Optimizing the Binding of Fullerene Inhibitors of the HIV-1 Protease through Predicted Increases in Hydrophobic Desolvation

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Abstract
We have developed and applied a computational strategy to increase the affinity of fullerene-based inhibitors of the HIV protease. The result is a approximately 50-fold increase in affinity from previously tested fullerene compounds. The strategy is based on the design of derivatives which may potentially increase hydrophobic desolvation upon complex formation, followed by the docking of the hypothetical derivatives into the HIV protease active site and assessment of the model complexes so formed. The model complexes are generated by the program DOCK and then analyzed for desolvated hydrophobic surface. The amount of hydrophobic surface desolvated was compared with a previously tested compound, and if this amount was significantly greater, it was selected as a target. Using this approach, two targets were identified and synthesized, using two different synthetic approaches: a diphenyl C60 alcohol (5) based on a cyclopropyl derivative of Bingel (Chem.Ber. 1993, 126, 1957-1959) and a diisopropyl cyclohexyl C60 alcohol (4a) as synthesized by Ganapathi et al. (J. Org.Chem. 1995, 60, 2954-2955). Both showed tighter binding than the originally tested compound (diphenethylaminosuccinate methano-C60, Ki = 5 microM) with Ki values of 103 and 150 nM, respectively. In addition to demonstrating the utility of this approach, it shows that simple modification of fullerenes can result in high-affinity ligands of the HIV protease, for which they are highly complementary in structure and chemical nature.