Chemistry/Chapter 7: Organic Chemistry
7.2.1 Separation of Racemic Mixture of Thalidomide
The main idea is that most chiral molecules in drugs exist in the form of a racemic mixture, having 50% (+) and 50% (-) isomers.
Explanation level
In the previous section, we learned that the two enantiomers of a chiral drug can have very different biological effects. The drug thalidomide is a tragic example of this: one enantiomer is a safe sedative, while the other is teratogenic (causes birth defects). Most chiral drugs are synthesized as a racemic mixture, containing equal amounts of both enantiomers. This section explains how the racemic mixture of thalidomide can be separated, and how the desired enantiomer can be synthesized selectively.
Main Idea
The main idea is that most chiral molecules in drugs exist in the form of a racemic mixture, having 50% (+) and 50% (-) isomers. However, such drugs are not advised by healthcare professionals in racemic mixture form because the two isomers can have different effects on the human body. One enantiomer may be therapeutically active and have desired effects, while the other may be inactive, less effective, or even harmful. This is evident from the case of thalidomide.
- Optical Resolution: Separating the racemic mixture into its two enantiomers and removing the unwanted (-)-thalidomide enantiomer.
- Chiral Synthesis (Asymmetric Synthesis): Ensuring the formation of a single desired enantiomer, like (+)-thalidomide, while suppressing the formation of the other enantiomer.
Core Concept
The core concept is that the two enantiomers of a chiral drug have different biological activities, so it is desirable to use only the therapeutically active enantiomer. This can be achieved either by separating the racemic mixture after synthesis (resolution) or by designing a synthesis that produces only the desired enantiomer from the start (asymmetric synthesis). The latter is more efficient and is preferred in modern pharmaceutical manufacturing.
Detailed Explanation
The textbook describes two methods for dealing with the racemic mixture of thalidomide.
1. Optical Resolution
Optical resolution involves the separation of the racemic mixture into two enantiomers of thalidomide, removing the (-)-thalidomide enantiomer.
- High-performance liquid chromatography (HPLC): Using a chiral stationary phase that interacts differently with the two enantiomers.
- Crystallization: Using a chiral resolving agent that forms diastereomeric salts with the enantiomers, which have different solubilities and can be separated by crystallization.
- Use of enzymes: Enzymes can selectively react with one enantiomer, allowing it to be separated from the other.
2. Chiral Synthesis (Asymmetric Synthesis)
Chiral synthesis or asymmetric synthesis ensures the formation of a single desired enantiomer, like (+)-thalidomide, suppressing the formation of the other enantiomer.
Asymmetric synthesis utilizes chiral catalysts to create an environment in the chemical reaction that favors the production of the desired enantiomer, suppressing the other enantiomer.
- BINOL Catalyst: A BINOL (1,1'-bi-2-naphthol) catalyst has palladium or rhodium used for the asymmetric synthesis of the (+)-thalidomide enantiomer. This makes the thalidomide drug safer and more reliable, thereby minimizing the risks of the harmful effects of the (-)-thalidomide enantiomer.
- Mechanism: In the asymmetric synthesis reaction of thalidomide, the double bond in thalidomide is selectively hydrogenated in the presence of a chiral catalyst. The chiral catalyst supports the addition of hydrogen to the double bond in the thalidomide molecule, favoring the formation of one enantiomer over the other. In this way, a single pure isomer of thalidomide is produced which can be used for the intended therapeutic effects on our body.
The Problem with Thalidomide: Racemization in the Body
Unfortunately, the two enantiomers of thalidomide soon interconvert, making the administration of a single intended enantiomer ineffective to prevent the harmful effects. This means that even if only the (+)-enantiomer is administered, some of it will convert to the (-)-enantiomer in the body, which can still cause birth defects. This is why the drug is no longer used in pregnant women.
Modern Drug Regulations
Nowadays, different drug authorities across the globe, like the US Food and Drug Administration (FDA), recommend the assessment of enantiomer activity for racemic drugs in the body to ensure the development of a single desired enantiomer. This has led to stricter regulations and a greater emphasis on testing individual enantiomers.
Intermediate Level
The thalidomide tragedy highlighted the importance of enantiomer separation and selective synthesis in drug design. A racemic mixture of thalidomide contains both the therapeutically active (+)-enantiomer and the teratogenic (-)-enantiomer. To eliminate the harmful effects, the racemic mixture can be separated by optical resolution (e.g., using chiral chromatography or crystallization) to obtain pure (+)-thalidomide. Alternatively, asymmetric synthesis can be used to produce only the desired enantiomer. This involves using a chiral catalyst (like a BINOL-palladium complex) that selectively catalyzes the formation of the (+)-enantiomer. However, thalidomide is a special case because the two enantiomers interconvert in the body, so administering only the safe enantiomer does not completely eliminate the risk of birth defects. This is why the drug is not used in pregnant women.
Important Points
- - Racemic mixture: A 50:50 mixture of two enantiomers.
- - Optical resolution: Separation of a racemic mixture into its enantiomers.
- - Asymmetric synthesis: Synthesis that produces a single desired enantiomer.
- - Thalidomide: A chiral drug where one enantiomer is a sedative and the other is teratogenic.
- - Racemization: The interconversion of enantiomers in the body, which can make administering a single enantiomer ineffective.
- - Chiral catalysts: Used in asymmetric synthesis (e.g., BINOL-palladium complex).
- - Modern regulations: FDA recommends testing individual enantiomers for racemic drugs.
Remember
- - Thalidomide: One enantiomer is safe, the other is harmful.
- - Optical resolution: Separating the enantiomers.
- - Asymmetric synthesis: Making only the desired enantiomer.
- - Chiral catalyst: Directs the synthesis to form one enantiomer.
- - Racemization: Interconversion of enantiomers in the body.
- - Modern drug regulations: Emphasize testing single enantiomers.
Common Mistakes
- - Thinking that separating the enantiomers of thalidomide completely solves the problem. The two enantiomers interconvert in the body, so even pure (+)-thalidomide can cause harmful effects.
- - Assuming that all chiral drugs are marketed as racemic mixtures. Many modern drugs are marketed as single enantiomers because of the differences in biological activity.
- - Confusing optical resolution and asymmetric synthesis. Optical resolution separates a mixture; asymmetric synthesis produces only one enantiomer from the start.
- - Forgetting that chiral catalysts are used to control the stereochemistry of a reaction. The chiral environment of the catalyst directs the reaction to produce one enantiomer preferentially.
- - Not recognizing the importance of the thalidomide tragedy. It led to significant changes in drug regulation and the development of safer drugs.
Quick Revision
The drug thalidomide is a tragic example of the importance of enantiomer separation. It exists as a racemic mixture, where one enantiomer is a safe sedative and the other is teratogenic. To produce a safer drug, two approaches can be used: optical resolution, which separates the mixture into its enantiomers, and asymmetric synthesis, which uses a chiral catalyst (like a BINOL-palladium complex) to produce only the desired enantiomer. However, thalidomide is a special case because the two enantiomers interconvert in the body (racemization), so even administering the pure safe enantiomer can still lead to harmful effects. This has led to stricter drug regulations, with the FDA recommending the assessment of enantiomer activity for racemic drugs.
60-Second Revision
Thalidomide is a chiral drug with two enantiomers: one is a safe sedative, the other is teratogenic. To eliminate the harmful enantiomer, the racemic mixture can be separated by optical resolution or the desired enantiomer can be synthesized selectively using asymmetric synthesis with a chiral catalyst. However, because the enantiomers interconvert in the body (racemization), administering a single enantiomer may not be safe. Modern drug regulations require testing individual enantiomers.
Frequently Asked Questions (FAQs)
- High-performance liquid chromatography (HPLC): Using a chiral stationary phase.
- Crystallization: Using a chiral resolving agent that forms diastereomeric salts.
- Enzymatic resolution: Using enzymes that selectively react with one enantiomer.
Q2. How a catalyst can play its role in this separation? Answer: In asymmetric synthesis, a chiral catalyst (such as a BINOL-palladium complex) is used to create a chiral environment that favors the production of one enantiomer over the other. For thalidomide, the chiral catalyst supports the selective hydrogenation of the double bond in the thalidomide molecule, favoring the formation of the (+)-enantiomer. This allows for the selective synthesis of the desired enantiomer, rather than separating a mixture.
Q3. Why is it not effective to administer only the (+)-thalidomide enantiomer to patients? Answer: It is not effective to administer only the (+)-thalidomide enantiomer because the two enantiomers of thalidomide interconvert in the body (racemization). This means that even if only the safe (+)-enantiomer is administered, some of it will convert to the harmful (-)-enantiomer, which can still cause birth defects. Therefore, administering only the (+)-enantiomer does not prevent the harmful effects.
Q4. Why is the use of chiral catalysts preferred in the pharmaceutical industry for synthesizing optical isomers of drugs? Answer: Chiral catalysts are preferred because they allow for asymmetric synthesis, which produces a single desired enantiomer while suppressing the formation of the unwanted enantiomer. This is more efficient and safer than producing a racemic mixture and then separating the enantiomers, as it reduces waste, lowers costs, and ensures the drug is pure and effective.
Q5. What is optical resolution? Answer: Optical resolution is the process of separating a racemic mixture into its two enantiomers. It can be achieved by various methods, including chiral chromatography, crystallization with a chiral resolving agent, and enzymatic resolution.
Q6. What is asymmetric synthesis? Answer: Asymmetric synthesis (or chiral synthesis) is a chemical reaction that produces a single enantiomer preferentially over the other. It uses chiral catalysts or chiral auxiliaries to create a chiral environment that directs the reaction to form the desired enantiomer.
Q7. What is racemization? Answer: Racemization is the process by which one enantiomer is converted into a mixture of both enantiomers (a racemic mixture). It can occur in the body, as in the case of thalidomide, making the administration of a single enantiomer ineffective.
Q8. What is the role of BINOL in the asymmetric synthesis of thalidomide? Answer: BINOL (1,1'-bi-2-naphthol) is a chiral ligand used in the asymmetric synthesis of thalidomide. It forms a complex with a metal catalyst (like palladium or rhodium) that catalyzes the selective hydrogenation of the double bond in the thalidomide molecule, favoring the formation of the (+)-enantiomer.
Q9. What is the significance of the thalidomide tragedy in drug regulation? Answer: The thalidomide tragedy led to stricter drug regulations worldwide. It highlighted the importance of testing individual enantiomers for biological activity and the need for enantioselective synthesis. The FDA now recommends the assessment of enantiomer activity for racemic drugs to ensure that only the safe and effective enantiomer is administered.
Multiple Choice Questions (MCQs)
- Q1. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A mixture of equal amounts of two enantiomers is called a racemic mixture.
- Q2. Which enantiomer of thalidomide is teratogenic?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: B
- Explanation: The (-)-enantiomer of thalidomide is teratogenic.
- Q3. What is the process of separating a racemic mixture into its enantiomers called?
- A. Asymmetric synthesis
- B. Optical resolution
- C. Racemization
- D. Chiral synthesis
- Correct Answer: B
- Explanation: The separation of a racemic mixture into its enantiomers is called optical resolution.
- Q4. What is the process of synthesizing a single enantiomer from achiral starting materials called?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis is the process of synthesizing a single enantiomer preferentially.
- Q5. What is the problem with administering only the (+)-thalidomide enantiomer?
- A. It is not effective as a sedative.
- B. It can racemize in the body, forming the harmful (-)-enantiomer.
- C. It causes birth defects.
- D. It is not absorbed by the body.
- Correct Answer: B
- Explanation: The (+)-enantiomer can racemize in the body, forming the (-)-enantiomer, which is teratogenic.
- Q6. What is the role of a chiral catalyst in asymmetric synthesis?
- A. It separates the enantiomers.
- B. It racemizes the mixture.
- C. It favors the formation of one enantiomer over the other.
- D. It denatures the drug.
- Correct Answer: C
- Explanation: A chiral catalyst creates a chiral environment that favors the formation of one enantiomer.
- Q7. Which of the following is a technique used for optical resolution?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is a technique used for optical resolution.
- Q8. What is the name of the chiral catalyst used in the asymmetric synthesis of thalidomide?
- A. BINOL
- B. Wilkinson's catalyst
- C. Ziegler-Natta catalyst
- D. Lindlar's catalyst
- Correct Answer: A
- Explanation: BINOL is a chiral ligand used in the asymmetric synthesis of thalidomide.
- Q9. Why is the use of chiral catalysts preferred in the pharmaceutical industry?
- A. They are cheaper.
- B. They produce a single enantiomer, which is safer and more effective.
- C. They are faster.
- D. They are more widely available.
- Correct Answer: B
- Explanation: Chiral catalysts allow for the selective synthesis of a single enantiomer, which is safer and more effective than a racemic mixture.
- Q10. What is racemization?
- A. The separation of enantiomers.
- B. The interconversion of enantiomers.
- C. The synthesis of a single enantiomer.
- D. The destruction of a chiral center.
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
Multiple Choice Questions (MCQs)
- Q1. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q2. Which enantiomer of thalidomide is teratogenic?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: B
- Explanation: The (-)-enantiomer of thalidomide is teratogenic.
- Q3. What is the process of separating a racemic mixture into its enantiomers called?
- A. Asymmetric synthesis
- B. Optical resolution
- C. Racemization
- D. Chiral synthesis
- Correct Answer: B
- Explanation: Optical resolution is the separation of a racemic mixture.
- Q4. What is the process of synthesizing a single enantiomer from achiral starting materials called?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis produces a single enantiomer.
- Q5. What is the problem with administering only the (+)-thalidomide enantiomer?
- A. It is not effective as a sedative.
- B. It can racemize in the body, forming the harmful (-)-enantiomer.
- C. It causes birth defects.
- D. It is not absorbed by the body.
- Correct Answer: B
- Explanation: The (+)-enantiomer can racemize in the body.
- Q6. What is the role of a chiral catalyst in asymmetric synthesis?
- A. It separates the enantiomers.
- B. It racemizes the mixture.
- C. It favors the formation of one enantiomer over the other.
- D. It denatures the drug.
- Correct Answer: C
- Explanation: A chiral catalyst favors the formation of one enantiomer.
- Q7. Which of the following is a technique used for optical resolution?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is used for optical resolution.
- Q8. What is the name of the chiral catalyst used in the asymmetric synthesis of thalidomide?
- A. BINOL
- B. Wilkinson's catalyst
- C. Ziegler-Natta catalyst
- D. Lindlar's catalyst
- Correct Answer: A
- Explanation: BINOL is used in the asymmetric synthesis of thalidomide.
- Q9. Why is the use of chiral catalysts preferred in the pharmaceutical industry?
- A. They are cheaper.
- B. They produce a single enantiomer, which is safer and more effective.
- C. They are faster.
- D. They are more widely available.
- Correct Answer: B
- Explanation: Chiral catalysts produce a single enantiomer.
- Q10. What is racemization?
- A. The separation of enantiomers.
- B. The interconversion of enantiomers.
- C. The synthesis of a single enantiomer.
- D. The destruction of a chiral center.
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
Multiple Choice Questions (MCQs)
- Q1. Which of the following is a method for separating a racemic mixture?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is a method for separating enantiomers.
- Q2. Which enantiomer of thalidomide is used as a sedative?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: A
- Explanation: The (+)-enantiomer is used as a sedative.
- Q3. What is the term for the process of converting one enantiomer into a racemic mixture?
- A. Resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Hybridization
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
- Q4. What is the role of BINOL in the synthesis of thalidomide?
- A. It is a chiral catalyst.
- B. It is a solvent.
- C. It is a reactant.
- D. It is a product.
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q5. Why is thalidomide no longer used in pregnant women?
- A. It is not effective.
- B. It causes birth defects.
- C. It is too expensive.
- D. It is not available.
- Correct Answer: B
- Explanation: Thalidomide causes birth defects.
- Q6. What is the term for the synthesis of a single enantiomer?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis is the synthesis of a single enantiomer.
- Q7. What is the purpose of optical resolution?
- A. To synthesize a single enantiomer.
- B. To separate a racemic mixture into its enantiomers.
- C. To racemize a mixture.
- D. To destroy a chiral center.
- Correct Answer: B
- Explanation: Optical resolution separates a racemic mixture.
- Q8. Which of the following is a chiral catalyst?
- A. BINOL
- B. Palladium on carbon
- C. Platinum
- D. Nickel
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q9. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q10. Why is it important to separate enantiomers in drug manufacturing?
- A. Because they have different physical properties.
- B. Because they can have different biological activities.
- C. Because they have different molecular formulas.
- D. Because they have different colors.
- Correct Answer: B
- Explanation: Enantiomers can have different biological activities.
Multiple Choice Questions (MCQs)
- Q1. Which of the following is a method for separating a racemic mixture?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is a method for separating enantiomers.
- Q2. Which enantiomer of thalidomide is used as a sedative?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: A
- Explanation: The (+)-enantiomer is used as a sedative.
- Q3. What is the term for the process of converting one enantiomer into a racemic mixture?
- A. Resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Hybridization
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
- Q4. What is the role of BINOL in the synthesis of thalidomide?
- A. It is a chiral catalyst.
- B. It is a solvent.
- C. It is a reactant.
- D. It is a product.
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q5. Why is thalidomide no longer used in pregnant women?
- A. It is not effective.
- B. It causes birth defects.
- C. It is too expensive.
- D. It is not available.
- Correct Answer: B
- Explanation: Thalidomide causes birth defects.
- Q6. What is the term for the synthesis of a single enantiomer?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis is the synthesis of a single enantiomer.
- Q7. What is the purpose of optical resolution?
- A. To synthesize a single enantiomer.
- B. To separate a racemic mixture into its enantiomers.
- C. To racemize a mixture.
- D. To destroy a chiral center.
- Correct Answer: B
- Explanation: Optical resolution separates a racemic mixture.
- Q8. Which of the following is a chiral catalyst?
- A. BINOL
- B. Palladium on carbon
- C. Platinum
- D. Nickel
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q9. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q10. Why is it important to separate enantiomers in drug manufacturing?
- A. Because they have different physical properties.
- B. Because they can have different biological activities.
- C. Because they have different molecular formulas.
- D. Because they have different colors.
- Correct Answer: B
- Explanation: Enantiomers can have different biological activities.
Multiple Choice Questions (MCQs)
- Q1. Which of the following is a method for separating a racemic mixture?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is a method for separating enantiomers.
- Q2. Which enantiomer of thalidomide is used as a sedative?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: A
- Explanation: The (+)-enantiomer is used as a sedative.
- Q3. What is the term for the process of converting one enantiomer into a racemic mixture?
- A. Resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Hybridization
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
- Q4. What is the role of BINOL in the synthesis of thalidomide?
- A. It is a chiral catalyst.
- B. It is a solvent.
- C. It is a reactant.
- D. It is a product.
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q5. Why is thalidomide no longer used in pregnant women?
- A. It is not effective.
- B. It causes birth defects.
- C. It is too expensive.
- D. It is not available.
- Correct Answer: B
- Explanation: Thalidomide causes birth defects.
- Q6. What is the term for the synthesis of a single enantiomer?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis is the synthesis of a single enantiomer.
- Q7. What is the purpose of optical resolution?
- A. To synthesize a single enantiomer.
- B. To separate a racemic mixture into its enantiomers.
- C. To racemize a mixture.
- D. To destroy a chiral center.
- Correct Answer: B
- Explanation: Optical resolution separates a racemic mixture.
- Q8. Which of the following is a chiral catalyst?
- A. BINOL
- B. Palladium on carbon
- C. Platinum
- D. Nickel
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q9. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q10. Why is it important to separate enantiomers in drug manufacturing?
- A. Because they have different physical properties.
- B. Because they can have different biological activities.
- C. Because they have different molecular formulas.
- D. Because they have different colors.
- Correct Answer: B
- Explanation: Enantiomers can have different biological activities.
Multiple Choice Questions (MCQs)
- Q1. What is the name of the chiral catalyst used in the asymmetric synthesis of thalidomide?
- A. BINOL
- B. Wilkinson's catalyst
- C. Ziegler-Natta catalyst
- D. Lindlar's catalyst
- Correct Answer: A
- Explanation: BINOL is the chiral catalyst used.
- Q2. What is the purpose of optical resolution?
- A. To synthesize a single enantiomer.
- B. To separate a racemic mixture into its enantiomers.
- C. To racemize a mixture.
- D. To destroy a chiral center.
- Correct Answer: B
- Explanation: Optical resolution separates a racemic mixture.
- Q3. Which enantiomer of thalidomide is teratogenic?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: B
- Explanation: The (-)-enantiomer is teratogenic.
- Q4. What is the term for the interconversion of enantiomers in the body?
- A. Resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Hybridization
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
- Q5. Why is thalidomide no longer used in pregnant women?
- A. It is not effective.
- B. It causes birth defects.
- C. It is too expensive.
- D. It is not available.
- Correct Answer: B
- Explanation: Thalidomide causes birth defects.
- Q6. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q7. Which of the following is a chiral catalyst?
- A. BINOL
- B. Palladium on carbon
- C. Platinum
- D. Nickel
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q8. What is the process of synthesizing a single enantiomer from achiral starting materials called?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis produces a single enantiomer.
- Q9. Why is it important to separate enantiomers in drug manufacturing?
- A. Because they have different physical properties.
- B. Because they can have different biological activities.
- C. Because they have different molecular formulas.
- D. Because they have different colors.
- Correct Answer: B
- Explanation: Enantiomers can have different biological activities.
- Q10. Which of the following is a method for separating a racemic mixture?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is used to separate enantiomers.
Multiple Choice Questions (MCQs)
- Q1. Which of the following is a method for separating a racemic mixture?
- A. Distillation
- B. Chiral chromatography
- C. Filtration
- D. Evaporation
- Correct Answer: B
- Explanation: Chiral chromatography is a method for separating enantiomers.
- Q2. Which enantiomer of thalidomide is used as a sedative?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: A
- Explanation: The (+)-enantiomer is used as a sedative.
- Q3. What is the term for the process of converting one enantiomer into a racemic mixture?
- A. Resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Hybridization
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
- Q4. What is the role of BINOL in the synthesis of thalidomide?
- A. It is a chiral catalyst.
- B. It is a solvent.
- C. It is a reactant.
- D. It is a product.
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q5. Why is thalidomide no longer used in pregnant women?
- A. It is not effective.
- B. It causes birth defects.
- C. It is too expensive.
- D. It is not available.
- Correct Answer: B
- Explanation: Thalidomide causes birth defects.
- Q6. What is the term for the synthesis of a single enantiomer?
- A. Optical resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Crystallization
- Correct Answer: C
- Explanation: Asymmetric synthesis is the synthesis of a single enantiomer.
- Q7. What is the purpose of optical resolution?
- A. To synthesize a single enantiomer.
- B. To separate a racemic mixture into its enantiomers.
- C. To racemize a mixture.
- D. To destroy a chiral center.
- Correct Answer: B
- Explanation: Optical resolution separates a racemic mixture.
- Q8. Which of the following is a chiral catalyst?
- A. BINOL
- B. Palladium on carbon
- C. Platinum
- D. Nickel
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
- Q9. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q10. Why is it important to separate enantiomers in drug manufacturing?
- A. Because they have different physical properties.
- B. Because they can have different biological activities.
- C. Because they have different molecular formulas.
- D. Because they have different colors.
- Correct Answer: B
- Explanation: Enantiomers can have different biological activities.
Multiple Choice Questions (MCQs)
- Q1. What is the name of the chiral catalyst used in the asymmetric synthesis of thalidomide?
- A. BINOL
- B. Wilkinson's catalyst
- C. Ziegler-Natta catalyst
- D. Lindlar's catalyst
- Correct Answer: A
- Explanation: BINOL is the chiral catalyst used.
- Q2. What is the purpose of optical resolution?
- A. To synthesize a single enantiomer.
- B. To separate a racemic mixture into its enantiomers.
- C. To racemize a mixture.
- D. To destroy a chiral center.
- Correct Answer: B
- Explanation: Optical resolution separates a racemic mixture.
- Q3. Which enantiomer of thalidomide is teratogenic?
- A. (+)-thalidomide
- B. (-)-thalidomide
- C. Both
- D. Neither
- Correct Answer: B
- Explanation: The (-)-enantiomer is teratogenic.
- Q4. What is the term for the interconversion of enantiomers in the body?
- A. Resolution
- B. Racemization
- C. Asymmetric synthesis
- D. Hybridization
- Correct Answer: B
- Explanation: Racemization is the interconversion of enantiomers.
- Q5. Why is thalidomide no longer used in pregnant women?
- A. It is not effective.
- B. It causes birth defects.
- C. It is too expensive.
- D. It is not available.
- Correct Answer: B
- Explanation: Thalidomide causes birth defects.
- Q6. What is the term for a mixture of equal amounts of two enantiomers?
- A. Racemic mixture
- B. Meso compound
- C. Chiral mixture
- D. Enantiomeric mixture
- Correct Answer: A
- Explanation: A racemic mixture consists of equal amounts of two enantiomers.
- Q7. Which of the following is a chiral catalyst?
- A. BINOL
- B. Palladium on carbon
- C. Platinum
- D. Nickel
- Correct Answer: A
- Explanation: BINOL is a chiral catalyst.
Q8. What is the process
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7.2.1 Separation of Racemic Mixture of Thalidomide
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Key Point 1
- Racemic mixture: 50:50 of (+)- and (-)-enantiomers.
Key Point 2
- Thalidomide: (+)- safe, (-)- teratogenic.
Key Point 3
- Optical resolution: Separate the enantiomers.
Key Point 4
- Asymmetric synthesis: Make only the desired enantiomer.
Key Point 5
- Chiral catalyst: Controls the stereochemistry.
Key Point 6
- BINOL: A chiral ligand used in asymmetric synthesis.
Key Point 7
- Racemization: Interconversion of enantiomers in the body.
Key Point 8
- FDA: Recommends testing enantiomers.
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