Following is the structural formula of the antihypertensive drug labetalol, a

Chapter 22, Problem 22.57

(choose chapter or problem)

Following is the structural formula of the antihypertensive drug labetalol, a non-specific b-adrenergic blocker with vasodilating activity. Members of this classhave received enormous clinical attention because of their effectiveness in treatinghypertension (high blood pressure), migraine headaches, glaucoma, ischemic heartdisease, and certain cardiac arrhythmias. This retrosynthetic analysis involves discon-nects to the a-haloketone (B) and the amine (C). Each is in turn derived from asimpler, readily available precursor. (a) Given this retrosynthetic analysis, propose a synthesis for labetalol from salicylicacid and benzyl chloride. [Note: The conversion of salicylic acid to (E) involvesa Friedel-Crafts acylation in which the phenolic !OH must be protected bytreatment with acetic anhydride to prevent the acylation of the !OH group.The protecting group is later removed by treatment with KOH followed byacidification.](b) Labetalol has two chiral centers and, as produced in this synthesis, is a racemicmixture of the four possible stereoisomers. The active stereoisomer is dilevalol,which has the R,R configuration at its chiral centers. Draw a structural formula ofdilevalol showing the configuration of each chiral center.