SAR of Muscarinic Antagonists

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Chapter: Medicinal Chemistry : Anticholinergic Drugs

For the potent cholinergic antagonist, the groups R1 and R2 must be hydrophobic in nature (usually, phenyl, cyclohexyl, or cyclopentyl).


SAR of Muscarinic Antagonists


  • For the potent cholinergic antagonist, the groups R1 and R2 must be hydrophobic in nature (usually, phenyl, cyclohexyl, or cyclopentyl).

  • In the above general structure for amino alcohol, the substituent R1 and R2 should be a carbocyclic or a heterocyclic ring for maximal antagonistic potency.

  • The ring may be identical, but the more potent compounds have different rings. The one ring is aromatic and other may be saturated or possessing only one oleļ¬ne bond. Example: Propantheline.

  • Their ability to do these effectively is because of the large group of R1 and R2 that enhance the binding to receptors since the antagonistics are larger than agonists.

  • The R3 substituent may be a hydrogen atom, hydroxyl group, hydroxy methyl group or a carboxy amide, or it may be a component of R1 and R2 ring system. When the substituent is a hydroxyl group or hydroxy methyl group the antagonist is usually more potent. Due to the hydroxyl group presumably there might be an increase in the binding strength by participating in a hydrogen bond interaction at the receptor.

  • The X substituent in the most potent anticholinergic agent is an ester, but an ester functional group is not absolute necessary for muscarinic antagonistic activity.

  • The N substituent is a quaternary ammonium salt in the most potent anticholinergic agents. Tertiary amine also possesses antagonist activity presumably by binding to the receptors in the cationic form. The alkyl substitution is usually methyl group, ethyl group, propyl, or isopropyl group.

  • The distance between ring substituted carbon and amine nitrogen is apparently not critical, as much as the length of alkyl chain connecting this, may be from two to four carbons. The most potent anticholinergic agent has two methylene units in this chain.

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