Multiple Choice
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.
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What position(s) on the analog of labetalol would be considered stereocenters?
A) Positions 1 and 2 only
B) Position 2 only
C) Position 3 only
D) Positions 3 and 4 only
Correct Answer:

Verified
Correct Answer:
Verified
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