B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Pharmaceutical Chemistry 4 — Questions and Answers
Question 1: Which reaction is used industrially to synthesize aspirin from salicylic acid?
- Fischer esterification with acetic acid
- Acetylation with acetic anhydride (Correct answer)
- Grignard reaction with acetyl chloride
- Claisen rearrangement
Correct answer: Acetylation with acetic anhydride
Aspirin is synthesized by acetylating the phenolic -OH of salicylic acid with acetic anhydride under acidic catalysis.
Question 2: What does a high partition coefficient (logP) value indicate about a drug molecule?
- High water solubility and poor membrane permeability
- High lipophilicity and good membrane permeability (Correct answer)
- Strong ionization at physiological pH
- Low plasma protein binding
Correct answer: High lipophilicity and good membrane permeability
A high logP indicates the drug preferentially partitions into the lipid phase, indicating greater lipophilicity and enhanced membrane penetration.
Question 3: Which pharmacophore feature is essential for β-lactam antibiotics to inhibit bacterial cell wall synthesis?
- The amino group at the α-carbon
- The strained four-membered β-lactam ring (Correct answer)
- The carboxylic acid side chain
- The thiazolidine ring nitrogen
Correct answer: The strained four-membered β-lactam ring
The strained β-lactam ring acylates the active-site serine of transpeptidase enzymes, irreversibly inhibiting bacterial cell wall cross-linking.
Question 4: In the context of pharmaceutical chemistry, what is meant by bioisosterism?
- Replacing a drug with a prodrug of identical structure
- Substituting one atom or group with another of similar size and electronic properties to maintain biological activity (Correct answer)
- Using isotopically labeled compounds for pharmacokinetic studies
- Designing drugs that mimic endogenous hormones exactly
Correct answer: Substituting one atom or group with another of similar size and electronic properties to maintain biological activity
Bioisosterism involves substituting atoms or groups with similar steric and electronic properties to optimize pharmacokinetics while retaining pharmacological activity.
Question 5: What is the primary degradation pathway of penicillins in aqueous solution?
- Photodegradation
- Hydrolysis of the β-lactam ring (Correct answer)
- Oxidation of the sulfur atom
- Decarboxylation of the carboxylic acid
Correct answer: Hydrolysis of the β-lactam ring
The strained β-lactam ring is highly susceptible to hydrolysis in aqueous conditions, especially under acidic or basic pH, leading to loss of antibacterial activity.
Question 6: Which analytical technique measures drug concentration in a sample based on the interaction of plane-polarized light with chiral molecules?
- High-performance liquid chromatography (HPLC)
- Polarimetry (Correct answer)
- Mass spectrometry
- Atomic absorption spectroscopy
Correct answer: Polarimetry
Polarimetry measures optical rotation caused by chiral compounds interacting with plane-polarized light, and is used to assess enantiomeric purity.
Question 7: Which class of pharmaceutical excipients is used as a disintegrant in tablet formulations?
- Magnesium stearate
- Sodium starch glycolate (Correct answer)
- Polyvinylpyrrolidone (PVP)
- Microcrystalline cellulose (as binder)
Correct answer: Sodium starch glycolate
Sodium starch glycolate is a superdisintegrant that rapidly absorbs water and swells, breaking apart tablets for drug release.
B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Pharmaceutical Chemistry 4
Which reaction is used industrially to synthesize aspirin from salicylic acid?