Free Master of Chemistry: Pharmaceutical Chemistry Questions and Answers — Questions and Answers

Question 1: In the aforementioned reaction, dichlorocarbene, a reactive intermediate, transforms phenol into 2-hydroxy benzaldehyde.

Shapiro reaction
Mannich reaction
Perkin reaction
Riemer Tiemann reaction (Correct answer)

Correct answer: Riemer Tiemann reaction

The Reimer-Tiemann reaction is a classic organic reaction used for the ortho-formylation of phenols. It involves the reaction of a phenol with chloroform (CHCl3) in the presence of a strong base, which generates dichlorocarbene (:CCl2) as the key reactive intermediate. This intermediate then attacks the activated ortho position of the phenoxide ion, leading to the formation of 2-hydroxy benzaldehyde (salicylaldehyde from phenol).

Question 2: Which of the following chemical reactions produces 2,3-epoxyalcohols from primary and secondary allylic alcohols in an enantioselective manner?

Smiles rearrangement
Mitsunobu reaction
Sharpless epoxidation (Correct answer)
Perkin reaction

Correct answer: Sharpless epoxidation

The Sharpless epoxidation is a highly enantioselective chemical reaction that converts primary and secondary allylic alcohols into 2,3-epoxyalcohols. This reaction utilizes a titanium isopropoxide catalyst, an organic hydroperoxide (typically t-butyl hydroperoxide), and a chiral diethyl tartrate ligand to achieve excellent stereocontrol, producing a specific enantiomer of the epoxide.

Question 3: In this described reaction, which is thought to take place in two phases and involves an aldehyde, a dicarbonyl, and ammonia, the dicarbonyl and ammonia first condense to produce a diimine with an unusual orientation of N-H groups:

Combe’s quinoline synthesis
Pinner pyrimidine synthesis
Debus-Radziszewski imidazole synthesis (Correct answer)
Knorr’s pyrazole synthesis

Correct answer: Debus-Radziszewski imidazole synthesis

The Debus-Radziszewski imidazole synthesis is a multi-component reaction that forms imidazoles from an aldehyde, a dicarbonyl compound (like glyoxal), and ammonia. The mechanism involves initial condensation steps between the dicarbonyl and ammonia to form a diimine, followed by further reactions with the aldehyde and cyclization to yield the imidazole ring. This synthesis is known for its versatility in preparing substituted imidazoles.

Question 4: Which of the following medications has two isomers, R and S, that compete with one another to engage the enzyme binding site, inhibiting the metabolism of the other isomer?

Felodipine
Warfarin (Correct answer)
Propaphenon
Propranalol

Correct answer: Warfarin

Warfarin is an anticoagulant drug administered as a racemic mixture of R- and S-warfarin, which are metabolized by different cytochrome P450 enzymes. S-warfarin is significantly more potent, but both isomers can interact with enzyme binding sites and influence each other's metabolism. This competition and differential metabolism contribute to warfarin's complex pharmacokinetics and the need for careful dosage monitoring due to its narrow therapeutic index.

Question 5: Which of the following antiviral medications inhibits DNA polymerase and is an adenosine analog?

Ritonavir
Lamivudine
Vidarabine (Correct answer)
Zidovudine

Correct answer: Vidarabine

Vidarabine, also known as adenine arabinoside (Ara-A), is an antiviral medication that functions as an adenosine analog. It is a purine nucleoside analog where the ribose sugar is replaced by arabinose. Vidarabine acts by inhibiting viral DNA polymerase, thereby interfering with the replication of viral DNA and consequently suppressing viral proliferation.

Question 6: The 4-amino-5-nitrosopyrimidine and phenylacetonitrile process was originally used to create which of the following drugs?

Alprazolam
Sulfamerazine
Trimethoprim (Correct answer)
Triamterene

Correct answer: Trimethoprim

Trimethoprim is an antibacterial drug that inhibits bacterial dihydrofolate reductase, an enzyme essential for bacterial DNA synthesis. Its synthesis involves specific pyrimidine intermediates, and the reaction between 4-amino-5-nitrosopyrimidine and phenylacetonitrile is a known synthetic route to construct the pyrimidine core of the trimethoprim molecule, leading to the final drug product.

Question 7: In the presence of sodium amide, 3-chloro-N-phenylbenzeneamine reacts with sulfur before being alkylated with 3-o-dimethylaminopropyl chloride.

Ketoconazole
Alprazolam (Correct answer)
Sulfamerazine
Chloropromazine

Correct answer: Alprazolam

The synthesis of Alprazolam, a benzodiazepine derivative, involves a multi-step process. One known route includes the reaction of 3-chloro-N-phenylbenzeneamine with sulfur in the presence of sodium amide, followed by alkylation with 3-o-dimethylaminopropyl chloride. This sequence of reactions is specific to the formation of the complex heterocyclic structure characteristic of Alprazolam.

Question 8: Which of the following is a xanthene oxidase enzyme inhibitor that works to stop the production of uric acid and treat gout?

Dimercaprol
Allopurinol (Correct answer)
Albuterol
Pyrimethamine

Correct answer: Allopurinol

Allopurinol is a widely used medication for the treatment of gout and other conditions involving elevated uric acid levels. It acts as a xanthine oxidase enzyme inhibitor, preventing the conversion of hypoxanthine to xanthine and then to uric acid. By blocking this enzymatic pathway, allopurinol effectively reduces the production of uric acid, thereby lowering its concentration in the blood and preventing the formation of uric acid crystals that cause gout.

Question 9: By converting its phenolic groups to Bis-dimethylcarbamate, which would otherwise undergo rapid pre-systemic metabolism, bambuterol is the prodrug of this medication used to treat asthma.

Levalbuterol
Terbutaline (Correct answer)
Salbutamol
Albuterol

Correct answer: Terbutaline

Bambuterol is a prodrug of Terbutaline, a beta-2 adrenergic agonist used to treat asthma. Bambuterol is designed to improve oral bioavailability and prolong the duration of action by converting the phenolic hydroxyl groups of terbutaline into Bis-dimethylcarbamate esters. These carbamate groups protect the drug from rapid pre-systemic metabolism, allowing for sustained release of the active terbutaline in the body.

Question 10: Which of the following types of enzyme inhibitors is irreversible?

Suicide inhibitor (Correct answer)
Competitive inhibitor
Non competitive inhibitor
uncompetitive inhibitor

Correct answer: Suicide inhibitor

Suicide inhibitors, also known as mechanism-based inhibitors, are a type of irreversible enzyme inhibitor. These molecules are initially unreactive but are processed by the target enzyme's active site, converting them into a highly reactive species. This reactive intermediate then forms a covalent bond with a functional group in the enzyme's active site, permanently inactivating the enzyme.

Question 11: Which of the following is an illustration of a bioisosteric replacement cyanomino group for thioamide?

Uracil and 5-Fluorouracil
Metiamide and cimetidine (Correct answer)
Cholesterol and diazacholesterol
Procainamide and procaine

Correct answer: Metiamide and cimetidine

Bioisosteric replacement involves substituting one functional group with another that exhibits similar physical, chemical, or biological properties. A classic example in drug design is the development of Cimetidine from Metiamide, both H2-receptor antagonists. In this case, the thioamide (thiourea) group in Metiamide was replaced by a cyanoguanidine group (which contains a cyanomino moiety) in Cimetidine, leading to reduced toxicity while maintaining pharmacological activity.

Question 12: Which medication from the list below is not regarded as a lead molecule's fragmented analog?

Meperidine (Correct answer)
Codeine
Metazocine
Levorphanol

Correct answer: Meperidine

Fragmentation is a drug design strategy where a lead molecule is broken down into smaller, simpler components to identify essential pharmacophores or reduce complexity. Codeine, Metazocine, and Levorphanol are structurally related to morphine and can be considered as derivatives or analogs that retain key structural features. Meperidine, while an opioid, has a significantly different and simpler chemical structure that was developed based on a different structural hypothesis, making it less of a direct 'fragmented analog' of morphine compared to the others.

Question 13: Which of the following antitubercular medications is known to cause blindness while the (S,S)-(+)-enantiomer is used to treat tuberculosis?

Ethionamide
Rifampin
Isoniazid
Ethambutol (Correct answer)

Correct answer: Ethambutol

Ethambutol is an antitubercular drug used in the treatment of tuberculosis. It is administered as the (S,S)-(+)-enantiomer, which is the active form. The (R,R)-(-)-enantiomer and the racemic mixture are known to cause optic neuritis, a severe side effect that can lead to blindness, highlighting the critical importance of enantiomeric purity for this medication.

Question 14: This is the only common amino acid that contains an electrophilic side chain and can be changed with suitable nucleophilic agents when creating covalently binding enzyme inhibitors.

Arginine
Tyrosine
Serine (Correct answer)
Threonine

Correct answer: Serine

Serine is a common amino acid with a primary alcohol (-CH2OH) side chain. While the hydroxyl group itself is nucleophilic, its carbon can be activated or modified to become an electrophilic center, allowing it to react with suitable nucleophilic agents. This unique reactivity makes serine a frequent target for covalent modification in enzyme active sites, which is exploited in the design of covalently binding enzyme inhibitors.

Question 15: Which of the following is an example of a medicine with a rationally chosen mechanism as its basis?

Cimetidine
Lisinopril
Vigabatrin (Correct answer)
Sulfanilamide

Correct answer: Vigabatrin

Rational drug design involves creating drugs based on a detailed understanding of the target's structure and mechanism of action. Vigabatrin is an excellent example of a rationally designed drug; it is a mechanism-based (suicide) inhibitor of GABA transaminase. Its structure was specifically engineered to irreversibly inhibit this enzyme, thereby increasing levels of the inhibitory neurotransmitter GABA in the brain to treat epilepsy.

Question 16: What theory of drug-receptor interactions maintains that a receptor is in a state of dynamic equilibrium between an activated form (Ro), which is responsible for the biological response, and an inactive form (To), even in the absence of drugs?

Macromolecular Perturbation Theory
Activation-Aggregation Theory (Correct answer)
Induced fit theory
Occupation theory

Correct answer: Activation-Aggregation Theory

The Activation-Aggregation Theory (also known as the Two-State Model or Conformational Selection Model) proposes that receptors exist in a dynamic equilibrium between an active (Ro or R*) and an inactive (To or R) conformational state, even in the absence of a ligand. Agonists preferentially bind to and stabilize the active state, shifting the equilibrium towards a biological response, while inverse agonists stabilize the inactive state.

Free Master of Chemistry: Pharmaceutical Chemistry Questions and Answers

In the aforementioned reaction, dichlorocarbene, a reactive intermediate, transforms phenol into 2-hydroxy benzaldehyde.