesized compounds were screened for their in vitro antimicrobial activity. Some of titled compounds exhibited significant antimicrobial activity on several strains of microbes.

Keywords: nitrilimines, α‒aminoesters, sulfa drugs, antimicrobial activity, 1,2,4‒triazinones, HZ, TMS

Sulfa drugs are sulfonamide antibiotics and they are synthetic antimicrobial agents with widely uses for the treatment of various infectious diseases.^1-7 These drugs were the first efficient treatment to be employed systematically for the prevention and cure of bacterial infections.^8-11 One of the first sulfonamides identified by Domagk et al.^8,9 was the red azo dye known as Prontosil.^8,9 It was active against streptococcal infection in vivo. There have been many analogues of sulfanilamide developed as pharmacological agents that display a wide range of biological activities.^12,13 For example, glibenclamide has found use as a hypoglycemic agent, indisulam (E7070) as an anticancer agent, amprenavir and tipranavir are used in HIV therapy, Furosemide as a diuretic, acetazolamide as a carbonic anhydrase inhibitor, and sulfathiazole, sulfaquinoxaline, silver sulfadiazine (silvadene®), sulfasalazine (azulfidine®) and sulfamethoxazole (gantanol®) as an antibacterial agents.^{7,10,11,14-16} In addition, dorzolamide, and brinzolamide have been launched as topically acting antiglaucoma pharmacological agents.^17,18 Till date, thousands of sulfonamide derivatives, analogues, and related compounds have been synthesized, which are effective as diuretics, anti-malarial, leprosy and antithyroid agents and employed for other diseases.^17,19 Moreover, aryl sulfonamides celecoxib and vadecoxib are used as COX-II inhibitors and anticancer agents .^20,21 Sildenafil was launched in 1998 as an anti-impotence drug and responsible for inhibiting the degradation of cyclic guanosine monophosphate.^22,9 It has been observed that sulfa drugs show increased biological activity when administered in the form of metal complexes.^18,23

The development of nitrogen and sulfur containing heterocyclic compounds in medicinal chemistry and pharmaceutical communities as these molecules has potent biological activities. Among them, 1,2,4-triazine derivatives are known to exhibit various pharmacological^24,9 and medicinal applications.^25-27 Taking into account all previous commentaries of the biological activities of sulfonamides and in continuation of our study on the synthesis of biologically active heterocycles,^28,29 efforts have been made to synthesize a series of new 1,2,4-triazinone derivatives incorporating sulfonamide moiety via cyclocondensation reaction of nitrilimines bearing moiety of sulfonamide with α-aminoesters in anticipation of expected interesting biological activities.

Apparatus and chemicals

Melting points were determined using an electro thermal melting temperature apparatus and are uncorrected. The IR spectra were measured as KBr pellets using a Satellite 3000 Mid infrared spectrometer. ¹H NMR and ¹³C NMR spectra were recorded on a Bruker AM 300 MHz spectrometer at room temperature in DMSO-d₆ solution using tetramethyl silane (TMS) as internal reference. Chemical shifts are expressed in δ (ppm) downfield from TMS and coupling constants are in Hertz (Hz). Electron impact (EI) mass spectra were run on a Shimadzu GCMS-QP1000 EX spectrometer at 70 eV. Elemental analysis was carried out at micro analytical laboratory, Cairo University, Cairo, Egypt. Ethyl mercapto acetate 6 was purchased from Avocado Research Chemicals, England, and used without further purification. Hydrazonoyl chlorides 1a-c employed in this study, were prepared via direct coupling of the appropriate sulfa drug diazonium chloride with α-chloroacetoacetanilide in sodium acetate/ethanol solution following standard procedures.³⁰ α-Aminoester hydrochlorides 3 employed in this work were obtained by reacting the appropriate α-amino acids with thionyl chloride in excess methanol following reported procedures.³¹

General procedure for synthesis of 1,2,4-triazinones 5a-o.

To a stirred solution of the appropriate hydrazonoyl halides (5 mmol) in tetrahydrofuran (70 mL) was added a solution of the particular α-aminoester hydrochloride (10 mmol) in methanol (30 mL). To the resulting reaction mixture, cooled in an ice-salt bath (-5-0°C), was drop wise added triethylamine (30mmol). After addition was complete, stirring was continued for 2-4 hours at 0°C, and then at room temperature overnight. The solvent was removed under reduced pressure, and the residue was washed with water. The resulting solid product was collected and recrystallized from ethanol/water solution to give the desired 4,5-dihydro-1,2,4-triazinones 5a-o. The following compounds were prepared using this method:

3-phenylaminocarbonyl-1-[4-(thizol-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5a): Yield 71%, m.p. 248-250 °C. IR (KBr): cm^-1 3360, 3272, 3246 (NH), 1675 (lactam C=O), 1655 (amide C=O), 1630 (C=N), 1346, 1145 (SO₂). ¹H NMR (DMSO-d₆): δ/ppm 12.63 (s, 1H, SO₂NH), 10.96 (s, 1H, PhNH), 8.71 (d, 1H, thiazole), 7.93-7.04 (m, 9H, aromatic), 6.62 (d, 1H, thiazole), 6.35 (s, 1H, NH triazinone ring), 4.32 (s, 2H, CH₂); ¹³C NMR (DMSO-d₆): δ/ppm 160.33 (lactam C=O), 157.10 (amide C=O), 139.34 (C=N), 142.21-119.12 (8 Ar-C), 168.02, 135.45, 116.50 (3 thiazole-C), 43.77 (CH₂). MS: m/z = 456 [M⁺]. Anal. Calcd. for C₁₉H₁₆N₆O₄S₂ (456.51): C, 49.99; H, 3.53; N, 18.41; Found C, 50.24; H, 3.65; N, 18.32.

5-Methyl-3-phenylaminocarbonyl-1-[4-(thizol-2-yl-sulfamoyl)phenyl]-4,5-di-hydro-1,2,4-tri-azin-6-one (5b): Yield 68%, m.p. 235-237°C. IR (KBr): cm^-1 3355, 3273, 3242 (NH), 1676 (lactam C=O), 1650 (amide C=O), 1628 (C=N), 1349, 1142 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.66 (s, 1H, SO₂NH), 10.02 (s, 1H, PhNH), 8.68 (d, 1H, thiazole), 7.96-7.05 (m, 9H, aromatic), 6.60 (d, 1H, thiazole), 6.32 (s, 1H, NH triazinone ring), 4.42-4.36 (q, 1H, CH), 1.58-1.56 (d, 3H, CH₃); ¹³C NMR (DMSO-d₆): δ/ppm 160.25 (lactam C=O), 157.3 (amide C=O), 139.31 (C=N), 141.94-119.18 (8 Ar-C), 168.00, 135.42, 116.46 (3 thiazole-C), 49.68 (CH), 19.87 (CH₃). MS: m/z = 470 [M⁺]. Anal. Calcd. for C₂₂H₂₂N₆O₄S₂ (470.53): C, 51.05; H, 3.86; N, 17.86; Found C, 50.90; H, 3.98; N, 17.75.

5-Isopropyl-3-phenylaminocarbonyl-1-[4-(thizol-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-tri-azin-6-one (5c): Yield 65%, m.p. 240-242°C. IR (KBr): cm^-1 3360, 3268, 3246 (NH), 1673 (lactam C=O), 1652 (amide C=O), 1634 (C=N), 1343, 1137 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.62 (s, 1H, SO₂NH), 10.98 (s, 1H, PhNH), 8.73 (d, 1H, thiazole), 7.98-7.06 (m, 9H, aromatic), 6.62 (d, 1H, thiazole), 6.32 (s, 1H, NH triazinone ring), 4.25-4.23 (d, 1H, CH), 2.58-2.40 (m, 1H, CH), 1.12-1.05 (d, 6H, 2CH₃); ¹³C NMR (DMSO-d₆): δ/ppm 160.72 (lactam C=O), 157.70 (amide C=O), 139.00 (C=N), 141.98-119.82 (8 Ar-C), 167.92, 135.32, 116.57 (3 thiazole-C), 59.36 (CH), 32.87 (CH), 18.32, 16.76 (2 CH₃). MS: m/z = 498[M⁺]. Anal. Calcd. for C₂₂H₂₂N₆O₄S₂ (498.59): C, 53.00; H, 4.45; N, 16.86; Found C, 53.25; H, 4.35; N, 16.97.

5-Benzyl-3-phenylaminocarbonyl-1-[4-(thizol-2-yl-sulfamoyl)phenyl]-4,5-di-hydro-1,2,4-tri-azin-6-one (5d): Yield 70%, m.p. 234-236°C. IR (KBr): cm^-1 3376, 3273, 3239 (NH), 1678 (lactam C=O), 1656 (amide C=O), 1634 (C=N), 1344, 1135 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.65 (s, 1H, SO₂NH), 11.01 (s, 1H, PhNH), 8.74 (d, 1H, thiazole), 7.96-7.02 (m, 14H, aromatic), 6.66 (d, 1H, thiazole), 6.35 (s, 1H, NH triazinone ring), 4.55-4.52 (t, 1H, CH), 3.26-3.18 (d, 1H, CH₂); ¹³C NMR (DMSO-d₆): δ/ppm 161.37 (lactam C=O), 157.37 (amide C=O), 139.70 (C=N), 142.19-119.29, (12 Ar-C), 168.02, 135.42, 116.17 (3 thiazole-C), 55.64 (CH), 40.43 (CH₂). MS: m/z = 546 [M⁺]. Anal. Calcd. for C₂₆H₂₂N₆O₄S₂ (546.63): C, 57.13; H, 4.06; N, 15.37; Found C, 56.90; H, 3.95; N, 15.52.

5-Phenyl-3-phenylaminocarbonyl-1-[4-(thizol-2-yl-sulfamoyl)phenyl]-4,5-di-hydro-1,2,4-tri-azin-6-one (5e): Yield 62%, m.p. 254-256°C. IR (KBr): cm^-1 3375, 3273, 3236 (NH), 1675 (C=O lactam), 1650 (amide C=O), 1631 (C=N), 1349, 1148 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.67 (s, 1H, SO₂NH), 11.03 (s, 1H, PhNH), 8.76 (d, 1H, thiazole), 7.95-7.03 (m, 14H, aromatic), 6.64 (d, 1H, thiazole), 6.33 (s, 1H, NH triazinone ring), 5.35 (s, 1H, CH); ¹³C NMR (DMSO-d₆): δ/ppm 160.78 (lactam C=O), 157.76 (amide C=O), 139.10 (C=N), 142.11-119.83 (12 Ar-C), 167.96, 135.35, 116.12 (3 thiazole-C), 56.80 (CH). MS: m/z = 532 [M⁺]. Anal. Calcd. for C₂₅H₂₀N₆O₄S₂ (532.60): C, 56.38; H, 3.79; N, 15.78; Found C, 56.60; H, 3.90; N, 15.65.

3-phenylaminocarbonyl-1-[4-(pyrimidin-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5f): Yield 72%, m.p. 275-277 °C. IR (KBr): cm^-1 3387, 3261, 3229 (NH), 1681 (lactam C=O), 1655 (amide C=O), 1627 (C=N), 1350, 1155 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.62 (s, 1H, SO₂NH), 10.97 (s, 1H, PhNH), 7.93-7.02 (m, 9H, aromatic), 8.41 (d, 2H, pyrimidine), 6.83 (t, 1H, pyrimidine), 6.40 (s, 1H, NH triazinone ring), 4.34 (s, 2H, CH2); ¹³C NMR (DMSO-d₆): δ/ppm 161.50 (lactam C=O), 158.74 (amide C=O), 141.04 (C=N), 142.61-116.20 (8 Ar-C), 168.42, 156.62, 110.54 (3 pyrimidine-C), 43.92 (CH₂). MS: m/z = 451 [M⁺]. Anal. Calcd. for C₂₀H₁₇N₇O₄S (451.47): C, 53.21; H, 3.80; N, 21.72; Found C, 53.01; H, 3.91; N, 21.62.

5-Methyl-3-phenylaminocarbonyl-1-[4-(pyrimidin-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-tri-azin-6-one (5g): Yield 70%, m.p. 258-260°C. IR (KBr): cm^-1 3358, 3264, 3220 (NH), 1682 (lactam C=O), 1657 (amide C=O), 1626 (C=N), 1356, 1149 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.65 (s, 1H, SO₂NH), 10.94 (s, 1H, PhNH), 7.91-6.93 (m, 9H, aromatic), 8.32 (d, 2H, pyrimidine), 6.86 (t, 1H, pyrimidine), 6.41 (s, 1H, NH triazinone ring), 4.41-4.35 (q, 1H, CH), 1.58-1.56 (d, 3H, CH₃); ¹³C NMR (DMSO-d₆): δ/ppm 161.55 (lactam C=O), 158.77 (amide C=O), 141.60 (C=N), 142.15-115.87 (8 Ar-C), 168.42, 156.67, 110.43 (3 pyrimidine-C), 49.88 (CH), 19.85 (CH₃). MS: m/z = 465 [M⁺]. Anal. Calcd. for C₂₁H₁₉N₇O₄S (465.49): C, 54.19; H, 4.11; N, 21.06; Found C, 53.95; H, 3.98; N, 20.94.

5-Isopropyl-3-phenylaminocarbonyl-1-[4-(pyrimidin-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5h): Yield 74%, m.p. 266-268°C. IR (KBr): cm^-1 3375, 3258, 3232 (NH), 1677 (lactam C=O), 1655 (amide C=O), 1628 (C=N), 1353, 1155 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.63 (s, 1H, SO₂NH), 10.97 (s, 1H, PhNH), 7.90-6.96 (m, 9H, aromatic), 8.48 (d, 2H, pyrimidine), 6.85 (t, 1H, pyrimidine), 6.38 (s, 1H, NH triazinone ring), 4.31 (d, 1H, CH), 2.58-2.41 (m, 1H, CH), 1.14-1.08 (d, 6H, 2CH₃); ¹³C NMR (DMSO-d6): δ/ppm 161.73 (lactam C=O), 158.73 (amide C=O), 141.00 (C=N), 142.73-116.25 (8 Ar-C), 168.18, 156.52, 110.41 (3 pyrimidine-C), 59.65 (CH), 33.19 (CH), 18.60, 16.82 (2 CH₃). MS: m/z = 493 [M⁺]. Anal. Calcd. for C₂₃H₂₃N₇O₄S (493.55): C, 55.97; H, 4.70; N, 19.87; Found C, 56.20; H, 3.82; N, 19.66.

5-Benzyl-3-phenylaminocarbonyl-1-[4-(pyrimidin-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-tri-azin-6-one (5i): Yield 67%, m.p. 229-231 °C. IR (KBr): cm^-1 3366, 3261, 3231 (NH), 1685 (lactam C=O), 1652 (amide C=O), 1626 (C=N), 1351, 1156 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.62 (s, 1H, SO₂NH), 10.96 (s, 1H, PhNH), 7.98-7.00 (m, 14H, aromatic), 8.61 (d, 2H, pyrimidine), 6.83 (t, 1H, pyrimidine), 6.35 (s, 1H, NH triazinone ring), 4.52-4.48 (t, 1H, CH), 3.22-3.14 (d, 2H, CH₂); ¹³C NMR (DMSO-d6): δ/ppm 161.37 (lactam C=O), 158.67 (amide C=O), 141.70 (C=N), 142.40-116.39, (12 Ar-C), 168.09, 156.12, 110.19 (3 pyrimidine-C), 55.71(CH), 40.59 (CH₂). MS: m/z = 541 [M⁺]. Anal. Calcd. for C₂₇H₂₃N₇O₄S (541.59): C, 59.88; H, 4.28; N, 18.10; Found C, 60.10; H, 4.37; N, 17.98.

5-Phenyl-3-phenylaminocarbonyl-1-[4-(pyrimidin-2-yl-sulfamoyl)phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5j): Yield 70%, m.p. 263-265°C. IR (KBr): cm^-1 3356, 3255, 3234 (NH), 1683 (C=O lactam), 1656 (amide C=O), 1627 (C=N), 1356, 1152 (SO₂); ¹H NMR (DMSO-d6): δ/ppm 12.63 (s, 1H, SO₂NH), 11.02 (s, 1H, PhNH), 7.95-6.94 (m, 14H, aromatic), 8.64 (d, 2H, pyrimidine), 6.86 (t, 1H, pyrimidine), 6.36 (s, 1H, NH triazinone ring), 5.34 (s, 1H, CH); ¹³C NMR (DMSO-d₆): δ/ppm 161.75 (lactam C=O), 158.67 (amide C=O), 141.10 (C=N), 142.38-116.14 (12 Ar-C), 168.22, 156.10, 110.14 (3 pyrimidine-C), 56.86 (CH). MS: m/z = 527 [M⁺]. Anal. Calcd. for C₂₃H₂₁N₇O₄S (527.57): C, 59.19; H, 4.01; N, 18.58; Found C, 58.95; H, 3.92; N, 18.69.

3-phenylaminocarbonyl-1-[4-(5-methyloxazol-3-yl-sulfamoyl)phenyl]-4,5-di-hydro-1,2,4-tri-azin-6-one (5k): Yield 63%, m.p. 268-270°C. IR (KBr): cm^-1 3360, 3272, 3224 (NH), 1676 (lactam C=O), 1655 (amide C=O), 1622 (C=N), 1341, 1175 (SO₂). ¹H NMR (DMSO-d₆): δ/ppm 12.59 (s, 1H, SO₂NH), 10.92 (s, 1H, PhNH), 7.92-7.04 (m, 9H, aromatic), 6.38 (s, 1H, NH triazinone ring), 6.21 (s, 1H, oxazole proton), 4.30 (s, 2H, CH₂), 2.35 (s, 3H, CH₃ of oxazole nucleus); ¹³C NMR (DMSO-d₆): δ/ppm 160.33 (lactam C=O), 157.84 (amide C=O), 140.68 (C=N), 140.96-119.21 (8 Ar-C), 168.30, 155.61, 95.23 (oxazole-C), 43.77 (CH2), 12.36 (CH₃). MS: m/z = 454 [M⁺]. Anal. Calcd. for C₂₀H₁₈N₆O₅S (454.47): C, 52.86; H, 3.99; N, 18.49; Found C, 52.65; H, 4.10; N, 18.38.

5-Methyl-3-phenylaminocarbonyl-1-[4-(5-methyloxazol-3-yl-sulfamoyl)-phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5l): Yield 66%, m.p. 235-237°C. IR (KBr): cm^-1 3355, 3273, 3228 (NH), 1675 (lactam C=O), 1654 (amide C=O), 1626 (C=N), 1348, 1177 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.57 (s, 1H, SO₂NH), 10.93 (s, 1H, PhNH), 7.94-7.05 (m, 9H, aromatic), 6.35 (s, 1H, NH triazinone ring), 6.28 (s, 1H, oxazole proton), 4.40-4.34 (q, 1H, CH), 2.34 (s, 3H, CH₃ on oxazole ring), 1.62-1.58 (d, 3H, CH₃); ¹³C NMR (DMSO-d6): δ/ppm 160.55 (lactam C=O), 157.78 (amide C=O), 140.31 (C=N), 140.94-119.28 (8 Ar-C), 168.24, 155.80, 95.23 (oxazole-C), 49.42 (CH), 19.77 (CH₃), 12.74 (CH₃ oxazole). MS: m/z = 468 [M⁺]. Anal. Calcd. for C₂₁H₂₀N₆O₅S (468.49): C, 53.84; H, 4.30; N, 17.94; Found C, 54.07; H, 3.18; N, 18.05.

5-Isopropyl-3-phenylaminocarbonyl-1-[4-(5-methyloxazol-3-yl-sulfamoyl)phenyl]-4,5-di-hydro-1,2,4-triazin-6-one (5m): Yield 65%, m.p. 260-262°C. IR (KBr): cm^-1 3360, 3267, 3223 (NH), 1678 (lactam C=O), 1658 (amide C=O), 1623 (C=N), 1346, 1175 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.55 (s, 1H, SO₂NH), 10.96 (s, 1H, PhNH), 7.92-7.03 (m, 9H, aromatic), 6.37 (s, 1H, NH triazinone ring), 6.24 (s, 1H, oxazole proton), 4.35-4.24 (d, 1H, CH), 2.58-2.46 (m, 1H, CH), 2.33 (s, 3H, CH₃ on oxazole ring), 1.12-1.06 (d, 6H, 2CH₃); ¹³C NMR (DMSO-d6): δ/ppm 160.82 (lactam C=O), 157.79 (amide C=O), 139.96 (C=N), 141.01-119.82 (8 Ar-C), 168.30, 155.63, 96.02 (oxazole-C), 59.23 (CH), 32.85 (CH), 18.32, 16.71 (2 CH₃), 12.34 (CH₃ oxazole). MS: m/z = 512 [M⁺]. Anal. Calcd. for C₂₄H₂₈N₆O₅S (512.59): C, 56.24; H, 5.51; N 16.40; Found C, 55.98; H, 5.60; N, 16.51.

5-Benzyl-3-phenylaminocarbonyl-1-[4-(5-methyloxazol-3-yl-sulfamoyl)-phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5n): Yield 60%, m.p. 246-248°C. IR (KBr): cm^-1 3376, 3273, 3224 (NH), 1680 (lactam C=O), 1655 (amide C=O), 1622 (C=N), 1345, 1170 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.53 (s, 1H, SO₂NH), 10.94 (s, 1H, PhNH), 7.96-7.04 (m, 14H, aromatic), 6.35 (s, 1H, NH triazinone ring), 6.26 (s, 1H, oxazole proton), 4.55-4.52 (t, 1H, CH), 3.24-3.15 (d, 2H, CH₂), 2.38 (s, 3H, CH3); ¹³C NMR (DMSO-d₆): δ/ppm 161.37 (lactam C=O), 158.17 (amide C=O), 140.21 (C=N), 140.69-119.19, (12 Ar-C), 167.97, 155.63, 96.02 (oxazole-C), 55.16 (CH), 40.46 (CH₂), 12.33 (CH₃). MS: m/z = 544 [M⁺]. Anal. Calcd. for C₂₇H₂₄N₆O₅S (544.59): C, 59.55; H, 4.44; N, 15.43; Found C, 59.34; H, 4.35; N, 15.52.

5-Phenyl-3-phenylaminocarbonyl-1-[4-(5-methyloxazol-3-yl-sulfamoyl)-phenyl]-4,5-dihydro-1,2,4-triazin-6-one (5o): Yield 67%, m.p. 256-258 °C. IR (KBr): cm^-1 3355, 3271, 3220 (NH), 1675 (C=O lactam), 1650 (amide C=O), 1615 (C=N) 1342, 1172 (SO₂); ¹H NMR (DMSO-d₆): δ/ppm 12.51 (s, 1H, SO₂NH), 10.98 (s, 1H, PhNH), 7.94-7.03 (m, 14H, aromatic), 6.39 (s, 1H, NH triazinone ring), 6.21 (s, 1H, oxazole proton), 5.33 (s, 1H, CH), 2.38 (s, 3H, CH₃); ¹³C NMR (DMSO-d6): δ/ppm 160.87 (lactam C=O), 157.76 (amide C=O), 139.94 (C=N), 140.03-119.03 (12 Ar-C), 167.78, 155.81, 95.32 (oxazole-C), 56.38 (CH), 12.32 (CH₃). MS: m/z = 530 [M⁺]. Anal. Calcd. for C₂₆H₂₂N₆O₅S (530.57): C, 58.86; H, 4.18, N; 15.84; Found C, 59.05; H, 4.05; N, 15.72.

The required nitrilimines 2 having sulfonamide moieties were generated in situ from the respective hydrazonoyl chlorides 1 upon the action of base, and found to react with α-aminoester hydrochlorides 3 at low temperature in the presence of triethylamine to give sulfomylphenyl-4,5-dihydro-1,2,4-triazin-6-ones 5a-o (Scheme 1). The formation of these triazinones can be considered to involve an initial nucleophilic addition of an α-amino acid methyl esters 3 to the nitrilimines 2 yielding the open-chain amidrazone ester intermediate 4, which cyclized to produce 4,5-dihydro-1,2,4-triazinones 5a-o with the elimination of methanol. According to Baldwin, this type of cyclization is classified as an allowed 6-exo-trig process.³² No investigations were carried out concerning optical purity and activity. The characteristic data of compounds 5a-o are given in details in the experimental section.

Scheme 1 Synthetic pathway of sulfamoylphenyl-4,5-dihydro-1,2,4-triazin-6-ones 5a-o.

Spectral data analysis for compounds 5a-o

All compounds gave satisfactory combustion analysis for the proposed structures which were confirmed on the basis of their spectroscopic data. The mass spectra of the synthesized 1,2,4-triazin-6-ones 5a-o displayed the correct molecular ion peaks (M‏⁺) in accordance with the suggested structures and showed the loss of methanol molecule (Experimental part). A main fragmentation mode of the closely related substituted 4,5-dihydro-1,2,4-triazin-6-ones was reported to involve hetero ring-scission, leading to fragment ion M-29 as a base peak for compounds 5a,f,k, for compounds 5b,g,l is M-43, for compounds 5c,h,m is M-71, for compounds 5d,i,n is M-119 and the base peak for compounds 5e,j,o is M-105.³³

The IR spectra of compounds 5a-o in KBr revealed the presence of three NH absorption bands in the region 3370-3220 cm^-1. The lactam carbonyl (C=O) appeared in the region 1680-1670 cm^-1, and the amide C=O at about 1655 cm^-1. The stretching band of C=N of triazinone ring appeared in the region 1630-1610 cm-1. The sharp bands appeared around 1340 and 1140 cm^-1 attributed to SO₂ of sulfonamide group. The ¹H NMR spectra of compounds 5a-o showed all the signals of the proposed structures, indicating the appearance of three NH proton signals as singlets at 12.6-12.5 ppm (SO₂NH), 11.0-10.9 ppm (PhNH) and 6.4-6.3 ppm (NH of triazinone ring).

Furthermore, the signals of thiazole ring protons appeared as a doublet at 8.7, 6.6 ppm for compounds 5a-e, signals of pyrimidine ring protons as doublet at 8.6 and triplet at 6.8 ppm for compounds 5f-j, and signal of oxazole ring proton appeared as a singlet at 6.3-6.2 ppm for compounds 5k-o. Other signals can be concluded as follows: for compounds 5a,f,k containing a glycine residue, methylene protons appeared as a singlet in the range of 4.3-4.0 ppm, in addition to the signals of aromatic protons. For compounds 5b, g, l containing an alanine rest, methyl protons appeared as doublets in the range of 1.6-1.5 ppm and methinyl proton appeared as a quartet in the range of 4.4-4.3 ppm, in addition to the signals resulting from the protons of the aromatic rings. In compounds 5c, h, m containing a valine residue, methyl proton signals appeared as a doublet in the range 1.2-1.0 ppm, a methinyl proton as a multiplet in the range of 2.6-2.4 ppm, and the ring methinyl proton as a doublet in the range of 4.3-4.2 ppm, in addition to the signals of aromatic protons. For compounds 5d, i, n containing phenyl alanine rest, methylene protons of the benzyl group appeared as a doublet in the range 3.2-3.1 ppm. The methinyl proton appeared as a triplet in the range of 4.5-4.4 ppm, in addition to the signals resulting from the protons of the aromatic rings. In compounds 5e, j, o containing a phenyl glycine residue, the methinyl proton appeared as a singlet in the range of 5.4-5.3 ppm, in addition to the signals of aromatic protons. The entire ¹H NMR data are presented in the Experimental Section.

The structure of the prepared compounds 5a-o is also supported by ¹³C NMR measurements which displayed the characteristic signals of the suggested structures. The signal of the carbonyl carbon of the amide group appeared in the range of 158-157 ppm, and that of the lactam resonated in the range of 161-160 ppm. The signal at about 141-139 ppm, is attributed to C=N of the triazinone ring, in addition to those recorded for the different carbons of thiazole, pyrimidine and oxazole rings. The ¹³C NMR spectral data of the synthesized compounds are presented in the Experimental part.

Antimicrobial activity

Various sulfonamide moieties substituents were placed on the triazinone and thiadiazinone rings in order to study their effects on an antimicrobial activity in vitro. Most of the synthesized compounds were screened in vitro for their antimicrobial activity against a variety of bacterial strains such as Enterococci, Escherichia coli, Staphylococcus aureus, Klebsiella spp, Proteus spp, and fungi such as Aspergillus niger, Candida albicans, employing the nutrient agar disc diffusion method^34,35 at 1-100 mg/mL concentration in dimethyl sulfoxide (DMSO) which used as solvent control, by measuring the average diameter of the inhibition zone in mm. All experiments were carried out in triplicate. The results showed that all the tested compounds exhibited good degree of activity against different strains of bacteria and fungi compared with well-known antibacterial and antifungal substances such as tetracycline and fluconazole respectively. The results are given in Table 1.

According to NCCLS,³⁶ zones of inhibition for tetracycline and fluconazole < 14 mm were considered resistant, between 15 and 18 mm were considered weakly sensitive and > 19 mm were considered sensitive. From the screening results, it found to possess various antimicrobial activities towards all the microorganisms tested. The results confirm that, the antimicrobial activity is strongly dependent on the nature of the substituents on triazinone and thiadiazinone nucleus. The presence of sulfonamide moieties showed a better spectrum of activity than the reference drug (Table 1).

New series of novel functionalized 1,2,4-triazinones 5a-o containing benzene sulfonamide moiety were synthesized using hydrazonoyl halides as a precursor of nitrilimines and evaluated for their in vitro antibacterial, and antifungal activities. From the screening results, it found to possess various antimicrobial activities towards all the microorganisms tested. The results confirm that, the antimicrobial activity is strongly dependent on the nature of the substituents on triazinone nucleus. The pyrimidinyl, thiazolyl methoxzolyl derivatives generally led to dramatic improvements in activity against both bacteria and fungi. In short, the present study can lead medicinal chemists to design and synthesize similar compounds with enhanced biological potency in future.

The authors are great thankful to the Qatar Charity for the financial support of this research through Ibhath grant (GCC‒07‒06).

The author declares no conflict of interest.

1. Fathalla OA, Awad SM, Mohamed MS. Synthesis of new 2–thiouracil–5–sulphonamide derivatives with antibacterial and antifungal activity. Arch Pharm Res. 2005;28(11):1205–1212.
2. Willsteed E, Lee M, Wong LC, et al. Sulfasalazine and dermatitis herpetiformis. Aust J Dermat. 2005;46(2):101–103.
3. Giordanetto F, Fowler PW, Saqi M, et al. Large scale molecular dynamics of native and mutant dihydroptreoate synthase–sulphanilamide complexes suggest the molecular basis for dihyropteroate synthase drug resistance. Trans R Soc London. 2005;363(1833):2055–2073.
4. Holm RH, O’Connor MJ. The Stereochemistry of Bis–Chelate Metal (II) Complexes. Prog Inorg Chem. 1971;14:241–401.
5. Tiwari GD, Mishra MN. Studies on metal chelates of 5,7–di–iodo, 8–hydroxy quinolino–4–(p–tolyl) sulphonamide as potential drugs. Curr Sci. 1980;49:8–9.
6. Williams DR. Metals, ligands, and cancer. Chem Rev. 1972;72(3):203–213.
7. Pholpramool C, Ruchirawat S, Verawatnapakul V, et al. Structural requirements of some sulphonamides that possess an antifertility activity in male rats. J Reprod Fertil. 1991;92(1):169–178.
8. Domagk G. Ein Beitrag zur Chemotherapie der bakteriellen Infektionen. Dtsch Med Wochensch. 1935;61(17):250–253.
9. Domagk G. A contribution to the Chemotherapy of bacterial infections. Angew Chem. 1935;48:657–667.
10. Ul–H Mahmood, Scozzafava A, Chohan ZH, et al. Carbonic anhydrase inhibitors: Schiff's bases of aromatic and heterocyclic sulfonamides and their metal complexes. J Enz Inhib Med Chem. 2004;19(3):263–267.
11. Carta F, Scozzafva A, Supuran C. Sulfonamides: a patent review (2008–2012). Expert Opin Ther Pat. 2012;22(7):747–758.
12. Mok BL. Investigating cellular factors and mechanisms that are involved in vaccinia virus genome uncoating, and new virion assembly during the infectious life cycle. UK: PhD Thesis, Chemistry Department, University College London; 2008.
13. Abdul Qadir M, Ahmed M, Aslam H, et al. Amidine sulfonamides and benzene sulfonamides: Synthesis and their biological evaluation. J Chem. 2015;2015:1–8.
14. Suparan CT, Innocenti A, Mastrolorenzo A, et al. Antiviral sulfonamide derivatives. Mini Rev Med Chem. 2004;4(2):189–200.
15. Supuran C, Casini A, Scozzafava A. Protease inhibitors of the sulfonamide type: Anticancer, anti‒inflammatory, and antiviral agents. Med Res Rev. 2003;23(5):535–558.
16. Fukuoka K, Usuda J, Iwamoto Y, et al. Mechanisms of Action of the Novel Sulfonamide Anticancer Agent E7070 on Cell Cycle Progression in Human Non–Small Cell Lung Cancer Cells. Invest New Drugs. 2001;19(3):219–227.
17. Casini A, Scozzafava A, Mastrolorenzo A, et al. Sulfonamides and sulfonylated derivatives as anticancer agents. Curr Cancer Drug Targets. 2003;2(1):55–75.
18. Singh V, Kaushik NK, Singh R. Metallosulphadrugs: Synthesis and Bioactivity. Asian J Res Chem. 2011;4(3):339–347.
19. Scozzafava A, Owa T, Mastrolorenzo A, et al. Anticancer and antiviral sulfonamides. Curr Med Chem. 2003;10(11):925–953.
20. Talley JJ, Brown DL, Carter JS, et al. 4–[5–Methyl–3–phenylisoxazol–4–yl]– benzene sulfonamide, valdecoxib: a potent and selective inhibitor of COX–2. J Med Chem. 2000;43(5):775–777.
21. Thun MJ, Henley SJ, Patrono C. Nonsteroidal anti–inflammatory drugs as anticancer agents: mechanistic, pharmacologic, and clinical issues. J Natl Cancer Inst. 2002;94(4):252–266.
22. Patrick G. In an Introduction to Medicinal Chemistry. 2nd ed. India: Oxford university press; 2001. p. 375–387.
23. Bult A. In Metal Ions in Biological Systems. In: Sigel H, et al. editors. New York, USA; 1983. p. 261–268.
24. Abdel–Rahman RM, Morsy JM, Hanafy F, et al. Synthesis of Heterobicyclic Nitrogen Systems Bearing the 1,2,4–Triazine Moiety as Anti–HIV and Anticancer Drugs: Part I. Pharmazie. 1999;54(5):347–667.
25. El–Gendy Z, Morsy JM, Allimony HA, et al. Synthesis of Heterobicyclic Nitrogen Systems Bearing the 1,2,4–Triazine Moiety as Anti–HIV and Anticancer Drugs, Part III. Pharmazie. 2001;56(5):376–383.
26. El–Ashry ESH, Rashed N, Taha M, et al. Condensed 1, 2, 4–triazines:I. Fused to heterocycles with three–, four–, and five–membered rings. Adv Heterocycl Chem. 1994;59:39–177.
27. Abdel–Rahman RM, Saeda M, Fawzy M, et al. Synthesis of some new 1, 6–dihydro–3–substituted 6–spiro–(9'–fluorene)–1,2,4–triazin–5–(4H)–ones as potential anti HIV and anticancer drugs. Pharmazie. 1994;49(10):729–733.
28. Habib NS, Soliman R, Ismail K, et al. Pyrimidines. Part II: Synthesis of novel pyrimidines, 1,2,4–triazolo[4,3–a]pyrimidin–7–ones and pyrimidino[2,1–c][1,2,4]triazin–8–ones for their antimicrobial and anticancer activities. Boll Chim Fran. 2003;142(90:396–405.
29. Holla BS, Rao BS, Gonsalves R, et al. Synthesis of some new biologically active thiadiazole–triazinones–part III. Farmaco. 2002;57(8):693–696.
30. Frohberg P, Drutkowski G, Wagner C. Synthesis and Structural Assignment of Oxanilo–Narylhydra–zonoyl Chlorides. Eur J Org Chem. 2002;2002(10):1654–1663.
31. El–Abadelah MM, Hussein AQ, Thaher BA. Heterocycles from Nitrile Imines. Part IV. Chiral 4,5–Di–hydro–1,2,4–triazin–ones. Heterocycles. 1991;32(10):1879–1895.
32. Baldwin JE. Rules for ring closure. J Chem Soc Chem Commun. 1976;(18):734–738.
33. Dalloul HM, Mohamed EA, Shorafa HZ, et al. Heterocyclic synthesis using nitrilimines: Part 10. Synthesis of 1–aryl–3–phenylaminocarbonyl–4,5–dihydro–1,4,5–triazin–6–ones. Arkivoc (xiii). 2008:207–217.
34. Irobi ON, Moo Young M, Anderson WA. Antimicrobial activity of Annatto (Bixaorellana) extract. Inter J Pharm. 1996;34(2):87–90.
35. Grayer RJ, Harborne JB. A survey of antifungal compounds from higher plants, 1982–1993. Phytochemistry. 1994;37(1):19–42.
36. Methods for dilution antimicrobial susceptibility tests for bacteria grow aerobically, Approved Standard M7–A4. USA: Clinical and Laboratory Standards Institute; 2015.