B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Pharmaceutical Chemistry 3 — Questions and Answers
Question 1: Which physicochemical property is described by Lipinski's Rule of Five for oral drug-likeness?
- Molecular weight ≤500 Da, logP ≤5, H-bond donors ≤5, H-bond acceptors ≤10 (Correct answer)
- Molecular weight ≤300 Da, logP ≤3, melting point <200°C
- LogP ≤7, PSA ≤140 Ų, rotatable bonds ≤5
- Molecular charge ≤2, pKa between 4–9
Correct answer: Molecular weight ≤500 Da, logP ≤5, H-bond donors ≤5, H-bond acceptors ≤10
Lipinski's Rule of Five states orally bioavailable drugs typically have MW ≤500, logP ≤5, H-bond donors ≤5, and H-bond acceptors ≤10.
Question 2: What is the principal difference between a racemate and a meso compound?
- A racemate has an internal plane of symmetry; a meso compound does not
- A meso compound is optically inactive due to internal symmetry; a racemate is a 50:50 mixture of enantiomers (Correct answer)
- Both are identical in all properties
- A racemate contains diastereomers; a meso compound contains enantiomers
Correct answer: A meso compound is optically inactive due to internal symmetry; a racemate is a 50:50 mixture of enantiomers
A meso compound is achiral due to an internal plane of symmetry, while a racemate is an equimolar mixture of two enantiomers.
Question 3: Which spectroscopic technique is MOST useful for determining the three-dimensional structure of a drug molecule in solution?
- UV-Vis spectroscopy
- Infrared spectroscopy
- Nuclear Magnetic Resonance (NMR) spectroscopy (Correct answer)
- Flame photometry
Correct answer: Nuclear Magnetic Resonance (NMR) spectroscopy
NMR spectroscopy provides detailed information about connectivity, stereochemistry, and three-dimensional conformation of molecules in solution.
Question 4: What is the purpose of a buffer system in a pharmaceutical formulation?
- To increase drug potency
- To maintain a constant pH and ensure drug stability and efficacy (Correct answer)
- To enhance color and appearance
- To reduce the drug's half-life
Correct answer: To maintain a constant pH and ensure drug stability and efficacy
Buffers resist changes in pH, protecting drug stability, preventing degradation, and ensuring consistent therapeutic effect.
Question 5: In phase I metabolic reactions, which enzyme superfamily is primarily responsible for oxidative drug biotransformation?
- UDP-glucuronosyltransferases (UGTs)
- Cytochrome P450 (CYP) enzymes (Correct answer)
- Sulfotransferases (SULTs)
- N-acetyltransferases (NATs)
Correct answer: Cytochrome P450 (CYP) enzymes
Cytochrome P450 enzymes, predominantly in the liver, catalyze oxidative reactions such as hydroxylation and epoxidation in phase I drug metabolism.
Question 6: Which chemical test is used to distinguish aldehydes from ketones using an ammoniacal silver nitrate solution?
- Fehling's test
- Tollens' test (Correct answer)
- Benedict's test
- Iodoform test
Correct answer: Tollens' test
Tollens' test uses ammoniacal silver nitrate; aldehydes reduce Ag⁺ to metallic silver (silver mirror), while ketones do not react.
Question 7: What structural modification converts morphine into heroin (diacetylmorphine)?
- Methylation of the nitrogen atom
- Acetylation of both hydroxyl groups (Correct answer)
- Oxidation of the double bond
- Reduction of the ketone group
Correct answer: Acetylation of both hydroxyl groups
Heroin is formed by acetylating both the 3-OH and 6-OH groups of morphine, increasing lipophilicity and CNS penetration.
B.Pharm. Bachelor of Pharmacy Bachelor of Pharmacy (B.Pharm.) Pharmaceutical Chemistry 3
Which physicochemical property is described by Lipinski's Rule of Five for oral drug-likeness?