Abstract
(3S)-2-[(2S)-3-Mercapto-2-methylpropionyl]-1, 2, 3, 4-tetrahydroisoquinoline-3-carboxylic acid [(3S), (2S)-6a] was prepared by the reaction of (3S)-1, 2, 3, 4-tetrahydroisoquinoline-3-carboxylic acid tert-butyl ester [(3S)-2a] or benzyl ester [(3S)-2b] with 3-benzoylthio-2-methylpropionyl chloride (3a), followed by fractional crystallization and removal of the protective group. The absolute configuration of (3S), (2S)-6a was confirmed by X-ray diffraction analysis of the thiazepino [4, 3-b] isoquinoline compound (7) derived from 6a. Resolution of 3-benzoylthio-2-methylpropionic acid (8) was completed by using optically active phenylalanine amide as a resolving agent. The other optical isomers of (3S), (2S)-6a were prepared by the reaction of (3S)- or (3R)-2b with optically active 3a. The in vitro ACE inhibitory activity of each isomer of 6a was evaluated. Among them, (3S), (2S)-6a was found to be the most potent inhibitor with an IC50 value of 8.6×10-9M. Compound (3S), (2S)-6a induced a dose-dependent inhibition of the pressor response to angiotensin I after oral administration to normotensive anesthetized rats. Moreover, (3S), (2S)-6a markedly reduced the systolic blood pressure in renal hypertensive rats (RHR) and spontaneously hypertensive rats (SHR). The in vivo ACE inhibitory activity and the hypotensive effects of (3S), (2S)-6a were comparable to those of captopril.
