Chirality And Stereoisomers - Dr. Neufeldt
-
Page 1 of 16Here is a quick refresher for stereochemistry:
-
.jpg "Chirality And Stereoisomers - Dr. Neufeldt - Quiz")
About This Quiz
Welcome to BACON AT UCLA.
You have recently been learning about chirality and stereoisomers. In this tutorial, you'll see how these topics connect to artificial sweeteners, medicines, the origins of life, and more! The estimated time needed to complete this tutorial is: 20-30 minutes.
Note: The tutorial includes short pre-BACON and post-BACON quizzes. Only your grades on See morethe post-BACON quiz will be recorded. There are also questions embedded throughout the tutorial, on which you will not be graded.
YOU MUST LOG IN AND COMPLETE THE TUTORIAL TO RECEIVE CREDIT.
Your password is your nine-digit UID (e. G. 001234567)
If you are having login issues please email: [email protected]/* */
WARNING…ONCE YOU START THIS TUTORIAL, THERE IS NO GOING BACK!
(LITERALLY – IT’S A SOFTWARE LIMITATION…SORRY!)
Also, please be very careful when selecting your answers because the software does not let you change your response after you click on an answer.
Quiz Preview
- 2.
Page 2 of 16 Here is a quick refresher of enantiomers and diastereomers:
- 3.
Page 3 of 16 Although enantiomers have the same physical properties (e.g.. melting point, boiling point, density, and solubility), they will usually interact differently with other chiral molecules. A common example of this involves the taste and smell receptors in the tongue and nose, respectively. Two famous examples involve the compounds limonene and carvone. The (–) enantiomer of limonene is recognized as an lemon smell, while the (+) enantiomer is recognized as a orange smell. Also, while (–)-carvone has a spearmint smell, (+)-carvone has a dill or caraway smell.
- 4.
Page 4 of 16 - SOLUTIONS Assign the absolute configuration in (–)-limonene:a. Rb. SExplanation: The correct answer is B (S configuration) – the explanation is shown below.
- 5.
Page 5 of 16 Another interesting example involves the artificial sweetener Equal and its key ingredient aspartame. Aspartame was first discovered in the 1960s and is now a common ingredient in consumer products, such as candy and soft drinks. Did you know that only one enantiomer of aspartame is used as a sweetener? The (–)-enantiomer of aspartame is sweet, but the (+)-enantiomer of aspartame is bitter. The difference in taste comes from the two enantiomers interacting differently with our chiral taste receptors.
- 6.
Page 6 of 16 – SOLUTIONS Identify the absolute configuration of the two chiral centers. a. Blue = R; Red = Sb. Blue = R; Red = Rc. Blue = S; Red = Sd. Blue = S; Red = RExplanation: The correct answer is C – the explanation is shown below. Make sure the lowest priority substituent (often hydrogen) is facing back when assigning R or S configuration.
- 7.
Page 7 of 16 Artificial sweeteners have long been a controversial topic. Are they safe? Do they cause cancer? Check out this video to learn more!
- 8.
Page 8 of 16Breaking BACONIn addition to having different interactions with taste and smell receptors, enantiomers will often have different biological properties. One striking example of this involves the Schedule II drug, methamphetamine (aka “meth”), which has received much attention from the hit TV show “Breaking Bad”. Methamphetamine systematically destroys the body and causes memory loss and psychotic behavior. It can also lead to heart and brain damage. It is estimated that nearly 500 metric tons of amphetamine-type stimulants are produced each year with over 24 million abusers worldwide. While methamphetamine is a very dangerous, highly addictive drug, its enantiomer levomethamphetamine is commonly used as a vasoconstrictor and helps to alleviate nasal congestion when used in small doses. Levomethamphetamine can be found in the popular over-the-counter medicine Vick’s Vapor Inhaler.
- 9.
Page 9 of 16Racemic vs Enantiopure Drugs It is often the case that enantiomers will have different effects on our bodies. However, in other cases, one enantiomer may be ‘active’, while the other enantiomer has no physiological effect. This allows pharmaceutical companies to sell some drugs as racemic mixtures. Notable examples include Ritalin (treatment of ADHD) and Zyrtec (treatment of allergies), although enantiopure versions have also been made for competitive purposes. In other cases, racemic drugs and their enantiopure versions have been marketed for very different purposes. For example, Imovane (racemic) was originally developed in the 1980’s as an antipsychotic. However, decades later, scientists found that a single enantiomer of this compound, branded as Lunesta, combats insomnia.
- 10.
Page 10 of 16 One of the most famous examples of the importance of stereochemistry and medicines is the story of thalidomide. In 1957, racemic thalidomide was marketed as a drug for the treatment of morning sickness and was viewed as a ‘wonder drug’ for pregnant women. However, reports soon surfaced of children being born with abnormalities. The drug was quickly recalled, but over 10,000 babies were born with birth defects, including mental illnesses and badly deformed or completely missing limbs. The drug is thought to have claimed the lives of over 2,000 children. What went wrong? Although the (R)-enantiomer of thalidomide was useful for the treatment of morning sickness, it turns out that the (S)-enantiomer is a teratogen and caused the birth defects. You might wonder if one can use the (R)-enantiomer of thalidomide as a drug. Unfortunately, this does not work either because thalidomide readily racemizes under physiological conditions to produce an equal mixture of R and S enantiomers. Even recently, scientists have been trying to get around this stereochemistry problem.
- 11.
Page 11 of 16 Nobel Prize in Chemistry Given the importance of chirality, chemists have put forth exhaustive efforts to develop reactions that give one enantiomer of a given compound, instead of racemic mixtures. Three heroes in the field are Professor K. Barry Sharpless, Dr. William S. Knowles, and Professor Ryoji Noyori. They shared the 2001 Nobel Prize in Chemistry for their “development of catalytic asymmetric synthesis.” Their work has been important in the syntheses of several drugs, including Dr. Knowles’ catalytic asymmetric synthesis of L-DOPA, a precursor to adrenaline. Other notable syntheses include (–)-menthol, fosfomycin (anti-biotic), and amphotericin B (anti-fungal).
- 12.
Page 12 of 16 – SOLUTIONS Synthesis of Pharmaceuticals Identify the stereochemistry of (+)-naproxen:a. Rb. Sc. Impossible to determineExplanation: The correct answer is B – the explanation is shown below. Make sure the lowest priority substituent (often hydrogen) is facing back when assigning R or S configuration.
- 13.
Page 13 of 16 Origins of Life Biomolecules such as proteins and DNA are assembled from chiral amino acid and sugar building blocks, respectively. Amino acids in nature predominately exist in the L-configuration. Although not abundant, D-amino acids like D-glutamic acid, D-glutamine, and D-alanine are found in the peptidoglycan layer of bacterial cell walls. Also, D-serine is a neurotransmitter synthesized in the brain from L-serine. Sugars, such as glucose and deoxyribose, naturally exist in the D-configuration. Many unnatural sugars have been made, including L-glucose, which tastes the same as D-glucose but cannot be broken down into energy in the body. L-deoxyribose has also been made and used to study ‘mirror-image DNA’.
- 14.
Page 14 of 16 The fact that DNA and proteins are always made with the same sense of chirality falls under a topic called homochirality, which has intrigued scientists for more than half a century. What is the origin of our homochirality? The answer is still unknown, but there are several theories. One of the most provocative ideas is that the chirality source is extraterrestrial. This thinking has largely been inspired by the discovery of chiral amino acids in the Murchison meteorite, a >1000 kg meteorite that landed in Australia in 1969. Click here for more information about the origin of biological homochirality.Click here to learn about another interesting theory called asymmetric autocatalysis.
- 15.
Page 15 of 16 Space exploration / Mars Rovers For centuries people have speculated about the existence of extraterrestrial life and questioned if life could exist on other planets. Mars has been a target for investigation due to its proximity and relative similarity to Earth.On January 24, 2014, NASA reported that its “Mars rovers” would be searching for evidence of life, including water, organic compounds, and chirality. Although chirality has not yet been detected on Mars, such a finding would suggest that life could exist beyond the planet Earth. Click here for more information on Mars rover investigation.Learn more about the Mars Rover missions by watching this National Geographic video.
- 16.
Page 16 of 16 Stereochemistry in Video Games? Believe it or not, there is a video game that features stereochemistry! In the first-person shooter game, “Mass Effect” an alien species based on D-amino acids, tries to destroy the human race. The aliens cannot consume any L-amino acid-based foods because it has no nutritional value to them and may cause a fatal allergic reaction. Since L-amino acids are more abundant in the universe, the aliens want to kill off all of the humans to increase the amount of the D-amino acids in the universe. Some of the food for D-amino acid-based sapients is even referred to as “dextro rations”. The game is available on Xbox 360 and PlayStation 3.
- 17.
Pre-BACON Quiz1. Which of the following compounds smells like lemons and is the enantiomer of a compound that smells like oranges?
Correct Answer
A. -
- 18.
Pre-BACON Quiz2. Which of the following correctly describes the enantiomer of “meth”, the drug frequently seen in the hit TV show “Breaking Bad”?
-
It is another drug that is just as dangerous as “meth”.
-
It is one of the ingredients used in the artificial sweetener Equal.
-
It provides evidence of extraterrestrial life.
-
It is used in an over-the-counter medicine to help alleviate nasal congestion.
Correct Answer
A. It is used in an over-the-counter medicine to help alleviate nasal congestion.Explanation
The enantiomer of "meth" is used in an over-the-counter medicine to help alleviate nasal congestion. An enantiomer is a molecule that is a mirror image of another molecule but cannot be superimposed on it. In the context of the question, the enantiomer of "meth" refers to a specific molecule that has similar properties and effects as "meth" but is used for a different purpose, namely to alleviate nasal congestion. This answer choice is the only one that accurately describes the enantiomer of "meth" and its usage.Rate this question:
-
- 19.
Pre-BACON Quiz3. In the 1950’s the ‘wonder drug’ thalidomide was prescribed to pregnant women for the treatment of morning sickness, but was halted because ___________________________________
-
The (S) enantiomer of the drug caused birth defects.
-
The (R) enantiomer of the drug caused brain damage.
-
The US government redirected their attention to space exploration.
-
Both enantiomers of the drug caused birth defects.
Correct Answer
A. The (S) enantiomer of the drug caused birth defects.Explanation
In the 1950s, thalidomide was prescribed to pregnant women as a treatment for morning sickness. However, it was halted because the (S) enantiomer of the drug caused birth defects. This means that one specific form of the drug, the (S) enantiomer, was responsible for the harmful effects on the developing fetus. The (R) enantiomer, on the other hand, did not cause birth defects. This discovery led to the withdrawal of thalidomide from the market and stricter regulations on the use of drugs during pregnancy.Rate this question:
-
- 20.
Pre-BACON Quiz4. What hypothesis has come about, at least in part, because of the discovery of chiral amino acids in the Murchison meteorite, which landed in Australia in 1969?
-
The universe is most likely expanding
-
Natural amino acids are D-amino acids
-
Homochirality originated on Earth
-
The origins of homochirality might be extraterrestrial
Correct Answer
A. The origins of homochirality might be extraterrestrialExplanation
The correct answer is "the origins of homochirality might be extraterrestrial." This hypothesis suggests that the presence of chiral amino acids in a meteorite implies that the origins of homochirality, the preference for one enantiomer over another, could be from extraterrestrial sources. This discovery raises the possibility that the building blocks of life on Earth may have originated from outer space.Rate this question:
-
- 21.
BACON at UCLA – Chirality and Stereoisomers Page 4 of 16 Assign the absolute configuration in (–)-limonene:
-
R
-
S
Correct Answer
A. SExplanation
In the given question, we are asked to assign the absolute configuration in (–)-limonene. The answer provided is S. Absolute configuration refers to the spatial arrangement of atoms or groups in a chiral molecule. In (–)-limonene, there is a chiral carbon atom, and the priority of the substituents attached to it can be determined using the Cahn-Ingold-Prelog priority rules. By assigning priorities to the substituents and rotating the molecule to align the lowest priority group away from us, we find that the rotation is counterclockwise, indicating an S configuration. Therefore, the correct answer is S.Rate this question:
-
- 22.
BACON at UCLA – Chirality and Stereoisomers Page 6 of 16 (–)-Aspartame can be made from L-aspartic acid and L-phenylalanine methyl ester. Identify the absolute configuration of the two chiral centers.
-
Blue = R; Red = S
-
Blue = R; Red = R
-
Blue = S; Red = S
-
Blue = S; Red = R
Correct Answer
A. Blue = S; Red = SExplanation
The absolute configuration of the two chiral centers in the compound (-)-Aspartame is Blue = S and Red = S.Rate this question:
-
- 23.
BACON at UCLA – Chirality and Stereoisomers Page 12 of 16 Synthesis of Pharmaceuticals Chiral reagents and catalysts can be used nowadays to make molecules of interest with control of absolute stereochemistry, but enzymes can also be used for this purpose. One important drug that can be synthesized on kilogram scale using an enzyme is (+)-naproxen, which is an anti-inflammatory drug used by millions of people around the world. In this reaction, the lipase enzyme only reacts with one of the enantiomers of the racemic methyl ester. This gives (+)-naproxen and the unreacted (–) enantiomer of the substrate. Identify the stereochemistry of (+)-naproxen:
-
R
-
S
-
Impossible to determine
Correct Answer
A. SExplanation
The stereochemistry of (+)-naproxen is S. This is because the lipase enzyme only reacts with one of the enantiomers of the racemic methyl ester, resulting in the formation of (+)-naproxen. Since the lipase enzyme is selective for a specific enantiomer, it determines the stereochemistry of the product. Therefore, the stereochemistry of (+)-naproxen is determined to be S.Rate this question:
-
- 24.
Post-BACON Quiz1. Which of the following compounds smells like lemons and is the enantiomer of a compound that smells like oranges?
Correct Answer
A.Explanation
The compound that smells like lemons and is the enantiomer of a compound that smells like oranges is called limonene. Limonene is a naturally occurring compound found in the peels of citrus fruits, particularly lemons and oranges. It has a strong citrus scent and is commonly used as a flavoring agent in food and beverages. The enantiomer of limonene, called perillyl alcohol, also has a citrus-like odor but smells more like oranges.Rate this question:
-
- 25.
Post-BACON Quiz2. Which of the following correctly describes the enantiomer of “meth”, the drug frequently seen in the hit TV show “Breaking Bad”?
-
It is another drug that is just as dangerous as “meth”.
-
It is one of the ingredients used in the artificial sweetener Equal.
-
It provides evidence of extraterrestrial life.
-
It is used in an over-the-counter medicine to help alleviate nasal congestion.
Correct Answer
A. It is used in an over-the-counter medicine to help alleviate nasal congestion.Explanation
The enantiomer of "meth" is used in an over-the-counter medicine to help alleviate nasal congestion.Rate this question:
-
- 26.
Post-BACON Quiz3. In the 1950’s the ‘wonder drug’ thalidomide was prescribed to pregnant women for the treatment of morning sickness, but was halted because ___________________________________
-
The (S) enantiomer of the drug caused birth defects.
-
The (R) enantiomer of the drug caused brain damage.
-
The US government redirected their attention to space exploration.
-
Both enantiomers of the drug caused birth defects.
Correct Answer
A. The (S) enantiomer of the drug caused birth defects.Explanation
In the 1950s, the drug thalidomide was prescribed to pregnant women for morning sickness. However, it was halted because the (S) enantiomer of the drug caused birth defects. This means that one specific form of the drug, the (S) enantiomer, was responsible for the harmful effects on developing fetuses. The discovery of this link led to the discontinuation of thalidomide as a treatment for pregnant women.Rate this question:
-
- 27.
Post-BACON Quiz4. What hypothesis has come about, at least in part, because of the discovery of chiral amino acids in the Murchison meteorite, which landed in Australia in 1969?
-
The universe is most likely expanding
-
Natural amino acids are D-amino acids
-
Homochirality originated on Earth
-
The origins of homochirality might be extraterrestrial
Correct Answer
A. The origins of homochirality might be extraterrestrialExplanation
The correct answer suggests that the discovery of chiral amino acids in the Murchison meteorite implies that the origins of homochirality (the preference for one enantiomer over the other) might be extraterrestrial. This means that the meteorite could have brought these chiral molecules to Earth, potentially playing a role in the development of life on our planet.Rate this question:
-
.jpg "Page 2 of 16 Here is a quick refresher of enantiomers and diastereomers:")
.jpg "Page 3 of 16 Although enantiomers have the same physical properties (e.g.. melting point, boiling point, density, and solubility), they will usually interact differently with other chiral molecules. A common example of this involves the taste and smell receptors in the tongue and nose, respectively. Two famous examples involve the compounds limonene and carvone. The (–) enantiomer of limonene is recognized as an lemon smell, while the (+) enantiomer is recognized as a orange smell. Also, while (–)-carvone has a spearmint smell, (+)-carvone has a dill or caraway smell.")
.jpg "Page 4 of 16 - SOLUTIONS Assign the absolute configuration in (–)-limonene:a. Rb. SExplanation: The correct answer is B (S configuration) – the explanation is shown below.")
.jpg "Page 5 of 16 Another interesting example involves the artificial sweetener Equal and its key ingredient aspartame. Aspartame was first discovered in the 1960s and is now a common ingredient in consumer products, such as candy and soft drinks. Did you know that only one enantiomer of aspartame is used as a sweetener? The (–)-enantiomer of aspartame is sweet, but the (+)-enantiomer of aspartame is bitter. The difference in taste comes from the two enantiomers interacting differently with our chiral taste receptors.")
.jpg "Page 6 of 16 – SOLUTIONS Identify the absolute configuration of the two chiral centers. a. Blue = R; Red = Sb. Blue = R; Red = Rc. Blue = S; Red = Sd. Blue = S; Red = RExplanation: The correct answer is C – the explanation is shown below. Make sure the lowest priority substituent (often hydrogen) is facing back when assigning R or S configuration.")
.jpg "Page 8 of 16Breaking BACONIn addition to having different interactions with taste and smell receptors, enantiomers will often have different biological properties. One striking example of this involves the Schedule II drug, methamphetamine (aka “meth”), which has received much attention from the hit TV show “Breaking Bad”. Methamphetamine systematically destroys the body and causes memory loss and psychotic behavior. It can also lead to heart and brain damage. It is estimated that nearly 500 metric tons of amphetamine-type stimulants are produced each year with over 24 million abusers worldwide. While methamphetamine is a very dangerous, highly addictive drug, its enantiomer levomethamphetamine is commonly used as a vasoconstrictor and helps to alleviate nasal congestion when used in small doses. Levomethamphetamine can be found in the popular over-the-counter medicine Vick’s Vapor Inhaler.")
.jpg "Page 9 of 16Racemic vs Enantiopure Drugs It is often the case that enantiomers will have different effects on our bodies. However, in other cases, one enantiomer may be ‘active’, while the other enantiomer has no physiological effect. This allows pharmaceutical companies to sell some drugs as racemic mixtures. Notable examples include Ritalin (treatment of ADHD) and Zyrtec (treatment of allergies), although enantiopure versions have also been made for competitive purposes. In other cases, racemic drugs and their enantiopure versions have been marketed for very different purposes. For example, Imovane (racemic) was originally developed in the 1980’s as an antipsychotic. However, decades later, scientists found that a single enantiomer of this compound, branded as Lunesta, combats insomnia.")
.jpg "Page 10 of 16 One of the most famous examples of the importance of stereochemistry and medicines is the story of thalidomide. In 1957, racemic thalidomide was marketed as a drug for the treatment of morning sickness and was viewed as a ‘wonder drug’ for pregnant women. However, reports soon surfaced of children being born with abnormalities. The drug was quickly recalled, but over 10,000 babies were born with birth defects, including mental illnesses and badly deformed or completely missing limbs. The drug is thought to have claimed the lives of over 2,000 children. What went wrong? Although the (R)-enantiomer of thalidomide was useful for the treatment of morning sickness, it turns out that the (S)-enantiomer is a teratogen and caused the birth defects. You might wonder if one can use the (R)-enantiomer of thalidomide as a drug. Unfortunately, this does not work either because thalidomide readily racemizes under physiological conditions to produce an equal mixture of R and S enantiomers. Even recently, scientists have been trying to get around this stereochemistry problem.")
.jpg "Page 11 of 16 Nobel Prize in Chemistry Given the importance of chirality, chemists have put forth exhaustive efforts to develop reactions that give one enantiomer of a given compound, instead of racemic mixtures. Three heroes in the field are Professor K. Barry Sharpless, Dr. William S. Knowles, and Professor Ryoji Noyori. They shared the 2001 Nobel Prize in Chemistry for their “development of catalytic asymmetric synthesis.” Their work has been important in the syntheses of several drugs, including Dr. Knowles’ catalytic asymmetric synthesis of L-DOPA, a precursor to adrenaline. Other notable syntheses include (–)-menthol, fosfomycin (anti-biotic), and amphotericin B (anti-fungal).")
.jpg "Page 12 of 16 – SOLUTIONS Synthesis of Pharmaceuticals Identify the stereochemistry of (+)-naproxen:a. Rb. Sc. Impossible to determineExplanation: The correct answer is B – the explanation is shown below. Make sure the lowest priority substituent (often hydrogen) is facing back when assigning R or S configuration.")
.jpg "Page 13 of 16 Origins of Life Biomolecules such as proteins and DNA are assembled from chiral amino acid and sugar building blocks, respectively. Amino acids in nature predominately exist in the L-configuration. Although not abundant, D-amino acids like D-glutamic acid, D-glutamine, and D-alanine are found in the peptidoglycan layer of bacterial cell walls. Also, D-serine is a neurotransmitter synthesized in the brain from L-serine. Sugars, such as glucose and deoxyribose, naturally exist in the D-configuration. Many unnatural sugars have been made, including L-glucose, which tastes the same as D-glucose but cannot be broken down into energy in the body. L-deoxyribose has also been made and used to study ‘mirror-image DNA’.")
.jpg "Page 14 of 16 The fact that DNA and proteins are always made with the same sense of chirality falls under a topic called homochirality, which has intrigued scientists for more than half a century. What is the origin of our homochirality? The answer is still unknown, but there are several theories. One of the most provocative ideas is that the chirality source is extraterrestrial. This thinking has largely been inspired by the discovery of chiral amino acids in the Murchison meteorite, a >1000 kg meteorite that landed in Australia in 1969. Click here for more information about the origin of biological homochirality.Click here to learn about another interesting theory called asymmetric autocatalysis.")
.jpg "Page 15 of 16 Space exploration / Mars Rovers For centuries people have speculated about the existence of extraterrestrial life and questioned if life could exist on other planets. Mars has been a target for investigation due to its proximity and relative similarity to Earth.On January 24, 2014, NASA reported that its “Mars rovers” would be searching for evidence of life, including water, organic compounds, and chirality. Although chirality has not yet been detected on Mars, such a finding would suggest that life could exist beyond the planet Earth. Click here for more information on Mars rover investigation.Learn more about the Mars Rover missions by watching this National Geographic video.")
.jpg "Page 16 of 16 Stereochemistry in Video Games? Believe it or not, there is a video game that features stereochemistry! In the first-person shooter game, “Mass Effect” an alien species based on D-amino acids, tries to destroy the human race. The aliens cannot consume any L-amino acid-based foods because it has no nutritional value to them and may cause a fatal allergic reaction. Since L-amino acids are more abundant in the universe, the aliens want to kill off all of the humans to increase the amount of the D-amino acids in the universe. Some of the food for D-amino acid-based sapients is even referred to as “dextro rations”. The game is available on Xbox 360 and PlayStation 3.")
.jpg)
.jpg)
.jpg)
.jpg)
.jpg "BACON at UCLA – Chirality and Stereoisomers Page 4 of 16 Assign the absolute configuration in (–)-limonene:")
.jpg "BACON at UCLA – Chirality and Stereoisomers Page 6 of 16 (–)-Aspartame can be made from L-aspartic acid and L-phenylalanine methyl ester. Identify the absolute configuration of the two chiral centers.")
.jpg "BACON at UCLA – Chirality and Stereoisomers Page 12 of 16 Synthesis of Pharmaceuticals Chiral reagents and catalysts can be used nowadays to make molecules of interest with control of absolute stereochemistry, but enzymes can also be used for this purpose. One important drug that can be synthesized on kilogram scale using an enzyme is (+)-naproxen, which is an anti-inflammatory drug used by millions of people around the world. In this reaction, the lipase enzyme only reacts with one of the enantiomers of the racemic methyl ester. This gives (+)-naproxen and the unreacted (–) enantiomer of the substrate. Identify the stereochemistry of (+)-naproxen:")
Quiz Review Timeline (Updated): Mar 20, 2023 +
Our quizzes are rigorously reviewed, monitored and continuously updated by our expert board to maintain accuracy, relevance, and timeliness.
-
Current Version
-
Mar 20, 2023Quiz Edited by
ProProfs Editorial Team -
Apr 15, 2015Quiz Created by
Catherine Halcomb
Back to top