General Description
Quinapril hydrochloride,(S)-[(S)-N-[(S)21-carboxy3-phenylpropyl]alanyl]-1,2,3,4-tetrahydro-3-isoquinolinecarboxylic acid 1-ethyl ester hydrochloride(Acuretic), forms the diacid quinaprilate in thebody. It is more potent than captopril and equipotent to theactive form of enalapril.
Synthesis
The general procedure for the synthesis of (S)-2-((S)-2-(((S)-1-ethoxy-1-oxo-4-phenylbutan-2-yl)amino)propanoyl)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid hydrochloride from quinapril benzyl ester maleate was as follows: 1.73 g (3.29 mmol) of quinapril benzyl ester obtained in Example 6 (IlIc, R = Bn) was dissolved in 40 ml of ethyl acetate and about 1 ml of dry HCl was added.The hydrogenation reaction was carried out at 15-20 °C and atmospheric pressure (using a hydrogen balloon) with the addition of 5% Pd/C catalyst (about 100 mg). The progress of the reaction was monitored by LC-MS and after complete consumption of the feedstock, the catalyst was removed by filtration and the filtrate was concentrated. Grinding with methyl tert-butyl ether (MTBE) afforded the target product (S)-2-((S)-2-(((S)-1-ethoxy-1-oxo-4-phenylbutan-2-yl)amino)propanoyl)-1,2,3,4-tetrahydroisoquinoline-3-carboxylic acid hydrochloride as a colorless powder in the yield of 1.40 g (90% yield) with a purity of >98% by LC-MS (MH+ 439).1H NMR (showing two rotary isomers) data were as follows: δ 1.18, 1.25 (2t, 3H, OCH2CH3), 1.52 (2d, 3H, CH3), 2.08-2.30 (m, 2H, PhCH2CH2), 2.62, 2.78 (2m, 2H, PhCH2), 3.10-3.35 (m, 2H , H-4), 3.80, 3.93 (2m, 1H, NCHC=O), 4.14, 4.21 (2m, 2H, OCH2), 4.45-4.90 (3m, 3H, Hi, H-i', H-3), 5.15 (m, 1H, NHCHCH3), 7.15-7.35 (m, 9H, ArH), 9.80 (wide m, 2H , NH2), 12.80 (wide m, 1H, COOH). Quinapril hydrochloride can be further purified by ethyl acetate/toluene mixed solvent crystallization as described by S. Klutchko et al. (J. Med. Chem. 1986, 29, 1953-1961).
References
[1] Patent: WO2014/202659, 2014, A1. Location in patent: Page/Page column 22
[2] Patent: WO2004/54980, 2004, A1. Location in patent: Page 25;13;16
