- H1-receptor antihistamine
- Alkylamine antihistamine
|S. NO.||PHYSICAL AND CHEMICAL PROPERTIES|
|5||Presence of ring||Pyridine, phenyl|
|6||Number of chiral centers||1|
Mechanism of Action
i. Pheniramine do competition for H1 receptor with histamine and after bounding with receptor, it acts as inverse agonist.
ii. Due to reduction in H1 receptor activity, there is reduction in itching, vasodillation and capillary leakage, which reduces redness and edema.
iii. Sedation is produced due to inverse agonism of H1 receptors in CNS.
iv. Reduction in itching ad antagonizing effects of pheniramine is due to binding of drug with H4 receptors.
Structure Activity Relationship
Structure activity of alkyl amines antihistamines can be summarized as:
- E- and Z- isomers in alkenes shows large difference in activity, where, E-isomers are more potent than Z-
- The two aromatic rings have different binding environments at the receptors.
- 5-6 angstrom distance is required between aromatic ring and tertiary aliphatic amine for biding at the receptor.
- S-enantiomers have greater affinity for H1 histamine receptors 
Method of synthesis
i. Benzyl cyanide and diclopentadienylcobalt catalyzer in presence of acetylene gas are reacted under high temperature and pressure to obtain benzyl-pyridine.
ii. N-dimethyl chloride ethane is reacted with benzyl-pyridine is presence of sodium amide to get pheniramine.
Pheniramine is used for treatment of:
- Hay fever
- Common cold
- Allergic conjunctivitis
- As a sleeping pill
Side effects of pheniramine are:
- Loss of consciousness
Q.1 IUPAC nomenclature of drug pheniramine is?
b) N,N-Dimethyl-3-phenyl-3-pyridin-2-yl-butan -1-amine
Q.2 Which amongst the following statements is/are incorrect related to the SAR of alkylamine antihistamine drugs?
I. E- and Z- isomers in alkenes shows large difference in activity, where, E-isomers are less potent than Z-isomers.
II. The two aromatic rings have different binding environments at the receptors.
III. 5-6 angstrom distance is required between aromatic ring and tertiary aliphatic amine for binding at the receptor.
IV. S-enantiomers have lesser affinity for H1 histamine receptors.
a) I, IV
b) II, IV
c) I, II, IV
Q.3 Correct sequence for synthesis of drug pheniramine from benzyl cyanide
I. Reaction with diclopentadienylcobalt catalyzer in presence of acetylene gas
II. Reaction with Sodium amide
III. Reaction with N-dimethyl chloride
a) II – III
b) I – IV
c) I – II – III
d) II – IV
Q.4 Side effects of drug Pheniramine is/are?
d) All of the above
Q.5 Match the following drugs with their correct melting point-
|i. Pheniramine||A.112-115 oC|
|ii. Auranofin||B. 230.5oC|
|iii. Mefenimic acid||C. 162-165 oC|
|iv. Ketorolac||D. <25oC|
a. i-A, ii-D, iii-C, iv-B
b. i-D, ii-A, iii-B, iv-C
c. i-C, ii-B, iii-A, iv-D
d. i-B, ii-C, iii-A, iv-D
Q.6 An example of drug from class alkylamine antihistamine drugs is?
Q.7 Type of ring present in the structure of pheniramine is?
d) All of the above
REFERENCES Lemke TL, Williams DA, editors. Foye’s principles of medicinal chemistry. Lippincott Williams & Wilkins; 2012 Jan 24.