Dopaminergic 2-aminotetralins: affinities for dopamine D2-receptors, molecular structures, and conformational preferences

AM Johansson, A Karlen, CJ Grol, S Sundell, L Kenne and U Hacksell

A combination of X-ray crystallography, NMR spectroscopy, and molecular mechanics (MMP2) calculations was used to determine the three- dimensional structures and conformational preferences of the enantiomers of 5-hydroxy-2-(di-n-propylamino)tetralin and their C1- methylated derivatives. In addition, the affinities of the compounds for striatal 3H-spiroperidol- and 3H-N-n-propylnorapomorphine-binding sites were determined. In the present series, the dopamine D2-receptor agonists have the S-configuration at the nitrogen-bearing carbon (C2), whereas the only established D2-receptor antagonist, 1S,2R-5-hydroxyl-1- methyl-2-(di-n-propylamino)tetralin (1S,2R-UH-242), has the opposite absolute configuration at C2. Two conformational parameters, the tetralin inversion angle (phi) and the dihedral angle tau(C1, C2, N, N- H or electron pair) (tau N), are shown to be critical for D2-receptor agonism; phi values around 0 degrees and tau N values around 60 degrees appear to be optimal. The low D2-affinity of 1S,2S-5-hydroxyl-1-methyl- 2-(di-n-propylamino)tetralin seems to be related to its inability to assume a low-energy "D2-receptor agonistic conformation." It is noted that the common structural denominator between the D2-receptor antagonists 1S,2R-UH-242 and 6aS-apomorphine is their inability to assume "dopamine D2-receptor agonistic nitrogen electron pair orientations."

Volume 30, Issue 3, pp. 258-269, 09/01/1986
Copyright © 1986 by American Society for Pharmacology and Experimental Therapeutics