1,2,4 Triazole is one of the organic heterocyclic compounds containing a five membered di-unsaturated ring structure compound with three nitrogen atoms and two carbon atoms at nonadjacent positions. Although most triazoles are readily prepared and stored. 1,2,4-Triazole is a basic aromatic heterocycles and one of a pair of isomeric chemical compounds with molecular formula C₂H₃N₃. This compound is screened for its anti cancerous, antibacterial and anti-microbial activity [1Mathew, V.; Keshavayya, J.; Vaidya, V.P. Heterocyclic system containing bridgehead nitrogen atom: synthesis and pharmacological activities of some substituted 1,2,4-triazolo[3,4-b]-1,3,4-thiadiazoles. Eur. J. Med. Chem., 2006, 41(9), 1048-1058.
[http://dx.doi.org/10.1016/j.ejmech.2006.03.018] [PMID: 16822595] -3Purohit, M.N.; Pujar, G.; Manohar, K.V.; Udupi, R.H.; Vijayakumar, G.S. Synthesis and antimicrobial activity of N-N- Bis{3-subsituted-5-mercapto1,2,4 triazole-4-yl}butane1,4-dicarboxamide derivatives. Indian J. Heterocycl. Chem., 2006, 16, 93-94.]. The molecular docking studies of 4- Phenyl -5-Pyrazinyl-3-mercapto 1,2,4 triazole with protein FAK [4André, E.; Becker-André, M. Expression of an N-terminally truncated form of human focal adhesion kinase in brain. Biochem. Biophys. Res. Commun., 1993, 190(1), 140-147.
[http://dx.doi.org/10.1006/bbrc.1993.1022] [PMID: 8422239] ] were performed by using Autodock. Docking studies have become nearly indispensable for the study of macromolecular structures and interactions.

The crystals of the compound 4- Phenyl -5-Pyrazinyl-3-mercapto 1,2,4 triazole were grown by the slow evaporation technique using ethanol as solvent. The x-ray intensity data of the crystals was collected on a Bruker smart CCD diffractometer graphite monochromatic Mokα radiation. From the diffraction data,it was seen that the title molecule C₁₂H₉N₅S crystallizes in monoclinic space group P2₁/c with unit cell dimensions, a=9.630(4) Å b=15.023(6) Å c=9.022 (4) Å and Z=4. The ortep diagram [6Farrugia, L.J. ORTEP3 for Windows- A version of OrtepIII with a graphical user interface. J. Appl. Cryst., 1997, 30, 565.
[http://dx.doi.org/10.1107/S0021889897003117] , 7Farrugia, L.J. WinGX suite for small-molecule single-crystal crystallography. J. Appl. Cryst., 1999, 32, 837-838.
[http://dx.doi.org/10.1107/S0021889899006020] ] of the ligand showing 50% probability displacement ellipsoids is shown in
Fig. (1). The crystal data of the compound are shown in Table 1.

Fig. (1) Ortep diagram of 4- Phenyl -5-Pyrazinyl-3-mercapto 1,2,4 triazole.

Table 1
Crystal data.

The 3D structure of FAK (PDB code: 2ETM) [8Andersen, C.B.; Ng, K.; Vu, C.; Ficarro, S.; Choi, H.-S.; Gray, N.; He, Y.; Lee, C.C. Crystal Structure of Focal Adhesion Kinase Domain Complexed with ATP and novel 7H- Pyrrolo [2,3-d] pyrimidine scaffolds. (to be Published).] was downloaded from the protein data bank. By adding the polar hydrogen bond to the receptor FAK which is required to convert PDB to PDBQT format. The water molecules around the ligand and cofactors were removed from the protein.

Docking allows the user to virtually screen a database of compounds and predict the strongest binders based on various scoring functions. The docking analysis of the ligand 4-Phenyl-5-pyrazinyl-3-mercapto-1,2,4 triazole (PYT3) and their analogs with focal adhesion kinase receptor was carried by using Autodock 4.2 and FlexX docking software. The reference ligand 7PY (7-Pyridin-2-Yl-N-(3,4,5-Trimethoxyphenyl)-7h-Pyrrolo[2,3-D] pyrimidin-2-Amine) was selected for the binding site analysis [9Rand, H.P.; Dale, M.M.; Ritter, M.M.; Moore, P.K. Pharmocology, 5^th ed.; NewYork, 2003, pp. 51-63., 10Golubovskaya, V.M.; Kweh, F.A.; Cance, W.G. Focal adhesion kinase and cancer. Histol. Histopathol., 2009, 24(4), 503-510.
[PMID: 19224453] ]. Docking of the protein ligand complex was mainly targeted at the predicted active site. The interaction was carried out to find the favorable binding geometries of the ligand with the protein. The selected residues of the receptor were defined to be part to the binding site. The molecules binding to a receptor, ideally must inhibit its function, and thus act as drug [11Srivastava, V.; Kumar, A.; Mishra, B.N.; Siddiqi, M.I. Molecular docking studies on DMDP derivatives as human DHFR inhibitors. Bioinformation, 2008, 3(4), 180-188.
[http://dx.doi.org/10.6026/97320630003180] [PMID: 19238244] ]. The collection of 1,2,4 triazole derivatives and receptor complexes was identified via docking. Molecular docking was carried out to find the favorable binding geometries of the ligand with the protein. 1,2,4 triazole derivatives were then docked at predicted active site of FAK, using Autodock4.2 (Lemarkian Genetic Algorithm) and Flexx (Incremental Docking Algorithm). The pose received with the highest dock score from Flexx as well as lowest binding free energy from Autodock4 was then selected for further analysis [12Kramer, B.; Rarey, M.; Lengauer, T. Evaluation of the FLEXX incremental construction algorithm for protein-ligand docking. Proteins, 1999, 37(2), 228-241.
[http://dx.doi.org/10.1002/(SICI)1097-0134(19991101)37:2<228::AID-PROT8>3.0.CO;2-8] [PMID: 10584068] ]. The best binding pose at the binding site is shown in Figs. (2-4). Table 2 shows different binding energies for different conformations of the ligand.

Fig. (2) Binding pose of ligand in binding site using flex.

Table 2
Best docking pose energy for ligand PyT3 with AutoDock.

Fig. (3) Binding pose of ligand in binding site using Autodock.

Fig. (4) The pharmacophore of the protein interacting with the ligand; residues forming hydrogen bonding.

The docking result showed the best 10 binding sites. The best dock energy -5.7 kcal/mol was campared with the reference ligand (7PY) and the docked energy was -5.87 kcal/mol, which showed that the protein ligand interactions are good fit with the target protein. The molecular docking studies shows good affinity of the ligand towards the protein. The higher the negative value of the energy of binding, the better is the affinity of the molecule to the receptor. The intermolecular interactions between the ligand and the protein were investigated. 1,2,4 Triazole for the most part, subsists in the 1H-1,2,4 triazole tautomeric form and the 4H-1,2,4 triazole form does not exist nor in solid state neither in solution form. In general amino substituted 1,2,4 triazoles were electronically preferred in a tautomeric equilibrium dominantly in 1H form [13Dolzhenko, A.V.; Pastorin, G.; Chui, W.K. An aqueous medium synthesis and tautomerism study of 3(5)-amino-1,2.4 Triazoles. Tetrahedron Lett., 2009, 50, 2124-2128.
[http://dx.doi.org/10.1016/j.tetlet.2009.02.172] ]. In the crystal lattice there were two intermolecular interactions, one potentially weak intramolecular and some C-π....π super molecular interactions [14Jeffrey, G.A.; Maluszynska, H.; Mitra, J. Hydrogen bonding in nucleosides and nucleotides. Int. J. Biol. Macromol., 1985, 7, 336-348.
[http://dx.doi.org/10.1016/0141-8130(85)90048-0] ]. In the solid state, supermolecular interactions stabilize the crystal structures.

The intermolecular interactions between the ligand and the protein were investigated. The synthesized chemical compound showed a good fit with the protein. Thus the bioactive compound interacting with the target can be used as a potent inhibitor to block the action of FAK protein. The docked value can be considered for further analysis.