Effects of solvation on the ionization and conformation of raclopride and other antidopaminergic 6-methoxysalicylamides: insight into the pharmacophore

J Med Chem. 1993 Jan 22;36(2):196-204. doi: 10.1021/jm00054a002.

Abstract

Previous work has shown that raclopride in water at neutral pH exists in a zwitterionic form, suggesting a stereoelectronic structure largely different from that of other benzamides. In the present study, the acid-base behavior of other 6-methoxysalicylamides is shown to be comparable to that of raclopride. An extensive investigation by high-temperature molecular dynamics gave insight into the conformational behavior of neutral and zwitterionic raclopride in vacuum and in water. Partitioning of raclopride and a more rigid analogue with characterization (by first-derivative UV spectroscopy) of the predominant forms in the organic phase indicated that only neutral, internally H-bonded forms partition into the organic solvent. Thus, the predominant forms of 6-methoxysalicylamides will be very different in the aqueous and organic phases. In the latter phase, and hence presumably also in the receptor phase, the drugs exist with a neutral, internally H-bonded phenolic group and are therefore stereoelectronically similar to other substituted benzamides.

Publication types

  • Comparative Study
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Dopamine D2 Receptor Antagonists*
  • Hydrogen-Ion Concentration
  • Molecular Conformation
  • Potentiometry
  • Raclopride
  • Salicylamides / chemical synthesis*
  • Salicylamides / chemistry*
  • Salicylamides / pharmacology
  • Solubility
  • Stereoisomerism
  • Structure-Activity Relationship

Substances

  • Dopamine D2 Receptor Antagonists
  • Salicylamides
  • Raclopride