A New Class of Inhibitors for the Metalloprotease Neprilysin Based on a Central Imidazole Scaffold

Neprilysin (NEP; neutral endopeptidase EC 3.4.24.11) is a Zn^II‐dependent, membrane‐bound endopeptidase. NEP is widely distributed in the organs, particularly in the kidneys and lungs, and it is involved in the metabolism of a number of smaller regulatory peptides. Inhibition of NEP has been proposed as a potential target for analgesic and antihypertensive therapies. In this study, new nonpeptidic inhibitors of neprilysin ((±)‐ 1 , (±)‐ 43 , (±)‐ 45 , and (±)‐ 46 ; Table) were designed, based on the X‐ray crystal structure of NEP complexed to phosphoramidon (Fig. 1). They feature an imidazole ring as the central scaffold, acting as a peptide bond isoster to undergo H‐bonding with the side chains of Asn542 and Arg717 (Fig. 2). The scaffold is decorated with a thiol group to ligate to the Zn^II ion and two aromatic residues to bind into the hydrophobic S1′ and S2′ pockets. The synthesis of the new inhibitors was approached by two routes (Schemes 1–4 and 5–8), with the second one involving a double directed ortho‐metallation of the imidazole platform and a Stille cross‐coupling, providing the desired target molecules as hydrochloride salts. In a fluorescence assay, inhibitors (±)‐ 1 , (±)‐ 43 , (±)‐ 45 , and (±)‐ 46 all exhibit IC₅₀ values in the single‐digit micromolar activity range (2–4 μM , Table), which validates the binding mode postulated by modeling. Useful guidelines for a next lead optimization cycle were obtained in several control runs.