Interaction of Angiotensin I-Converting Enzyme with Two Potent Tricyclic Inhibitors

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Abstract
Inhibition of rabbit lung angiotensin I-converting enzyme was studied with two inhibitors that combined tricyclic mimics of a substrate C-terminal dipeptide recognition unit with a 4-phenylbutanoic acid fragment. The overall inhibition constant for [4S-[4α,7α(R),12bB]]-7–[S-(l-carboxy-3-phenylpropyl)amino]-1,2,3,4,6,7,8,12b-octahydro-6-oxopyrido[2,1-a][2]benzazepine-4-carboxylic acid (MDL 27,088) was approximately 4pM, whereas that for [4R-[4α,7α(S),12β]]-7–[S-(1-carboxy-3-phenylpropyl)amino]-3,4,6,7,8,12b-hexahydro-6-oxo-1H-[1,4]thiazino[3,4-a][2]benzazepine-4-carboxylic acid (MDL 27,788) was estimated to be 46 pM. The formation of an initial complex of target enzyme and MDL 27,088 and its slower isomerization to a second complex were characterized kinetically. Both compounds appear to be among the most potent inhibitors known for this enzyme.