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.
-(S,R) - and (R,R) -labetalol, the active forms of the drug, can be described as which of the following?DiastereomersEnantiomersConformational isomers

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.
-(S,R) - and (R,R) -labetalol, the active forms of the drug, can be described as which of the following?DiastereomersEnantiomersConformational isomers

Quizplus · Accepted Answer

11ecba2d_125b_9865_a3bf_4354507839bb_MD0008_00 Stereoisomers are molecules that contain the same atom connectivity but differ in the spatial arrangements of the atoms. Diastereomers are stereoisomers that are not mirror images. These molecules contain at least two stereocenters in which one or more, but not all, of the corresponding stereocenters are in opposite configurations. (S,R)- and (R,R)-labetalol are stereoisomers that are not mirror images, and each compound contains two stereocenters. The two compounds have different configurations at the stereocenter in position 1 (one S and one R) and have the same configuration at the stereocenter in position 2 (both R). Therefore, (S,R)- and (R,R)-labetalol are diastereomers (Number I). (Number II) Enantiomers are stereoisomers that are nonsuperimposable mirror images. These molecules contain one or more stereocenters, and each stereocenter is the opposite configuration from the corresponding stereocenter in the other molecule. For example, the enantiomer of (S,R)-labetalol is (R,S)-labetalol. (Number III) Conformational isomers are different forms of the same molecule that are generated as atoms rotate about their bonds. Unlike other stereoisomers, conformational isomers can rapidly interconvert by rotation without the need to break any bonds. Educational objective: Diastereomers are stereoisomers that are not mirror images. They contain at least two stereocenters in which one or more, but not all, are in opposite configurations.

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