Both Enantiomers Have Independent Therapeutic Benefits

In some instances, both enantiomers of a drug may have different therapeutic values. The classical example of this behavior is the diastereomers quinine and quinidine (Figure 5.7). Quinine, which was originally obtained from the bark of cinchona trees was, for centuries, the only treatment for malaria. Quinidine, on the other hand, is used as a class 1A antiarrhythmic agent and acts by increasing action potential duration.

FIGURE 5.6 The ER for (S)- and (R)-propranolol is 13C.

(fi)-Propranolol (distomer)

(fi)-Propranolol (distomer)

Quinine (antimalarial)

Quinidine (antiarrhythmic)

Quinine (antimalarial)

Quinidine (antiarrhythmic)

DARVON (analgesic)

NOVRAD (antitussive)

FIGURE 5.7 Examples of drugs where both stereoisomers possess therapeutic benefits.

DARVON (analgesic)

NOVRAD (antitussive)

FIGURE 5.7 Examples of drugs where both stereoisomers possess therapeutic benefits.

The drug dextropropoxyphene marketed by Eli Lilly has trade names reflecting the different activities of the enantiomers. Thus the (2R, 3S)-enantiomer, DARVON has analgesic properties while the (2S, 3R)-enantiomer NOVRAD (Figure 5.7) is an antitussive.

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