Medicinal Chemistry SAR: Antineoplastics and antiviral agents MCQs With Answer

Introduction

This collection of MCQs on Medicinal Chemistry SAR: Antineoplastics and Antiviral Agents is tailored for M.Pharm students preparing for MPC 103T Advanced Medicinal Chemistry. The questions focus on structure–activity relationships, mechanisms of action, metabolic activation, resistance determinants, and key structural features that determine pharmacokinetics and toxicity of major anticancer and antiviral drug classes. Each item emphasizes chemical rationale behind biological effects and clinical properties, helping students link molecular modifications to therapeutic outcomes. Use these MCQs for self-assessment, revision before exams, or discussion in study groups to deepen understanding of drug design principles in oncology and antiviral therapy.

Q1. Which structural feature of cisplatin is primarily responsible for its DNA cross-linking activity?

• Planar double bond between platinum atoms
• Square planar Pt(II) center with two labile chloride ligands in cis position
• Octahedral Pt(IV) center with inert ligands
• Bulky cyclohexylamine chelate

Correct Answer: Square planar Pt(II) center with two labile chloride ligands in cis position

Q2. In nitrogen mustard alkylating agents, what role does an electron-withdrawing substituent on the aromatic ring play?

• Decreases formation of the aziridinium ion, reducing reactivity
• Increases lipophilicity and prevents DNA binding
• Stabilizes the aziridinium ion, increasing alkylation rate of DNA
• Makes the molecule unable to cross cell membranes

Correct Answer: Stabilizes the aziridinium ion, increasing alkylation rate of DNA

Q3. Which structural requirement is most critical for methotrexate’s high affinity for dihydrofolate reductase (DHFR)?

• Presence of a guanine-like heterocycle
• A glutamate-like polycarboxylate tail and a pteridine-like ring system
• A 3′-azido group on a ribose moiety
• Bulky lipophilic substituents at C-13

Correct Answer: A glutamate-like polycarboxylate tail and a pteridine-like ring system

Q4. Which SAR feature is essential for 5-fluorouracil (5-FU) to inhibit thymidylate synthase?

• Replacement of a 2′-OH with fluorine on ribose
• Fluorine substituent at the 5-position of the uracil ring to form a stable FdUMP-methylenetetrahydrofolate complex
• Bulky alkyl chain at N1 to improve DNA intercalation
• A phosphonate group to bypass phosphorylation

Correct Answer: Fluorine substituent at the 5-position of the uracil ring to form a stable FdUMP-methylenetetrahydrofolate complex

Q5. Why is the intact lactone ring essential for camptothecin activity as a topoisomerase I inhibitor?

• The lactone chelates magnesium necessary for topoisomerase II
• Lactone makes the molecule too polar to enter cells if opened
• The closed lactone binds in the topoisomerase I-DNA cleavable complex; hydrolysis to the carboxylate reduces binding
• Lactone ring undergoes reductive activation to a radical that damages DNA

Correct Answer: The closed lactone binds in the topoisomerase I-DNA cleavable complex; hydrolysis to the carboxylate reduces binding

Q6. Which change in anthracycline structure is most directly associated with increased cardiotoxicity via redox cycling?

• Introduction of a sugar moiety with an amino group
• Presence of the quinone-hydroquinone (anthraquinone) redox center in the aglycone
• Replacement of daunosamine with glucose
• Conversion of the aglycone to a nonplanar scaffold

Correct Answer: Presence of the quinone-hydroquinone (anthraquinone) redox center in the aglycone

Q7. Which structural modification of paclitaxel analogs (taxanes) generally improves binding to tubulin and potency?

• Removal of the C-13 side chain
• Substitution at C-2′ with bulky hydrophobic groups maintaining the ester linkage at C-13
• Opening the oxetane ring to increase flexibility
• Conversion of the diterpene core to a saturated hydrocarbon

Correct Answer: Substitution at C-2′ with bulky hydrophobic groups maintaining the ester linkage at C-13

Q8. Which SAR principle explains why transplatin is inactive compared to cisplatin?

• Trans geometry prevents formation of bifunctional intrastrand cross-links due to ligand arrangement
• Transplatin is too hydrophobic to enter cells
• Transplatin is rapidly reduced to Pt(0)
• Transplatin binds only to proteins and not DNA because of steric bulk

Correct Answer: Trans geometry prevents formation of bifunctional intrastrand cross-links due to ligand arrangement

Q9. Which functional group in zidovudine (AZT) is responsible for chain termination of viral DNA?

• 3′-Azido (-N3) group on the deoxyribose analog
• 5′-Triphosphate mimic at the sugar
• 2′-Fluoro substitution on the ribose
• A methoxy group at the nucleobase

Correct Answer: 3′-Azido (-N3) group on the deoxyribose analog

Q10. Acyclovir requires initial phosphorylation by a viral kinase for activation. Which SAR element of acyclovir facilitates selective activation in virus-infected cells?

• The guanine-like heterocycle that is a substrate for viral thymidine kinase
• A phosphate mimic at the 5′ position
• An aliphatic chain that binds host enzymes preferentially
• The presence of a ribose 2′-OH group

Correct Answer: The guanine-like heterocycle that is a substrate for viral thymidine kinase

Q11. Which substitution on oseltamivir improves oral bioavailability compared to zanamivir?

• Conversion of the carboxylate into an ethyl ester prodrug
• Introduction of a charged guanidinium group
• Removing the glycerol side chain entirely
• Adding a bulky sugar moiety to increase polarity

Correct Answer: Conversion of the carboxylate into an ethyl ester prodrug

Q12. Which structural motif in HIV protease inhibitors mimics the peptide bond transition state and is crucial for enzyme inhibition?

• Hydroxyethylene or hydroxyethylamine isostere
• A nucleoside triphosphate analog
• A rigid steroidal scaffold
• A phosphonate group mimicking phosphate

Correct Answer: Hydroxyethylene or hydroxyethylamine isostere

Q13. Lamivudine (3TC) shows enantioselective activity. What stereochemical feature is important for its antiviral potency?

• The D-enantiomer at the 2′ and 3′ positions is most active
• The L-nucleoside configuration (L-enantiomer) provides higher potency and lower toxicity
• Racemic mixture is required for activity
• Only the beta-D-ribofuranose is active

Correct Answer: The L-nucleoside configuration (L-enantiomer) provides higher potency and lower toxicity

Q14. Which property of tenofovir distinguishes it from classic nucleoside analogues and affects its activation pathway?

• It is a phosphonate nucleotide analog that bypasses the first phosphorylation step
• It contains a 3′-azido group causing chain termination directly
• It is a prodrug that yields a ribose with a 2′-fluoro
• It relies exclusively on viral kinases for activation

Correct Answer: It is a phosphonate nucleotide analog that bypasses the first phosphorylation step

Q15. Which SAR principle explains why adding polyglutamate tails to antifolates (e.g., methotrexate) increases intracellular retention and potency?

• Polyglutamation increases membrane permeability causing faster efflux
• Polyglutamate tails reduce binding to DHFR
• Polyglutamation increases negative charge and prevents diffusion out of cells while enhancing affinity for folate-dependent enzymes
• Polyglutamation converts the drug into an alkylating agent

Correct Answer: Polyglutamation increases negative charge and prevents diffusion out of cells while enhancing affinity for folate-dependent enzymes

Q16. In purine analog anticancer agents like 6-mercaptopurine, which enzymatic activation is crucial for incorporation into nucleic acids?

• Activation by thymidine kinase
• Phosphorylation by nucleoside diphosphate kinase only
• Conversion by hypoxanthine-guanine phosphoribosyltransferase (HGPRT) to nucleotide forms
• Methylation by catechol-O-methyltransferase

Correct Answer: Conversion by hypoxanthine-guanine phosphoribosyltransferase (HGPRT) to nucleotide forms

Q17. Which SAR aspect of oseltamivir resistance commonly occurs in influenza neuraminidase?

• Substitution of active-site residues that interact with the hydrophobic pentyl ether side chain reduces binding
• Deletion of the sialic acid binding pocket increases oseltamivir affinity
• Mutation that increases dependence on the prodrug form
• Glycosylation of the drug molecule by viral enzymes

Correct Answer: Substitution of active-site residues that interact with the hydrophobic pentyl ether side chain reduces binding

Q18. Which structural attribute of nitrosoureas allows them to cross the blood–brain barrier and be useful for brain tumors?

• High polarity due to multiple charged groups
• Formation of bulky DNA intercalating planar rings
• Lipophilic isocyanate-derived fragments and neutral species that enhance CNS penetration
• Permanent positive charge on nitrogen

Correct Answer: Lipophilic isocyanate-derived fragments and neutral species that enhance CNS penetration

Q19. For monoclonal antibody anticancer agents, which chemical modification most reduces immunogenicity and improves clinical tolerability?

• Conjugation to a small-molecule alkylator without humanization
• Humanization or fully human antibody engineering to replace murine sequences
• Increasing murine complementarity-determining regions (CDRs)
• Glycosylation with nonhuman sugars

Correct Answer: Humanization or fully human antibody engineering to replace murine sequences

Q20. Which SAR observation about influenza neuraminidase inhibitors explains why zanamivir has poor oral bioavailability compared to oseltamivir?

• Zanamivir contains a charged guanidino group and high polarity that reduce oral absorption
• Zanamivir is a large lipophilic prodrug that is not hydrolyzed
• Zanamivir requires conversion by hepatic esterases, which are absent
• Zanamivir lacks the sialic acid mimic and therefore cannot bind in the active site

Correct Answer: Zanamivir contains a charged guanidino group and high polarity that reduce oral absorption

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