Design and synthesis of potent, selective inhibitors of endothelin-converting enzyme

Endothelin-l is the most potent peptidic vasoconstrictor discovered to date. The final step of posttranslational processing of this peptide is the conversion of its precursor by endothelin-converting enzyme-1 (ECE-1), a metalloprotease which displays high amino acid sequence identity with neutral endopeptidase 24.11 (NEP) especially at the catalytic center. A series of potent and selective arylacetylene-containing ECE-1 inhibitors have been prepared. (S,S)-3-Cyclohexyl-2-[[5 -(2,4-difluorophenyl)-2-[(phosphonomethyl)amino]pent-4-ynoyl]amino]propionic acid (47), an arylacetylene amino phosphonate dipeptide, was found to inhibit ECE-1 and NEP with IC50 values of 14 nM and 2 mu M, respectively. Similarly, (S)-[[1-[(2-biphenyl-4-ylethyl)-carbamoyl]-4-(2-fluorophenyl)but-3-ynyl]a acid (56), an arylacetylene amino phosphonate amide, had IC50's of 33 nM and 6.5 mu M for ECE-1 and NEP, respectively. Slight modification of the aryl moiety was found to have dramatic effects on ECE-1/NEP selectivity. The 2-fluoro dipeptide analogue, (S,S)-2-[[5-(2-fluorophenyl)-2-[(phosphonomethyl)-amino]pent-4-ynoyl]amino]-4-methylpentanoic acid (40), showed a 72-fold selectivity for ECE-1 over NEP, while the 3-fluoro dipeptide analogue, (S,S)-2-[[5-(3-fluorophenyl)-2-[(phosphhonom-ethyl)amino]pent-4-ynoyl]amino]-4-methylpentanoic acid (22), was equipotent for ECE-1 and NEP. Several of these inhibitors were shown to be potent in blocking ET-1 production in vivo as demonstrated by the big ET-l-induced presser response in rats. These potent inhibitors are the most selective for ECE-1 reported to date and are envisaged to have a variety of therapeutic applications.