Glycosides: digitoxin, glycyrrhizin, bacosides, quercetin – chemistry and isolation MCQs With Answer

Glycosides: digitoxin, glycyrrhizin, bacosides, quercetin – chemistry and isolation MCQs With Answer

This quiz set focuses on important plant glycosides encountered in M.Pharm phytochemistry: digitoxin (a cardiac glycoside), glycyrrhizin (sweet triterpenoid glycoside), bacosides (triterpenoid saponins from Bacopa), and quercetin (a flavonol aglycone). Questions emphasize chemical structures, characteristic functional groups, sugar moieties, key chemical tests, hydrolysis products, spectral features and modern isolation/purification techniques (solvent extraction, chromatographic separation, hydrolysis and derivatization). Designed for M.Pharm students, these MCQs will strengthen conceptual understanding and practical approaches used during isolation, identification and characterization of glycosides in research and quality control labs.

Q1. Which structural feature is characteristic of digitoxin among cardiac glycosides?

• A steroidal aglycone attached to three deoxy-sugars
• A flavonoid nucleus with a rutinose moiety
• An oleanane-type triterpenoid saponin core
• A C-glycosylated xanthone scaffold

Correct Answer: A steroidal aglycone attached to three deoxy-sugars

Q2. Glycyrrhizin isolated from Glycyrrhiza glabra is best described chemically as:

• A flavonol glycoside of quercetin
• A triterpenoid diglucuronide of glycyrrhetic acid
• A cardenolide with a five-membered lactone
• A monoterpene glycoside containing glucose only

Correct Answer: A triterpenoid diglucuronide of glycyrrhetic acid

Q3. Which reagent is classically used to detect the unsaturated lactone in cardenolide glycosides like digitoxin?

• Kedde’s reagent
• Shinoda reagent
• Murexide reagent
• Benedict’s reagent

Correct Answer: Kedde’s reagent

Q4. Which hydrolysis product is expected after acid hydrolysis of glycyrrhizin?

• Quercetin and glucose
• Glycyrrhetinic (glycyrrhetic) acid and glucuronic acid residues
• Digitoxigenin and digitoxose
• Bacoside aglycone and rhamnose

Correct Answer: Glycyrrhetinic (glycyrrhetic) acid and glucuronic acid residues

Q5. Bacosides from Bacopa monnieri are classified chemically as which type of compounds?

• Flavonol glycosides
• Triterpenoid saponin glycosides
• Iridoid monoterpenes
• Alkaloid glycosides

Correct Answer: Triterpenoid saponin glycosides

Q6. Quercetin commonly occurs in plants as glycosides. Which sugar moiety is present in rutin (a common quercetin glycoside)?

• Two glucuronic acids
• Rutinose (rhamnose + glucose disaccharide)
• Three digitoxose units
• Fructose only

Correct Answer: Rutinose (rhamnose + glucose disaccharide)

Q7. Which solvent is most frequently used for the initial extraction of quercetin glycosides from plant material?

• n-Hexane
• Methanol or aqueous methanol
• Carbon tetrachloride
• Pyridine

Correct Answer: Methanol or aqueous methanol

Q8. During isolation of digitoxin from Digitalis species, which step is commonly applied to remove chlorophyll and non-polar impurities?

• Partitioning with petroleum ether or hexane
• Acid hydrolysis with 2 N HCl
• Precipitation with lead acetate
• Direct silylation and GC analysis

Correct Answer: Partitioning with petroleum ether or hexane

Q9. Which chromatographic technique is preferred for analytical separation and quantification of glycyrrhizin in herbal extracts?

• Normal-phase silica TLC with hexane
• Reversed-phase HPLC with UV detection
• Gas chromatography without derivatization
• Paper chromatography with benzene

Correct Answer: Reversed-phase HPLC with UV detection

Q10. Which spectroscopic feature is most characteristic of quercetin aglycone in UV-visible spectroscopy?

• An intense band near 260 nm and a bathochromic band near 370–380 nm
• A single maximum at 210 nm only
• No UV absorption due to absence of conjugation
• An absorption maximum at 500 nm giving a red color

Correct Answer: An intense band near 260 nm and a bathochromic band near 370–380 nm

Q11. Which general chemical test indicates the presence of all glycosides (sugar moiety) in an extract?

• Molisch’s test
• Kedde’s test
• Bornträger’s test
• Froth (foam) test

Correct Answer: Molisch’s test

Q12. In the structural classification of cardiac glycosides, digitoxin belongs to which subgroup?

• Bufadienolides
• Cardenolides (steroid glycosides with 5-membered lactone)
• Steroidal saponins with oleanane aglycone
• Flavonoid glycosides

Correct Answer: Cardenolides (steroid glycosides with 5-membered lactone)

Q13. Which preparative technique is commonly used to enrich saponin/bacoside fractions from an ethanolic extract?

• Liquid–liquid partitioning with n-butanol
• Direct crystallization from hexane
• Steam distillation
• Fractional precipitation with ammonium sulfate

Correct Answer: Liquid–liquid partitioning with n-butanol

Q14. Which acid hydrolysis condition is typically used to cleave O-glycosidic bonds of flavonoid glycosides to obtain aglycone quercetin?

• Strong alkaline hydrolysis at pH 13 and 100 °C
• Mild acid hydrolysis with diluted HCl or H2SO4 in alcohol under reflux
• Neutral hydrolysis with water at room temperature only
• Oxidative cleavage with KMnO4

Correct Answer: Mild acid hydrolysis with diluted HCl or H2SO4 in alcohol under reflux

Q15. Which mass spectrometric feature helps to identify glycosides versus their aglycones?

• Presence of characteristic sugar-loss fragment ions (e.g., -162 for hexose)
• Absence of any fragment peaks
• Only a single molecular ion with no fragments
• High volatility without derivatization

Correct Answer: Presence of characteristic sugar-loss fragment ions (e.g., -162 for hexose)

Q16. Which reagent is useful in TLC visualization for many flavonoids including quercetin derivatives?

• Anisaldehyde-sulfuric acid universally for all glycosides only
• Aluminum chloride (AlCl3) spray which gives characteristic fluorescence or color shifts
• Dragendorff’s reagent for flavonoids
• 2,4-DNP reagent for sugars

Correct Answer: Aluminum chloride (AlCl3) spray which gives characteristic fluorescence or color shifts

Q17. When isolating glycyrrhizin, which property of glycyrrhizin makes water-miscible alcoholic extraction favorable?

• High volatility allowing steam distillation
• Good solubility in polar solvents due to diglucuronide moiety
• Extreme insolubility in polar solvents
• Strong absorption into nonpolar lipids

Correct Answer: Good solubility in polar solvents due to diglucuronide moiety

Q18. Which statement about digitoxin stability is correct and relevant to isolation?

• Digitoxin is very water-soluble and therefore lost during organic extraction
• Digitoxin is stable to mild acid but can be degraded by strong alkaline conditions
• Digitoxin is a volatile terpene lost on drying
• Digitoxin is a polymer and cannot be separated by chromatography

Correct Answer: Digitoxin is stable to mild acid but can be degraded by strong alkaline conditions

Q19. Which chromatographic stationary phase is typically chosen for separation of complex saponin fractions such as bacosides?

• Normal-phase silica gel only with hexane eluents
• Reversed-phase C18 (RP-18) media or Diaion HP-20 for polar saponins
• GC capillary columns without derivatization
• Ion exchange columns for neutral terpenes

Correct Answer: Reversed-phase C18 (RP-18) media or Diaion HP-20 for polar saponins

Q20. For structural confirmation of a glycoside’s sugar identity after hydrolysis, which technique is most appropriate?

• Direct NMR of crude extract without hydrolysis
• Derivatization of released monosaccharides followed by GC-MS or HPLC comparison with standards
• Visual color comparison of crude powder
• Melting point determination of the intact glycoside

Correct Answer: Derivatization of released monosaccharides followed by GC-MS or HPLC comparison with standards

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