Naphthaquinones – Taxus MCQs With Answer

Naphthoquinones are a class of quinone natural products characterized by a fused naphthalene‑quinone core with diverse biological activities including antimicrobial, anticancer and redox‑mediated cytotoxicity. For B. Pharm students, understanding naphthoquinone chemistry—structure, biosynthesis, electron transfer, phase I/II metabolism, structure–activity relationships (SAR), analytical methods and formulation—is essential. Although Taxus species are best known for taxanes like paclitaxel, comparing taxane pharmacology with naphthoquinone mechanisms sharpens drug‑class knowledge. This topic integrates medicinal chemistry, pharmacology and pharmaceutics, focusing on extraction, stability, bioactivity and safety profiles relevant to drug development and therapeutics. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. Which structural feature defines a 1,4-naphthoquinone?

• A naphthalene ring with carbonyls at positions 1 and 4
• A single benzoquinone fused to a pyridine ring
• A benzene ring substituted with two adjacent hydroxyls
• A steroidal tetracyclic backbone with two ketones

Correct Answer: A naphthalene ring with carbonyls at positions 1 and 4

Q2. Which natural product is a well-known naphthoquinone with antimicrobial activity?

• Paclitaxel
• Plumbagin
• Atropine
• Quinidine

Correct Answer: Plumbagin

Q3. What is a primary biochemical mechanism by which many naphthoquinones exert cytotoxicity?

• Inhibition of microtubule polymerization
• Generation of reactive oxygen species via redox cycling
• Competitive antagonism of beta-adrenergic receptors
• Chelation of extracellular calcium

Correct Answer: Generation of reactive oxygen species via redox cycling

Q4. Which analytical technique is most useful for confirming the conjugated quinone chromophore in naphthoquinones?

• UV‑Visible spectroscopy showing characteristic absorption bands
• Flame photometry for halogen content
• Ion selective electrode for ionic species
• Polarimetry for optical rotation

Correct Answer: UV‑Visible spectroscopy showing characteristic absorption bands

Q5. Which reaction is naphthoquinone susceptible to because of its electrophilic α,β‑unsaturated carbonyls?

• Michael addition by nucleophiles
• Nucleophilic aromatic substitution at the ring junction only
• Pericyclic Diels–Alder with alkenes exclusively at C3–C4
• Claisen rearrangement with allylic alcohols

Correct Answer: Michael addition by nucleophiles

Q6. In comparison to Taxus taxanes, what major pharmacological difference is typical for naphthoquinones?

• Naphthoquinones primarily target microtubules like taxanes
• Naphthoquinones commonly act via redox biology rather than tubulin stabilization
• Naphthoquinones are large diterpenoids with high molecular weight
• Naphthoquinones are prodrugs activated by esterases similar to taxanes

Correct Answer: Naphthoquinones commonly act via redox biology rather than tubulin stabilization

Q7. Which functional group modification typically increases naphthoquinone cytotoxicity by enhancing electrophilicity?

• Addition of electron-donating methoxy groups to the ring
• Introduction of strong electron-withdrawing substituents like nitro groups
• Conversion to a saturated cyclohexanone
• Glycosylation at the quinone oxygen

Correct Answer: Introduction of strong electron-withdrawing substituents like nitro groups

Q8. During metabolic reduction of naphthoquinones in vivo, which intermediate is commonly formed?

• Semiquinone radical anion
• Stable epoxide
• Acyl chloride
• Carbocation stabilized by resonance

Correct Answer: Semiquinone radical anion

Q9. Which solvent is generally preferred for extraction of lipophilic naphthoquinones from plant material?

• Water
• Hexane
• Methanol or ethyl acetate
• Saline solution

Correct Answer: Methanol or ethyl acetate

Q10. Which assay is commonly used to assess ROS generation by naphthoquinones in cell studies?

• MTS cell proliferation assay only
• Dichlorofluorescein diacetate (DCFDA) fluorescence assay
• ELISA for interleukin‑2 exclusively
• Coagulation time assay

Correct Answer: Dichlorofluorescein diacetate (DCFDA) fluorescence assay

Q11. Which structural isomer of naphthoquinone has carbonyls at positions 1 and 2 rather than 1 and 4?

• 1,4-naphthoquinone
• 1,2-naphthoquinone
• 2,6-naphthoquinone
• Benzoquinone

Correct Answer: 1,2-naphthoquinone

Q12. Which type of toxicity concern is particularly relevant for naphthoquinone-based compounds during drug development?

• Cardiotoxicity due to hERG channel blockade typical for all naphthoquinones
• Hepatotoxicity from redox cycling and oxidative stress
• Immediate hypersensitivity due to protein crosslinking only
• Ototoxicity independent of dose

Correct Answer: Hepatotoxicity from redox cycling and oxidative stress

Q13. Which in vitro technique can separate naphthoquinones based on polarity for analytical quantification?

• Size‑exclusion chromatography
• Reverse‑phase HPLC with UV detection
• Paper chromatography with ninhydrin staining
• Gel electrophoresis under native conditions

Correct Answer: Reverse‑phase HPLC with UV detection

Q14. Which biosynthetic precursor class leads to many naphthoquinones in plants?

• Isoprenoid diterpenes from the mevalonate pathway
• Shikimate‑derived aromatic polyketide pathways
• Peptide nonribosomal synthetase products exclusively
• Sphingolipids from serine palmitoyltransferase

Correct Answer: Shikimate‑derived aromatic polyketide pathways

Q15. Which pharmacokinetic property is most likely for small lipophilic naphthoquinones?

• Poor membrane permeability and rapid renal excretion unchanged
• Good passive diffusion with high volume of distribution and hepatic metabolism
• Exclusive intravascular retention due to plasma protein covalent binding
• Elimination only via pulmonary exhalation

Correct Answer: Good passive diffusion with high volume of distribution and hepatic metabolism

Q16. In formulation, what strategy can reduce naphthoquinone instability from light and oxygen?

• Use transparent glass containers and open-air storage
• Formulate as protected lipid nanoparticles or include antioxidants and amber packaging
• Dry in sunlight to remove moisture and oxygen
• Add strong oxidants to maintain quinone state

Correct Answer: Formulate as protected lipid nanoparticles or include antioxidants and amber packaging

Q17. Which lab safety concern is important when handling concentrated naphthoquinone extracts?

• Naphthoquinones are inert and require no special PPE
• They can be cytotoxic and skin sensitizers; use gloves, goggles and fume hood
• Only risk is flammability, so no biological precautions are needed
• They only pose a radiological hazard

Correct Answer: They can be cytotoxic and skin sensitizers; use gloves, goggles and fume hood

Q18. Which experimental observation suggests a naphthoquinone acts via electrophilic protein modification?

• Loss of activity in presence of nucleophilic thiol donors like glutathione
• Increased activity after addition of reducing agents
• Enhanced potency with excess cysteine on target protein
• No change in activity upon addition of thiol scavengers

Correct Answer: Loss of activity in presence of nucleophilic thiol donors like glutathione

Q19. Which defensive plant role is commonly associated with naphthoquinones?

• Signaling for pollinator attraction only
• Allelopathy and defense against microbes and herbivores
• Structural component of cell walls providing rigidity
• Primary energy storage molecules like starch

Correct Answer: Allelopathy and defense against microbes and herbivores

Q20. Which spectroscopic feature in 1H NMR would indicate an aromatic proton adjacent to a quinone carbonyl?

• Sharp singlet at around 0.9 ppm
• Downfield aromatic signal between 7–8.5 ppm due to deshielding
• Strong peak at 3.3 ppm typical of exchangeable protons
• Multiplet at 1.2–1.5 ppm for aliphatic methyl groups

Correct Answer: Downfield aromatic signal between 7–8.5 ppm due to deshielding

Q21. Which chemical test can detect quinone functionality qualitatively in plant extracts?

• Ferric chloride test giving violet/green only for phenols
• Reduction with sodium borohydride causing color change or disappearance of quinone chromophore
• Biuret test for peptide bonds
• Molisch test for carbohydrates

Correct Answer: Reduction with sodium borohydride causing color change or disappearance of quinone chromophore

Q22. Which molecular target is least likely to be directly inhibited by naphthoquinones?

• Topoisomerases via oxidative DNA damage or covalent modification
• Electron transport chain components leading to mitochondrial dysfunction
• Tubulin polymerization stabilization identical to taxanes
• Thioredoxin reductase through covalent modification

Correct Answer: Tubulin polymerization stabilization identical to taxanes

Q23. Which strategy improves selectivity of cytotoxic naphthoquinones for tumor cells over normal cells?

• Exploiting higher ROS tolerance in tumor cells without targeting differences
• Designing prodrugs activated by tumor‑overexpressed reductases or hypoxia
• Increasing non-specific lipophilicity to enter all cells equally
• Avoiding any metabolic activation to remain inert

Correct Answer: Designing prodrugs activated by tumor‑overexpressed reductases or hypoxia

Q24. In contrast to Taxus paclitaxel, which statement about naphthoquinone natural products is true?

• Naphthoquinones are diterpenes synthesized via the MEP pathway
• Naphthoquinones are small aromatic compounds often formed via polyketide or shikimate routes
• Naphthoquinones are glycoproteins produced in the endoplasmic reticulum
• Naphthoquinones always act as prodrugs for taxane biosynthesis

Correct Answer: Naphthoquinones are small aromatic compounds often formed via polyketide or shikimate routes

Q25. Which regulatory consideration is important if developing a naphthoquinone-derived drug?

• Ignoring genotoxicity testing is acceptable for natural products
• Conduct thorough genotoxicity and safety pharmacology due to potential DNA damage from ROS
• No need for metabolism studies as natural products are always non-toxic
• Only animal efficacy is required without ADME profiling

Correct Answer: Conduct thorough genotoxicity and safety pharmacology due to potential DNA damage from ROS

Q26. Which chromatographic retention behavior is expected for a hydroxylated naphthoquinone versus its parent naphthoquinone in reverse‑phase HPLC?

• The hydroxylated derivative elutes later (more retained) due to increased polarity
• The hydroxylated derivative elutes earlier due to increased polarity and decreased retention
• Both elute identically regardless of polarity changes
• The parent naphthoquinone becomes ionic and is retained infinitely

Correct Answer: The hydroxylated derivative elutes earlier due to increased polarity and decreased retention

Q27. Which in vivo detoxification pathway commonly conjugates reduced naphthoquinone metabolites?

• Sulfation or glucuronidation during phase II metabolism
• Formation of ether linkages via cytochrome P450
• Conversion to elemental carbon and exhalation
• Direct incorporation into DNA as a nucleotide

Correct Answer: Sulfation or glucuronidation during phase II metabolism

Q28. Which structural feature differentiates a naphthoquinone from a simple benzoquinone in terms of ring system?

• Naphthoquinone has a fused bicyclic aromatic system (naphthalene) while benzoquinone is monocyclic
• Benzoquinone contains a steroid nucleus while naphthoquinone does not
• Naphthoquinone is saturated whereas benzoquinone is aromatic
• Benzoquinone always contains nitrogen in the ring

Correct Answer: Naphthoquinone has a fused bicyclic aromatic system (naphthalene) while benzoquinone is monocyclic

Q29. Which experimental control would help confirm that naphthoquinone cytotoxicity is ROS-dependent?

• Co‑treatment with antioxidants like N-acetylcysteine (NAC) to rescue viability
• Co‑treatment with additional ROS generators to increase effect
• Using only serum-free medium without antioxidants indefinitely
• Measuring cell pH instead of ROS markers

Correct Answer: Co‑treatment with antioxidants like N-acetylcysteine (NAC) to rescue viability

Q30. For exam-style differentiation: Which statement best contrasts Taxus-derived paclitaxel and plant-derived naphthoquinones?

• Both are small aromatic quinones with identical mechanisms
• Paclitaxel is a complex diterpenoid microtubule stabilizer, while naphthoquinones are smaller aromatic redox-active compounds with diverse targets
• Paclitaxel is a simple polyketide quinone produced via shikimate pathway
• Naphthoquinones exclusively stabilize tubulin in the same manner as paclitaxel

Correct Answer: Paclitaxel is a complex diterpenoid microtubule stabilizer, while naphthoquinones are smaller aromatic redox-active compounds with diverse targets

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