HETEROCYCLES

Paper | Regular issue | Vol. 78, No. 9, 2009, pp. 2217-2231
Received, 3rd March, 2009, Accepted, 23rd April, 2009, Published online, 23rd April, 2009.
DOI: 10.3987/COM-09-11696

■ The Synthesis and Microbiological Activity of New 4-Chloropyridin-2-yl Derivatives

Agnieszka Bogdanowicz,* Henryk Foks, Anna Kędzia, Ewa Kwapisz, Zofia Zwolska, and Ewa Augustynowicz-Kopeć

Department of Organic Chemistry, Medical University of Gdańsk, Al. Gen. Hallera 107, 80-416 Gdańsk, Poland

Abstract

Synthesis of 4-chloropicolinamidrazone derivatives starting from 4-chloropicolinamide is described. The desired compounds were formed by reactions of methyl 4-chloropicolinohydrazonamide or 4-chloro-N'-methylpicolinohydrazonamide with suitable counter partners (carbon disulfide, alkyl halides, aldehydes, ketones, carbohydrazonamides or isothiocyanates) or via 4-chloropicolinimidate, obtained by a convenient method from nitrile with catalytic amount of DBU. Selected products were screened for bacteriostatic and tuberculostatic activity.

INTRODUCTION
Development of mycobacterial resistance to conventional drugs is one of the major difficulties in the treatment of tuberculosis, and a major factor in increasing demand for new antituberculosis agents. Looking for new structures with potential tuberculostatic activity, we pay attention to a recent report suggesting that tuberculostatic activity of pyridin-2-yl-formamide thiosemicarbazones (A) is related to their co-planarity1. The hypothesis prompted us to synthesis of new 2-substituted pyridine derivatives. To increase probability that the prepared compounds will bear the desired activity, the pyridine ring was connected with structural fragments witch have already been present in tuberculostatic compounds namely: amidrazones (B),2 thiosemicarbazones (C), and thioureas (D)3 (Figure 1). Moreover some of them fulfill the requirement of co-planarity with the pyridine moiety.

CHEMISTRY
A first set of compounds possessing the desired, outlined above structural characteristic, was prepared from imidate 3, as the key intermediate. Starting 4-chloropicolinonitrile (2)4 was prepared, with one of general metods, from amide 14 using a dehydrating agent (Scheme 1). Treatment of methanolic solution of the nitrile (2) with catalytic amount of DBU resulted in formation of methyl 4-chloropicolinimidate (3). The DBU catalyzed formation of imidates was the best for our compound, and seems to be a viable alternative to the catalysis with alkali metal methanolate.5, 6 When sodium methanolate was used, chlorine atom was converted to methoxy group. Reaction of the formed in situ imidate 3 with 4-phenylpiperazine-1-carbothiohydrazide and 4-phenylpiperazine-1-carbohydrazide gave amidrazones 4a – 4b, respectively. 1H NMR spectra of the products demonstrated NH protons, as two-protons singlet at 6.28 (for 4a) and 6.58 (for 4b) and one-proton singlets at 8.58 (for 4a) and 8.60 (for 4b), which confirms structures shown at Scheme 1. Analogous reaction of imidate 3 with benzenesulfonamide and aminobenzenosulfonamide gave amidines 5a – 5b, respectively. 1H NMR spectra of the products demonstrated NH protons, as two broad singlets at 8.29 and 8.92 (for 5a) and two broad singlets at 8.12 and 8.88 (for 5b), which confirms structures shown at Scheme 1.
Next group of compounds originated from amidrazone 6 as the key intermediate. The starting material 4-chloropicolinohydrazonamide (6) was prepared by reaction of nitrile 2 with hydrazine monohydrate. Subsequently, it was reacted under various reaction conditions, with carbon disulfide. As expected, reaction of 6 with carbon disulfide in plane methanol gave 5-(4-chloropyridin-2-yl)-1,3,4-thiadiazole-2(3H)-thione (7). Two tautomers (7a and 7b) seem to be possible for the compound, and the δ value 14.96 for the exchangeable proton suggested that it is connected with nitrogen (7a).

The conclusion was supported by IR (KBr), which demonstrated a strong absorption at 1235 cm-1, which could correspond to C=S group. Thus, the reaction proceeded analogously as reported earlier7 for similar compounds. The same reagent 6 but with addition of methyl iodide gave corresponding S-methylthiadiazole derivative 8. Surprisingly, analogous condensation – alkylation reactions run in the presence of equimolar amount of triethylamine (TEA), resulted in formation of linear dithiocarbazoic acid monoesters 9a - c as the main products, while in the presence of excess of TEA, dithiocarbazoic acid diesters 10a, b were obtained. Replacement of methyl iodide by 1,3-dibromopropane gave 1,3-dithiolane derivative 11. Further, compound 6 was reacted with appropriate isothiocyanates to give N-methyl, allyl and p-chlorophenyl thiosemicarbazides 12a - c (Scheme 2).
In the next step of the work, compounds with differently modified side chain in position 2 of the pyridine moiety were obtained, by reactions of compound 6 with aldehydes, ketones and iminoesters (Scheme 3). Reaction of 4-chloropicolinohydrazonamide (6) with 4-chlorobenzaldehyde, 5-nitrofuran-2-carbaldehyde, 5-nitrothiophene-2-carbaldehyde, 4-hydroxy-3-methoxybenzaldehyde or 4-(dimethylamino)benzaldehyde gave corresponding condensation products 13a - e. Similarly, reaction with 1-(thiophen-2-yl)ethanone gave 4-chloro-N'-[1-(thiophen-2-yl)ethylidene]picolinohydrazonamide (14). Reaction of amidrazone 6 with iminoesters lead initially, at room temperature, to corresponding carbimidates 15a, b, while heating of the products in AcOH caused intramolecular cyclization to 1,2,4-triazole derivatives 16a, b.
Still another group of the required compounds originated from amidrazone 17, which itself was prepared by reaction of nitrile 2 with methylhydrazine (Scheme 4). The compounds were prepared to check, by comparison with products derived from 6, how methylation of the nitrogen atom will influence their

tuberculostatic activity. Essentially, the obtained results were similar to those for demethylated derivative 6 (Scheme 2) except the reaction with isothiocyanatomethane, which gave in the same conditions 1,2,4-triazole 20 (Scheme 4).

MICROBIOLOGICAL ACTIVITY
Antimicrobial activities of compounds were tested using the plate dilution technique in Brucella agar supplemented with 5 % lamb blood,8 against 26 strains of anaerobic bacteria and agar dilution technique with Miller-Hinton agar against 25 strains of aerobic bacteria (Table 1), isolated from the oral cavity, respiratory system and abdominal cavity. The antibacterial activity of the tested compounds was also performed against the following standard bacterial strains: Bacteroides fragilis ATCC 25285, Fusobacterium nucleatum ATCC 25586, Peptostreptococcus anaerobius ATCC 27337, Peptostreptococcus magnus ATCC 29328, Propionibacterium acnes ATCC 11827. Staphylococcus aureus ATCC 25923, Enterococcus faecalis ATCC 29212, Klebsiella pneumonia ATCC 13883, Acinetobacter baumannii ATCC 19606, Escherichia coli ATCC 25922 and Pseudomonas aeruginosa ATCC 27853. The minimal inhibitory concentration (MIC) was defined as the lowest concentration of derivative that inhibited growth of bacteria. Metronidazole and amikacin were used as the reference substances. The investigation of susceptibility of aerobic and anaerobic bacteria to the compounds 2, 6, 9a, 13a – e, 14 are summarized in Table 1. The tested derivatives exhibited diversified activity against aerobic and anaerobic bacteria. Compounds 9a (100 % of susceptible strains) and 13b (72 % of susceptible strains) were found to be more active then the other compounds at concentrations in the range from ≤ 6.2 to 100 µg/mL against the aerobes. The anaerobes were the most susceptible at concentrations in the range from ≤ 6.2 to 100 µg/mL to derivatives 9a (50 %) and 2 (35 %). Compounds 13c – e and 14 did not exhibit any activity against aerobic and anaerobic bacteria.
Selected compounds 2 – 10b, 12a – 20 were tested for their tuberculostatic activity towards the standard Mycobacterium tuberculosis H37Rv strain and two wild strains isolated from the tuberculotic patients: one (Spec. 210) resistant to p-aminosalicylic acid (PAS), isonicotinic acid hydrazide (INH), etambutol (ETB) and rifampicine (REP) and the other (Spec. 192) fully susceptible to the drugs administered. The tuberculostatic activity was determined in vitro by classical test tube method with Youman’s liquid medium containing 10 % of bovine serum. In comparison with some of tuberculosis drugs: isonicotinic acid hydrazide (MIC 0.5 μg/mL), viomycin (MIC 6.2 μg/mL), cycloserine (MIC 5 μg/mL) and pyrazinamid (MIC 25 μg/mL), it was concluded that tested compounds showed no significant tuberculostatic activity (MIC 25 – 100 μg/mL).

EXPERIMENTAL
Melting points were obtained with Boetius apparatus and are uncorrected. Elemental analyses for C, H, N and S were performed on Carlo-Erba 1108 instrument. The IR spectra were taken using Mattson Satellite spectrophotometer, and the 1H NMR spectra were obtained on Varian Gemini 200 MHz apparatus.
4-Chloropicolinonitrile (2)
4-Chloropicolinamide (1) (5.0 g, 32 mmol) was susspended in dry dioxane (30 mL) and POCl3 (5 mL, 53.6 mmol) was added. The mixture was refluxed for 1.5 h and then the solution was evaporated. Ice (20 g) was added to the residue, and the precipitated solid was collected by filtration and crystallized from H2O to give 4-chloropicolinonitrile (2) (2.21 g, 50 %) as colorless solid, mp 80 – 82 °C (83 – 84 °C).5 1H NMR (CDCl3) δ 7.56 (1H, dd, J1 = 1.9 Hz, J2 = 5.4 Hz), 7.73 (1H, d, J = 1.9 Hz), 8.64 (1H, d, J = 5.4 Hz); IR (KBr) ν 3086, 2240, 1570, 1547, 1461, 1381, 847, 465 cm-1.
4-Chloro-N'-(4-phenylpiperazine-1-carbonothioyl)picolinohydrazonamide (4a)
4-Chloropicolinonitrile (2) (0.511 g, 4 mmol) was dissolved in anhydrous MeOH (10 mL) containing DBU (0.2 mL), as a catalyst. The mixture was refluxed for 10 min. Next 4-phenylpiperazine-1-carbothiohydrazide (0.944 g, 4 mmol) was added, and reflux was continued for 1 min and the mixture was left at rt for 5 h. The reaction mixture was acidified with acetic acid (0.3 mL), the product was filtered off and crystallized from dioxane to give 4-chloro-N'-(4-phenylpiperazine-1-carbonothioyl)picolinohydrazonamide (4a) (0.78 g, 52 %) as a yellow crystals, mp 160 – 163 °C. 1H NMR (CDCl3) δ 3.28 (4H, m), 4.18 (4H, m), 6.86 (2H, s), 6.95 (5H, m), 7.41 (1H, dd, J1 = 2.0 Hz, J2 = 5.3 Hz), 7.98 (1H, d, J = 2.0 Hz), 8. 54 (1H, d, J = 5.3 Hz), 8.58 (1H, s); IR (KBr) ν 3388, 3269, 2923, 1599, 1340, 1227, 1017, 758 cm-1; Anal. Calcd for C17H19ClN6S: C, 54.46; H, 5.11; N, 22.42; S, 8.55. Found: C, 54.32; H, 5.09; N, 22.39; S, 8.53.
4-Chloro-N'-(4-phenylpiperazine-1-carbonyl)picolinohydrazonamide (4b)
4-Chloropicolinonitrile (2) (0.249 g, 1.8 mmol) was dissolved in anhydrous MeOH (5 mL) containing DBU (0.1 mL), as a catalyst. The mixture was refluxed for 10 min and then cooled. 4-Phenylpiperazine-1-carbohydrazide (0.396 g, 1.8 mmol) was added and the mixture was stirred at rt for 2 h. The reaction mixture was acidified with acetic acid, the obtained solid was filtered off, and crystallized from MeOH to give 4-chloro-N'-(4-phenylpiperazine-1-carbonyl)picolinohydrazonamide (4b) (0.312 g, 50 %) as a yellow crystals, mp 296 – 298 °C. 1H NMR (DMSO–d6) δ 3.17 (4H, d, J = 5.1 Hz), 3.57 (4H, d, J = 5.1 Hz), 6.58 (2H, s), 6.80 – 7.27 (5H, m), 7.56 (1H, dd, J1 = 2.1 Hz, J2 = 5.3 Hz), 8.02 (1H, d, J = 2.1 Hz), 8.53 (1H, d, J = 5.3 Hz), 8.60 (1H, s); IR (KBr) ν 3430, 3333, 3232, 2814, 1631, 1539, 1425, 1229, 1156, 999, 761 cm-1. Anal. Calcd for C17H19ClN6O: C, 56.90; H, 5.34; N, 23.42. Found: C, 56.79; H, 5.32; N, 23.40.
4-Chloro-N'-(phenylsulfonyl)picolinimidamide (5a)
4-Chloropicolinonitrile (2) (0.277 g, 2 mmol) was dissolved in anhydrous MeOH (5 mL) containing DBU (0.2 mL), as a catalyst. The mixture was refluxed for 10 min, then the benzenosulfonamide (0.309 g, 1.8 mmol) was added, and the mixture was refluxed for 10 h. The reaction was cooled to rt, and the precipitated solid was filtered off and washed with water. The product was crystallized from MeOH to give 4-chloro-N'-(phenylsulfonyl)picolinimidamide (5a) (0.235 g, 40 %) as colorless crystals, mp 119 – 121 °C. 1H NMR (CDCl3) δ 7.58 – 7.67 (3H, m), 7.85 (1H, dd, J1 = 1.9 Hz, J2 = 5.3 Hz), 8.00 (2H, d, J = 7.3 Hz), 8.10 (1H, d, J = 1.9 Hz), 8.29 (1H, bs), 8.68 (1H, d, J = 5.3 Hz), 8.92 (1H, bs); IR (KBr) ν 3418, 3311, 1618, 1574, 1285, 1142, 1084, 791, 590 cm-1. Anal. Calcd for C12H10ClN3O2S: C, 48.73; H, 3.41; N, 14.21; S, 10.84. Found: C, 48.61; H, 3.40; 14.19; S, 10.81.
N'-(4-aminophenylsulfonyl)-4-chloropicolinimidamide (5b)
4-Chloropicolinonitrile (2) (0.257 g, 1.85 mmol) was dissolved in anhydrous MeOH (5 mL) containing DBU (0.1 mL), as a catalyst. The mixture was refluxed for 10 min. Then 4-aminobenzenosulfonamide (0.287 g, 1.67 mmol) was added and the mixture was refluxed for 1.5 h. After cooling down the precipitated solid was filtered off and crystallized from EtOH to give N'-(4-aminophenylsulfonyl)-4-chloropicolinimidamide (5b) (0.197 g, 34 %) as a bright solid, mp 206 - 209 °C. 1H NMR (DMSO-d6) δ 5.96 (2H, s), 6.58 (2H, d, J = 8.7 Hz), 7.59 (2H, d, J = 8.7 Hz), 7.81 (1H, dd, J1 = 1.9 Hz, J2 = 5.3 Hz), 8.04 (1H, d, J = 1.9 Hz), 8.12 (1H, bs), 8.65 (1H, d, J = 5.3 Hz), 8.88 (1H, bs); IR (KBr) ν 3447, 3423, 3336, 1613, 1589, 1503, 1429, 1265, 1140,1084, 791, 572 cm-1. Anal. Calcd for C12H11ClN4O2S: C, 46.38; H, 3.57; N, 18.03; S, 10.32. Found: C, 46.30; H, 3.56; N, 17.99; S, 10.29.
4-Chloropicolinohydrazonamide (6)
A mixture of 4-chloropicolinonitrile (2) (1.385 g, 10 mmol) and hydrazine monohydrate (5 mL, 103 mmol) in MeOH (20 mL) was heated under reflux for 30 min and the solvent was evaporated. The residue was diluted with benzene (10 mL) and evaporated again. Ice (10 g) was added to the residue, the formed solid was filtered off and crystallized from MeOH to give 4-chloropicolinohydrazonamide (6) (1.15 g, 67 %) as a yellow solid, mp 107 – 109 °C. 1H NMR (CDCl3) δ 4.67 (2H, bs), 5.22 (2H, s), 7.29 (1H, s), 8.06 (1H,s), 8.41 (1H, d, J = 5.4 Hz); IR (KBr) ν 3439, 3330, 3203,1655, 1625,1550, 1577, 1345, 882, 724 cm-1. Anal. Calcd for C6H7ClN4: C, 42.24; H, 4.14; N, 32.84. Found: C, 42.18; H, 4.12; N, 32.79.
5-(4-Chloropyridin-2-yl)-1,3,4-thiadiazole-2(3H)-thione (7)
4-Chloropicolinohydrazonamide (6) (0.511 g, 3 mmol) was dissolved in MeOH (5 mL) and on cooling CS2 (1 mL, 16.5 mmol) was added. The mixture was left at rt for 24 h. Ice (20 g) was added to the reaction mixture and the precipitated solid was filtered off and crystallized from MeOH to give 5-(4-chloropyridin-2-yl)-1,3,4-thiadiazole-2-thiol (7) (0.24 g, 35 %) as a yellow solid, mp 175 – 177 °C. 1H NMR (DMSO–d6) δ 7.66 (1H, dd, J1 = 2.0 Hz, J2 = 5.7 Hz), 8.08 (1H, d, J = 2.0 Hz), 8.62 (1H, d, J = 5.7 Hz), 14.96 (1H, s); IR (KBr) ν 3088, 2994, 2890, 1574, 1471, 1401, 1294, 1235, 1073, 782, 728 cm-1. Anal. Calcd for C7H4ClN3S2: C, 36.60; H, 1.76; N, 18.29; S, 27.92. Found: C, 36.54; 1.75; N, 18.25; S, 27.88.
2-(4-Chloropyridin-2-yl)-5-(methylthio)-1,3,4-thiadiazole (8)
4-Chloropicolinohydrazonamide (6) (0.511 g, 3 mmol) was dissolved in anhydrous MeOH (10 mL). On cooling, CS2 (1 ml, 16.5 mmol) and MeI (0.24 mL, 3.9 mmol) were added, and the mixture was stirred at rt for 1 h. The precipitated solid was filtered off and crystallized from MeOH:H2O (1:1) to give 2-(4-chloropyridin-2-yl)-5-(methylthio)-1,3,4-thiadiazole (8) (0.42 g, 57 %) as colorless crystals, mp 122 – 123 °C. 1H NMR (CDCl3) δ 2.85 (3H, s), 7.36 (1H, dd, J1 = 2.0 Hz, J2 = 5,4 Hz), 8.32 (1H, d, J = 2.0 Hz), 8.53 (1H, d, J = 5.4 Hz); IR (KBr) ν 1577, 1554, 1396, 1360, 1082, 834, 739 cm-1. Anal. Calcd for C8H6ClN3S2: C, 39.42; H, 2.48; N, 17.24; S, 26.31. Found: C, 39.37; H, 2.47; N, 17.20; S, 26.27.
General method for synthesis of compounds 9a-c
A solution of 4-chloropicolinohydrazonamide (6) (0.852 g, 5 mmol) in MeOH (15 mL) containing 0.83 mL of triethylamine (6 mmol) was cooled to 0 ºC and then CS2 (0.36 mL, 6 mmol) was added, and the mixture was stirred at rt for 1 h. Next, iodomethane (5 mmol) (for compound 9a), buthyl iodid (5 mmol) (for 9b), (chloromethyl)benzene (5 mmol) (for 9c) was added, and the mixture was stirred at rt for 2 h. The precipitated solid was filtered off and crystallized.
Methyl 2-[amino(4-chloropyridin-2-yl)methylene]hydrazinecarbodithioate (9a)
The crude product was crystallized from MeOH to give yellow solid (89 %), mp 159 – 160 °C. 1H NMR (Acetone) δ 2.56 (3H, s), 6.99 (2H, s), 7.59 (1H, dd, J1 = 2.1 Hz, J2 = 5.1 Hz), 8.22 (1H, d, J = 2.1 Hz), 8.57 (1H, d, J = 5.1 Hz), 10.93 (1H, s); IR (KBr) ν 3384, 3280, 2911, 1665, 1577, 1365, 1317, 1002, 958, 741 cm-1. Anal. Calcd for C8H9ClN4S2: C, 36.85; H, 3.48; N, 21.49; S, 24.59. Found: C, 36.79; H, 3.46; N, 21.44; S, 24.54.
Butyl 2-[amino(4-chloropyridin-2-yl)methylene]hydrazinecarbodithioate (9b)
The crude product was crystallized from EtOH to give yellow solid (32 %), mp 121 – 122 °C. 1H NMR (Acetone) δ 0.95 (3H, s), 1.45 (2H, m), 1.67 (2H, m), 3.25 (2H, t, J = 7.2 Hz), 6.99 (2H, s), 7.58 (1H, dd, J1 = 2.0 Hz, J2 = 5.5 Hz), 8.22 (1H, d, J = 2.0 Hz), 8.57 (1H, d, J = 5.5 Hz), 10.83 (1H, s); IR (KBr) ν 3404, 3311, 2957, 1661, 1508, 1366, 1318, 994, 737 cm-1. Anal. Calcd for C11H15ClN4S2: C, 43.63; H, 4.99; N, 18.50; S, 21.18. Found: C, 43.56; H, 4.97; N, 18.45; S, 21.14.
Benzyl 2-[amino(4-chloropyridin-2-yl)methylene]hydrazinecarbodithioate (9c)
The crude product was crystallized from MeOH to give yellow solid (38 %), mp 218 – 221 °C. 1H NMR (CDCl3) δ 4.34 (2H, s), 7.06 - 7.98 (9H, m), 8.45 (1H, d, J = 4.9 Hz), 9.74 (1H, s); IR (KBr) ν 3434, 3323, 2923, 1660, 1574, 1469, 1361, 1312, 1241, 1068, 1000, 831, 735, 693, 473 cm-1. Anal. Calcd for C14H13ClN4S2: C, 49.92; H, 3.89; N, 16.63; S, 19.04. Found: C, 49.79; H, 3.87; N, 16.59; S, 18.98.
Dimethyl amino(4-chloropyridin-2-yl)methylenecarbonohydrazonodithioate (10a)
A solution of 4-chloropicolinohydrazonamide (6) (0.852 g, 5 mmol) and triethylamine (1.66 mL, 11.5 mmol) in MeOH (10 mL) was cooled to 0 ºC and then CS2 (0.3 mL, 5 mmol) was added, and the mixture was stirred at rt for 0.5 h. Iodomethane (0.62 mL, 10 mmol) was added, and the mixture was stirred at rt for 2 h. The solvent was evaporated and diethyl eter (30 mL) was added to the residue. The precipitated solid was filtered off and crystallized from EtOH to give dimethyl amino(4-chloropyridin-2-yl)methylenecarbonohydrazonodithioate (10a) (1.09 g, 79 %) as a yellow solid, mp 101 – 103 °C. 1H NMR (CDCl3) δ 2.55 (3H, s), 2.59 (3H, s), 6.15 (2H, s), 7.34 (1H, dd, J1 = 1.9 Hz, J2 = 5.3Hz), 8.35 (1H, s), 8.46 (1H, d, J = 5.3Hz); IR (KBr) ν 3469, 3359, 1613, 1548, 1460, 1345, 1035, 944, 745 cm-1. Anal. Calcd for C9H11ClN4S2: C, 39.34; H, 4.03; N, 20.39; S, 23.34. Found: C, 39.29; H, 4,02; N, 20.35; S, 23.30.
Dibenzyl amino(4-chloropyridin-2-yl)methylenecarbonohydrazonodithioate (10b)
A solution of 4-chloropicolinohydrazonamide (6) (0.341 g, 2 mmol) and triethylamine (0.84 mL, 6 mmol) in MeOH (10 mL) was cooled to 0 ºC and then CS2 (0.18 mL, 3 mmol) was added. The mixture was stirred at rt for 1 h. Next, benzyl chloride (0.46 mL, 4 mmol) was added and the mixture was stirred at rt for 24 h. The formed precipitate was filtered off and crystallized from MeOH:H2O (1:1) to give dibenzyl amino(4-chloropyridin-2-yl)methylenecarbonohydrazonodithioate (10b) (0.28 g, 33 %) as a yellow solid, mp 83 – 84 °C. 1H NMR (CDCl3) δ 4.31 (2H, s), 4.42 (2H, s), 5.95 (2H, s), 7.31 – 7.45 (10H, m), 7.47 (1H, d, J = 2.1 Hz), 8.26 (1H, d, J = 2.1 Hz), 8.44 (1H, d, J = 5.4 Hz); ); IR (KBr) ν 3456, 3365, 1616, 1548, 1461, 1416, 1348, 1239, 1011, 742, 696 cm-1. Anal. Calcd for C21H19ClN4S2: C, 59.07; H, 4.49; N, 13.12; S, 15.02, Found: C, 58.94; H, 4.47; N, 13.08; S, 14.99.
4-Chloro-N'-(1,3-dithian-2-ylidene)picolinohydrazonamide (11)
A solution of 4-chloropicolinohydrazonamide (6) (0.511 g ,3 mmol) and triethylamine (1.05 mL, 7.5 mmol) in MeOH (10 mL) was cooled to 0 ºC and then CS2 (0.27 mL, 4.5 mmol) was added. The mixture was stirred at rt for 1 h. Next, 1,3-dibromopropane (0.36 mL, 3.6 mmol) was added, and the mixture was stirred at rt for 3 h. The mixture was neutralized with diluted acetic acid and extracted with dichloromethane (3 x 30 mL). The organic layer was dried over anhydrous MgSO4 (2 g) for 12 h and evaporated give 4-chloro-N'-(1,3-dithian-2-ylidene)picolinohydrazonamide (11) (0.27 g, 31 %) as a yellow solid, mp 166 – 169 °C. 1H NMR (CDCl3) δ 2.48 (2H, m), 3.23 (2H, m), 3.74 (2H, t, J = 5.2 Hz), 6.31 (2H, s), 7.41 (1H, dd, J1 = 3.3 Hz, J2 = 5.1 Hz), 8.36 (1H, s), 8.47 (1H, d, J = 5.1 Hz); IR (KBr) ν 3437, 3307, 2937, 2677, 2491, 1627, 1574, 1433, 1170, 1036, 952 cm-1. Anal. Calcd for C10H11ClN4S2: C, 41.88; H, 3.87; N, 19.53; S, 22.36. Found: C, 41.81; H, 3.86; N, 19.49; S, 22.32.

General method for compounds 12a-c
A solution of 4-chloropicolinohydrazonamide (6) (0.511 g, 3 mmol) in dry dioxane (5 mL) was treated with isothiocyanatomethane (0.22 g, 3 mmol) (for 12a), allyl isothiocyanate (0.291 mL, 3 mmol) (for 12b) and 1-chloro-4-isothiocyanatobenzene (0.508 g, 3 mmol) (for 12c) and heated under reflux for 15 min. The reaction mixture was then cooled and poured into petroleum ether (30 mL). The product was filtered off and crystallized from MeOH:H2O (2:1) or dioxane (12c).

2-[Amino(4-chloropyridin-2-yl)methylene]-N-methylhydrazinecarbothioamide (12a)
Reaction with isothiocyanatomethane. Product 12a was isolated as a yellow solid (0.31g, 42 %), mp 175 – 177 °C. 1H NMR (DMSO–d6) δ 3.02 (3H, d, J = 4.6 Hz), 6.92 (2H, s), 7.56 (1H, dd, J1 = 2.1 Hz, J2 = 5.4 Hz), 8.42 (1H, d, J = 4.6 Hz), 8.53 (1H, d, J = 5.4 Hz), 8.62 (1H, d, J = 2.1 Hz), 10.07 (1H, s); IR (KBr) ν 3440, 3405, 3351, 3279, 3175, 1656, 1550, 1430, 1259, 1070, 711 cm-1. Anal. Calcd for C8H10ClN5S: C, 39.43; H, 4.14; N, 28.74; S, 13.16. Found: C, 39.38; H, 4.13; N, 28.69; S, 13.13.
N-Allyl-2-[amino(4-chloropyridin-2-yl)methylene]hydrazinecarbothioamide (12b)
Reaction with allyl isothiocyanate. Product 12b was isolated as a yellow solid (0.66 g, 82 %), mp 158 – 160 oC. 1H NMR (CDCl3) δ 4.43 (2H, s), 5.24 (1H, s), 5.32 (1H, d, J = 15.6 Hz), 6.00 (1H, s), 6.44 (2H, s), 7.35 (1H, s), 7.59 (1H, s), 8.06 (1H, s), 8.45 (1H, s), 9.81 (1H, s); IR (KBr) ν 3423, 3365, 3269, 1655, 1575, 1541, 1431, 1295, 1222, 828, 714 cm-1. Anal. Calcd for C10H12ClN5S: C, 44.52; H, 4.48; N, 25.96; S, 11.89. Found: C, 44.46; H, 4.46; N, 25.90; S, 11.85.
2-[Amino(4-chloropyridin-2-yl)methylene]-N-(4-chlorophenyl)hydrazinecarbothioamide (12c)
Reaction with 1-chloro-4-isothiocyanatobenzene. Product 12c was isolated as a white solid (0.20 g, 20 %), mp 164 – 166 °C. 1H NMR (DMSO–d6) δ 7.14 (2H, s), 7.42 (2H, d, J = 8.3 Hz), 7.57 (2H, d, J = 8.3 Hz), 7.59 (1H, d, J = 5.3 Hz), 8.54 (1H, d, J = 5.3 Hz), 8.77 (1H, s), 10.03 (1H, s), 10.50 (1H, s); IR (KBr) ν 3401, 3281, 3229, 2968, 1665, 1577, 1533, 1467, 1334, 1200, 1090, 828, 721 cm-1. Anal. Calcd for C13H11Cl2N5S: C, 45.89; H, 3.26; N, 20.58; S, 9.42. Found: C, 45.79; H, 3.25; N, 20.52; S, 9.39.

General procedure for compound 13a-e
A solution of 4-chloropicolinohydrazonamide (6) (0.341 g, 2 mmol) in MeOH (5 mL) was treated with 4-chlorobenzaldehyde (0.281 g, 2 mmol) (for 13a), 5-nitrofuran-2-carbaldehyde (0.282 g, 2 mmol) (for 13b), 5-nitrothiophene-2-carbaldehyde (0.314 g, 2 mmol) (for 13c), 4-hydroxy-3-methoxybenzaldehyde (0.304 g, 2 mmol) (for 13d) or 4-(dimethylamino)benzaldehyde (0.298 g, 2 mmol) (for 13e) and stirred at rt for 1h. The product was filtered off and crystallized from MeOH to give compounds 13a-e, respectively.
4-Chloro-N'-(4-chlorobenzylidene)picolinohydrazonamide (13a)
Reaction with 4-chlorobenzaldehyde. Product 13a was isolated as a yellow solid (0.304 g, 52 %), mp 132 – 134 ºC. 1H NMR (DMSO–d6) δ 7.17 (1H, s), 7.32 (1H, s), 7.51 (2H, d, J = 7.8 Hz), 7.71 (1H, d, J = 4.8 Hz), 7.98 (2H, d, J = 7.8 Hz), 8.23 (1H, s), 8.50 (1H, s), 8.65 (1H, d, J = 4.8 Hz); IR (KBr) ν 3491, 3375,1623,1548, 1464, 1327, 1087, 1011, 836, 732 cm-1. Anal. Calcd for C13H10Cl2N4: C, 53.26; H, 3.44; N, 19.11. Found: C, 53.13; H, 3.43; N, 19.08.
4-Chloro-N'-[(5-nitrofuran-2-yl)methylene]picolinohydrazonamide (13b)
Reaction with 5-nitrofuran-2-carbaldehyde. Produkt 13b was isolated as a red solid (0.4 g, 68 %), mp 174 – 177 ºC. 1H NMR (DMSO–d6) δ 7.43 (1H, d, J = 3.9 Hz), 7.59 (2H, bs), 7.74 (1H, dd, J1 = 1.9 Hz, J2 = 5.4 Hz), 7.84 (1H, d, J = 3.9 Hz), 8.24 (1H, d, J = 1.9 Hz), 8.41 (1H, s), 8.67 (1H, d, J = 5.4 Hz); IR (KBr) ν 3474, 3348, 1624, 1551, 1467, 1347, 1252, 1179, 1008, 735 cm-1. Anal. Calcd for C11H8ClN5O3: C, 44.99; H, 2.75; N, 23.85. Fund: C, 44.87; H, 2.74; N, 23.79.
4-Chloro-N'-[(5-nitrothiophen-2-yl)methylene]picolinohydrazonamide (13c)
Reaction with 5-nitrothiophene-2-carbaldehyde. Product 13c was isolated as a yellow solid (0.276 g, 45 %), mp 218 – 220 oC. 1H NMR (CDCl3) δ 7.03 (1H, s), 7.04 (1H, s), 7.29 (1H, d, J = 3.6 Hz), 7.47 (1H, dd, J1 = 5.1 Hz, J2 = 1.9 Hz), 7.94 (1H, d, J = 1.9 Hz); 8.08 (1H, s); 8.54 (1H, d, J = 3.6 Hz); 8.56 (1H, d, J = 1.9 Hz); IR (KBr) ν 3454, 3356, 1614, 1551, 1486, 1337, 1205, 1060, 814, 733, 708 cm-1. Anal. Calcd for C11H8ClN5O2S: C, 42.66, H, 2.60; N, 22.61; S, 10.35. Found: C, 42.59; H, 2.59; N, 22.56; S, 10.32.
4-Chloro-N'-(4-hydroxy-3-methoxybenzylidene)picolinohydrazonamide (13d)
Reaction with 4-hydroxy-3-methoxybenzaldehyde. Product 13d was isolated as a yellow solid (0.438 g, 74 %), mp 130 – 131 oC. 1H NMR (DMSO–d6) δ 3.85 (3H, s); 6.79 (1H, d, J = 7.8 Hz); 7.05 (2H, s); 7.17 (1H, d, J = 7.8 Hz); 7.62 (1H, s); 7.66 (1H, d, J = 5.1 Hz); 8.20 (1H, s); 8.36 (1H, s); 8.61 (1H, d, J = 5.1 Hz); 9.49 (1H, s); IR (KBr) ν 3476, 3362, 1621, 1521, 1465, 1285, 1117, 1032, 854, 728, 501 cm-1. Anal. Calcd for C14H13ClN4O2: C, 55.18; H, 4.30; N, 18.39. Found: C, 55.04; H, 4.28; N, 18.35.
4-Chloro-N'-[4-(dimethylamino)benzylidene]picolinohydrazonamide (13e)
Reaction with 4-(dimethylamino)benzaldehyde. Product 13e was isolated as a yellow solid (0.168 g, 28 %), mp 149 – 151 oC. 1H NMR (DMSO–d6) δ 2.97 (6H, s); 6.71 (2H, d, J = 8.5 Hz); 6.88 (2H, s); 7.64 (1H, d, J = 3.3 Hz); 7.69 (2H, d, J = 8.5 Hz); 8.20 (1H, s); 8.36 (1H, s); 8.61 (1H, d, J = 5.4 Hz); IR (KBr) ν 3494, 3376, 1604, 1546, 1369, 1175, 812, 728, 587 cm-1. Anal. Calcd for C15H16ClN5: C, 59.70; H, 5.34; N, 23.21. Found: C, 59.64; H, 5.32; N, 23.17.
4-Chloro-N'-[1-(thiophen-2-yl)ethylidene]picolinohydrazonamide (14)
A solution of 4-chloropicolinohydrazonamide (6) (0.341 g, 2 mmol) in MeOH (10 mL) containing 1 mL of acetic acid, as a catalyst, was treated with 1-(thiophen-2-yl)ethanone (0.252 g, 2 mmol). The mixture was left at rt for 1 h. The formed precipitate was filtered off, and crystallized from MeOH to give 4-chloro-N'-[1-(thiophen-2-yl)ethylidene]picolinohydrazonamide (14) as a yellow solid (0.456 g, 82 %), mp 167 – 169 oC. 1H NMR (DMSO–d6) δ 2.52 (3H, s); 7.04 (2H, bs); 7.15 (1H, t, J = 4.8 Hz); 7.63 (1H, d, J = 3.4 Hz); 7.71 (1H, dd, J1 = 5.3 Hz, J2 = 1.4 Hz); 7.85 (1H, d, J = 4.8 Hz); 8.45 (1H, d, J = 1.4 Hz); 8.66 (1H, d, J = 5.3 Hz); IR (KBr) ν 3438, 3311, 1613, 1548, 1466, 1417, 1294, 1018, 832, 717 cm-1. Anal. Calcd for C12H11ClN4S: C, 51.70; H, 3.98; N, 20.10; S, 11.50. Found: C, 51.61; H, 3.96; N, 20.05; S, 11.47.
N'-[Amino(4-chloropyridin-2-yl)methylene]pyrimidine-2-carbohydrazonamide (15a)
A solution of pyrimidine-2-carbonitrile (0.525 g, 5 mmol) and triethylamine (0.5 mL) in MeOH (10 mL), was refluxed for 2 h. Next, the solvent was evaporated, and MeOH (5 mL) followed by 4-chloropicolinohydrazonamide (6) (0.852 g, 5 mmol) and acetic acid (0.2 mL) were added to the residue. The mixture was stirred for 5 min, and the formed precipitate was filtered off and crystallized from MeOH/H2O (1:1) to give N'-[amino(4-chloropyridin-2-yl)methylene]pyrimidine-2-carbohydrazonamide (15a) (0.497 g, 35 %) as a yellow crystals, mp 188 – 190 oC. 1H NMR (DMSO–d6) δ 6.39 (2H, s); 6.52 (2H, s); 7.31 (2H, m); 8.39 (1H, d, J = 1.9 Hz); 8.46 (1H, d, J = 5.4 Hz); 8.84 (2H, d, J = 4.8 Hz); IR (KBr) ν 3296, 1611, 1547, 1443, 1349, 1038, 817, 639 cm-1. Anal. Calcd for C11H10ClN7: C, 47.92; H, 3.66; N, 35.56. Found: C, 47.82; H, 3.65; N, 35.49.
N'-[Amino(4-chloropyridin-2-yl)methylene]pyrazine-2-carbohydrazonamide (15b)
Methyl pyrazine-2-carbimidate (0.274 g, 2 mmol) was added to a solution of 4-chloropicolinohydrazonamide (6) (0.341 g, 2 mmol) and acetic acid (o.1 mL) in MeOH (10 mL) and the mixture was stirred at rt for 5 min. The formed solid was filtered off and crystallized from EtOH to give N'-[amino(4-chloropyridin-2-yl)methylene]pyrazine-2-carbohydrazonamide (15b) (0.418 g, 76 %) as a yellow crystals, mp 255 – 257 oC. 1H NMR (DMSO–d6) δ 7.45 (2H, s), 8.54 - 8.70 (6H, m), 9.65 (2H, s); IR (KBr) ν 3400, 3293, 1605, 1548, 1464, 1425, 1020, 714 cm-1. Anal. Calcd for C11H10ClN7: C, 47.92; H, 3.66; N, 35.56. Found: C, 47.81; H, 3.65; N, 35.48.

General method for compounds 16a and 16b.
A solution of 1 mmol of N'-[amino(4-chloropyridin-2-yl)methylene]pyrimidine-2-carbohydrazonamide (15a) or N'-[amino(4-chloropyridin-2-yl)methylene]pyrazine-2-carbohydrazonamide (15b) in glacial acetic acid (3 mL) was refluxed for 1 h. The reaction mixture was then cooled and poured into cold water. The formed solid product was filtered off, and crystallized from MeOH/H2O (2:1) to give compounds 16a and 16b, respectively.
2-[5-(4-Chloropyridin-2-yl)-4H-1,2,4-triazol-3-yl]pyrimidine (16a)
Reaction with methyl pyrimidine-2-carbimidate. Product 16a was isolated as colorless solid (0.219 g, 85 %), mp 204 – 205 oC. 1H NMR (DMSO–d6) δ 7.62 (2H, m), 8.20 (1H, s), 8.71 (1H, d, J = 5.4 Hz), 9.01 (2H, d, J = 4.8 Hz), 11.25 (1H, s); IR (KBr) ν 3444, 1565, 1452, 1396, 1210, 1152, 789, 754 cm-1. Anal. Calcd for C11H7ClN6: C, 51.08; H, 2.73; N, 32.49. Found: C, 50.96; H, 2.72; N, 32.41.
2-[5-(4-chloropyridin-2-yl)-4H-1,2,4-triazol-3-yl]pyrazine (16b)
Reaction with methyl pyrazine-2-carbimidate. Product 16b was isolated as colorless solid (0.229 g, 89 %), mp 217 – 219 oC. 1H NMR (DMSO–d6) δ 6.92 (1H, m), 7.61 (1H, s), 8.41 (1H, d, J = 5.2 Hz), 8.74 (2H, m), 9.32 (1H, m), 11.15 (1H, s); IR (KBr) ν 3435, 1633, 1556, 1380, 1160, 1019, 788, 763 cm-1. Anal. Calcd for C11H7ClN6: C, 51.08; H, 2.73; N, 32.49. Found: C, 51.01; H, 2.72; N, 32.43.
4-Chloro-N'-methylpicolinohydrazonamide (17)
A mixture of 4-chloropicolinonitrile (0.415 g, 3 mmol) and methyl hydrazine (0.32 mL, 6 mmol) in MeOH (3 mL) was refluxed for 30 min and the solvent was evaporated. The residue was diluted with benzene (10 mL), and evaporated again. Ice (10 g) was added to the residue, the product was filtered off and crystallized from benzene: petroleum ether (1:10) to give 4-chloro-N'-methylpicolinohydrazonamide (17) (0.26 g, 47 %) as a yellow crystals, mp 102 – 104 °C. 1H NMR (CDCl3) δ 3.01 (3H, s), 5.15 (2H, s), 7.25 (1H, dd, J1 = 1.9 Hz, J2 = 5.3 Hz), 7.28 (1H, s), 8.12 (1H, d, J = 1.9 Hz), 8.39 (1H, d, J = 5.3 Hz); IR (KBr) ν 3326, 3206, 1648, 1574, 1548, 1475, 1346, 1071, 829, 735 cm-1. Anal. Calcd for C7H9ClN4: C, 45.54; H, 4.91; N, 30.35. Found: C, 45.46; H, 4.89; N, 30.29.
Methyl 2-[amino(4-chloropyridin-2-yl)methylene]-1-methylhydrazinecarbodithioate (18)
A solution of 4-chloro-N'-methylpicolinohydrazonamide (17) (0.554 g, 3 mmol) and triethylamine (0.5 mL, 3.6 mmol) in MeOH (15 mL) was cooled to 0 ºC and then CS2 (0.22 mL, 3.6 mmol) was added. The reaction mixture was stirred at rt for 1.5 h. Next, iodomethane (0.19 mL, 3 mmol) was added and the mixture was stirred at rt for next 1 h. The solvent was evaporated and petroleum ether (20 mL) was added to the residue. The precipitated solid was filtered off and crystallized from MeOH:H2O (3:2) to give methyl 2-[amino(4-chloropyridin-2-yl)methylene]-1-methylhydrazinecarbodithioate (18) (0.230 g, 28 %) as a yellow solid, mp 175 – 177 °C. 1H NMR (CDCl3) δ 2.55 (3H, s), 3.73 (3H, s), 6.15 (2H, s), 7.47 (1H, dd, J1 = 2.1 Hz, J2 = 5.2 Hz), 8.37 (1H, d, J = 2.1 Hz), 8.53 (1H, d, J = 5.2 Hz); IR (KBr) ν 3409, 3294, 2917, 1629, 1575, 1368, 1100, 987, 740 cm-1. Anal. Calcd for C9H11ClN4S2: C, 39.34; H, 4.03; N, 20.39; S, 23.34. Found: C, 39.28; H, 4.01; N, 20.34; S, 23.28.
5-(4-Chloropyridin-2-yl)-3-methyl-1,3,4-thiadiazole-2(3H)-thione (19)
A solution of 4-chloro-N'-methylpicolinohydrazonamide (17) (0.554 g, 3 mmol) in MeOH (5 mL) was cooled to 0 ºC and then CS2 (1 mL, 16.5 mmol) was added. The reaction mixture was left at rt for 12 h. The solid product was filtered off and crystallized from EtOH:H2O (4:1) to give 5-(4-chloropyridin-2-yl)-3-methyl-1,3, 4-thiadiazole-2(3H)-thione (19) (0.432 g, 59 %) as a yellow crystals, mp 181 – 183 °C. 1H NMR (CDCl3) δ 3.97 (3H, s), 7.38 (1H, dd, J1 = 2.0 Hz, J2 = 5.4 Hz), 8.01 (1H, d, J = 2.0 Hz), 8.51 (1H, d, J = 5.4 Hz); IR (KBr) ν 3056, 1572, 1404, 1295, 1135, 1101, 757 cm-1. Anal. Calcd for C8H6ClN3S2: C, 39.42; H, 2.48; N, 17.24; S, 26.31. Found: C, 39.33; H, 2.47; N, 17.20; S, 26.26.
3-(4-Chloropyridin-2-yl)-1,4-dimethyl-1H-1,2,4-triazole-5(4H)-thione (20)
Method A:
A solution of 4-chloro-N'-methylpicolinohydrazonamide (17) (0.369 g, 2 mmol) in dry dioxane (5 mL) was treated with isothiocyanatomethane (0.15 g, 2 mmol) and refluxed for 15 min. The reaction mixture was then cooled and poured into petroleum ether (30 mL). The product was filtered off and crystallized from H2O to give 3-(4-chloropyridin-2-yl)-1,4-dimethyl-1H-1,2,4-triazole-5(4H)-thione (20) (0.147 g, 31 %) as a yellow solid, mp 169 – 170 °C.
Method B:
Isothiocyanatomethane (0.15 g, 2 mmol) was added to a solution of 4-chloro-N'-methylpicolinohydrazonamide (17) (0.369 g, 2 mmol) in MeOH (5 mL), and the mixture was stirred at rt for 1 h. Next, the solvent was evaporated and ice (20 g) was added to the residue. The precipitate was filtered off and crystallized from MeOH:H2O (1:1) to give 3-(4-chloropyridin-2-yl)-1,4-dimethyl-1H-1,2,4-triazole-5(4H)-thione (20) (0.25 g, 52 %) as a yellow solid, mp 169 – 170 °C. 1H NMR (CDCl3) δ 3.91 (3H, s), 4.06 (3H, s), 7.41 (1H, dd, J1 = 2.0 Hz, J2 = 5.4 Hz), 8.05 (1H, d, J = 2.0 Hz), 8.57 (1H, d, J = 5.4 Hz); IR (KBr) ν 3054, 1576, 1480, 1364, 1162, 1343, 767 cm-1. Anal. Calcd for C9H9ClN4S: C, 44.91; H, 3.77; N, 23.28; S, 13.32. Found: C, 44.82; H, 3.76; N, 23.22; S, 13.29.

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