Vasopeptidase inhibitors: incorporation of geminal and spirocyclic substituted azepinones in mercaptoacyl dipeptides

Advances in the structural basis for angiotensin-1 converting enzyme (ACE) inhibitors

Human somatic angiotensin-converting enzyme (ACE) is a key zinc metallopeptidase that plays a pivotal role in the renin-angiotensin-aldosterone system (RAAS) by regulating blood pressure and electrolyte balance. Inhibition of ACE is a cornerstone in the management of hypertension, cardiovascular diseases, and renal disorders. Recent advances in structural biology techniques have provided invaluable insights into the molecular mechanisms underlying ACE inhibition, facilitating the design and development of more effective therapeutic agents. This review focuses on the latest advancements in elucidating the structural basis for ACE inhibition. High-resolution crystallographic studies of minimally glycosylated individual domains of ACE have revealed intricate molecular details of the ACE catalytic N- and C-domains, and their detailed interactions with clinically relevant and newly designed domain-specific inhibitors. In addition, the recently elucidated structure of the glycosylated form of full-length ACE by cryo-electron microscopy (cryo-EM) has shed light on the mechanism of ACE dimerization and revealed continuous conformational changes which occur prior to ligand binding. In addition to these experimental techniques, computational approaches have also played a pivotal role in elucidating the structural basis for ACE inhibition. Molecular dynamics simulations and computational docking studies have provided atomic details of inhibitor binding kinetics and energetics, facilitating the rational design of novel ACE inhibitors with improved potency and selectivity. Furthermore, computational analysis of the motions observed by cryo-EM allowed the identification of allosteric binding sites on ACE. This affords new opportunities for the development of next-generation allosteric inhibitors with enhanced pharmacological properties. Overall, the insights highlighted in this review could enable the rational design of novel ACE inhibitors with improved efficacy and safety profiles, ultimately leading to better therapeutic outcomes for patients with hypertension and cardiovascular diseases.

Novel Therapeutic Approaches Targeting the Renin-Angiotensin System and Associated Peptides in Hypertension and Heart Failure

Despite the success of renin-angiotensin system (RAS) blockade by angiotensin-converting enzyme (ACE) inhibitors and angiotensin II type 1 receptor (AT1R) blockers, current therapies for hypertension and related cardiovascular diseases are still inadequate. Identification of additional components of the RAS and associated vasoactive pathways, as well as new structural and functional insights into established targets, have led to novel therapeutic approaches with the potential to provide improved cardiovascular protection and better blood pressure control and/or reduced adverse side effects. The simultaneous modulation of several neurohumoral mediators in key interconnected blood pressure-regulating pathways has been an attractive approach to improve treatment efficacy, and several novel approaches involve combination therapy or dual-acting agents. In addition, increased understanding of the complexity of the RAS has led to novel approaches aimed at upregulating the ACE2/angiotensin-(1-7)/Mas axis to counter-regulate the harmful effects of the ACE/angiotensin II/angiotensin III/AT1R axis. These advances have opened new avenues for the development of novel drugs targeting the RAS to better treat hypertension and heart failure. Here we focus on new therapies in preclinical and early clinical stages of development, including novel small molecule inhibitors and receptor agonists/antagonists, less conventional strategies such as gene therapy to suppress angiotensinogen at the RNA level, recombinant ACE2 protein, and novel bispecific designer peptides.

Targeting Metalloenzymes for Therapeutic Intervention

Metalloenzymes are central to a wide range of essential biological activities, including nucleic acid modification, protein degradation, and many others. The role of metalloenzymes in these processes also makes them central for the progression of many diseases and, as such, makes metalloenzymes attractive targets for therapeutic intervention. Increasing awareness of the role metalloenzymes play in disease and their importance as a class of targets has amplified interest in the development of new strategies to develop inhibitors and ultimately useful drugs. In this Review, we provide a broad overview of several drug discovery efforts focused on metalloenzymes and attempt to map out the current landscape of high-value metalloenzyme targets.

Continuous flow photolysis of aryl azides: Preparation of 3H-azepinones

Photolysis of aryl azides to give nitrenes, and their subsequent rearrangement in the presence of water to give 3H-azepinones, is performed in continuous flow in a photoreactor constructed of fluorinated ethylene polymer (FEP) tubing. Fine tuning of the reaction conditions using the flow reactor allowed minimization of secondary photochemical reactions.

A computational approach to the study of the binding mode of dual ACE/NEP inhibitors

Combined blockade of the renin-angiotensin-aldosterone system (RAAS) is an attractive therapeutic strategy for the treatment of cardiovascular diseases. Vasopeptidase inhibitors are a group of compounds capable of inhibiting more than one enzyme, which leads to potentiation of natriuretic peptide actions and suppression of the RAAS. In this study, molecular modeling has been used to elucidate key structural features that govern the binding and/or selectivity of a single compound toward the zinc catalytic sites of the N- and C-domains of the angiotensin-converting enzyme (ACE) and the neutral endopeptidase (NEP). Eleven dual inhibitors were categorized in three classes, according to their zinc binding groups. Analysis of their docked conformers revealed the molecular environment of the catalytic sites and the specific interactions between the inhibitors and amino acid residues that are important for selectivity and cooperativity. In addition, inhibitors were predicted to bind to the C-domain of the ACE with greater affinity than the N-domain, with an average difference in the free energy of binding approximately 2-3 kcal mol(-1). Residues that were identified to actively participate in the binding and stabilizing of the enzyme-inhibitor complexes were analyzed in a consensus way for both the ACE and the NEP. These atomic-level insights into enzyme-ligand binding can be used to drive new structure-based drug design processes in the quest for more selective and effective vasopeptidase inhibitors.

Structural determination of epsilon-lactams by 1H and 13C NMR

The thermodynamic products (epsilon-lactams) of the degradation of ten different spirocyclic oxaziridines were analyzed by 1H and 13C NMR spectroscopy. The preferred conformations were determined by examining the homonuclear spin-spin coupling constant and the chemical shift effects of the N-substituent and the alkyl group of the aliphatic ring on 1H and 13C NMR spectra.

Structure–activity relationship study between Ornithyl-Proline and Lysyl-Proline based tripeptidomimics as angiotensin-converting enzyme inhibitors

A designed library of tripeptidomimics of Ornithyl-Proline (Orn-Pro) and Lysyl-Proline (Lys-Pro) conjugated with various unnatural amino acids and carboxylic acid derived heterocyclics was synthesized and screened for possible inhibitors of angiotensin-converting enzyme (ACE). Among the tripeptidomimics 10[MTP-Orn-Pro], 11[HTP-Orn-Pro], 14[TA-Orn-Pro] and 20[BPA-Orn-Pro] showed prominent inhibition with IC50 values in micromolar concentrations. Structure-activity relationship study indicated that C3 side chain of Orn as compared to C4 side chain of Lys at P1' position was better suited to inhibit ACE, with propionic acid (C3) derived heterocyclics and unnatural amino acids.

METABOLISM OF [14C]GEMOPATRILAT AFTER ORAL ADMINISTRATION TO RATS, DOGS, AND HUMANS

This study describes the pharmacokinetic parameters of gemopatrilat, a potent vasopeptidase inhibitor, in humans and the comparative biotransformation of the compound in rats, dogs, and humans after administration of a single oral dose of [14C]gemopatrilat. Gemopatrilat was rapidly absorbed in humans with an oral bioavailability of 49%. Within 5 h after dose, the mean concentrations of gemopatrilat were less than 1% of the mean Cmax values. The total area under the first-moment time curve extrapolated to infinity [AUC(INF)] value for gemopatrilat was only 2% of the AUC(INF) of radioactivity in plasma. Gemopatrilat showed a large apparent steady-state volume of distribution (2500 liters) and a prolonged terminal-phase decline in plasma concentration. These results are consistent with the idea that the free sulfhydryl group of gemopatrilat forms reversible disulfide linkages with plasma and tissue proteins and is thus eliminated from the body at a very slow rate. Approximately half of the drug-related radioactivity in 1-h plasma samples from rat, dog, and human was reduced chemically with dithiothreitol to gemopatrilat, suggesting that disulfide linkage occurred in all species. In addition, metabolites formed through S-methylation and amide hydrolysis were also detected in rat, dog, and human plasma. No gemopatrilat was detected in urine and fecal samples from all three species, indicating that the compound is extensively metabolized in vivo. The major metabolites identified in human urine and feces were also present in rat and dog. These data suggest that the metabolism of gemopatrilat in all three species were qualitatively very similar.

Efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921

[reaction: see text] An efficient asymmetric synthesis of the vasopeptidase inhibitor BMS-189921 was accomplished. Two short enantioselective syntheses of the common key intermediate (S)-alpha-aminoazepinone 6b were developed. Olefin 3 was converted to 6b via asymmetric hydrogenation. Alternatively, enyne 12 was converted to racemic alpha-aminoazepinone 15b, which was transformed to 6b by a practical dynamic resolution.

Comparative biotransformation of radiolabeled [(14)C]omapatrilat and stable-labeled [(13)C(2)]omapatrilat after oral administration to rats, dogs, and humans

Omapatrilat, a novel vasopeptidase inhibitor, is under development for the treatment of hypertension and congestive heart failure. This study describes the comparative biotransformation of radiolabeled [(14)C]- and stable-labeled [(13)C(2)]omapatrilat after administration of single oral doses to rats, dogs, and humans. The metabolites were identified by a combination of methods including reduction, hydrolysis, and comparison of high performance liquid chromatography retention times with those of the synthetic standards. Urinary metabolites were further characterized by liquid chromatography tandem mass spectrometry analysis. Prominent metabolites identified in human plasma, which were also present in rat and dog plasma, were S-methyl omapatrilat and S-2-thiomethyl-3-phenylpropionic acid. Omapatrilat accounted for only a small portion of the extractable radioactivity in plasma in all three species. A portion of the plasma radioactivity was unextractable in all three species (27-53%). The majority of unextractable radioactivity in plasma was characterized after dithiothreitol reduction to be omapatrilat and (S)-2-thio-3-phenylpropionic acid, both apparently bound to plasma proteins by reversible disulfide bonds. The major human urinary metabolites were the amine hydrolysis product, diasteromeric sulfoxide of (S)-2-thiomethyl-3-phenylpropionic acid, acyl glucuronide of S-methyl omapatrilat, and S-methyl omapatrilat. The minor metabolites were acyl glucuronide of (S)-2-thiomethyl-3-phenylpropionic acid, L-cysteine mixed disulfide of omapatrilat, diastereomers of S-methyl sulfoxide of omapatrilat, and S-methyl omapatrilat ring sulfoxide. The metabolic profiles of dog and human urine were qualitatively similar whereas rat urine showed only metabolites arising from hydrolysis of omapatrilat. Unchanged omapatrilat was not found in rat, dog, or human urine samples indicating extensive metabolism in vivo.

Novel peptidomimics as angiotensin-converting enzyme inhibitors: a combinatorial approach

One of the efficient mode of treatments of chronic hypertension and cardiovascular disorders has been to restrain the formation of angiotensin-II by inhibiting the action of angiotensin-converting enzyme (ACE) on angiotensin-I. A number of ACE inhibitors (ACEIs) have been put to therapeutic use during the last two decades. The efforts continue towards achieving superior molecules or drugs with improved affinities, better bioavailability and thus long duration of action with minimum side effects. The present work evolves around similar objectives. In order to understand the mode of interaction of inhibitors with the active site of the enzyme and subsequently to have lead compounds as possible inhibitors the novel dipeptidomimics and tripeptidomimics have been designed and synthesized using combinatorial chemistry approach. A Focussed library of 10 di- and tri-peptides, eight dipeptidomemics and forty tripeptidomemics was generated. The pharmacophoric heterocyclic moieties and the amino acids have been selected to have affinities with the S1, S1', and S2' subsites of the active site of the enzyme. ACE inhibition studies clearly demonstrated the structural-activity relationships within these classes of peptidomimics. The dipeptidomimics interacted only with S1' and S2' subsites, whereas the tripeptidomemics had additional interaction with S1 subsite, which accounted for their significant ACE inhibition potencies. The in-vitro screening of these peptidomimics have resulted in identification of four promising tripeptidomimics 34[2-benzimidazolepropionyl-Val-Trp], 35[5hydroxytryptophanyl-Val-Trp], 40[2-benzimidazolepropionyl-Ile-Trp] and 45[2-benzimidazolepropionyl-Lys-Trp] with IC50 values in micromolar concentrations.

Vasopeptidase inhibition in a canine model of exercise-induced left ventricular dysfunction

1. The present study compared the acute efficacies of vasopeptidase inhibition with omapatrilat, nitroglycerin and angiotensin-converting enzyme (ACE) inhibition in exercise-induced myocardial dysfunction. Omapatrilat, a vasopeptidase inhibitor, inhibits both neutral endopeptidase and ACE. Whereas vasopeptidase inhibitors have demonstrated clinical efficacy in hypertension and heart failure, their effects in myocardial ischaemia remain unclear. 2. Omapatrilat (0.3 mg/kg) was compared with vehicle (saline), an ACE inhibitor (fosinoprilat; 0.44 mg/kg) and nitroglycerin (8.0 microg/kg per min), in an established canine model of exercise-induced myocardial dysfunction induced by progressive closure of an ameroid constrictor placed about the proximal circumflex coronary artery. Maximal treadmill exercise tests, terminated when heart rate failed to increase with increasing workload or failure to continue exercise, were performed in chronically instrumented dogs. 3. During exercise, omapatrilat and nitroglycerin similarly increased ischaemic wall thickening (P< or = 0.0001, ANOVA, 12 d.f.), whereas fosinoprilat and vehicle were without effect. Ischaemic zone ST changes were decreased with nitroglycerin (P = 0.0006, ANOVA, 12 d.f.) and tended to decrease with omapatrilat (P = 0.07, ANOVA, 12 d.f.). Peak exercise capacity was increased with nitroglycerin (9.7 +/- 1.1 vs 11.2 +/- 1.0 kcal, control vs 4 h, respectively; n = 6) and omapatrilat (9.7 +/- 0.8 vs 11.4 +/- 0.6 kcal, control vs 4 h, respectively; n = 6) and was unchanged with ACE inhibition (9.0 +/- 1.2 vs 9.5 +/- 1.1 kcal, control vs 4 h, respectively; n = 7). Omapatrilat differentially increased double product during exercise (P = 0.001, ANOVA, 12 d.f.) compared with other treatments. 4. During exercise-induced myocardial dysfunction, acute ACE inhibition did not attenuate ischaemic changes and failed to improve exercise capacity. Increased exercise capacity with omapatrilat was accompanied by a differential increase in double product, consistent with increased oxygen supply and demand. Improvements in ischaemic function were comparable between omapatrilat and nitroglycerin, suggesting that omapatrilat may represent a novel therapy in demand-induced ischaemia.

Vasopeptidase inhibitors

Vasopeptidase inhibitors are a new class of drugs that have dual inhibitory effects on two key enzymes involved in the metabolism of vasoactive peptides. Essentially, they inhibit angiotensin-converting enzyme (ACE), thereby blocking the generation of angiotensin II (Ang II); at the same time they prevent the breakdown of natriuretic peptides by the enzyme neutral endopeptidase. The combination of reduction of Ang II on a background of increased natriuretic peptide activity has several potential advantages for the treatment of cardiovascular and renal disease and in particular, hypertension and congestive heart failure (CHF). Several vasopeptidase inhibitors, such as sampatrilat, fasidotril, gemopatrilat and omapatrilat (Vanlev, the most clinically developed vasopeptidase inhibitor to date) are under intensive clinical investigation. Recent clinical trials have demonstrated effective antihypertensive activity in hypertension, independent of age, renin and salt status or ethnic origin, and have also highlighted the potential for vasopeptidase inhibition as a new therapeutic modality for the treatment of CHF. Moreover, ongoing research suggests that this new class of drugs may be an important approach, not only for the treatment of hypertension and of conditions associated with overt volume overload but also for ischaemic heart disease.

Vasopeptidase inhibitors

Vasopeptidase inhibitors are a new class of cardiovascular drug that simultaneously inhibit both neutral endopeptidase and angiotensin-converting enzyme (ACE). They increase the availability of peptides that have vasodilatory and other vascular effects; they also inhibit production of angiotensin II. In animal models vasopeptidase inhibitors decrease blood pressure in low, medium, and high renin forms of hypertension, and they also appear to confer benefits in models of heart failure and ischaemic heart disease. Studies in human hypertension show that these agents are effective in decreasing blood pressure regardless of race or age. Experience with omapatrilat, the most clinically advanced of these drugs, has shown it to be more effective than currently available ACE inhibitors or other widely used antihypertensive agents. Studies with omapatrilat in congestive heart failure have shown beneficial effects on haemodynamics and symptoms. The vasopeptidase inhibitors appear to have safety profiles similar to ACE inhibitors, though the frequency of side-effects such as angio-oedema and cough remains to be established. Large trials with clinical endpoints, some already in progress, are needed to establish the place of this class of drug beside that of established therapies in conditions such as hypertension, heart failure, ischaemic heart disease, and nephropathy.

Structure of human neutral endopeptidase (Neprilysin) complexed with phosphoramidon

Neutral endopeptidase is a mammalian type II integral membrane zinc-containing endopeptidase, which degrades and inactivates a number of bioactive peptides. The range of substrates cleaved by neutral endopeptidase in vitro includes the enkephalins, substance P, endothelin, bradykinin and atrial natriuretic factor. Due to the physiological importance of neutral endopeptidase in the modulation of nociceptive and pressor responses there is considerable interest in inhibitors of this enzyme as novel analgesics and anti-hypertensive agents. Here we describe the crystal structure of the extracellular domain (residues 52-749) of human NEP complexed with the generic metalloproteinase inhibitor phosphoramidon at 2.1 A resolution. The structure reveals two multiply connected folding domains which embrace a large central cavity containing the active site. The inhibitor is bound to one side of this cavity and its binding mode provides a detailed understanding of the ligand-binding and specificity determinants.