Ligand-receptor 3-D similarity studies using multiple 4-point pharmacophores

A new method for 3-D similarity is presented based on the multiple potential 4-point 3-D pharmacophores expressed by ligands and complementary to receptors. These are calculated for ligands taking conformational flexibility into account, and for receptors through the use of complementary site-points. Through this common frame of reference both ligand-ligand and ligand-receptor similarity studies are possible. The application of the method to selectivity between different serine proteases (thrombin, factor Xa and trypsin) is discussed, and the need to use 4-point pharmacophores rather than 3-point pharmacophores is illustrated. A novel refinement to the potential pharmacophore method that uses a "special" feature to give a relative measure of similarity/diversity is also discussed.