Process for the production of lisinopril

The present invention provides a process for preparing N2-[1(S)-ethoxycarbonyl-3-phenylpropyl]-N6-trifluoroacetyl-L-lysine and lisinopril thereof. Lisinopril shows excellent angiotensin converting enzyme inhibitor activity. Friedel-Crafts acylation of benzene with maleic anhydride in the presence of AlCl3 affords trans-beta-benzoylacrylic acid. Treatment of benzoylacrylic acid with HCl gas in ethanol gives ethyl 2-chloro-4-oxo-4-phenylbutyrate in high yield. The coupling reaction between ethyl 2-chloro-4-oxo-4-phenylbutyrate and trifluoroacetyl-L-lysine benzyl ester in the presence of a base pair and sodium iodide produces alkyl lydine derivative with a good diastereoselectivity. Catalytic hydrogenation of lysine derivative with palladium gives N2-[1(S)-ethoxycarbonyl-3-phenylpropyl]-N6-trifluoroacetyl-L-lysine. This intermediate is activated to form cyclic N-anhydride by using N,N-carbonyldiimidazole and coupled with L-proline methyl ester hydrochloride to give fully protected lisinopril derivative, which is converted into crude lisinopril by hydrolysis.