Iridoids – Gentian MCQs With Answer

Iridoids – Gentian MCQs With Answer
Iridoids are a class of monoterpenoid secondary metabolites characterized by a cyclopentanoid pyran framework, abundant in Gentiana species. For B.Pharm students, understanding iridoid chemistry, biosynthesis (from geraniol via iridoid synthase), common gentian markers such as gentiopicroside and amarogentin, and pharmacological roles (bitter stomachic, choleretic, hepatoprotective, anti-inflammatory) is essential for pharmacognosy, phytochemistry, and formulation studies. Key laboratory skills include extraction (aqueous/alcoholic), HPLC/HPTLC standardization, identification by MS/NMR, and stability/quality control considerations. This set emphasizes detailed concepts, analytical methods, and therapeutic relevance to prepare you for exams and practical work. Now let’s test your knowledge with 30 MCQs on this topic.

Q1. What structural feature defines iridoids?

• A bicyclic diterpene skeleton
• A cyclopentanoid pyran monoterpenoid framework
• A steroidal tetracyclic core
• A flavonoid C6-C3-C6 backbone

Correct Answer: A cyclopentanoid pyran monoterpenoid framework

Q2. Which biosynthetic precursor mainly gives rise to iridoids?

• Squalene
• Geraniol (a monoterpenoid alcohol)
• Acetyl-CoA via polyketide pathway
• Shikimic acid

Correct Answer: Geraniol (a monoterpenoid alcohol)

Q3. Which enzyme catalyzes the cyclization step in iridoid biosynthesis?

• Iridoid synthase (ISY)
• Terpene cyclase
• Polyketide synthase
• Phenylalanine ammonia-lyase

Correct Answer: Iridoid synthase (ISY)

Q4. Gentian roots are especially rich in which iridoid glycoside used as a marker?

• Menthol
• Gentiopicroside
• Quercetin
• Curcumin

Correct Answer: Gentiopicroside

Q5. Amarogentin, found in Gentiana, is best known for which property?

• Strong antioxidant activity
• Extremely high bitterness
• Anticoagulant effect
• Sedative action

Correct Answer: Extremely high bitterness

Q6. What distinguishes secoiridoids from iridoids?

• Secoiridoids lack oxygen atoms
• Secoiridoids have an opened (cleaved) cyclopentane ring
• Secoiridoids are polyphenolic polymers
• Secoiridoids are nitrogen-containing alkaloids

Correct Answer: Secoiridoids have an opened (cleaved) cyclopentane ring

Q7. Which analytical technique is most commonly used for quantitative determination of gentiopicroside?

• Thin-layer chromatography with visual inspection only
• High-performance liquid chromatography (HPLC)
• Polarimetry
• Atomic absorption spectroscopy

Correct Answer: High-performance liquid chromatography (HPLC)

Q8. Which solvent system is frequently used for extracting iridoid glycosides from gentian root?

• Hexane
• Methanol or aqueous methanol
• Chloroform
• Petroleum ether

Correct Answer: Methanol or aqueous methanol

Q9. In TLC analysis of gentian extracts, which visualization helps detect iridoid glycosides?

• Dragendorff reagent (for alkaloids)
• UV light and specific spray reagents after hydrolysis
• Flame test
• Fluorescamine reagent

Correct Answer: UV light and specific spray reagents after hydrolysis

Q10. Which pharmacological action is classically attributed to gentian iridoids?

• Cardiac glycoside activity
• Bitter stomachic and choleretic effects
• Strong opioid-like analgesia
• Direct antihypertensive vasodilation

Correct Answer: Bitter stomachic and choleretic effects

Q11. Which gentian iridoid is often used as a bitterness reference standard?

• Gentiopicroside
• Amarogentin
• Swertiamarin
• Loganin

Correct Answer: Amarogentin

Q12. What is a common pharmacokinetic change for iridoid glycosides after oral administration?

• They are highly volatile and exhaled unchanged
• Glycosides are hydrolyzed to aglycones by gut enzymes/microbiota
• They form irreversible adducts with hemoglobin
• They are completely absorbed intact without metabolism

Correct Answer: Glycosides are hydrolyzed to aglycones by gut enzymes/microbiota

Q13. Which species belongs to Gentiana used pharmaceutically for bitter preparations?

• Gentiana lutea
• Ginkgo biloba
• Digitalis purpurea
• Panax ginseng

Correct Answer: Gentiana lutea

Q14. Which NMR signal region would you expect for glycosidic protons in iridoid glycosides?

• 0.5–1.5 ppm (aliphatic methyls)
• 3.0–5.5 ppm (sugars and oxygenated methines)
• 6.5–8.5 ppm (aromatic protons)
• 9.5–10.5 ppm (aldehydic protons only)

Correct Answer: 3.0–5.5 ppm (sugars and oxygenated methines)

Q15. Which stability factor most threatens iridoid glycosides during processing?

• Exposure to neutral buffers
• Acidic hydrolysis and heat leading to glycosidic cleavage
• Storage at low humidity only
• Light-insensitive decomposition exclusively

Correct Answer: Acidic hydrolysis and heat leading to glycosidic cleavage

Q16. For quality control of gentian extracts, which parameter is most relevant?

• Total alkaloid content
• Content of marker iridoid glycosides (e.g., gentiopicroside)
• Chlorophyll concentration
• Essential oil refractive index

Correct Answer: Content of marker iridoid glycosides (e.g., gentiopicroside)

Q17. Which biological activity has been demonstrated for several iridoids in preclinical studies?

• Pro-inflammatory cytokine induction
• Anti-inflammatory and hepatoprotective effects
• Potent DNA intercalation causing mutagenesis
• Selective beta-adrenergic agonism

Correct Answer: Anti-inflammatory and hepatoprotective effects

Q18. Which preparative form is commonly used to deliver gentian’s bitter principles in pharmacy?

• Volatile oil inhalers
• Tinctures or ethanolic extracts
• Intravenous injections of raw powder
• Topical ointments only

Correct Answer: Tinctures or ethanolic extracts

Q19. Swertiamarin is classified as which type of compound?

• An iridoid glycoside
• A flavonol glycoside
• A triterpenoid saponin
• A bisbenzylisoquinoline alkaloid

Correct Answer: An iridoid glycoside

Q20. Which mass spectrometry information is most useful for confirming an iridoid glycoside?

• Characteristic molecular ion and loss of sugar (neutral loss of 162 Da for hexose)
• Only isotope pattern of chlorine
• Presence of intact nitrogen adducts only
• Very high m/z > 2000 peaks exclusively

Correct Answer: Characteristic molecular ion and loss of sugar (neutral loss of 162 Da for hexose)

Q21. Which phytopharmaceutical concept is critical when standardizing gentian root preparations?

• Standardize by color intensity only
• Standardize by content of bioactive marker iridoids
• Standardize by ash value alone
• Standardize by smell profile

Correct Answer: Standardize by content of bioactive marker iridoids

Q22. Which of the following is a common in vitro test to screen anti-inflammatory potential of iridoids?

• COX or NO inhibition assays
• Blood coagulation time only
• Skin irritation patch test in humans
• Chromatographic retention time shifts

Correct Answer: COX or NO inhibition assays

Q23. In Gentian pharmacognosy, what is the primary sensory basis for its traditional use as a digestive aid?

• Sweet flavor stimulating salivation
• Bitter taste stimulating digestive secretions and appetite
• Sour taste neutralizing stomach acid
• Umami flavor aiding protein digestion

Correct Answer: Bitter taste stimulating digestive secretions and appetite

Q24. Which regulatory practice is important for herbal products containing gentian iridoids?

• Ignoring batch-to-batch variation
• Batch standardization and stability testing
• Assurance of absence of aromatic oils only
• Only organoleptic assessment

Correct Answer: Batch standardization and stability testing

Q25. Which structural change converts an iridoid into a secoiridoid?

• Addition of a benzene ring
• Oxidative cleavage of the cyclopentane ring to open form
• Saturation of all double bonds
• Removal of sugar moiety only

Correct Answer: Oxidative cleavage of the cyclopentane ring to open form

Q26. Which chromatographic visualization reagent can be used to detect glycosides after TLC separation?

• Anisaldehyde–sulfuric acid reagent
• Iodine vapor only
• Ninhydrin reagent specific for sugars
• None; glycosides are invisible on TLC

Correct Answer: Anisaldehyde–sulfuric acid reagent

Q27. Which safety consideration is relevant when formulating gentian extracts into oral dosage forms?

• Potential bitter taste requiring masking or suitable excipients
• High flammability making them unsuitable for capsules
• Incompatibility with water only
• Guaranteed lack of interaction with drugs

Correct Answer: Potential bitter taste requiring masking or suitable excipients

Q28. Which public health application might benefit from gentian iridoid research?

• Development of synthetic opioids
• Discovery of safe digestive bitters and hepatoprotective agents
• Replacement for insulin therapy
• Use as a primary vaccine adjuvant

Correct Answer: Discovery of safe digestive bitters and hepatoprotective agents

Q29. Which laboratory method is preferred for fingerprinting gentian extracts in quality control?

• Naked-eye comparison only
• HPTLC or HPLC fingerprinting combined with reference standards
• Simple pH measurement
• Counting root fragments visually

Correct Answer: HPTLC or HPLC fingerprinting combined with reference standards

Q30. What is a likely reason for different iridoid profiles among Gentiana species?

• Differences in soil mineral sodium only
• Genetic variation, environmental factors, and biosynthetic enzyme expression
• Uniform chemistry across all species regardless of environment
• Presence of animal contaminants only

Correct Answer: Genetic variation, environmental factors, and biosynthetic enzyme expression

G S Sachin

I am a Registered Pharmacist under the Pharmacy Act, 1948, and the founder of PharmacyFreak.com. I hold a Bachelor of Pharmacy degree from Rungta College of Pharmaceutical Science and Research. With a strong academic foundation and practical knowledge, I am committed to providing accurate, easy-to-understand content to support pharmacy students and professionals. My aim is to make complex pharmaceutical concepts accessible and useful for real-world application.

Mail- Sachin@pharmacyfreak.com