Discriminating D1 and D2 agonists with a hydrophobic similarity index

Currently, methods for calculating molecular similarity indices have been developed for comparing steric, charge density, and molecular electrostatic potential (MEP) properties. Much of the existing technology may, however, be applied to the quantitative comparison of molecular hydrophobicities. In this article we present an empirical hydrophobic similarity index. We utilize atomic hydrophobic parameters derived from a quantum mechanical semiempirical wavefunction. Hydrophobicity at points on a grid is computed with a recently introduced "molecular lipophilicity potential." The overlap of pairs of molecules is calculated with the metric introduced by Carbó. This approach is applied to a case in which steric and electrostatic criteria have already been shown to be inadequate in rationalizing selectivity, namely, requirements for recognition at the dopamine D1 and D2 receptors. We demonstrate that, for a set of dopamine agonists, D1 ligands show higher similarity in this property that D2 analogs. This indicator of similarity is more successful at accounting for D1 selectivity than previous methods.