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

The synthesis is reported of new 1,3,4-thiadiazole, imidazopyridine, á-pyranone, pyrazolo[1,5-a]pyrimidine, polysubstituted benzene, pyridine , pyrazoles and pyrazolo[3,4-d]pyridazine using 1-{(5Z)-5-[(4-methoxyphenyl)imino]-4-phenyl-4,5-dihydro-1,3,4-thiadiazol-2-yl}ethanone as starting material.

Finally, hydrazonyl halides 5a,b has been reported to add to α,b-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). 1 H-NMR spectrum provided a firm support for structure 23 and ruled out the other possible structure 21.Thus, 1 H-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 -4 23 .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).

Molecular Modeling Docking studies
From analysis X-ray crystal structure of cytochrome P450 14á-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
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).

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 (í, cm -1 ).The 1 HNMR spectra were recorded in (CDCl 3 & DMSO-d 6 ) at (300) MHz on a Varian Mercury VX-300 NMR spectrometer (ä, 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.

R e a c t i o n o f a c e t y l t h i a d i a z o l e w i t h 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).

Table 1 : Docking energy scores (kcal/mol) derived from the MVD with MOE for isolated ligands
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.