Synthesis and antiviral properties of novel 7-heterocyclic substituted 7-deaza-adenine nucleoside inhibitors of Hepatitis C NS5B polymerase.

Previous investigations in our laboratories resulted in the discovery of a novel series of potent nucleoside inhibitors of Hepatitis C virus (HCV) NS5B polymerase bearing tetracyclic 7-substituted 7-deaza-adenine nucleobases. The planarity of such modified systems was suggested to play a role in the high inhibitory potency observed. This paper describes how we envisaged to maintain the desired planarity of the modified nucleobase by means of an intra-molecular H-bond, engaging a H-bond donor atom on an appropriately substituted 7-heterocyclic residue with the adjacent amino group of the nucleobase. The success of this strategy is reflected by the identification of several novel potent nucleoside inhibitors of HCV NS5B bearing a 7-heterocyclic substituted 7-deaza-adenine nucleobase. Amongst these, the 1,2,4-oxadiazole analog 11 showed high antiviral potency against HCV replication in replicon cells and efficient conversion to the corresponding NTP in vivo, with high and sustained levels of NTP measured in rat liver following intravenous and oral administration.

Inhibitors of hepatitis C virus NS3/4A: alpha-ketoamide based macrocyclic inhibitors.

A novel series of hepatitis C virus (HCV) NS3/4A protease inhibitors bearing a P2-P4 macrocycle and a P1-P1' alpha-ketoamide serine trap is reported. The NS3 protease, which is essential for viral replication, is considered one of the most attractive targets for developing novel anti-HCV therapies. The optimization of both the macrocycle and the warhead portions led to the discovery of compounds 8b and 8 g with a good activity both in the enzyme as well as in the cell based (replicon) assays with favorable PK profile in a preclinical species.

2-(3-Thienyl)-5,6-dihydroxypyrimidine-4-carboxylic acids as inhibitors of HCV NS5B RdRp.

A series of 2-(3-thienyl)-5,6-dihydroxypyrimidine-4-carboxylic acid inhibitors of the hepatitis C virus (HCV) NS5B polymerase enzyme are reported. Sulfonyl urea substituted analogs in this series proved to be the most potent active site non-nucleoside inhibitors of NS5B reported to date. These compounds had low nanomolar enzyme inhibition across HCV genotypes 1-3 and showed single digit micromolar inhibition in the HCV replicon assay. This improved cell-based activity allowed the binding mode of these compounds to be probed by selection of resistant mutations against compound 21. The results generated are in broad agreement with the previously proposed binding model for this compound class.

Development and preliminary optimization of indole-N-acetamide inhibitors of hepatitis C virus NS5B polymerase.

Allosteric inhibition of the hepatitis C virus (HCV) NS5B RNA-dependent RNA polymerase enzyme has recently emerged as a viable strategy toward blocking replication of viral RNA in cell-based systems. We report here a novel class of allosteric inhibitor of NS5B that shows potent affinity for the NS5B enzyme and effective inhibition of subgenomic HCV RNA replication in HUH-7 cells. Inhibitors from this class have promising characteristics for further development as anti-HCV agents.

Potent inhibitors of subgenomic hepatitis C virus RNA replication through optimization of indole-N-acetamide allosteric inhibitors of the viral NS5B polymerase.

Infections caused by hepatitis C virus (HCV) are a significant world health problem for which novel therapies are in urgent demand. Compounds that block replication of subgenomic HCV RNA in liver cells are of interest because of their demonstrated antiviral effect in the clinic. In followup to our recent report that indole-N-acetamides (e.g., 1) are potent allosteric inhibitors of the HCV NS5B polymerase enzyme, we describe here their optimization as cell-based inhibitors. The crystal structure of 1 bound to NS5B was a guide in the design of a two-dimensional compound array that highlighted that formally zwitterionic inhibitors have strong intracellular potency and that pregnane X receptor (PXR) activation (an undesired off-target activity) is linked to a structural feature of the inhibitor. Optimized analogues devoid of PXR activation (e.g., 55, EC(50) = 127 nM) retain strong cell-based efficacy under high serum conditions and show acceptable pharmacokinetics parameters in rat and dog.

Synthesis and antiviral properties of novel tetracyclic nucleoside inhibitors of hepatitis C NS5B polymerase.

As part of an ongoing medicinal chemistry effort to identify novel nucleoside inhibitors of HCV NS5B polymerase, we report the discovery of a novel series of 2'-C-Methyl-ribose nucleoside derivatives bearing a 7-aryl and 7-heteroaryl- substituted 7-deaza-adenine nucleobase. A reliable platform for the synthesis and simplified purification of the corresponding nucleoside triphosphates (NTPs) was established, enabling a solid understanding of the SAR relationship within the series. By this approach, we identified the novel analogs 13a and 13b that demonstrated micromolar levels of cellular activity, and the NTPs of which, 16a and 16b, are excellent inhibitors of NS5B with IC(50) = 0.1 µM, a level of intrinsic potency similar to that of previous and current clinical candidates.

Advances in the development of macrocyclic inhibitors of hepatitis C virus NS3-4A protease.

Hepatitis C virus (HCV) is a major cause of acute hepatitis and chronic liver disease, including cirrhosis and hepatocellular carcinoma (HCC). No vaccine is currently available to prevent hepatitis C, and the current standard of care (SOC) - pegylated interferon-α (PEG-IFN-α) in combination with ribavirin (RBV) - is only partially effective and it also presents side effects. Novel treatment options now under intensive development are focused on the discovery of inhibitors of HCV-specific enzymes. The HCV NS3 protease plays an essential role for viral replication and it is recognized as one of the most attractive targets for developing novel anti-HCV therapies. After two decades of research efforts a number of potent active-site inhibitors of the NS3 protease have been generated and some of them are in late stage of clinical trials. A particularly interesting class of HCV NS3 protease inhibitors are based on depeptidized macrocyclic structures. The article reviews the recent progresses made in the discovery and development of macrocyclic inhibitors of the HCV NS3 protease as described in the most recent scientific literature (patent excluded), from a medicinal chemistry perspective.

Active site inhibitors of HCV NS5B polymerase. The development and pharmacophore of 2-thienyl-5,6-dihydroxypyrimidine-4-carboxylic acid.

5,6-Dihydroxypyrimidine-4-carboxylic acids are a promising series of hepatitis C virus (HCV) NS5B polymerase inhibitors that bind at the active site of the enzyme. Here we report a simple 2-thienyl substituted analogue that shows 10-fold improved activity over the original lead, and which allowed us to further delineate the key elements of the pharmacophore of this class of inhibitor. This work led to the identification of a trifluoromethyl acylsulfonamide group as a viable replacement for the C4 carboxylic acid in this series.