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

Abstract

A new class of nonpeptidic inhibitors of the Zn II -dependent metalloprotease neprilysin with IC 50 values in the nanomolar activity range (0.034 ± 0.30 mm) 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 p-p stacking interactions with the imidazole ring of His711. The platform is decorated with a thiol vector to coordinate to the Zn II 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-resolution (Fig. 4 and Table 2). The ligand coordinates with its sulfanyl residue to the Zn II 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 p-p 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 imidazopyridine 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.1. Introduction. ± In the preceding paper [1], we described a new class of inhibitors of the metalloprotease neprilysin with a central 1H-imidazole platform, featuring IC 50 values (IC 50 : concentration of inhibitor at which 50% V max is observed) in the low micromolar range. The de novo design of these compounds was based on the X-ray crystal structure of NEP complexed with phosphoramidon (Protein Data Bank (PDB) file name 1DMT) [2]. For the design of the second-generation inhibitors, we reverted to an unpublished X-ray crystal structure [3] of NEP complexed with the inhibitor thiorphan [4]. During the analysis, we carefully compared the active sites of the two

A fluorine scan of non-peptidic inhibitors of neprilysin: Fluorophobic and fluorophilic regions in an enzyme active site

“…The active site of neprilysin complexed to a non-peptidic ligand Compounds (+)-1a/(+)-2a with a central imidazo [4,5-c]pyridine platform and (+)-1b/(+)-2b with a benzimidazole scaffold were found to be potent inhibitors of NEP with IC 50 values in the nanomolar range (Table 1) [29]. In fact, their activities are actually higher than previously determined when optimized assay conditions, preventing oxidative thiol deterioration, are applied as in the present study (see below).…”

Predicting and Tuning Physicochemical Properties in Lead Optimization: Amine Basicities

“…Specifically, we present fluorine effects on the pK a values of benzimidazoles, common scaffolds in medicinal chemistry and used as a central platform in our inhibitors of the metalloprotease neprilysin (NEP). [29,30] Figure 10 gives the pK a values for the protonation (pK a1 ) and deprotonation (pK a2 ) of benzimidazole (48 a) and its differently fluorinated derivatives 48 b-j. Interesting correlations between the pK a values and the degree of fluorination at the benzene ring were observed.…”

Crystal structure, optical and magnetic properties of the bis(perchlorate) of 3,4-diaminopyridine

“…This characteristic complicates the elucidation of the mechanism and site of action [10,11]. Second generation inhibitors of metalloprotease Neprilysin based on heterocyclic derivatives, including 3,4-diaminopyridine have been synthesized, spectroscopically characterized, structurally elucidated and biologically tested [12]. Theoretical studies of the molecular determinants responsible for the biological activity of aminopyridines have been presented [13] at B3LYP/cc-pVDZ level of theory.…”