Alkaloids: biosynthesis, isolation and structure (ephedrine, quinine, strychnine, piperine, berberine, vincristine/vinblastine) MCQs With Answer

Introduction

Alkaloids are a diverse group of nitrogen-containing natural products with significant pharmacological importance. This quiz set focuses on the biosynthesis, isolation and structures of key alkaloids—ephedrine, quinine, strychnine, piperine, berberine and the vinca alkaloids (vincristine/vinblastine)—topics essential for M.Pharm students studying phytochemistry. Questions cover amino-acid precursors, signature biosynthetic enzymes (e.g., norcoclaurine synthase, strictosidine synthase), isolation strategies (acid–base extraction, chromatographic techniques) and structural classifications (benzylisoquinoline, indole, piperidine, quinoline frameworks). These MCQs are designed to deepen conceptual understanding and prepare you for advanced discussions in natural product chemistry and pharmaceutical applications.

Q1. Which amino acid is the primary biosynthetic precursor for benzylisoquinoline alkaloids such as berberine?

• Tryptophan
• Tyrosine
• Lysine
• Phenylalanine

Correct Answer: Tyrosine

Q2. Which enzyme catalyzes the stereoselective Pictet–Spengler–type condensation that generates (S)-norcoclaurine in benzylisoquinoline biosynthesis?

• Strictosidine synthase
• Norcoclaurine synthase
• Tyrosine decarboxylase
• Phenylalanine ammonia-lyase

Correct Answer: Norcoclaurine synthase

Q3. Vincristine and vinblastine are formed biosynthetically by coupling which two monomeric indole alkaloids?

• Tryptamine and secologanin
• Catharanthine and vindoline
• Strictosidine and ajmalicine
• Serotonin and geraniol

Correct Answer: Catharanthine and vindoline

Q4. What is the common key intermediate produced by the union of tryptamine and secologanin in many monoterpenoid indole alkaloid pathways?

• Strictosidine
• Norcoclaurine
• Salsolinol
• Camptothecin

Correct Answer: Strictosidine

Q5. The piperidine ring in piperine is biosynthetically derived from which amino acid?

• Arginine
• Ornithine
• Lysine
• Phenylalanine

Correct Answer: Lysine

Q6. Ephedrine-type alkaloids are biosynthesized primarily from which aromatic amino acid?

• Tryptophan
• Tyrosine
• Phenylalanine
• Histidine

Correct Answer: Phenylalanine

Q7. In a standard acid–base extraction for alkaloid isolation, which step transfers the alkaloid into the organic phase as the free base?

• Acidify the aqueous extract to form alkaloid salts
• Add water to dissolve alkaloid salts
• Basify the aqueous solution and extract with an organic solvent
• Evaporate the aqueous layer directly

Correct Answer: Basify the aqueous solution and extract with an organic solvent

Q8. Which TLC visualization reagent is particularly sensitive and widely used for detecting alkaloids?

• Anisaldehyde–sulfuric acid
• Ninhydrin
• Dragendorff’s reagent
• Potassium permanganate

Correct Answer: Dragendorff’s reagent

Q9. Berberine is classified structurally as which type of alkaloid?

• Indole alkaloid
• Pyrrolizidine alkaloid
• Benzylisoquinoline (protoberberine) alkaloid
• Quinoline alkaloid

Correct Answer: Benzylisoquinoline (protoberberine) alkaloid

Q10. The biosynthesis of quinine in Cinchona species requires which two major precursors?

• Tyrosine and cinnamic acid
• Tryptophan and secologanin
• Lysine and isopentenyl pyrophosphate
• Phenylalanine and mevalonate

Correct Answer: Tryptophan and secologanin

Q11. Strychnine belongs to which broad structural class of alkaloids?

• Monoterpenoid indole alkaloids
• Benzylisoquinoline alkaloids
• Pyrrolizidine alkaloids
• Tropane alkaloids

Correct Answer: Monoterpenoid indole alkaloids

Q12. Which analytical technique is most appropriate for separating enantiomers of chiral alkaloids?

• Normal-phase TLC
• Reverse-phase HPLC
• Chiral HPLC
• GC with non-chiral column

Correct Answer: Chiral HPLC

Q13. Which property is characteristic of berberine and aids its detection and identification?

• Strong blue fluorescence under UV
• Quaternary ammonium structure with yellow color and fluorescence
• Volatile oil with camphor-like odor
• Insoluble in most organic solvents

Correct Answer: Quaternary ammonium structure with yellow color and fluorescence

Q14. The biosynthetic formation of vinblastine involves which key reaction step?

• Oxidative decarboxylation of tyrosine
• Dimerization/coupling of catharanthine and vindoline
• Epoxidation of berberine
• Acylation of piperidine with piperic acid

Correct Answer: Dimerization/coupling of catharanthine and vindoline

Q15. Which heterocyclic nucleus is a defining structural feature of quinine?

• Indole nucleus
• Isoquinoline nucleus
• Quinoline nucleus
• Pyrrolidine nucleus

Correct Answer: Quinoline nucleus

Q16. During alkaloid isolation, which reagent is commonly used to basify an acidic aqueous extract and liberate the free base for extraction?

• Sulfuric acid
• Ammonium hydroxide (or sodium hydroxide)
• Hydrochloric acid
• Acetic acid

Correct Answer: Ammonium hydroxide (or sodium hydroxide)

Q17. For determination of absolute stereochemistry of a complex alkaloid, which technique provides unambiguous configuration when single crystals are available?

• 1H NMR spectroscopy
• Infrared spectroscopy (IR)
• Ultraviolet-visible spectroscopy (UV-Vis)
• X-ray crystallography

Correct Answer: X-ray crystallography

Q18. Piperine contains which type of linkage connecting the aromatic (piperoyl) moiety to the piperidine ring?

• Ester
• Amide
• Ether
• Lactone

Correct Answer: Amide

Q19. Historically and pharmaceutically, quinine is commonly isolated and administered as which salt?

• Quinine chloride
• Quinine sulfate
• Quinine nitrate
• Quinine acetate

Correct Answer: Quinine sulfate

Q20. What is the principal cellular mechanism of action of vinca alkaloids such as vincristine and vinblastine?

• Inhibition of DNA topoisomerase II
• Cross-linking of DNA strands
• Inhibition of microtubule polymerization (tubulin binding)
• Activation of G-protein coupled receptors

Correct Answer: Inhibition of microtubule polymerization (tubulin binding)

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