A novel class of conformationally restricted heterocyclic muscarinic agonists

J Med Chem. 1986 Jun;29(6):1004-9. doi: 10.1021/jm00156a018.


A series of conformationally restricted compounds containing the 4,5,6,7-tetrahydroisoxazolo[4,5-c]pyridin-3-ol (THPO) skeleton, including O-methyl-THPO (10a) and O,5-dimethyl-THPO (11a), were synthesized. The compounds were designed by bioisosteric replacement of the methyl ester groups of the muscarinic cholinergic agonists norarecoline and arecoline by the 3-methoxyisoxazole group, and their interactions with central and peripheral muscarinic receptors were tested in vitro. The compounds 10a, 11a, O-ethyl-THPO (10b), O-propargyl-THPO (10j), and O-ethyl-5-methyl-THPO (11b) were inhibitors of the binding of the muscarinic mustard [3H]PrBCM to rat brain membranes with an increasing order of potency. There was, however, a very low degree of correlation between these binding data and the effects of the compounds on peripheral (ileal) muscarinic receptors, where 11a, 10j, 11b, and 10a were agonists with a decreasing order of potency, whereas O-isopropyl-THPO (10e) showed antagonistic effects. The relatively low pKa values of the compounds (7.5-7.7 for compounds with secondary and 6.1-7.0 for compounds with tertiary amino groups) are likely to allow the compounds to penetrate the blood-brain barrier.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Brain / metabolism
  • Guinea Pigs
  • Ileum / drug effects
  • In Vitro Techniques
  • Molecular Conformation
  • Parasympathomimetics / chemical synthesis*
  • Parasympathomimetics / pharmacology
  • Propylbenzilylcholine Mustard / metabolism
  • Rats
  • Receptors, Muscarinic / drug effects*
  • Receptors, Muscarinic / metabolism
  • Structure-Activity Relationship
  • Tritium


  • Parasympathomimetics
  • Receptors, Muscarinic
  • Tritium
  • Propylbenzilylcholine Mustard