KAPS Pharmaceutical Chemistry and Analysis 3 — Questions and Answers
Question 1: Which metabolic reaction is considered a Phase I biotransformation reaction?
- Glucuronidation
- Sulfation
- Oxidation via CYP450 (Correct answer)
- Acetylation
Correct answer: Oxidation via CYP450
CYP450-mediated oxidation is a Phase I reaction that introduces or unmasks a functional group on the drug molecule.
Question 2: In UV-Vis spectroscopy, Beer-Lambert's law states that absorbance is directly proportional to:
- Temperature and pressure
- Concentration and path length (Correct answer)
- Wavelength and refractive index
- Molecular weight and polarity
Correct answer: Concentration and path length
Beer-Lambert's law: A = εcl, where absorbance is proportional to molar absorptivity, concentration, and path length.
Question 3: Which functional group undergoes hydrolysis most readily under aqueous conditions, making it a common instability site in drugs?
- Alkene
- Ester (Correct answer)
- Ether
- Alkane
Correct answer: Ester
Ester bonds are susceptible to hydrolysis by water (acid- or base-catalyzed), making esters a frequent degradation site in pharmaceuticals.
Question 4: What does a positive ninhydrin test indicate in the analysis of pharmaceutical compounds?
- Presence of reducing sugars
- Presence of primary or secondary amines (amino acids) (Correct answer)
- Presence of aldehyde groups
- Presence of phenolic hydroxyl groups
Correct answer: Presence of primary or secondary amines (amino acids)
Ninhydrin reacts with primary and secondary amines to produce a purple color (Ruhemann's purple), used to detect amino acids.
Question 5: Which parameter in chromatography is defined as the ratio of the time a solute spends in the stationary phase to the time it spends in the mobile phase?
- Retention factor (k) (Correct answer)
- Selectivity factor (α)
- Plate number (N)
- Asymmetry factor
Correct answer: Retention factor (k)
The retention factor k = (tR - tM) / tM, representing the ratio of time spent in stationary versus mobile phase.
Question 6: Oxidative stability of a drug formulation can be improved primarily by:
- Increasing pH above 9
- Adding antioxidants such as BHA or ascorbic acid (Correct answer)
- Increasing storage temperature
- Adding preservatives like benzalkonium chloride
Correct answer: Adding antioxidants such as BHA or ascorbic acid
Antioxidants like BHA, BHT, and ascorbic acid scavenge free radicals or reduce oxidizing species to protect drug molecules.
Question 7: Which reaction mechanism involves simultaneous bond breaking and bond formation in a single concerted step, commonly seen in SN2 reactions?
- Radical chain mechanism
- Electrophilic addition
- Nucleophilic substitution via carbocation intermediate
- Backside attack with inversion of configuration (Correct answer)
Correct answer: Backside attack with inversion of configuration
SN2 reactions proceed via backside nucleophilic attack with simultaneous leaving group departure, resulting in Walden inversion.
KAPS Pharmaceutical Chemistry and Analysis 3
Which metabolic reaction is considered a Phase I biotransformation reaction?