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andom sampling algorithms. The starting conformation was sketched in 2D and wassubjected to an unconstrained conformational search on Discovery Studio with theGenerate Conformations protocol and the BEST method which includes randomconformation search and torsion search algorithms and ensures the best coverage ofconformational space. The Generalized Born with a Simple SWitching (GBSW) implicitsolvent model was applied, which is a molecular surface approximation that uses a van derWaals based surface with a smooth dielectric boundary, was used. The SHAKE algorithmwas also implemented to satisfy bond geometry constraints and keep fixed bond lengthsduring all simulations. The dielectric constant (ε) was set to 81 (H 2 O) and 37 (DMF)respectively in order to simulate in the most approximate way the environment of thedifferent solvents used in the NMR studies. Among the 1000 conformers extracted for eachsolvent environment, the ones that satisfied the critical ROE data were chosen. Theseconformers were assigned as the starting ones for the molecular dynamics simulationsunder constraints.Distance constraints from ROESY experiments were set prior to all further MDsimulations. The procedure included an initial minimization stage for 200 steps, a secondminimization stage for 200 steps, using the Adopted Basis Newton algorithm, a heatingstage from 0 o K to 300 o K gradually, followed by an equilibration stage at 300 o K with a timestep of 0.002 ps for 0.2 ns and finally a production stage for 30 ns. 500 minimization stepswith each of the SD and ABNR algorithms respectively were applied, to relax the generatedconformations and remove steric overlaps.Parameters on saving result frequencies were set in such a way in order to extract 1000conformations for each molecule. The same implicit solvent model was used, as for thegeneration of the initial conformations, with the dielectric constant (ε) set to ε = 81 for theD 2 0 and ε = 37 for the DMF environments. All minimizations had the limit of an RMSD of0.01 Å as an energy convergence criterion. Five energy local minimum conformations wereextracted from the MD run according to their Potential Energy.When visualising results, it is clear that the most representative conformations ofaliskiren in H 2 O and DMF solutions are by far different in terms of situation of thepharmacophore groups compared to the conformation of the X-ray crystallography ofaliskiren bounded to the recombinant glycosylated human renin receptor.Apart from the significantly “curved” structures of this antihypertensive agent in H 2 Oand DMF, the essential structural difference is the position of the “backbone” of themolecule. In general the two different solvents impose a “curved” structure in both casesbut a different orientation to the pharmacophoric groups. Overall, both are very differentfrom the crystal structure indicating the flexibility of the compound and that in a dynamicreceptor – ligand interaction, the molecule might undergo simple but essential structuralchanges in order to approach and fit the binding site.AcknowledgmentsWe gratefully acknowledge the support of ELDRUG SA, Patras Science Park, Greece. We also thankProf. Leonardo Pardo (Universitat Autònoma de Barcelona) for computer facilities and software use.References1. Hanessian, S., Guesne, S., Chenard, E. Org. Lett. 12, 1816-1819 (2010).2. Rahuel, J., Rasetti, V., Maibaum, J., Rüeger, H., Göschke, R., Cohen, N.C., Stutz, S., Cumin, F.,Fuhrer, W., Wood, J.M., Grütter, M.G. Chem. Biol. 7, 493-504 (2000).3. Matsoukas, J., Agelis, G., Hondrelis, J., Yamdagni, R., Wu, Q., Ganter, R., Moore, D., Moore, G.J.J. Med. Chem. 36, 904-911, (1993).253