Second‐Generation Inhibitors for the Metalloprotease Neprilysin Based on Bicyclic Heteroaromatic Scaffolds: Synthesis, Biological Activity, and X‐Ray Crystal‐Structure Analysis

Abstract

AbstractA new class of nonpeptidic inhibitors of the ZnII‐dependent metalloprotease neprilysin with IC50 values in the nanomolar activity range (0.034–0.30 μM) were developed based on structure‐based de novo design (Figs. 1 and 2). The inhibitors feature benzimidazole and imidazo[4,5‐c]pyridine moieties as central scaffolds to undergo H‐bonding to Asn542 and Arg717 and to engage in favorable π‐π stacking interactions with the imidazole ring of His711. The platform is decorated with a thiol vector to coordinate to the ZnII ion and an aryl residue to occupy the hydrophobic S1′ pocket, but lack a substituent for binding in the S2′ pocket, which remains closed by the side chains of Phe106 and Arg110 when not occupied. The enantioselective syntheses of the active compounds (+)‐1, (+)‐2, (+)‐25, and (+)‐26 were accomplished using Evans auxiliaries (Schemes 2, 4, and 5). The inhibitors (+)‐2 and (+)‐26 with an imidazo[4,5‐c]pyridine core are ca. 8 times more active than those with a benzimidazole core ((+)‐1 and (+)‐25) (Table 1). The predicted binding mode was established by X‐ray analysis of the complex of neprilysin with (+)‐2 at 2.25‐Å resolution (Fig. 4 and Table 2). The ligand coordinates with its sulfanyl residue to the ZnII ion, and the benzyl residue occupies the S1′ pocket. The 1H‐imidazole moiety of the central scaffold forms the required H‐bonds to the side chains of Asn542 and Arg717. The heterobicyclic platform additionally undergoes π‐π stacking with the side chain of His711 as well as edge‐to‐face‐type interactions with the side chain of Trp693. According to the X‐ray analysis, the substantial advantage in biological activity of the imidazo‐pyridine inhibitors over the benzimidazole ligands arises from favorable interactions of the pyridine N‐atom in the former with the side chain of Arg102. Unexpectedly, replacement of the phenyl group pointing into the deep S1′ pocket by a biphenyl group does not enhance the binding affinity for this class of inhibitors.