Structure-activity correlations for psychotomimetics. 1. Phenylalkylamines: electronic, volume, and hydrophobicity parameters.

CNDO/2 calculations have been performed on a series of alkyl, alkoxy, and alkylthio derivatives of phenethylamine and phenylisopropylamine. The results of these, of van der Waals volume calculations, and of Hansch type hydrophobicity calculations were correlated with psychotomimetic activity by chemometric methods. Eight parameters, involving seven chemical descriptors, were found to be highly significant. Directional hydrophobicity and volume effects were found, which suggests that steric and hydrophobic interactions in the neighborhood of the receptor site are important. A puzzling but strong interaction effect between meta and para substituents was noted. Electronic terms may be explicable in terms of formation of charge-transfer complexes by accepting, rather than by donating, charge, as has been believed in the past. A charge effect indicates that a charge or dipole is influential at the binding site, or alternatively, a specific reactivity at the meta position is involved.