Relationships between chemical structure and affinity for acetylcholine receptors

Area of Science:

• Medicinal Chemistry
• Pharmacology
• Neuroscience

Background:

• Acetylcholine is a key neurotransmitter involved in various physiological processes.
• Understanding acetylcholine receptor interactions is crucial for developing targeted therapeutics.
• Structure-activity relationships of acetylcholine analogues provide insights into receptor binding.

Purpose of the Study:

• To synthesize and characterize novel acetylcholine analogues with modified acetyl and trimethylammonium groups.
• To investigate the agonist and antagonist properties of these analogues on guinea-pig ileum.
• To determine the binding affinities of these compounds to postganglionic muscarinic acetylcholine receptors.

Main Methods:

• Synthesis of a diverse series of acetylcholine analogues with variations in the ester and quaternary ammonium moieties.
• Pharmacological testing on isolated guinea-pig ileum to assess agonist/antagonist activity.
• Competitive binding assays to quantify affinity for muscarinic acetylcholine receptors (expressed as log K).

Main Results:

• A range of affinities (log K from 3.7 to 9.8) was observed, with some compounds exhibiting agonist or partial agonist activity.
• Antagonist activity was predominant across most synthesized analogues.
• Optimal affinity was achieved with a combination of phenyl and cyclohexyl groups, surpassing individual substitutions or increased onium group size.

Conclusions:

• Molecular modifications, particularly the combination of aromatic and aliphatic bulky groups, significantly influence binding affinity to muscarinic receptors.
• The study highlights complex structure-activity relationships, where synergistic effects between different molecular regions enhance receptor interaction.
• Findings contribute to the understanding of acetylcholine receptor pharmacology and the design of novel ligands.