Abstract

Complete neglect of differential overlap (CNDO) calculations indicate that 6-hydroxydopamine (2,4,5-trihydroxyphenethylamine), 2,3,5-trihydroxyphenethylamine, and 2,3,4,5-tetrahydroxyphenethylamine have the same minimum energy conformations. 6-Hydroxydopamine is known to cause neurodegeneration; all three compounds have recently been shown to have long-term effects on the accumulation of [³H]norepinephrine in mouse heart in vivo. The minimum energy conformations are gauche forms in which the proton on the nitrogen atom, at the end of the rotated side chain, and the 2-hydroxyl oxygen atom are 1.29 A apart, a likely intramolecular hydrogen bonding distance. All three of these compounds contain para-oriented hydroxyl groups. These 2,5-dihydroxy substituents display about the same interatomic distance as that between the oxygen atom in the 5-hydroxyl group and the nitrogen atom in the minimum energy conformers, and it is proposed that this distance might be important for interaction of these compounds with macromolecules. The criteria of a specific interatomic distance, combined with their ease of oxidation to 1,4-quinones via anion-radical mechanisms when a third hydroxyl group is present in the molecule, and adequate uptake at the active site are sufficient to define the biological activity of longterm reduction in the cardiac uptake of norepinephrine. The minimum energy conformations, interatomic distances, and net electronic charge distributions in isomeric 2,3,4-, 3,4,5-, 2,3,6-, and 2,4,6-trihydroxyphenethylamines and 2,5-dihydroxyphenethylamine have also been obtained. These compounds do not meet one or more of the listed criteria for inducing long-term reduction in cardiac uptake of [²H]norepinephine.