Adrenergic blockers bind to adrenergic receptors but inhibit stimulation of the sympathetic nervous system. They have opposite effects of adrenergic agents and are also known as adrenergic antagonists or sympatholytics. Adrenergic blockers are classified as α-adrenergic blockers or β-adrenergic blockers depending on whether they antagonize effects of drugs acting on α or β receptors. Examples of commonly used adrenergic blockers include prazosin, propranolol, metoprolol, tolazoline and ergot alkaloids like dihydroergotamine.

2.  Bind to adrenergic receptors, but inhibit or block stimulation of the
sympathetic nervous system (SNS) .
 Have the opposite effect of adrenergic agents
 Also known as adrenergic antagonists or sympatholytics

3. α-adrenergic blockers
 Antagonise effects produced by drugs acting on α-receptor
β -adrenergic blockers
 Antagonise effects produced by drugs acting on β -receptor

4. • Non-selective α-adrenergic blockers
 Imidazoline derivatves: Phentolamine, Tolazoline
 Haloalkylamines: Phenoxybenzamine
Ergot alkaloids – Dihydroergotamine, Methylsergide
• Selective α1-adrenergic blockers
 Prazosin
• Selective α2-adrenergic blockers
 Yohimbine

5.  Reduce blood pressure, cause nasal congestion.
 Produce miosis.

6.  Vasodilator that is used to treat spasms of peripheral blood vessels
 Used as antihypertensive drugs.
 Also stimulate GIT smooth muscles and increase gastric acid secretion.
Imidazoline derivatives (Reversible and thus competitive blockers)
Phentolamine
(Reversible)
Tolazoline (Reversible)
Used to antagonise overdose of clonidine

7.  Irreversible
 Chemically related to nitrogen mustards and thus get covalently
conjugated with alpha receptor.
 Used as antihypertensive and in treatment of urinary retention.
(Irreversible blocker)

8. Obtained from dried sclerotium of fungus Claviceps purpurea
Dihydroergotamine
Ergot alkaloid used to treat migraines due to vasoconstrictive effect.
It is a derivative of ergotamine.
Administered as nasal spray or injection and has an efficacy similar to
that of sumatriptan

9. Methyl sergide
Ergot derived prescription drug used for the prophylaxis of difficult to
treat migraine and headaches.
It is potent serotonin antagonist also
Oxytocic also.

10.  Antagonise effect of α1 receptor agonist leading to
vasodilation and fall in blood pressure due to decreased
peripheral resistance.
 Helpful as antihypertensive drugs.
 Treatment of Raynaud syndrome (numbness in some areas of
body)
Prazosin

11.  Used in the treatment hypertension, coronary artery disease,
arrhythmiasis and open angle glaucoma.

12.  β - blockers are structurally similar to β – agonist i.e. Phenylethylamine or
similar hydrophobic moeity is necessary for activity. However, catechol ring
can be replaced by variety of ring system without loss of antagonistic activity.
 Replacement of catechol hydroxyl group with chlorine or phenyl ring system
retains β-blocking activity. eg. Pronethalol, Dichloro isoproterenol.
 N, N - disubstitution decreases β-blocking activity. Activity is maintained
when phenyl ethyl, hydroxy phenyl ethyl or methoxy phenyl ethyl groups are
added to amine as a part of the molecule.
 p-substitution (to the phenoxy): increased beta 1 selectivity (eg: metoprolol,
atenolol, acebutolol).

13.  Non selective blockers: Propranolol (Decrease renin release, cardiac
output)
 Selective β1- Blockers: Atenolol, Betazolol, Bisoprolol, Esmolol,
Metoprolol
 Both α and β Blocker: Carvedilol, Labetolol

14. Atenolol
Betazolol
Bisoprolol
Esmolol
Metoprolol

15. Carvedilol
Labetolol

16.  Write a note on adrenoreceptor blocker.
 Classify adrenoreceptor blockers with examples.
 Give SAR of beta adrenergic blockers.
 Give structure and use of following: Prazosin, Propranolol,
Metoprolol, Tolazoline.
 Write a note on Ergot alkaloids.

17. Synthesis of phenyl ephrine

18. Synthesis of tolazoline
Synthesis of propranolol