Medicinal Chemistry SAR: Antihypertensives and psychoactive drugs MCQs With Answer

Medicinal Chemistry SAR: Antihypertensives and psychoactive drugs MCQs With Answer is designed for M.Pharm students preparing for MPC 103T Advanced Medicinal Chemistry. This collection focuses on structure–activity relationships (SAR) that determine potency, selectivity, pharmacokinetics and adverse effect profiles of key antihypertensive and psychoactive drug classes. Each question probes molecular features — functional groups, stereochemistry, ring systems and electronic effects — that explain drug-receptor interactions and metabolic fates. The questions are aimed at deepening understanding beyond memorization, linking chemical modifications to therapeutic outcomes and side effects. Answers are provided to facilitate self-assessment and targeted revision for advanced coursework and exams.

Q1. Which structural feature is essential for the classical ACE inhibitor activity seen in drugs like captopril and enalapril?

• A bulky lipophilic tricyclic nucleus
• A zinc-binding group such as a sulfhydryl, carboxylate or phosphonate
• A protonated tertiary amine at physiological pH
• A tetrazole ring mimicking a carboxylate

Correct Answer: A zinc-binding group such as a sulfhydryl, carboxylate or phosphonate

Q2. Which SAR element of ARBs (angiotensin II receptor blockers) is most critical for high affinity to the AT1 receptor?

• A fused heterocyclic diazepine core
• A biphenyl moiety with a para-substituted acidic group (carboxylate or tetrazole)
• A bulky adamantane substituent
• A primary alcohol adjacent to an amide

Correct Answer: A biphenyl moiety with a para-substituted acidic group (carboxylate or tetrazole)

Q3. In beta-adrenergic blockers (beta-blockers), which structural motif is characteristic and required for receptor interaction?

• An aryloxypropanolamine side chain linking an aromatic ring to a secondary/tertiary amine
• A sulfonylurea moiety attached to a pyrimidine ring
• A benzothiazole fused to an imidazole
• A tertiary alcohol adjacent to an ester group

Correct Answer: An aryloxypropanolamine side chain linking an aromatic ring to a secondary/tertiary amine

Q4. The stereochemistry at the beta-blocker side chain (propanolamine carbon) commonly influences activity. Which is generally more active at β-receptors?

• The R-enantiomer
• The S-enantiomer
• Activity is independent of stereochemistry
• Only racemates are active

Correct Answer: The S-enantiomer

Q5. For dihydropyridine calcium channel blockers (e.g., nifedipine), which modification increases vascular selectivity over cardiac effects?

• Replacing ester groups at positions 3 and 5 with bulky tert-butyl groups
• Introducing electron-withdrawing substituents at the phenyl C4′ position
• Removing all ester functionalities to increase polarity
• Adding a permanently charged quaternary ammonium

Correct Answer: Introducing electron-withdrawing substituents at the phenyl C4′ position

Q6. Which structural change in tricyclic antidepressants (TCAs) shifts selectivity from norepinephrine reuptake inhibition towards serotonin reuptake inhibition?

• Conversion of the tertiary amine to a secondary amine
• Lengthening the three-carbon side chain to five carbons
• Replacing the tricyclic core with a benzisoxazole
• Removing the ring junction double bond

Correct Answer: Conversion of the tertiary amine to a secondary amine

Q7. Fluoxetine (an SSRI) SAR identifies which feature as important for serotonin reuptake inhibition?

• A para-trifluoromethyl-substituted phenoxyphenyl structure with a secondary amine separated by three atoms
• A dihydropyridine core with two ester groups
• A tetrazole-carboxylate bioisostere on a biphenyl
• A hydrazine moiety adjacent to an aromatic ring

Correct Answer: A para-trifluoromethyl-substituted phenoxyphenyl structure with a secondary amine separated by three atoms

Q8. Monoamine oxidase (MAO) irreversible inhibitors like tranylcypromine derive activity from which SAR feature?

• A propargyl or cyclopropylamine group that forms a covalent bond with the flavin in MAO
• A bulky diisopropyl carbinol that prevents enzyme binding
• An aromatic nitro group meta to an anilide
• A tertiary amine tertiary alcohol motif

Correct Answer: A propargyl or cyclopropylamine group that forms a covalent bond with the flavin in MAO

Q9. Benzodiazepine hypnotics/anxiolytics show increased potency when which substitution is present?

• An electron-withdrawing substituent (e.g., nitro or halogen) at C7 of the benzodiazepine core
• A methyl group at the imine nitrogen rendering it tertiary
• A long aliphatic side chain at C3 replacing a carbonyl
• Removal of the phenyl at C5

Correct Answer: An electron-withdrawing substituent (e.g., nitro or halogen) at C7 of the benzodiazepine core

Q10. Typical antipsychotics of the phenothiazine class show high D2 antagonism when which side-chain feature is present?

• A three-carbon aliphatic chain ending in a dimethylamino group (tertiary amine)
• An alpha, beta-unsaturated ketone linked to the ring
• A sulfonamide directly attached to the tricyclic nucleus
• An ester linkage at the 2-position of the tricyclic ring

Correct Answer: A three-carbon aliphatic chain ending in a dimethylamino group (tertiary amine)

Q11. In atypical antipsychotics like clozapine, which structural attribute contributes to lower extrapyramidal side effects compared to typical antipsychotics?

• Higher selectivity for serotonin 5-HT2A receptors relative to dopamine D2 receptors due to a dibenzodiazepine core
• Presence of a para-trifluoromethyl phenyl group that irreversibly binds D2
• Inclusion of a quaternary ammonium that restricts CNS penetration
• Replacement of all aromatic rings by aliphatic chains

Correct Answer: Higher selectivity for serotonin 5-HT2A receptors relative to dopamine D2 receptors due to a dibenzodiazepine core

Q12. Barbiturates’ sedative potency correlates with which SAR parameter?

• Alkyl substitution at C5 increasing lipophilicity enhances CNS penetration and potency
• Introduction of polar hydroxyl groups to improve water solubility
• Replacing the ureide oxygen with sulfur always decreases activity
• Shortening the carbonyl-to-carbonyl distance in the ring increases selectivity

Correct Answer: Alkyl substitution at C5 increasing lipophilicity enhances CNS penetration and potency

Q13. For angiotensin-converting enzyme inhibitors that are prodrugs (e.g., enalapril), what SAR rationale explains using esterified carboxylates?

• Esters increase lipophilicity to improve oral absorption and are hydrolyzed to the active carboxylate in vivo
• Ester groups directly coordinate with the ACE zinc ion to inhibit enzyme
• Esters prevent the drug from crossing cell membranes
• Esterification converts reversible inhibitors into irreversible ones

Correct Answer: Esters increase lipophilicity to improve oral absorption and are hydrolyzed to the active carboxylate in vivo

Q14. Structural modification that reduces peripheral beta-1 selectivity of beta-blockers and increases β2 blockade (more bronchoconstriction risk) is typically:

• Increasing lipophilicity on the aromatic ring without steric hindrance near the amine
• Incorporating a bulky para-substituent ortho to the aryloxy linkage
• Changing the propanolamine to a rigid bicyclic system that favors β1 binding
• Introducing a polar sulfonate group to reduce CNS penetration

Correct Answer: Increasing lipophilicity on the aromatic ring without steric hindrance near the amine

Q15. Which SAR aspect of calcium channel blocker verapamil differentiates its mechanism from dihydropyridines?

• Verapamil is a phenylalkylamine that binds the intra-cellular pore region of L-type channels; bulky N,N-dialkyl groups on the tertiary amine are important
• Verapamil contains two ester groups at positions 3 and 5 of a dihydropyridine ring
• Verapamil requires a tetrazole ring to mimic angiotensin II
• Verapamil is a beta-blocker with an aryloxypropanolamine motif

Correct Answer: Verapamil is a phenylalkylamine that binds the intra-cellular pore region of L-type channels; bulky N,N-dialkyl groups on the tertiary amine are important

Q16. Which substitution pattern on the phenyl rings of SSRIs tends to increase selectivity for 5-HT reuptake blockade?

• Electron-withdrawing groups (e.g., CF3, F) at para or meta positions improving binding to SERT
• Large electron-donating groups at ortho positions to increase steric bulk
• Introduction of a charged sulfonate to the aromatic ring
• Conversion to a rigid polycyclic steroid-like scaffold

Correct Answer: Electron-withdrawing groups (e.g., CF3, F) at para or meta positions improving binding to SERT

Q17. Amphetamine-like psychostimulants show increased CNS potency when which SAR feature is present?

• An alpha-methyl group adjacent to the amine (alpha-methylation) that increases resistance to MAO metabolism and enhances CNS activity
• A bulky carboxylate substituent on the aromatic ring
• A primary alcohol replacing the amine
• A long polyether chain attached to the para position

Correct Answer: An alpha-methyl group adjacent to the amine (alpha-methylation) that increases resistance to MAO metabolism and enhances CNS activity

Q18. Which SAR feature of escitalopram (active S-enantiomer of citalopram) contributes to higher potency compared to the R-enantiomer?

• Stereochemical orientation of the bicyclic aryl-amine scaffold allowing optimal fit into SERT binding pocket
• Replacement of the nitrile with a carboxylic acid
• Introduction of a propargyl group that forms a covalent bond with SERT
• Conversion to a quaternary ammonium to limit CNS access

Correct Answer: Stereochemical orientation of the bicyclic aryl-amine scaffold allowing optimal fit into SERT binding pocket

Q19. Which modification in ACE inhibitors reduces the risk of sulfhydryl-related adverse effects (e.g., taste disturbance, rash) but retains potency?

• Replacing the sulfhydryl group with a carboxylate or phosphonate bioisostere (as in enalapril or fosinopril)
• Adding another free sulfhydryl to increase zinc binding
• Removing the zinc-binding moiety entirely
• Converting to a quaternary ammonium salt to prevent absorption

Correct Answer: Replacing the sulfhydryl group with a carboxylate or phosphonate bioisostere (as in enalapril or fosinopril)

Q20. Which SAR principle explains why many antipsychotics with high D2 antagonism also produce hyperprolactinaemia?

• High affinity for D2 receptors in the tuberoinfundibular pathway due to basic tertiary amine side chains that favor D2 binding
• Presence of polar esters preventing brain penetration and selectively acting on pituitary D2
• Excessive lipophilicity causing irreversible D2 receptor alkylation
• Incorporation of a tetrazole ring that acts as a prolactin secretagogue

Correct Answer: High affinity for D2 receptors in the tuberoinfundibular pathway due to basic tertiary amine side chains that favor D2 binding

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