Pharmacy Pharmaceutical Chemistry 5 — Questions and Answers
Question 1: Which functional group is present in ACE inhibitors like captopril that binds to the zinc ion at the active site of angiotensin-converting enzyme?
- Carboxylic acid
- Thiol (-SH) (Correct answer)
- Phosphonate
- Hydroxamic acid
Correct answer: Thiol (-SH)
Captopril's thiol (-SH) group coordinates directly to the zinc ion in the ACE active site, providing potent enzyme inhibition.
Question 2: The process by which a drug salt dissolves and the parent drug is released is called:
- Solvation
- Dissociation (Correct answer)
- Solvolysis
- Hydrolysis
Correct answer: Dissociation
Dissociation of a drug salt in aqueous solution separates the drug molecule (free acid or base) from its counterion, affecting solubility and absorption.
Question 3: Glucuronidation, a major Phase II metabolic reaction, involves the transfer of glucuronic acid from:
- UDP-glucuronic acid (UDPGA) to the drug (Correct answer)
- GDP-glucose to the drug
- ADP-glucuronate to the drug
- Glucose-6-phosphate to the drug
Correct answer: UDP-glucuronic acid (UDPGA) to the drug
UDP-glucuronosyltransferase (UGT) enzymes transfer glucuronic acid from UDPGA to hydroxyl, carboxyl, amino, or thiol groups on drug molecules.
Question 4: Which type of drug-receptor interaction is strongest and irreversible under physiological conditions?
- Hydrogen bonding
- Van der Waals interactions
- Covalent bonding (Correct answer)
- Ionic interactions
Correct answer: Covalent bonding
Covalent bonds are the strongest drug-receptor interactions, generally irreversible, as seen with aspirin's acetylation of COX or organophosphate inhibition of acetylcholinesterase.
Question 5: The polymorphic forms of a drug substance are important in pharmacy because they can differ in:
- Molecular formula only
- Solubility, stability, and bioavailability (Correct answer)
- Only their optical rotation
- Their elemental composition
Correct answer: Solubility, stability, and bioavailability
Polymorphs have the same chemical composition but different crystal packing, affecting dissolution rate, solubility, stability, and ultimately bioavailability.
Question 6: What type of chemical bond is formed when a phenol group in a drug molecule reacts with acetyl-CoA during Phase II metabolism?
- O-glucuronide (ether bond)
- O-sulfate (sulfate ester bond)
- O-acetyl (ester bond) (Correct answer)
- O-methyl (ether bond)
Correct answer: O-acetyl (ester bond)
Acetylation of a phenol by acetyl-CoA via N-acetyltransferase or O-acetyltransferase forms an ester bond (O-acetyl product).
Question 7: Tetracycline antibiotics are chelated and inactivated by divalent cations (Ca2+, Mg2+, Fe2+) because tetracycline contains:
- A thiol group that forms metal sulfides
- A 1,3-diketone/enol system that forms stable chelate complexes with metal ions (Correct answer)
- A phosphate group that precipitates with calcium
- An amine group that reacts with metal ions
Correct answer: A 1,3-diketone/enol system that forms stable chelate complexes with metal ions
The beta-diketone/enol system in tetracyclines forms stable 5- or 6-membered chelate rings with divalent metal ions, reducing oral absorption.
Pharmacy Pharmaceutical Chemistry 5
Which functional group is present in ACE inhibitors like captopril that binds to the zinc ion at the active site of angiotensin-converting enzyme?