These pharmacophores sites were used as queries for screening. Asinex database was used for pharmacophore screening. The ligands were selected based on the fitness score. Fitness score is the sum of RMSD site matching, vector alignments, and volume terms. The ligands showing the best fitness scores were docked using IFD studies into the binding site of the protein. E-pharmacophore buy PD0325901 hypothesis was developed and a similarity search from Asinex database was performed toward the search for inhibitors for dengue virus NS5 MTase. Docking calculations were performed for three known inhibitors – RTP, SAH and SAM, to

analyze the important interactions between protein and the ligand, to generate a structural model for e-pharmacophore hypothesis. All docking calculations were performed using the ‘Extra Precision’ (XP) mode of GLIDE program and with OPLS-AA 2001 force field. All the compounds were docked in the active site of the receptor and the pose viewer files were generated. The Glide score and Glide energy of the e-pharmacophore hypothesis of the known inhibitors – RTP, SAH and SAM are shown in Table 1.

The e-pharmacophore combines aspects of structure-based and ligand-based techniques. Incorporating Fulvestrant protein–ligand contacts into ligand-based pharmacophore approaches has been shown to produce enhanced enrichments over using ligand information alone. The method attempts to take a step beyond simple contact scoring by incorporating structural and energetic information using the scoring function in Glide XP.26 The pharmacophore sites were predicted for RTP, SAH and SAM with seven features; of which, at least three were expected for all of these three ligands. The pharmacophore sites were listed based on the score; the top three highly scored sites were selected. The final pharmacophoric hypothesis for RTP consists of

two hydrogen bond donors (D) and a negative ionizable group (Fig. 2a), for SAH, a H-bond acceptor (A), a hydrogen bond donor (D) and a negative ionizable group (Fig. 2b) and for SAM, an H-bond acceptor (A), a hydrogen bond donor (D) and a negative ionizable group (Fig. 2c); their distances are shown in Fig. 2 a–c. These energetically favorable sites have the specific interactions for ligands Terminal deoxynucleotidyl transferase and this information should prove helpful in the development of new dengue MTase inhibitors. With this pharmacophore hypothesis, compound screening was performed against Asinex database. Receptor-based excluded volumes were included in order to reduce false positives by eliminating inactive compounds that cannot simultaneously match the hypothesis and avoid clashing with the receptor. Total of 38 compounds with fitness scores of more than 1.0 for RTP, 2.0 for SAH and 2.0 for SAM respectively were selected and were subjected to IFD in Glide. The best pose of compounds for each targeted binding site was short-listed by Glide score.