Quinapril inhibits angiotensin converting enzyme, an enzyme which catalyses the formation of angiotensin II from its precursor, angiotensin I. Angiotensin II is a powerfulvasoconstrictor and increases blood pressure through a variety of mechanisms. Due to reduced angiotensin production, plasma concentrations of aldosterone are also reduced, resulting in increased excretion of sodium in the urine and increased concentrations ofpotassium in the blood.
The condensation of alanine tert-butyl ester (I) with ethyl 2-bromo-4-phenylbutanoate (II) by means of triethylamine in hot DMF gives ethyl 2-[[1-(tert-butoxycarbonyl)ethyl]amino]-4-phenylbutanoate (III), which is partially hydrolyzed with trifluoroacetic acid yielding ethyl 2-[[1-carboxyethyl]amino]-4-phenylbutanoate (IV). The condensation of (IV) with tert-butyl-1,2,3,4-tetrahydroisoquinoline-3-carboxylate (VIII) [prepared from the corresponding acid (VI) and isobutylene (B) by means of H2SO4] as before gives tert-butyl-2-[2-[[1-(ethoxycarbonyl)-3-phenylpropyl]amino]-1-oxopropyl]-1,2,3,4-tetrahydroisoquinoline-3-carboxylate (IX), which is finally hydrolyzed partially by treatment with trifluoroacetic acid.Hoefle, M.L.; Klutchko, S. (Pfizer Inc.); Substituted acyl derivatives of 1,2,3,4-tetrahydroisoquinoline-3-carboxylic acids. DD 201787; EP 0049605; EP 0096157; US 4344949