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High blood pressure, or hypertension, is a prevalent condition in the United States. One in three adults has hypertension, and approximately 20% do not know that they have it. If left untreated, high blood pressure can lead to major health issues, including stroke, heart attack, and kidney disease or failure. A number of drugs can help control hypertension, including those shown in Table 1. These drugs can be classified into different groups based on their mechanism of action.Table 1 Drugs Used to Treat High Blood Pressure
Labetalol (Figure 1) exists as four stereoisomers and is administered as a mixture of all four. This drug can be classified as a pseudohybrid drug because two of the isomers, (R,R) and (S,R) , exhibit biological activity; the other two isomers, (S,S) and (R,S) , are not active. The (R,R) isomer acts as a nonselective β-adrenergic receptor blocker, and the (S,R) isomer acts as a selective α-adrenergic receptor blocker.
Figure 1 Structure of (±) -labetalol and l-epinephrinel-epinephrine (Figure 1) is the agonist of the α- and β-adrenergic receptors. The structural motifs that allow l-epinephrine to bind to the adrenergic receptors include an amine separated from an aromatic ring by two carbon units, a hydroxyl group at a chiral center beta to the amine, and two hydroxyl groups on the aromatic ring in the meta and para positions. With a few structural modifications, the agonist l-epinephrine can be converted into the antagonist labetalol. Substitution of a hydroxyl on the aromatic ring with an amide group and extension of the methyl group on the amine transforms l-epinephrine into labetalol. These substitutions keep a majority of the structural motifs necessary for labetalol to mimic l-epinephrine and bind to the adrenergic receptors.
-The number of stereoisomers possible for a given molecule is 2ⁿ. The variable n denotes the number of:

Question

Passage
High blood pressure, or hypertension, is a prevalent condition in the United States. One in three adults has hypertension, and approximately 20% do not know that they have it. If left untreated, high blood pressure can lead to major health issues, including stroke, heart attack, and kidney disease or failure. A number of drugs can help control hypertension, including those shown in Table 1. These drugs can be classified into different groups based on their mechanism of action.Table 1 Drugs Used to Treat High Blood Pressure

Labetalol (Figure 1) exists as four stereoisomers and is administered as a mixture of all four. This drug can be classified as a pseudohybrid drug because two of the isomers, (R,R) and (S,R) , exhibit biological activity; the other two isomers, (S,S) and (R,S) , are not active. The (R,R) isomer acts as a nonselective β-adrenergic receptor blocker, and the (S,R) isomer acts as a selective α-adrenergic receptor blocker.

Figure 1 Structure of (±) -labetalol and l-epinephrinel-epinephrine (Figure 1) is the agonist of the α- and β-adrenergic receptors. The structural motifs that allow l-epinephrine to bind to the adrenergic receptors include an amine separated from an aromatic ring by two carbon units, a hydroxyl group at a chiral center beta to the amine, and two hydroxyl groups on the aromatic ring in the meta and para positions. With a few structural modifications, the agonist l-epinephrine can be converted into the antagonist labetalol. Substitution of a hydroxyl on the aromatic ring with an amide group and extension of the methyl group on the amine transforms l-epinephrine into labetalol. These substitutions keep a majority of the structural motifs necessary for labetalol to mimic l-epinephrine and bind to the adrenergic receptors.
-The number of stereoisomers possible for a given molecule is 2ⁿ. The variable n denotes the number of:

Quizplus · Accepted Answer

11ecba2d_125c_82c7_a3bf_cfe6333f93b2_MD0008_00 Stereoisomers are molecules that differ in spatial arrangement but have the same connectivity and molecular formula. The number of stereoisomers for a particular compound corresponds to the number of configurations possible for that compound and is directly related to the number of stereocenters in the molecule. Each stereocenter can adopt two different conformations, so the expression 2ⁿ, where n is the number of stereocenters in the molecule, provides the maximum number of stereoisomers possible for the particular compound. For example, labetalol has two stereocenters, and therefore 2² = 4 possible stereoisomers. A compound with three stereocenters would have 2³ = 8 possible configurations, and so on. (Choices A and C) Enantiomers and diastereomers are types of stereoisomers, and are included in the number of total stereoisomers that can exist. (Choice D) Epimers are a type of diastereomer that differs in configuration at only one stereocenter. The number of epimers is not factored into the calculation of the number of stereoisomers possible for a particular molecule. Educational objective: A molecule with n stereocenters can have a maximum of 2ⁿ stereoisomers.

Passage High Blood Pressure, or Hypertension, Is a Prevalent Condition in in the United