New ketomethylene inhibitor analogues: synthesis and assessment of structural determinants for N-domain selective inhibition of angiotensin-converting enzyme

Angiotensin-converting enzyme (ACE) is a zinc metallopeptidase containing two homologous domains. While the C-domain plays a major role in blood pressure regulation, the N-domain hydrolyzes the antifibrotic agent N-acetyl-Ser-Asp-Lys-Pro. Thus, N-domain selective (N-selective) inhibitors could be useful in the treatment of conditions relating to excessive tissue fibrosis. New keto-ACE analogues were designed that contained functionalities considered important for N-selective inhibitor RXP407 binding, namely, a P-2 Asp, N-acetyl group, and C-terminal amide. Such functionalities were incorporated to assess the structural determinants for N-selective binding in a novel inhibitor template. Inhibitors containing a C-terminal amide and modified P-2' group were poor inhibitors of the N-domain, with several of these displaying improved inhibition of the C-domain. Molecules with both a C-terminal amide and P-2 Asp were also poor inhibitors and not N-selective. Compounds containing a free C-terminus, a P-2 Asp and protecting group displayed a change of more than 1000-fold N-selectivity compared with the parent molecule. Molecular docking models revealed interaction of these P-2 groups with S-2 residues Tyr369 and Arg381. This study emphasizes the importance of P-2 functionalities in allowing for improved N-selective binding and provides further rationale for the design of N-selective inhibitors, which could be useful in treating tissue fibrosis.