Page 226 - Medicinal Chemistry Self Assessment

2.23 Quinapril 215

6. Although it is possible for quinapril to undergo all of the above metabolic transformations, pathway
B is the major pathway. Other metabolites have been identified, but only at very low levels. Provide
an explanation for this finding.
Answer
Remember that the major purpose of drug metabolism is to enhance the removal of the drug from
the body, and the number of metabolic transformations required to achieve this goal varies from
drug molecule to drug molecule. In the case of quinapril, ester hydrolysis can occur quickly and at
many locations within the body. The resulting metabolite, quinaprilat, contains three ionizable func-
tional groups and is easily eliminated from the body without the need for further metabolism.