HomeStudy cornerStructure Activity Relationship (SAR) in medicinal chemistry

Structure Activity Relationship (SAR) in medicinal chemistry

The structure–activity relationship is the relationship between the chemical or 3D structure of a molecule and its biological activity. The analysis of SAR enables the determination of the chemical groups responsible for evoking a target biological effect in the organism. This allows modification of the effect or the potency of a bioactive compound by changing its chemical structure. 

A Structure-Activity Relationship is the relationship of the molecular structure of a chemical with a physicochemical property, environmental fate attribute, and/or specific effect on human health or an environmental species.


Part 1

Sympathomimetic agents

directly bind to the adrenergic receptors in the postsynaptic membrane.

SAR of catecholamines:

  • Catechol ring is important.
  • β-hydroxyl group is important.
  • Stereochemistry at β position should be R.
  • Bulkiness of groups attached to the amino has a significant effect on selectivity (alpha or Beta receptor activity).
  • alpha substitution increases stability and selectivity but reduces activity.

Examples of sympathomimetics

Isoproterenol (Isoprenaline):

Acts mainly on β1 and β2More stable to MAO metabolism.


10 X more potent on β2 than on cardiac β1


Selective β2 agonist. Long-acting bronchodilator


Selective β2 agonist. Long-acting bronchodilator.


Used as bronchodilator and cardiac stimulant. Orally available


Used as nasal decongestant.

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