HCV NS3/4a protease inhibitors are proven therapeutic agents against chronic hepatitis C virus infection, with boceprevir and telaprevir having recently received regulatory approval as add-on therapy to pegylated interferon/ribavirin for patients harboring genotype 1 infections. Overcoming antiviral resistance, broad genotype coverage, and a convenient dosing regimen are important attributes for future agents to be used in combinations without interferon. In this communication, we report the preclinical profile of MK-5172, a novel P2-P4 quinoxaline macrocyclic NS3/4a protease inhibitor currently in clinical development. The compound demonstrates subnanomolar activity against a broad enzyme panel encompassing major hepatitis C virus (HCV) genotypes as well as variants resistant to earlier protease inhibitors. In replicon selections, MK-5172 exerted high selective pressure, which yielded few resistant colonies. In both rat and dog, MK-5172 demonstrates good plasma and liver exposures, with 24-h liver levels suggestive of once-daily dosing. When administered to HCV-infected chimpanzees harboring chronic gt1a or gt1b infections, MK-5172 suppressed viral load between 4 to 5 logs at a dose of 1 mg/kg of body weight twice daily (b.i.d.) for 7 days. Based on its preclinical profile, MK-5172 is anticipated to be broadly active against multiple HCV genotypes and clinically important resistance variants and highly suited for incorporation into newer all-oral regimens.C hronic hepatitis C virus (HCV) infection afflicts more than 170 million people worldwide and is the major etiological cause of fibrosis, liver cirrhosis, and hepatocellular carcinoma (20,53). Current treatment relies on a backbone of interferon and ribavirin, a regimen with poor tolerability and toxicity (31, 34). Efforts to develop novel therapies to improve treatment have focused largely on direct acting antiviral agents (DAAs) (19), which therapeutically intervene with virally encoded components essential for HCV replication.Hepatitis C virus, a member of the Flaviviridae family of viruses in the Hepacivirus genus, is encoded by a 9.6-kb positivestrand RNA genome (8). It is initially translated into a single polypeptide that is subsequently cleaved into individual protein components by a combination of both host-and virally encoded proteases (2, 38). HCV protease inhibitors currently in clinical development span a variety of structural classes. The most advanced of these are keto amide compounds, which covalently bind to the active-site serine of the protease in a slowly reversible manner. Boceprevir (29) and telaprevir (37), both from this class, recently received regulatory approval as add-on therapy to pegylated interferon/ribavirin in the treatment of genotype 1-infected patients. A number of rapidly reversible NS3/4a protease inhibitors, including the P1-P3 constrained macrocyclic inhibitors TMC 435 (23) and danoprevir (45), the P2-P4 constrained macrocyclic inhibitor vaniprevir (33), the linear inhibitors BI 201335 (52), BMS650032 (47), and ABT-450 ...

As part of a continued effort to identify inhibitors of hepatitis C viral (HCV) replication, we report here the synthesis and evaluation of a series of nucleoside analogues and their corresponding triphosphates. Nucleosides were evaluated for their ability to inhibit HCV RNA replication in a cell-based, subgenomic replicon system, while nucleoside triphosphates were evaluated for their ability to inhibit in vitro RNA synthesis mediated by the HCV RNA-dependent RNA polymerase, NS5B. 2'-C-Methyladenosine and 2'-C-methylguanosine were identified as potent inhibitors of HCV RNA replication, and the corresponding triphosphates were found to be potent inhibitors of HCV NS5B-mediated RNA synthesis. The data generated in the cell-based assay demonstrated a fairly stringent structure-activity relationship around the active nucleosides. Increase in steric bulk beyond methyl on C2, change in the stereo- or regiochemistry of the methyl substituent, or change of identity of the heterobase beyond that of the endogenous adenine or guanine was found to lead to loss of inhibitory activity. The results highlight the importance of the ribo configuration 2'- and 3'-hydroxy pharmacophores for inhibition of HCV RNA replication in the cell-based assay and demonstrate that inclusion of the 2'-C-methylribonucleoside pharmacophore leads to increased resistance to adenosine deaminase and purine nucleoside phosphorylase mediated metabolism.

A new class of HCV NS3/4a protease inhibitors containing a P2 to P4 macrocyclic constraint was designed using a molecular modeling-derived strategy. Building on the profile of previous clinical compounds and exploring the P2 and linker regions of the series allowed for optimization of broad genotype and mutant enzyme potency, cellular activity, and rat liver exposure following oral dosing. These studies led to the identification of clinical candidate 15 (MK-5172), which is active against genotype 1−3 NS3/4a and clinically relevant mutant enzymes and has good plasma exposure and excellent liver exposure in multiple species.KEYWORDS: hepatitis C, HCV, MK-5172, macrocycle, genotype 3a, mutant enzymes H epatitis C virus (HCV) is a chronic liver infection that affects an estimated 130−170 million people worldwide. 1,2 HCV displays a high degree of genetic heterogeneity and can be classified into six major genotypes with different geographic distributions: genotypes 1, 2, and 3 account for more than 90% of the infections in the developed world. Treatment for HCV is based on combination therapy with pegylated interferon-α and ribavirin. 3 Sustained viral response is seen in ∼45% of HCV genotype 1-infected patients treated for 48 weeks and in ∼80% of genotype 2-and 3-infected patients treated for 24 weeks. Interferon and ribavirin therapy is also associated with a number of serious side effects, limiting the number of patients who may be treated. 4 There is a compelling medical need for new oral therapeutic agents with improved efficacy and tolerability. Several promising antiviral targets for HCV have emerged, 5 with NS3/4a protease inhibitors showing perhaps the most dramatic antiviral effects. 6 Clinical proof of concept for this mechanism was first achieved with BILN-2061. 7 Other compounds have entered clinical trials, including telaprevir 8 and boceprevir, 9 both of which are now marketed treatments for use in combination with a standard of care. Compounds currently in development include TMC-435 10 and We have disclosed a molecular modeling-derived strategy that led us to design HCV NS3/4a protease inhibitors that contain the P2 to P4 macrocyclic constraint. 12 This design arose from an analysis of the crystal structure of full-length NS3/4A with and without inhibitors docked in the active site. 13 Our strategy coupled with a modular synthetic approach, which relies on a key ring-closing metathesis (RCM) reaction, 14 allowed for the rapid exploration of these molecules and the identification of clinical candidates, vaniprevir (1) 15,16 and MK-1220 (2). 17 Herein, we describe the discovery of a clinical candidate with broad activity across genotypes (gt) and resistant HCV variants. 18,19 With the development of vaniprevir progressing, we set a goal for the ongoing discovery program to be the identification of a second generation NS3/4a protease inhibitor. We wanted to maintain or improve the PK profile seen with our previous compounds and make significant improvements in activity against the gt 3a enz...

Hepatitis C virus infection constitutes a significant health problem in need of more effective therapies. We have recently identified 2'-C-methyladenosine and 2'-C-methylguanosine as potent nucleoside inhibitors of HCV RNA replication in vitro. However, both of these compounds suffered from significant limitations. 2'-C-Methyladenosine was found to be susceptible to enzymatic conversions by adenosine deaminase and purine nucleoside phosphorylase, and it displayed limited oral bioavailability in the rat. 2'-C-Methylguanosine, on the other hand, was neither efficiently taken up in cells nor phosphorylated well. As part of an attempt to address these limitations, we now report upon the synthesis and evaluation of a series of heterobase-modified 2'-C-methyl ribonucleosides. The structure-activity relationship within this series of nucleosides reveals 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine as potent and noncytotoxic inhibitors of HCV RNA replication. Both 4-amino-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine and 4-amino-5-fluoro-7-(2-C-methyl-beta-d-ribofuranosyl)-7H-pyrrolo[2,3-d]pyrimidine display improved enzymatic stability profiles as compared to that of 2'-C-methyladenosine. Consistent with these observations, the most potent compound, 4-amino-5-fluoro-7H-pyrrolo[2,3-d]pyrimidine ribonucleoside, is orally bioavailable in the rat. Together, the potency of the 2'-C-methyl-4-amino-pyrrolo[2,3-d]pyrimidine ribonucleosides and their improved pharmacokinetic properties relative to that of 2'-C-methyladenosine suggests that this class of compounds may have clinical utility.

Current therapies for chronic pain can have insufficient efficacy and lead to side effects, necessitating research of novel targets against pain. Although originally identified as an oncogene, Tropomyosinrelated kinase A (TrkA) is linked to pain and elevated levels of NGF (the ligand for TrkA) are associated with chronic pain. Antibodies that block TrkA interaction with its ligand, NGF, are in clinical trials for pain relief. Here, we describe the identification of TrkA-specific inhibitors and the structural basis for their selectivity over other Trk family kinases. The X-ray structures reveal a binding site outside the kinase active site that uses residues from the kinase domain and the juxtamembrane region. Three modes of binding with the juxtamembrane region are characterized through a series of ligand-bound complexes. The structures indicate a critical pharmacophore on the compounds that leads to the distinct binding modes. The mode of interaction can allow TrkA selectivity over TrkB and TrkC or promiscuous, pan-Trk inhibition. This finding highlights the difficulty in characterizing the structure-activity relationship of a chemical series in the absence of structural information because of substantial differences in the interacting residues. These structures illustrate the flexibility of binding to sequences outside of-but adjacent to-the kinase domain of TrkA. This knowledge allows development of compounds with specificity for TrkA or the family of Trk proteins.TrkA | kinase | pain | inhibition | selectivity

In the present paper, design, synthesis, X-ray crystallographic analysis, and HIV-1 protease inhibitory activities of a novel class of compounds are disclosed. Compounds 28-30, 32, 35, and 40 were synthesized and found to be inhibitors of the HIV-1 protease. The crucial step in their synthesis involved an unusual endo radical cyclization process. Absolute stereochemistry of the three asymmetric centers in the above compounds have been established to be (4S,2'R,3'S) for optimal potency. X-ray crystallographic analysis has been used to determine the binding mode of the inhibitors to the HIV-1 protease.

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Thrombin-activatable fibrinolysis inhibitor (TAFI) is an important regulator of fibrinolysis, and inhibitors of this enzyme have potential use in antithrombotic and thrombolytic therapy. Appropriately substituted imidazole acetic acids such as 10j were found to be potent inhibitors of activated TAFI and selective versus the related carboxypeptidases CPA, CPN, and CPM but not CPB. Further, 10j accelerated clot lysis in vitro and was shown to be efficacious in a primate model of thrombosis.