Bethanechol

• Bethanechol is a synthetic choline ester and a direct-acting parasympathomimetic agent that selectively stimulates muscarinic receptors (especially M3) in the gastrointestinal (GI) tract and urinary bladder.
• It mimics the effect of acetylcholine on smooth muscle without significant effects on nicotinic receptors or the central nervous system.

Chemical Formula:

• C₇H₁₇NO₂

Mechanism of Action:

• Selective muscarinic agonist (very little nicotinic activity).
• Resistant to hydrolysis by AChE.

Uses of Bethanechol:

• Urinary retention
• Postoperative ileus
• Neurogenic bladder

Side Effects:

• Salivation
• Sweating
• Bronchospasm
• Bradycardia
• GI discomfort

SAR of Bethanechol:

1. Beta-methyl substitution → increases selectivity for muscarinic
2. Carbamate ester → resistant to AChE degradation.
3. Quaternary amine → no CNS penetration (limited systemic effects).

General Synthesis:

1. Beta-methylcholine is used as starting compound.
2. React with methyl isocyanate or carbamoyl chloride to form carbamoyl ester.
3. Quaternize to form chloride.

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