Tautomers of styrylquinoline derivatives containing a methoxy substituent: computation of their population in aqueous solution and their interaction with RSV integrase catalytic core.

8-Hydroxy-2-[2-(3-hydroxy-4-methoxyphenyl)ethenyl]-7-quinoline carboxylic acid and 8-hydroxy-2-[2-(3-methoxy-4-hydroxyphenyl)ethenyl]-7-quinoline carboxylic acid inhibit the processing and strand transfer reactions catalyzed by HIV-1 integrase with an IC50 of 2 microM. Some of their spectral properties are briefly reported. Their fluorescence is so weak that it is of no use in an experimental determination of the binding to the protein and we resorted to computer simulation. Both styrylquinoline derivatives, in their monoanionic form, have several dozens of tautomers and each of these forms has four planar rotamers. In this work computer simulations have been performed to determine which tautomer is the most abundant in aqueous solution and which binds to the Rous sarcoma virus (RSV) integrase catalytic core. As the substituents on the quinoline moiety are the same as on salicylic acid, the energies of hydroxy benzoic acid tautomers were also computed both in vacuo and embedded in a continuous medium which had the dielectric constant of bulk water, using the recent CPCM technique. The CPCM method was then applied to the two integrase inhibitors to estimate the tautomer population in water. The binding site of the compounds on the RSV integrase catalytic core was determined through a docking protocol, consisting of coupling a grid search method with full energy minimization. The designed method is a way leading to identification of potent integrase inhibitors using in silico experiments.