Synthesis of 1,3,4-Thiadiazoles, α -Pyranone ,Pyridine, Polysubstituted Benzene from 1,3,4-Thiadiazolyl Ethanone and Testing Against Tuberculosis Based on Molecular Docking Studies

Introduction

1,3,4-Thiadiazoles have been screened for their antibacterial and antifungal activities^1-4, anti-inflammatory⁵,anti-tuberculosis activity⁶.The development of efficient methods for the synthesis of 1,3,4-thiadiazoles has attracted significant interest. Substituted 1,3,4-thiadiazoles have become very useful compounds in medicine , agriculture, and in many fields of technology such as dyes⁷,lubricating compositions⁸, optically active liquid crystals⁹, photographic materials¹⁰, and many others. Also, applications of 1,3,4- thiadiazoles in agriculture as herbicides¹¹,fungicides¹², and bacteriocides¹³ have been patented. Also, 1,3,4-thiadiazole derivatives have shown anti-inflammatory activity^14-16.

Results and Discussion

Chemistry

The synthetic strategies adopted to obtain the target compound are depicted in Schemes1. The key intermediate 1-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}ethanone (3) was prepared in an excellent yield  by condensing methyl (4-methoxyphenyl)carbamodithioate(1) with (1E)-2-oxo-N-phenylpropanehydrazonoyl chloride  (2). the structure of 3 was established on the basis of analytical and spectral data. The ¹HNMR spectrum showed signals at 2.61(s,3H,COCH₃) 3.81 (s,3H ,OCH₃) 6.91 , 6.97 (dd, 4H, Ar-H AB-system ) 7.36 – 8.01 (m,5H,ArH).

 

Scheme 1 Click here to View Scheme

 

Treatment of 1-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}ethanone (3) with methyl/ or benzyl hydrazinecarbodithioate^17,18 in ethanol at reflux condenser afforded  the corresponding dithioesters (4a,b).The ¹HNMR spectrum of 4a showed signals at δ = 2.37(s, 3H, CH₃-C=N), 2.62 (s, 3H, SCH₃),3.73(s,3H,OCH₃) ,7.16 – 7.97 (9H, m, Ar-H), 9.99 ppm (s, 1H, NH).while ¹HNMR spectrum of 4b showed signals at δ=2.41(s, 3H, CH₃-C=N), 3.77(s,3H,OCH₃),4.53 (s, 2H, SCH₂),7.10-7.93(14H, m, Ar-H),9.93 ppm(s, 1H, NH).

 

Scheme 2  Click here to View Scheme

 

Interaction of methyl dithioester (4a) with hydrazonoyl halides (5a,b)^19,20 in ethanol containing triethylamine at reflux temperature gave bis -1,3,4-thiadiazoles (8a,b). The structure of 8 was deduced from their spectral data and elemental analysis, Scheme (3). The ¹HNMR spectrum of 8a showed signals at δ=2.32(s, 3H, CH₃CO), 2.49 (s, 3H, CH₃-C=N) , 3.78(s,3H,OCH₃) ,7.02 – 7.99 ppm (14H, m, Ar-H) .Similarly, benzyldithioester (4b) reacted with the former hydrazonyl halides (5a,b) and produced products which were found to be identical in all respects (m.p, mixed m.p and spectra) with (8a,b). The formation of (8) can be explained via elimination of methyl mercaptan (or benzyl mercaptan) from the corresponding cycloadduct (7), which is assumed to be formed from 1,3-dipolar cycloaddition of nitrile imides (prepared in situ from 5 and triethylamine) to the C=S double bond in (4a) or (4b), (Scheme 3).

 

Scheme 3  Click here to View Scheme

 

Enaminones are readily obtainable reagents and constitute an interesting class of compounds that are versatile precursors for the synthesis of several heterocyclic aromatic compounds. Thus, treatment of equimolar quantities of 1-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}ethanone (3) with dimethylformamide-dimethylacetal (DMF-DMA) in refluxing xylene afforded the corresponding enaminone as (2E)-3-(dimethylamino)-1-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}prop-2-en-1-one (9)  (Scheme 4).

 

Scheme 4 Click here to View Scheme

 

¹H-NMR (δ ppm) spectrum (CDCl₃) indicated signals at : 2.96 and 3.17 (2s, 6H, N(CH₃)₂) , 3.81 (s,3H,OCH₃) , 5.90 and 7.85 (dd, 2H, olefinic CH=CH; J= 12 Hz), which support that the structure in (E-form), not (Z-form), 6.89 , 7.02 (dd, 4H, Ar-H AB-system ) 7.27 – 8.03 (m,5H,ArH).Enaminone  (9)  reacted with acetylglycine and benzoyl-glycine in acetic anhydride to give a products that were identified as N-(6-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}-2-oxo-2H-pyran-3-yl)acetamide  and N-(6-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}-2-oxo-2H-pyran-3-yl)-benzamide (10a,b) respectively, which confirmed on the basis of elemental analysis and spectral data, (Scheme 5).

 

Scheme 5  Click here to View Scheme

 

Interaction of enaminone (9) with 1,4-benzoquinone and 2-cyanomethylbenzimidazole afforded 11 and 12  respectively, (Scheme 5).condensation of enaminone (2) with diethyl acetonedicarboxylate in refluxing acetic acid afforded tetrasubstituted benzene derivative (13) (Scheme 6)¹HNR of 13 showed signals at δ= 1.25 ,1.43 (2 t ,6H ,2CH₂CH₃) ,3.82(s ,3H ,OCH₃) , 4.31, 4.44 (q , 4H ,2 CH₂CH₃ ) , 6.92-7.94 (m,11H, Ar-H) and 11.30ppm.(s , 1H, OH).

 

Scheme 6 Click here to View Scheme

 

Furthermore , reaction of enaminone 9 with other active methylene such as pentane-2,4-dione and 2-aminoprop-1-ene-1,1,3-tricarbonitrile afforded pyridine (14) and polysubstituted benzene (15) derivatives, respectively(Scheme 6).

Next, the reaction of enaminone 9 with heterocyclic amines was investigated. Refluxing of enaminone 9 with 5-amino-3-(methylsulfanyl)-1H-pyrazole-4-carbonitrile  in glacial acetic acid gave 7-{(5E)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}-2-(methylsulfanyl)pyrazolo[1,5-a]-pyrimidine-3-carbonitrile (16) via elimination of water and dimethyl amine molecules (Scheme 6) .

Condensation of enaminone 9 with ethyl 3-oxobutanoate were carried out in glacial acetic acid in the presence of ammonium acetate furnished a single product, for which the two possible structures 17 and 18 can be investigated (Scheme 7), but elemental analyses and spectral data were in complete accordance with the pyridinecarboxylate structure 18 .The IR spectrum of compound 18 revealed the absence of hydroxy band. Its ¹H-NMR spectrum revealed a signals at δ 1.42 (t ,3H ,CH₂CH₃ ) and 4.41(q , 2H , CH₂CH₃) corresponding to ethyl ester protons , The structures of the products were confirmed by spectral (IR, MS and 1H-NMR) and elemental analyses (see Experimental).

 

Scheme 7  Click here to View Scheme

 

Finally, hydrazonyl halides 5a,b has been reported to add to α,β-unsaturated carbonyl compounds to yield a mixture of isomeric pyrazolines^21,22_.    In the present work the reaction of enaminone  (9)  with nitrileimine (19a,b) (generated in situ from the treatment of the hydrazonoyl halide (5a,b) with triethylamine in refluxing m-xylene) gave only one isolable product (TLC). From which two proposed structures 21a,b or 23a,b seemed possible, (Scheme 8). ¹H-NMR spectrum provided a firm support for structure 23 and ruled out the other possible structure 21. Thus, ¹H-NMR spectrum of 23a and 23b exhibits a singlet at 8.52 and at 8.57 ppm , respectively which indicates the presence of pyrazole H-5 rather than H_–4²³. Pyrazole derivative  (23)  was assumed to be formed via initial 1,3-dipolar cycloaddition of nitrileimine (19) to the activated double bond in compound 9  forming non isolable intermediate  (22) followed by the loss of dimethylamine, (Scheme 8).Treatment of pyrazole 23a with hydrazine afforded pyrazolopyrdazine derivative 24 (Scheme 8).

 

Scheme 8 Click here to View Scheme

 

Molecular Modeling.

Docking studies

From analysis X-ray crystal structure of  cytochrome P450 14α-sterol Demethylase (14DM) from Mycobacterium   in   complex   with   4-phenylimidazole[24], through interaction with amino  acid residues of (14DM), and demonstrated that, His-259 have a structural and functional evidence for the importance for inhibiting action of protein[24]. In order to obtained biological data on a structural basis, through rationalized ligand–protein interaction behavior, the molecular docking into the active site of (14DM) from Mycobacterium  was performed for the synthesized compounds using flexible method.  All calculations for docking experiment were preformed with MOE 2008.10 [24]. The tested compounds were evaluated in silico (docking), using X-ray crystal structures of (PDB entry code 1E9X) [24]) complexes with phenylimidazole.  The tested compounds were docked into active sites of both enzymes (14DM). The active site of the enzyme was defined, to include residues within a 10.0 Å radius to any of the inhibitor atoms. The scoring functions were applied for the most stable docking model to evaluate the binding affinities of the inhibitors, which complexes with (14DM) active sites, table (1). The complexes were energy-minimized with an MMFF94 force field [26] until the gradient convergence 0.05 kcal/mol was reached.  All isolated compounds were docked successfully, and compared with reference inhibitor (phenylimidazol 1), and exhibited that, the highest MOE binding scores for synthesized compounds 15<  16 < 4a < 4b Kcal/mol, respectively, (table 1).

The other  parameters  like  hydrogen interaction energy, electrostatic interaction with the receptor, van der Waals  and salvation energy were  also  taken  into  consideration  for  the evaluation  of  the  docking  results;  the  values  of  the  energy  and  E-model  were  found  to  be  significant,  and  accepted this fact that, a good van der Waals interactions  decides  the  binding  affinity  for  any  ligand  with receptor enzyme protein, and bad van der waals interactions shows ugly contacts through steric  clashes  after  docking  which  should  be  less  for good  activity. 

Structures activity relationships

 

Fig1: The reference ligand was Docked into the active site of (14DM) using MOE tool.   Click here to View Figure

 

Table1: Docking energy scores (kcal/mol) derived from the MVD with MOE for isolated ligandsClick here to View table

 

d.G.: free binding energy of the ligand from a given conformer, Int.: binding energy of hydrogen bond  interaction with receptor, Eele: the electrostatic interaction with the receptor, Evdw: van der Waals  energies between the ligand and the receptor, Esol.: Solvation energy.

 

Fig2: The most active  compound (15)   was Docked into the active site of (14DM) using MOE tool. Click here to View Figure

 

In order to get  a  deeper  insight  into  the  nature  and  type  of  interactions of docked compounds,  the  complexes  between  each compound and (14DM) receptor were visualized, and depicted in (Figs. 1 and 2).  Since, the H bond interactions playing an important role in the structure and function of biological molecules, the current ligand-receptor interactions were analyzed on the basis of  H bonding. In order to reduce the complexity, hydrophobic and π-cation interactions (>6Å) are not shown in (Figs. 1 and 2).

The results obtained  clearly revealed  that,  the  amino  acid  residues  close  to  the  reference  molecules phenylimidazol (1) are mostly the same as observed in the currently compounds under investigation, which complexes with proteins . The higher binding energies and binding process interaction were observed in case of compounds 4a, 4b,15 and 16 act as inhibitors against (14DM).

Conclusion.

1,3,4-thiadiazolyl ethanone is a good starting material for the synthesis of different heterocyclic derivatives  which gave a good results when tested against tuberculosis especially poly substituted benzene 15 ,pyrazolopyrimidine 16 and hydrazone 4 derivatives .

Experimental

All melting points and antimicrobial activities are uncorrected. IR spectra (KBr) were recorded on FT-IR 5300 spectrometer and Perkin Elmer spectrum RXIFT-IR system (ν, cm^-1). The ¹HNMR spectra were recorded in (CDCl₃ & DMSO-d₆) at (300) MHz on a Varian Mercury VX-300 NMR spectrometer (δ, ppm) using TMS as an internal standard. Mass spectra were obtained on GC Ms-QP 1000 EX mass spectrometer at 70 ev. Elemental analyses were carried out by the Micro analytical Research Center, Faculty of Science, Cairo University.

1-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}ethanone 3

A mixture of (1; 0.01 mol) and hydrazonoyl chloride 2 (0.01 mol) in ethanol (50 ml) triethylamine (0.5 ml) was added. The reaction mixture was refluxed for 3h. The resulting product was collected by filtration and recrystallized from EtOH to give 3 as yellow crystals .(yield 78%), m.p.130-132, ir(vcm^-1) : 3076(CH-arom.) , 2958 (CH-aliph.) and 1678 (C=O), ¹H NMR (300MHz δ ppm CDCl₃) 2.61 (s, 3H, COCH₃), 3.81 (s,3H,OCH₃), 6.91 , 6.97(dd, 4H, Ar-H AB-system )  7.39 (m, 1H, Ar-H),7.50(m,2H,Ar-H) and 8.01(d,2H,Ar-H). ms, m/z (intensity %) 325 (15.7).M.F. C₁₇H₁₅N₃O₂S. Calculated: C, 62.75, H, 4.65, N, 12.91. Found: C, 62.69, H, 4.60, N, 12. 87 .

Reaction of acetylthiadiazole with hydrazincarbodithioate

General procedure

A mixture of acetylthiadiazole (0.01 mol) and alkyl hydrazine carbodithioate (0.012 mol) in ethanol (50 ml) was refluxed for one hour. The separated solid on heating was filtered off and recrystallized from the proper solvent to give (4 a,b).

Methyl (E)-2-(1-((z)-5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)hydrazine-1-carbodithioate  4a

acetylthiadiazole (0.01 mol) and methyl hydrazine carbodithioate (0.012 mol)  recrystallized from EtOH to give 4a as yellow crystals .(yield 84%), m.p.212-214⁰C, ir(vcm^-1) :3159(NH), 3088(CH-arom.) and 2907 (CH-aliph.). ¹H NMR (300MHz δ ppm CDCl₃) 2.37 (s, 3H, CH₃C=N), 2.62 (s,3H,SCH₃)3.73 (s,3H,OCH₃), 7.16-7.97 (m, 9H, Ar-H),and 9.99(s,1H,NH). M.F. C₁₉H₁₉N₅OS₃. Calculated: C, 53.12, H, 4.46, N, 16.30. Found: C, 53.09, H, 4.43, N, 16. 25 .

Benzyl (E)-2-(1-((Z)-5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethylidene)hydrazine-1-carbodithioate 4b

acetylthiadiazole (0.01 mol) and benzyl hydrazine carbodithioate (0.012 mol)  recrystallized from EtOH to give 4b as yellow crystals .(yield 81%), m.p.207-209⁰C, ir(vcm^-1) : 3174(NH), 3098(CH-arom.) and 2870 (CH-aliph.). ¹H NMR (300MHz δ ppm CDCl₃) 2.36 (s, 3H, CH₃C=N), 2.61 (s,3H,SCH₃)3.75 (s,3H,OCH₃),4.53(s,2H,CH₂) 7.10-7.93 (m, 14H, Ar-H),and 9.93(s,1H,NH). M.F. C₂₅H₂₃N₅OS₃. Calculated: C, 73.33, H, 5.66, N, 17.1. Found: C, 73.29, H, 5.59, N, 17. 04 .

Synthesis of 8 a,b

A mixture of (4a,b; 0.01 mol) and the appropriate hydrazonoyl halide (0.01 mol) in ethanol (50 ml) triethylamine (0.5 ml) was added .The reaction mixture was refluxed for 3h. The resulting product was collected by filtration and recrystallized from the proper solvent to give 8 .

1 1-((Z)-5-(((Z)-2-((Z)-5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)prop-1-en-1-yl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)ethan-1-one 8a

3 (0.01 mol) and(1E)-2-oxo-N-phenylpropanehydrazonoyl chloride  (0.01 mol)  recrystallized from benzene to give 8a as yellow crystals .(yield 76%), m.p.200-202⁰C, ir(vcm^-1) : 3088(CH-arom.) , 2932

(CH-aliph.)and1685(CO). ¹H NMR (300MHz δ ppm CDCl₃) 2.32 (s, 3H, CH₃C=N), 2.49 (s,3H,COCH₃)3.81 (s,3H,OCH₃),7.02-7.99 (m, 9H, Ar-H),and 9.93(s,1H,NH). M.F. C₂₅H₂₃N₅OS₃. Calculated: C, 73.33, H, 5.66, N, 17.1. Found: C, 73.29, H, 5.59, N, 17. 04 .

4.4.3 ((Z)-5-(((Z)-2-((Z)-5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)prop-1-en-1-yl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)(phenyl)methanone 8b.

3 (0.01 mol) and(1Z)-2-oxo-N,2-diphenylethanehydrazonoyl bromide  (0.01 mol)  recrystallized from benzene to give 8b as yellow crystals .(yield 75%), m.p.177-179⁰C, ir(vcm^-1) : 3084(CH-arom.) 2931 (CH-aliph.)and1678(CO). ¹H NMR (300MHz δ ppm CDCl₃) 2.32 (s, 3H, CH₃C=N), 3.74(s,3H,OCH₃), 7.03-8.20 (m, 19H, Ar-H),and 9.93(s,1H,NH). M.F. C₂₅H₂₃N₅OS₃. Calculated: C, 73.33, H, 5.66, N, 17.1. Found: C, 73.29, H, 5.59, N, 17. 04 .

3 -(dimethylamino)-1-((Z)-5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)prop-2-en-1-one 9 

A mixture of acetylthiadiazole (3; 0.01 mol) and DMF-DMA (0.012 mol) in dry benzene (40 ml) was heated under reflux for 5hrs. the separated solid was filtered off, washed with ethanol and recrystallized from benzene ,orange crystals .(yield 77%), m.p.165-166⁰C , ir(vcm^-1) : 2924 (CH-aliph.) and 1662 (C=O), ¹H NMR (300MHz δ ppm CDCl₃) 2.96 and 3.17 (2s, 6H, N(CH₃)₂), 3.81(s,3H,OCH₃)5.86 and 7.85 (dd, 2H, olefinic CH=CH; J= 12 Hz),  6.89 , 7.02(dd, 4H, Ar-H AB-system )  7.31 (m, 1H, Ar-H),7.47(m,2H,Ar-H) and 8.02(d,2H,Ar-H),C¹³NMR(DMSO-d6): δ =175.01 ,155.77, 155.64, 154.55 , 150.38 , 144.62 , 139.01 , 128.74 , 126.65 , 122.94 , 121.37 , 120.77 , 120.71 , 114.78 , 88.23 , 55.16 , 44.78 , 40.1  and 39.55(2C). ms, m/z (intensity %) 293 (82.7).M.F. C₁₃H₁₂BrNO₂. Calculated: C, 53.08, H, 4.11, N, 4.76. Found: C, 53.01, H, 4.08, N, 4.69.

Reaction of acylglycine with enaminone 9

A mixture of enaminone 9 (0.01 mol) and acetylglycine or benzoylglycine (0.01 mol) in acetic anhydride (30 ml) was heated under reflux for 2h. The reaction mixture was concentrated in vacuo. The solid product which formed upon cooling was filtered off then washed with ethanol and recrystallized from the appropriate solvents to give (10a,b).

1 N-(6-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}-2-oxo-2H-pyran-3-yl)acetamide 10a

Recrystallized from benzene. (yield 74%), m.p.242-244⁰C, ir  (vcm^-1): 3323 (NH), 1720 and 1673 (2C=O), ¹H NMR (300MHz δ ppm DMSO-d6) 2.13 (s, 3H, CH₃),3.74(s,3H,OCH₃) , 6.91-7.51 (m, 9H, Ar-H), 7.94 and 8.20 (dd, 2H pyranone; J = 7.8 Hz), 9.85 (s, 1H, NH), C¹³NMR(DMSO-d6): δ =170.35,156.59,156.04,153.38,144.52,143.07,138.84,138.45,128.23, 126.60 ,122.41,121.33,114.89,106.59,55.19,40.37,39.81,38.70, M.F. C₂₂H₁₈N₄O₄S Calculated: C, 65.34, H, 4.98, N, 13.85.  Found: C, 65.30, H, 4.95, N, 13.83.

N-(6-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}-2-oxo-2H-pyran-3-yl)benzamide 10b

Recrystallized from benzene. (yield 81%), m.p.233-235⁰C, ir  (vcm^-1): 3386 (NH), 1719 and 1668(2C=O), ¹H NMR (300MHz δ ppm DMSO-d6) 3.78(s,3H,OCH₃), 6.95-7.85 (m, 9H, Ar-H),7.83 and 8.11 (dd, 2H pyranone; J=7.5 Hz), 9.90 (s, 1H, NH).ms, m/z (intensity %) 496 (32.9). M.F: C₂₇H₂₀N₄O₄S. Calculated: C, 69.82,   H, 4.34, N, 12.06  Found: C, 69.78, H, 4.31, N, 12.02.

(Z)-3-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)benzofuran-5-ol  (11).

To a stirred solution of enaminone 9 (0.01 mol) in glacial acetic acid (25 ml), 1,4-benzoquionone (0.01 mol) was added, stirring was continued for 3h. at room temperature.  The reaction mixture was evaporated in vacuo and the solid product was isolated by filtration and recrystallized from acetic acid (yield 68%), m.p.189-190⁰C, ir  (vcm^-1): 3380 (OH); ¹H NMR (300MHz δ ppm DMSO-d6) 3.76(s,3H,OCH₃), 6.87-8.05 (m, 12H, Ar-H), 9.12 (s, 1H furan), 9.52 (s, 1H, OH). ms, m/z (intensity %) 399 (8.5). M.F: C₂₃H₁₇N₃O₃S. Calculated: C, 69.17,   H, 4.29, N, 10.52  Found: C, 69.13, H, 4.26, N, 10.48.

(Z)-1-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)benzo[4,5] imidazo[1,2-a]pyridine-4-carbonitrile 12

A mixture of enaminone (9; 0.01 mol) and 2-cyanomethyl benzoimidazole (0.01 mol) in glacial acetic acid (30 ml) was refluxed for 3hrs. the solid product which obtained after cooling was collected by filtration and recrystallized from EtOH (yield 64%), m.p.148-150⁰C, ir  (vcm^-1): 2200 (CN); ¹H NMR (300MHz δ ppm DMSO-d6) 3.77(s,3H,OCH₃), 6.96-8.42 (m, 15H, Ar-H), m/z (intensity %) 426 (5.7). M.F: C₂₇H₁₈N₆OS. Calculated: C, 76.04,   H, 4.25, N, 19.71  Found: C, 76.01, H, 4.23, N, 19.68.

Diethyl (Z)-2-hydroxy-4-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)isophthalate  13

A mixture of enaminone (9; 0.01 mol) and diethyl acetonedicarboxylate (0.01 mol) in glacial acetic acid (30 ml) was refluxed for 2h. the solid product which obtained after cooling was collected by filtration and recrystallized from EtOH (yield 66%), m.p.170-172⁰C, ir  (vcm^-1): 1725 (CO); ¹H NMR (300MHz δ ppm CDCl₃)1.25(t,3H,CH₂CH₃) 1.43 (t,3H,CH₂CH₃), 3.82(s,3H,OCH₃), 4.31(q,2H,CH₂CH₃), 4.44(q,2H,CH₂CH₃) , 6.92 – 7.94 (m, 11H, Ar-H),and 11.30 (s,1H,OH)M.F: C₂₇H₂₄N₃O₆S. Calculated: C, 66.66,   H, 4.97, N, 8.64  Found: C, 66.61, H, 4.93, N, 8.63.

Ethyl (Z)-4-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-2-methylbenzoate 14

To a solution of enaminone 9 (0.01 mol) and acetyl acetone (0.01 mol) in acetic acid (20 mL) was added ammonium acetate (0.02 mol). The reaction mixture was heated under reflux for 3 h. After cooling, the solid product was collected by filtration and crystallized from ethanol (yield71%) ; m.p.118-120⁰C, ir  (vcm^-1): 1677 (CO); ¹H NMR (300MHz δ ppm CDCl₃)2.62(s,3H,CH₃) 2.73 (s,3H,COCH₃), 3.82(s,3H,OCH₃) and 6.94 – 8.06 (m, 11H, Ar-H)^; M.F: C₂₃H₁₈N₄O₂S. Calculated: C, 61.88,   H, 4.06, N, 12.55  Found: C, 61.85, H, 4.03, N, 12.51.

(Z)-2,4-diamino-5-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazole-2-carbonyl)isophthalonitrile 15

A mixture of enaminone 9 (0.01 mol) and 3-amino-2-cyanopent-2-enedinitrile (0.01 mol) in dioxan (25 mL) containing  1 ml of triethyl amine was heated under reflux for 3 h (followed until completion by TLC using 1:1 ethyl acetate–petroleum ether as eluent). The mixture was then cooled .The solid, so formed, was collected by filtration and crystallized from AcOH (yield 62%); m.p.280-282⁰C, ir  (vcm^-1): 3406,3331 (NH₂) , 2211(CN) and1649(CO), ¹H NMR (300MHz δ ppm DMSO-d6) 3.77(s,3H,OCH₃),4.09(s,4H,2NH₂) 6.96-7.89 (m, 10H, Ar-H); ms, m/z (intensity %) 576 (32.9); M.F: C₂₄H₁₇N₇O₂S. Calculated: C, 66.05,   H, 4.16, N, 22.46  Found: C, 66.02, H, 4.12, N, 22.43.

(Z)-7-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-2-(methylthio)pyrazolo[1,5-a]pyrimidine-3-carbonitrile 16

A mixture of enaminone 9 (0.01 mol) and 5-amino-3-(methylsulfanyl)-1H-pyrazole-4-carbonitrile  (0.01 mol), in glacial acetic acid (20 mL), was refluxed for 3 h. The solid that formed was filtered off, and crystallized from ethanol to afford compounds 16 (yield 73%); m.p.170-172⁰C, ir  (vcm^-1): 2226(CN), ¹H NMR (300MHz δ ppm CDCl₃) 2.48(s,3H,SCH₃) 3.80 (s,3H,OCH₃) and 6.90-8.29 (m, 11H, Ar-H , pyrimidine-H); ms, m/z (intensity %) 407 (12.5) M.F: C₂₃H₁₇N₇OS₂  Calculated: C, 60.64,   H, 3.76, N, 21.52  Found: C, 60.61, H, 3.73, N, 21.47.

Ethyl (Z)-6-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)-2-methylnicotinate 18

To a solution of enaminone 9 (0.01 mol) and ethyl 3-oxobutanoate (0.01 mol) in acetic acid (20 mL) was added ammonium acetate (0.0 2 mol). The reaction mixture was heated under reflux for 2 h. After cooling, the solid product was collected by filtration and crystallized from  ethanol (yield 76%); m.p.130-132⁰C, ir  (vcm^-1): 1720(CO), ¹H NMR (300MHz δ ppm CDCl₃) 1.42(t,3H,CH₂CH₃), 2.81(s,3H,CH₃), 3.83 (s,3H,OCH₃),4.39(q,2H,CH₂CH₃), 6.92 , 7.02(dd, 4H, Ar-H AB-system;j = 8.4Hz)  7.33 (m, 1H, Ar-H),7.49(m,2H,Ar-H)  7.97(d,2H,Ar-H), (dd, 2H, pyridine-H;J = 8.4Hz); M.F: C₂₄H₂₀N₄O₃S  Calculated: C, 60.49,   H, 4.23, N, 11.76  Found: C, 60.46, H, 4.19, N, 11.73.

Synthesis of 23a,b

To a mixture of enaminone 9 (0.01 mol) and the hydrazonoyl halide 19a,b (0.01 mol) in benzene (30 ml) an equivalent amount of triethylamine was added. The reaction mixture was heated under reflux for 3h. the solvent was distilled at reduced pressure and the residual viscous liquid was taken in ethanol then the resulting solid was collected by filtration, washed thoroughly with ethanol, dried and finally crystallized from ethanol to give 23a,b.

Methyl (E)-4-(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazole-2-carbonyl)-1-phenyl-1H-pyrazole-3-carboxylate 23a

(yield 64%); m.p.144-145⁰C; ir (vcm^-1): 1696 (CO), ¹H NMR (300MHz δ ppm CDCl₃)  2.68 (s, 3H, CH₃), 3.82(s, 3H, OCH₃), 6.91-8.08 (m, 14H, Ar-H), 8.52 (s, 1H, pyrazole-H5); calcd for C₂₇H₂₁N₅O₃S : C, 65.44 , H, 4.27, N, 14.13 Found: C, 65.40, H, 4.25, N, 14.09.

(E)-(3-benzoyl-1-phenyl-1H-pyrazol-4-yl)(5-((4-methoxyphenyl)imino)-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl)methanone 23b

(yield 66%); m.p.148-150⁰C; ir  (vcm^-1): 1656 (CO) ; ¹H NMR (300MHz δ ppm CDCl₃) 3.80 (s, 3H, OCH₃), 6.88 – 8.02 (m, 14H, Ar-H),8.58 (s, 1H, pyrazole-H5); calcd for C₃₂H₂₃N₅O₃S : C, 69.18, H, 3.81, N, 12.60. Found: C, 69.15, H, 3.78, N, 12.57

(E)-N-(4-methoxyphenyl)-5-(7-methyl-2-phenyl-2H-pyrazolo[3,4-d]pyridazin-4-yl)-3-phenyl-1,3,4-thiadiazol-2(3H)-imine 24

A mixture of pyrazole derivative 23a (0.01 mol) and hydrazine hydrate (0.012 mol) in ethanol (40 ml) was heated under reflux for 2h. The separated solid was filtered off, washed with ethanol and crystallized from ethanol (yield71%); m.p.248-250⁰C; ir (vcm^-1): 1608 (C=N); ¹H NMR (300MHz δ ppm DMSO-d6) 2.23(s,3H,CH₃), 3.79(s,3H,OCH₃), 6.72-7.81 (m, 14H, Ar-H), 8.43 (s, 1H, pyrazole-H5); ms: m/z (intensity %) 491 (74.4); calcd for C₂₇H₂₁N₇OS: C, 61.94, H, 4.04, N, 18.73. Found: C, 61.91, H, 4.02, N, 18.69.

References

1.  kandapalli, V.G.; Vajja,S.R. Bull. Korean Chem. soc. 2010, 35, 1219-1222.
2. Feray, A.; Cigdem, Y. Bull. Korean Chem. soc. 2001, 22, 476-480 .
3. Dogan, H. N.;  Rollas, S.;  Erdeniz,  H. , IL Farmaco 1998, 53, 462-467.
4. Dogan, H. N. ; Duran A.; Rollas,  S.; Sener,  G.; Uysal,  M. K.;  Gulen  D.  Bioorg. Med.Chem. 2002 , 10, 2893-2898 .
5. Palaska,  E.; Sahin,  G. ; Kelicen,  P. ; Turlu, N. T. ; Altinok G. IL Farmaco 2002, 57,101-107.
6. Karakus, S. ; Rollas, S. IL Farmaco 2002, 57, 577-581.
7. Zareba, S.  Pharmazie 1993, 48, 782–783.
8. Gao, Y. J. ;  Zhang, Z. J.;  Xue, Q. J. Mater. Res. Bull. 1999, 34, 1867–1874.
9. Choi, U. S.; Kim, T. W.; Jung,  S. W. ;  Kim  C. J. Bull. Korean Chem. Soc. 1998, 19, 299–307.
10. Chen, S. L.;  Ji,  S. X.;  Zhu,  Z. H. ; Yao  Z. G. Dyes Pigments 1993, 23, 275–283.
11. Jin,  G. Y.;  Hou,  Z.;  Zhao,  G. F.;  Cao,  C. Y. ;  Li  Y. C. Chem. J. Chin. Univ. 1997, 18, 409–412.
12. Lu, S. M.;  Chen,  R. Y. Org. Prep. Proced. Int. 2000, 32, 302–306.
13. Hui,  X. P.; Zhang,  L. M.; Zhang,  Z. Y.;  Wang,  Q. ;  Wang,  F. Indian  J. Chem. Sect. B, 1999 , 38, 1066-1069 .
14. Kumar,  H.; Javed,  S. A.;  Khan,  S. A. ; Amir,  M.  Eur. J. Med. Chem. 2008 , 43 , 2688–26983.
15. Mullican,  M. D.; Wilson,  M. W.; Connor,  D. T.; Kostlan,  C. R.; Schrier,  D. J. ;  Dyer,  R. D. J. Med. Chem. 1993, 36, 1090–1099.
16. Song,  Y.;  Connor,  D. T.;  Sercel,  A. D.;  Sorenson,  R. J.;  Doubleday  R.; Unangst  P. C.; Roth  B.D.; Beylin,  V. G.; Gilbertsen,  R. B.; Chan,  K.; Schrier  D. J.;  Guglietta,  A.; Bornemeier,  D. A.; Dyer, R. D.  J. Med. Chem. 1999, 42, 1161–1169.
17. Danie,l  L. K.; Joseph,  F.; Scott,  T. G.; Carl,  J. M. ; John,  P. S. J. Med. Chem., 1979 , 22, 855 -862.
18. Korosi,  J. Ger. Offen. 1, 934, 89929 Jan (1979), C. A. 72, 100334s (1970).
19. Eweiss,  N. F.; Abdelhamide,  A.O. J. Heterocyclic. Chem. 1980 , 17, 1713 -1717 .
20. Shawali,  A. S.; Abdelhamide, A. O. Bull. Soc. Japan 1976 , 49, 321-324.
21. Al-Zaydi, K.M. Molecules, 2003, 8 , 541-555.
22. Helmut, B.;, Irmgard, B. ; Joachim, F. K. Arch. Pharm. (Weinheim) 1983 , 316 , 608-616.
23. El-Taweel, F.M. ; Elnagdi, M. H. J. Heterocyclic Chem. 2001, 38 , 981-984.

---

This work is licensed under a Creative Commons Attribution 4.0 International License.